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Journal of Nepal Geological Society, 2012, Vol. 45, (Sp. Issue)

The 27th Himalaya-Karakoram-Tibet Workshop (HKT) Kathmandu, Nepal

28-30 November, 2012

Organized by Nepal Geological Society

andDepartment of Mines and Geology

Govt. of Nepal

Coordinator: Er. Uttam Bol Shrestha, President, NGS Convener: Dr. Dibya Ratna KansakarCo-convener: Dr. Som Nath Sapkota

15th Executive Committee of NGS Dr. Khum Narayan Paudayal, Vice President Mr. Sudhir Rajaure, General SecretaryMr. Kabi Raj Paudyal, Deputy General SecretaryMr. Ram Prasad Ghimire, TreasurerMr. Jagadish N. Shrestha, (Immediate Past President)

Member Mr. Kumar K. C., MemberMr. Sunil Raj Paudel, Member Mr. Diwakar Khadka, MemberMs. Suchita Shrestha, MemberMr. Kushal Nandan Pokharel, MemberDr. Subodh Dhakal, MemberMr. Mahesh Pokharel, Member

Organizing Committee of 27th HKT WorkshopProf. Dr. Bishal Nath Upreti, Tribhuvan UniversityMr. Sarbjeet Prasad Mahato, Director General, Department

of Mines and GeologyProf. Dr. Prakash Chandra Adhikari, Member Secretary,

NASTDirector General, Department of IrrigationDirector General, Department of Water Induced Disaster

PreventionManaging Director, Nepal Electricity AuthorityMr. Bharat Mani Jnawali, CAIRN Energy, NepalProf. Dr. Megh Raj Dhital, Tribhuvan UniversityProf. Dr. Vishnu Dangol, Tribhuvan UniversityProf. Dr. Ram Bahadur Sah, Tribhuvan UniversityMr. Gopal Singh Thapa, Former President, NGSMr. Nirendra Dhoj Maskey, Former President, NGSDr. Ramesh Prasad Bashyal, Former President, NGSMr. Achyutanand Bhandary, Former President, NGSMr. Amod Mani Dixit, Former President, NGSMr. Krishna Prasad Kaphle, Former President, NGSMr. Ramesh Kumar Aryal, Former President, NGSMr. Pratap Singh Tater, Former President, NGSMr. Jagadish Nath Shrestha, Former President, NGSDr. Tara Nidhi Bhattarai, Tribhuvan UniversityDr. Santa Man Rai, Tribhuvan UniversityDr. Lalu Prasad Paudel, Tribhuvan University

Mr. Shree Ram Maharjan, Department of Mines and Geology

Mr. Hifzur Rehman, Department of Mines and GeologyMr. Siddhi Pratap Khan, Department of Irrigation (DOI)Mr. Moti Bahadur Kunwar, Ministry of EnergyMr. Pradeep Kumar Mool, ICIMODMr. Devi Nath Subedi, Special Economic Zone, Ministry of

IndustryMr. Shyam Bahadur K. C., Former Vice President, NGSMr. Rajendra Prasad Khanal, Petroleum Exploration

Promotion Project, DMGMr. Shailendra Bhakta Shrestha, Former Vice President,

NGSMr. Basu Dev Kharel, Former Vice President, NGSMr. Ganga Bahadur Tuladhar, Former General Secretary,

NGSMr. Govinda Sharma Pokharel, Vice President, NGSMr. Shardesh Raj Sharma, Former Treasurer, NGSMr. Jayendra Man Tamrakar, Nepal Electricity AuthorityMr. Ashok Kumar Duvadi, Department of Mines and

GeologyDr. Suresh Das Shrestha, Tribhuvan UniversityDr. Ranjan Kumar Dahal, Tribhuvan UniversityMr. Nir Shakya, Ground Water Resource Development

Board (GWRDB)Er. Ramashis Mandal, Godavari Marble Industries P. Ltd.Dr. Dinesh Pathak, Tribhuvan UniversityMr. Lila Nath Rimal, Department of Mines and GeologyDr. Ananta Gajurel, Tribhuvan UniversityDr. Sandip Shah, SN Power, NepalMr. Dilip Sadaula, Department of Soil Conservation and

Watershed ManagementMr. Chatur Bahadur Shrestha, Department of Electricity

DevelopmentDr. Naresh Kazi Tamrakar, Tribhuvan UniversityMr. Jay Raj Ghimire, Department of Mines and GeologyDr. Rajendra Prasad Bhandari, Ground Water Resource

Development Board (GWRDB)Mr. Dinesh Nepali, Department of Mines and GeologyMr. Dinesh Napit, Department of Mines and GeologyEr. Tuk Lal Adhikari, ITECO, NepalProf. Dr. Kazunori Arita, Japan, Honorary Member, NGS

208

27th Himalaya-Karakoram-Tibet Workshop (HKT)

Prof. Dr. Berhard Grassman, AustriaProf. Dr. Harutaka Sakai, JapanProf. Dr. Nigel Harris, UKProf. Dr. Jean Philippe Avouac, USAProf. Dr. Arnaud Pecher, FranceProf. Dr. Stephane, Guillot, CNRS, FranceProf. Dr. C. S. Dubey, Delhi University, IndiaProf. Dr. Asif Khan, PakistanProf. Dr. Rodolfo Carosi, ItalyProf. Dr. Erwin Appel, GermanyProf. Dr. Paul Tapponnier, SingaporeProf. Dr. Kyle Larson, CanadaProf. Dr. Tandong Yao, Peoples' Republic of China

Advisory committeeVice-Chairman, National Planning Commission (NPC),

KathmanduVice Chancellor, Tribhuvan University (TU), KathmanduVice-Chancellor, Nepal Academy of Science & Technology

(NAST), KathmanduVice Chancellor, Kathmandu University

Vice Chancellor, Pokhara UniversitySecretary, Ministry of Science and Technology,

Government of NepalSecretary, Ministry of Industry, Government of NepalSecretary, Ministry of Energy, Government of NepalSecretary, Ministry of Irrigation, Government of NepalProf. V. C. Thakur, Deharadoon, IndiaMr. Thierry Heritier, Departement Analyse Surveillance

Environnement (DASE), FranceProf. Dr. Koshiro Kizaki, Japan, Honorary Member, NGSMr. Madhav Raj Pandey, Nepal, Honorary Member, NGSProf. Dr. K. S. Valdiya, India, Honorary Member, NGSDr. Patrick Le Fort, France, Honorary Member, NGSMr. Biswa Man Pradhan, Nepal, Honorary Member, NGSProf. Dr. M. Qasim Jan, Pakistan, Honorary Member, NGSProf. Dr. Gerhard Fuchs, Austria, Honorary Member, NGSProf. Dr. Madhav Prasad Sharma, Nepal, Honorary

Member, NGSDr. Dinesh Chandra Devkota, Former Vice Chancellor,

NPC

209


Acknowledgements

Nepal Geological Society is pleased to host the 27th Himalaya-Karakoram-Tibet (HKT) workshop in Kathmandu, Nepal, during November 28-30, 2012. The HKT workshops have been a forum instrumental in the advancement of geologic understanding of this part of the earth. Geoscientists from across the world have contributed and have benefi ted much from each other during such workshops in the past. This event is going to add again one more building block in furthering the geosciences and the understanding of the geologic phenomena in this part of the globe. After the 9th workshop in 1994, the HKT workshop has returned to Nepal. The HKT workshop is a forum of all geoscientists for a collegial discussion and for sharing of their new fi ndings from research in the HKT region. The Nepal Geological Society is happy to host this important workshop in which a large number of geoscientists from around the world have contributed their latest scientifi c fi ndings.

This volume contains 152 abstracts from scientists from 19 different countries; 2 from Austria, 1 from Bangladesh, 1 from Bhutan, 4 from Canada, 7 from China, 19 from France, 9 from Germany, 23 from India, 2 from Israel, 12 from Italy, 6 from Japan, 42 from Nepal, 4 from Pakistan, 1 from Poland, 2 from Russia, 2 from Spain, 1 from Switzerland, 7 from UK and 7 from USA. The abstracts cover a wide range of topics under the geosciences such as regional geology, tectonics, seismology, seismotectonics, geohazard, engineering geology, climate change, quaternary geology and environmental geology.

The Nepal Geological Society and 27th HKT Organizing Committee are grateful to the following organizations and individuals for their fi nancial and other necessary supports to organize this event.

Department Analyse Surviellance Environnment (DASE), France

California Institute of Technology, Tectonic Observatory (Caltech, TO), USA

Nanyang Technological University, Earth Observatory, Singapore

Academy of Sciences for the Developing World (TWAS), Trieste, Italy

B. P. Koirala India-Nepal Foundation, Nepal

Himalayan Nappe and Uplift Project, Kyoto University, Japan

Central Department of Geology, Tribhuvan University, Nepal

Department of Geology, Tri-chandra Campus, Tribhuvan University, Nepal

Shakti Mineral Pvt. Ltd., Nepal

Shivam Cements Pvt. Ltd., Nepal

Palpa Cements Pvt. Ltd., Nepal

Argha Khanchi Cements Pvt. Ltd., Nepal

Maruti Cements Pvt. Ltd., Nepal

Coal Association of Nepal

Sidhartha Minerals Pvt. Ltd., Nepal

Ambuja Cements Pvt. Ltd., Nepal

Ghorahi Cements Pvt. Ltd., Nepal

Sarbottam Cements Pvt. Ltd., Nepal

United Cements Pvt. Ltd., Nepal

Sonapur Cements Pvt. Ltd., Nepal

Annapurna Quarries Pvt. Ltd., Nepal

Nava Durga Marble Industries Pvt. Ltd., Nepal

210


Bhardeu Cements Pvt. Ltd., Nepal

Kanchan Quarries, Nepal

Narayani Cements Pvt. Ltd., Nepal

GIEF Consultancy, Nepal

Cosmos Cements, Nepal

Nigale Cement Mills Pvt. Ltd., Nepal

Barahi Quarries Pvt. Ltd., Nepal

Dolomite Chun Dhunga Pvt. Ltd., Nepal

ICGS Nepal, Nepal

Godavari Marbles Industries Pvt. Ltd., Nepal

3 D Consultants, Nepal

Himalaya Quartz, Nepal

Bipin and Abhi Minerals Pvt. Ltd., Nepal

Jagritee Industries Pvt. Ltd., Nepal

Ganga Mala Minerals Pvt. Ltd., Nepal

Prof. Dr. D. R. Kansakar, Nepal Engineering College, Pokhara University

We are greatful to the members of Nepal Geological Society, various organizations and individuals who provided generous support for successful organization of the Workshop.

Nepal Geological Society and

27th HKT Organizing Committee

225


ContentsThe South Tibet Detachment is a backthrust: New evidence from studies along the length of the Himalayan orogenA. Alexander G. Webb and Dian He ........................................................................................................................1

Structurally-controlled melt formation and accumulation: Evidence for channel fl ow in the HimalayaA. K. Jain, Sandeep Singh, Sushmita, Puneet Seth and Mrinal Shreshtha .............................................................2

Tunnel deformation in Chameliya Hydro–Electric Project: A case studyA. S. Mahara ............................................................................................................................................................3

Neotectonic control on the alluvial fan development south of the Shillong Plateau, BangladeshA. K. M. Khorshed Alam and Md. Badrul Islam .....................................................................................................4

Crustal geoelectric structure of the Sikkim Himalaya and adjoining Ganga foreland basinA. Manglik, G. Pavankumar and S. Thiagarajan ...................................................................................................5

Comments on paleobiogeography of family Cervidae from the Sub-Himalayan Siwalik Group of PakistanAbdul Ghaffar ..........................................................................................................................................................6

Crustal and lithospheric mantle structures in central Asia derived from geoid, elevation and thermal analysisAlexandra Robert, Ivone Jiménez-Munt, Manel Fernàndez and Jaume Vergés ......................................................7

Stable isotope composition of precipitation across central Nepal HimalayaAnanta Gajurel, Christian France-Lanord and Jérôme Lavé .................................................................................9

The central Himalayan tectonic framework, fragile ecological balance and natural disasterAnshu Kumar Sinha ...............................................................................................................................................10

Paleoclimate analysis of the Neogene Thakkhola-Mustang Graben (central Nepal)B. R. Adhikari, M. Wagreich, Khum N. Paudayal and Ilse Draxler ..................................................................... 11

Climatic fl uctuations in the last 750 years from Indian Lesser Himalaya as inferred from speleothems: Evidence of a wetter Little Ice Age (LIA)B. S. Kotlia, F. Liang, G. A. Brook, S. M. Ahmad, Jian-Xin Zhao, L. B. Railsback, Waseem Raza, K. D. Collerson, L. M. Joshi and Jaishri Sanwal ...........................................................................................................12

Extrusion and bookshelf faulting revealed by InSAR in the Sulaiman range syntaxis (Pakistan)Béatrice Pinel-Puysségur, Laurent Bollinger and Christelle Baudry ....................................................................13

Paleoseismic signatures in the Karewas of Kashmir Valley (India) N/W Himalaya: Determination of magnitude of paleoearthquakes Bikram Singh and Rais Ahmad Khan .....................................................................................................................14

Late Quaternary sedimentation along the river valleys in Ladakh region of NW Trans Himalayan range: A climate-tectonic perspectiveBinita Phartiyal, Anupam Sharma and Girish Ch. Kothari ..................................................................................15

Anomalous thermal gradients in the South Tibetan Detachment System: Strain and heating in decoupling Tibetan Sedimentary Sequence and Higher Himalayan CrystallinesC. Montomoli, R. Carosi and C. Visonà ................................................................................................................16

226


An update on earthquake recurrence in the HimalayaC. P. Rajendran and Kusala Rajendran .................................................................................................................18

Local seismic network and seismicity of the Nepal HimalayaC. Timsina, D. R. Tiwari, U. Gautam, R. Pandey, S. N. Sapkota, L. B. Adhikari, P. L. Shrestha, B. P. Koirala, M. Bhattarai, M. Jha, T. Kandel, C. Gourraud, L. Bollinger .....................................................................................19

Using isotope geochemistry to unravel the mysteries of the Main Central Thrust, Sikkim HimalayaCatherine M. Mottram, Nigel B. W. Harris, Randy. R. Parrish, Tom W. Argles and Clare J. Warren .................20

Morphometric characteristics as indicators of active tectonics in Sikkim (Tista River, eastern Himalaya): Structural and seismotectonics constraintsChandra S. Dubey, Mohmmad Tajbakhsh, Ravindra P. Singh, Bhupendra K. Mishra, Dericks P. Shukla, Tarini Bhatnagar, Neelratan Singh, Arnold L. Usham, Lokrampum Thoithoi and Aunshi S. Ningreichon ....................22

First landslide inventory in the Karakoram National Park: The Chogo Lungma glacial valleyChiara Calligaris, Giorgio Poretti and Shahina Tariq .........................................................................................23

Low-pressure anatexis in the Higher Himalayan Crystallines of eastern Nepal revealed by cordierite-bearing lithologiesChiara Groppo, Franco Rolfo and Pietro Mosca .................................................................................................25

Tectono-metamorphic characterization of Higher Himalayan Crystallines in the Mugu-Karnali valley (Western Nepal): Preliminary dataChiara Montomoli, Salvatore Iaccarino, Carosi Rodolfo and Dario Visonà .......................................................27

Geodynamic signifi cance of HP metamorphism in Atbashi Range (South Tianshan, Kyrgyzstan) and inferences for crustal-scale structure of north Tarim-Tibet orogenic systemChloé Loury, Yann Rolland, Stéphane Guillot, Dmitriy V. Alexeiev and Alexander V. Mikolaichuk ....................29

An integrated landslide susceptibility assessment approach within DRR-related technical cooperation projects of the BGRD. Balzer, M. Fuchs, D. Kuhn and J. Torizin .........................................................................................................30

Climate change in the Nepal Himalaya: Observations, projections and adaptation challengesDanda Pani Adhikari .............................................................................................................................................31

Miocene gneiss-domes in the central Pamir: Burial and exhumationDaniel Rutte, Mike Stearns, Lothar Ratschbacher and Bradley Hacker ..............................................................32

Block rotations around the eastern Himalayan Syntaxis: Paleomagnetic investigations in the Gaoligong ShanDaniela Kornfeld, Sabine Eckert, Erwin Appel, Lin Ding and Deliang Liu .........................................................34

Testing variations in shortening estimates in central Nepal along the Modi and Kali Gandaki RiversDelores M. Robinson and Aaron J. Martin ............................................................................................................35

GLOF susceptibility of Sikkim HimalayasDericks P. Shukla, Chandra S. Dubey, R. P. Singh, B. K. Mishra and T. Luthra ..................................................36

227


Investigation of the Seti River disaster (May 5, 2012) and assessment of past and future mountain hazards facing Pokhara, Nepal and upstream communitiesDhananjay Regmi, Jeffrey Kargel, Lalu P. Paudel, Khagendra R. Poudel, Gregory Leonard, Bhabana Thapa and Anusha Sharma ..............................................................................................................................................38

New fi ndings from crystalline rocks of the frontal klippen, Nepal Himalaya, demonstrate mountain-building via underplatingDian He, A. Alexander G. Webb, Kyle P. Larson and Axel K. Schmitt .................................................................40

Petrographical analysis of crystalline rocks of the Higher Himalaya along the Marsyangdi ValleyDiwakar Khadka, Naresh Kaji Tamrakar and Prakriti Raj Joshi .........................................................................42

GPS constraints on Indo-Asian convergence in the Bhutan Himalaya: Segmentation and potential for a 8.2<Mw<8.8 earthquakeDowchu Drukpa, Phuntsho Pelgay, Anjan Bhattacharya, Phillipe Vernant, Walter Szeliga and Roser Bilham ..43

Infl uence of geodynamic processes on social developmentE. Nesterov .............................................................................................................................................................45

Tectonic geomorphology and active megathrust traces in the East-Himalayan SyntaxisElise Kali, Paul Tapponnier, Jérôme van der Woerd, Swapnamita Choudhury, Saurabh Baruah, A. K. M. Khorshed Alam, Aktarul Ahsan, Catherine Dorbath, Laurent Bollinger and Paramesh Banerjee ......................47

Patterns of mineral’s distribution in the folded regions Evgeny M. Nesterov ...............................................................................................................................................48

Hillslope erosion and landslide dynamics in the central HimalayasFlorian Gallo, Jérôme Lavé, Guillaume Morin, Christian France-Lanord, and Ananta Prasad Gajurel ...........50

The M8 Jan. 15th, 1934 Bihar earthquake: Intensity inversion and source update with instrumental dataFranco Pettenati, Livio Sirovich and Stefano Picotti ............................................................................................51

Looking for metamorphic CO2 degassing in the active Himalayan orogenFranco Rolfo, Chiara Groppo, Pietro Mosca, Simona Ferrando, Emanuele Costa and Krishna P. Kaphle .......53

From low-grade metamorphism to anatexis: a petrologic journey across the eastern Nepal Himalaya and implications for the “channel fl ow” modelFranco Rolfo, Chiara Groppo, Pietro Mosca and Bruno Lombardo ...................................................................54

Calc-silicate rocks from different structural levels of the Greater Himalayan Sequence (eastern Nepal): Garnet-bearing vs. garnet-absent assemblagesGiulia Rapa, Chiara Groppo, Simona Ferrando and Franco Rolfo ....................................................................56

Engineering geological mapping and geo-hazard and geo-environmental studies of Quaternary deposits of Birendranagar Municipality and its surrounding area, Surkhet Valley, Rapti ZoneGyani Raja Chitrakar, Birendra Piya, Dinesh Nepali and Surya Prakash Manandhar .......................................57

Emplacement of hot metamorphic nappe during 15-10 Ma and thermal imprint on the underlying early Miocene fl uvial Dumri Formation in Jumla-Surkhet area, western NepalHarutaka Sakai, Hideki Iwano, Tohru Danhara, Takafumi Hirata and Yutaka Takigami ....................................58

228


Rift-related origin of the Paleoproterozoic Kunchha Formation and cooling history of the Kunchha nappe and Taplejung granites, eastern Nepal Lesser Himalaya: A multichronological approachHarutaka Sakai, Hideki Iwano, Tohru Danhara, Yutaka Takigami, Santa Man Rai, Bishal Nath Upreti and Takafumi Hirata ....................................................................................................................................................60

Assembly of the Lesser Himalayan duplex along the Tons Valley, northwestern India Hongjiao Yu and A. Alexander G. Webb ................................................................................................................61

Differential exhumation rates in the High Himalaya perpendicular to the orogenic convergence: From Mt. Everest to the Arun River gorgeItai Haviv, Jean-Philippe Avouac, Ken A. Farley, Mark T. Harrison, Prabhat Neupane and Matt Heizler ........63

Contemporary crustal deformation measured by the Caltech-NSC-DASE Nepal cGPS NetworkJ. Genrich, J. Galetzka, F. Chowdhury, K. Chanard, T. Ader, J.-P. Avouac, M. Flouzat, S. Sapkota and the NSC Team ......................................................................................................................................................................64

Shortening rates and seismotectonic model along the Himalayan arc of NepalJ. Lavé, D. Yule and S. Sapkota ............................................................................................................................65

Landslide recognition and analysis: A case study in the Three-Gorges Area, ChinaJ. Rohn, R. Bi, M. Schleier, C. Dumperth, D. Ehret and W. Xiang .......................................................................66

Landslide dams in the western Himalayan range and mitigation measuresJean F. Schneider ...................................................................................................................................................67

Seismic hazard in the Himalaya of Nepal: Recent progress and perspectivesJean-Philippe Avouac ............................................................................................................................................68

The May 5th fl ood disaster in Pokhara Nepal: A last warning sign sent by nature?Jörg Hanisch, Achyuata Koirala and Netra Prakash Bhandary ...........................................................................69

Asian summer monsoon history in southern Tibet for the late Holocene: Results from a network of tree-ring isotope chronologiesJussi Griessinger and A. Bräuning ........................................................................................................................70

Nannofossil biostratigraphy from Bhuban Fomation, Mizoram, Norheastern India and its palaeoenvironmental interpretationsJyotsana Rai, J. Malsawma, C. Lalrinchhana, Lalchawimawii and V. Z. Ralte ...................................................72

The Kahun Crystalline Klippe, Tanahu, central Nepal: Westward continuation of the Kathmandu Nappe?Kabi Raj Paudyal, Roshan Koirala and Lalu P. Paudel ........................................................................................74

Soils as proxies of the history of landscape and climate: Examples from eastern BhutanKarma D. Dorji and Rupert Bäumler 75 Vegetation and climate during 50 kyr BP in the Kathmandu basinKhum N. Paudayal, Sudarshan Bhandari and Arata Momohara .........................................................................76

Constrains on the visco-elastic structure of the Tibetan Plateau from deformation induced by variations in hydrological surface loading over multiple time scalesKristel Chanard, Sylvain Barbot1, Jean-Philippe Avouac and William Amidon ..................................................77

Disequilibrium between short term and long term exhumation rates in the Gongga granite, western SichuanKristen L. Cook, Yuan-his Lee and Arjun Heimsath .............................................................................................78

229


Tectonic Insight from P-T-t paths, upper Tama Kosi region, NepalKyle P. Larson, Felix Gervais and Dawn A. Kellett ..............................................................................................79

Earthquakes surface ruptures in the Sir Khola valley: Implications for the recurrence time of great Himalayan earthquakesL. Bollinger, S. Sapkota, P. Tapponnier, Y. Klinger, Y. Gaudemer and D. Tiwari .................................................80

Geology of Dharan-Mulghat area in east Nepal with special reference to microstructure and strain analysisLalit Kumar Rai, Kamala Kant Acharya and Megh Raj Dhital ............................................................................81

Stratigraphic classifi cation of the central Nepal Lesser Himalaya by Stöcklin (1980): Does it need modifi cation?Lalu P. Paudel, Kabi Raj Paudyal, Sujan Devkota, Tara Pokhrel, Naresh Maharjan, Deo Kumar Limbu, Roshan Koirala and Pramod Pandey ................................................................................................................................82

Detrital rutile U–Pb geochronology by LA–MC–ICP–MS: New approach, reference materials and applications to sedimentary provenance in the Bhutan HimalayasLaura Bracciali, Randall R. Parrish, Daniel J. Condon, Matthew S.A. Horstwood, Yani Najman .....................83

Stable isotope compositions in modern gastropod shells from the Tibetan Plateau and the Pamirs mirror hydrologic and climatic signals in sub-seasonal resolutionLinda Taft, Uwe Wiechert, Hucai Zhang, Steffen Mischke, Birgit Plessen, Marc Weynell, Andreas Winkler and Frank Riedel ..........................................................................................................................................................85

Coupling of tectonics and crustal anatexis and the formation of Cenozoic granites in the Himalayan collisional orogenic beltLingsen Zeng, Li-E Gao, Jing Liu, Kejia Xie and Guyue Hu ...............................................................................86

Detailed monazite chronology of Greater Himalayan Series metapelites from BhutanLucy V. Greenwood, Tom W. Argles, Randall R. Parrish, Nicholas M.W. Roberts, Clare Warren and Nigel B.W. Harris .....................................................................................................................................................................88

Characteristic vertical throw and slow Late-Quaternary uplift rate on the Karaxingar Push-up Thrust, Xinjiang, ChinaM. Etchebes, P. Tapponnier, Y. Klinger, J. Van Der Woerd, Xu Xiwei, Sun Xinzhe, Tan Xibin, M. Rizza and Tsang Lok Hang ................................................................................................................................................................90

Seismological overview of 18th September Mw=6.9 earthquake at the Sikkim-Nepal borderM. Jha, D. R. Tiwari, S. N. Sapkota, L. Bollinger, R. Pandey, C. Timsina, U. Gautam, P. Shrestha, B. P. Koirala, L. B. Adhikari, M. Bhattarai, T. Kandel and C. Gourraud ....................................................................................91

Modern and Late Holocene average erosion rates of the central Himalayan arcM. Lupker, J. Lavé, C. France-Lanord and P. H. Blard .........................................................................................92

Petrogenesis of alkaline mafi c dykes in the Nagar Parkar igneous complex, southeastern Sindh, PakistanM. Qasim Jan, Amanullah Laghari, M. Asif Khan and M. Hassan Agheem ........................................................93

Towards improved snow and glacier melt simulation in a distributed hydrological framework: Application at Narayani river basin of central Nepal HimalayaMaheswor Shrestha, Lei Wang, Toshio Koike, Yongkang Xue and Yukiko Hirabayashi ......................................95

230


Integrated pressure-temperature-time constraints for the Tso Morari dome (Northwest India) Part II: Implications for the burial and exhumation path of UHP units in the western HimalayaMarc R. St-Onge, Nicole Rayner, Richard M. Palin, Michael P. Searle, Dave J. Waters .....................................96

High-mountain geohazards in the Pamir (Tajikistan) induced by climate changeMartin Mergili, Fabian E. Gruber, Johannes P. Mueller and Jean F. Schneider ..................................................98

Timing of prograde metamorphism in the High Himalaya of NW Lahul (NW India)Martin Robyr, Sriparna Banerjee and Afi fé El Korh ..........................................................................................101

Forming global geoparks in the Nepal HimalayaMasaru Yoshida, Khem Raj Nepal and Bishal Nath Upreti .................................................................................103

Elasto-plastic fi nite element modeling along the Project INDEPTH profi le: Implication for the Himalayan tectonicsMatrika Prasad Koirala and Daigoro Hayashi ..................................................................................................105

Distribution of frontal faults in Nepal HimalayaMegh Raj Dhital ...................................................................................................................................................106

Late Paleozoic and Mesozoic evolution of the Peri-Gondwanan plates and paleobiogeographical evidences of the Early Jurassic position of the Lhasa BlockMichal Krobicki, Jan Golonka and *Iuliana Lazar ............................................................................................107

Crustal melt granites and migmatites along the Nepal Himalaya: Implications for channel fl owMike Searle, John Cottle, Micah Jessup, Mike Streule, Rick Law and Dave Waters .........................................109

The Muzaffarabad earthquake of 8 October and the 8 August 2012 Sheikhupura earthquake: New insights into Himalayan seismicity and tectonicsMonalisa and M. Qasim Jan .................................................................................................................................111

Evolution and depositional characteristics of the Late Quaternary Kathmandu basinMukunda Raj Paudel ............................................................................................................................................ 113

Engineering geological investigation for hydropower development in the Himalaya: A case study on Upper Trishuli-1 Hydropower ProjectNarayangopal Ghimire and Lalu P. Paudel and Sangbae Lee ............................................................................ 115

Ring shear strength and mineralogical perspective on large-scale landslides on the mid-Nepal HimalayaNetra P. Bhandary, Ryuichi Yatabe, Ranjan K. Dahal, Shuichi Hasegawa and Manita Timilsina .................... 116

Cretaceous-Cenozoic magmatism in the Pamir and a comparison with TibetNicole Malz, Jörg A. Pfänder, Lothar Ratschbacher and Bradley R. Hacker ..................................................... 119

Integrated pressure-temperature-time constraints for the Tso Morari dome (Northwest India) Part I: In situ U-Pb geochronology of monazite and zirconNicole Rayner, Marc R. St-Onge, Richard M. Palin, Michael P. Searle and Dave J. Waters .............................121

231


What drives variations in the Indian summer monsoon?Nigel B. W. Harris, Dave Mattey, Peter van Calsteren, Louise Thomas and Talat Ahmad ................................122

Lithostratigraphy and structural pattern of the Siwaliks in Surkhet and Bardiya Districts, mid-western NepalNirmal Kafl e, Kamalakanta Acharya and Megh Raj Dhital ................................................................................124

Barrovian metamorphism and crustal anatexis in the Danba structural culmination, E Tibet: Was it polymetamorphic?Owen Weller, Marc St-Onge, David Waters, Nicole Rayner, Mike Searle, Sun-Lin Chung, Richard Palin, Yuan-Hsi Lee and Xi-Wei Xu ........................................................................................................................................125

Precise magnetostratigraphy (13–10 Ma) and rock-magnetic zonation of the Siwaliks from the lower part of Tinau Khola north section, Nepal P. Gautam, P. D. Ulak, K. N. Paudayal, B. R. Gyawali and S. Bhandari ............................................................127

Synkinematic magmatism, heterogeneous deformation, and progressive strain localization in a strike-slip shear zone: The case of the right-lateral Karakorum FaultP. H. Leloup, E. Boutonnet, N. Arnaud, J. L. Paquette, W. J. Davis and K. Hattori ...........................................128

Seismic behavior of the Main Himalayan Thrust: Giant events or clustering of great earthquakes?Paul Tapponnier, Soma Nath Sapkota, Laurent Bollinger and Yann Klinger ......................................................129

Deciphering high-pressure metamorphism in collisional context using microprobe-mapping methods: Application to the Stak eclogitic massif (NW-Himalaya)Pierre Lanari, Stéphane Guillot, Nicolas Riel, Olivier Vidal, Keiko H. Hattori, Stéphane Schwartz and Arnaud Pêcher .................................................................................................................................................................130

Glacial lakes mapping in the Hindu Kush Himalayas and risk assessment of their outburst fl oodsPradeep K. Mool, Wu Lizong, Sharad P. Joshi, Arun Shrestha and Rajendra B. Shrestha ................................131

Dynamics of the Bagmati River in relation to geological terrains, central Nepal Lesser and Sub-HimalayasPramila Shrestha and Naresh Kazi Tamrakar .....................................................................................................132

Physical, mechanical and petrographic properties of Lesser Himalayan rocks from Kavre area: An assessment of quality for concrete aggregatesPrem Nath Paudel and Naresh Kazi Tamrakar....................................................................................................133

Role of Indian plate obliquity vis-à-vis interplate deformation behind the generation of large earthquakes along the arcuate Himalayan segmentProsanta Kumar Khan and Md. Afroz Ansari ......................................................................................................134

Geological, engineering geological and geotechnical study of the Mai Khola Hydroelectric Project, Ilam, Eastern, NepalPusker Raj Joshi, Kamala Kant Acharya and Rabindra Dhakal .........................................................................135

Plio-Quaternary exhumation history of the Garhwal-Kumaon Himalayas, NW-India: An analysis on low-temperature thermochronological dataR. C. Patel, Paramjeet Singh and Nand Lal ........................................................................................................136

Electro-chemical technique for base metal explorationR. C. Talukdar ......................................................................................................................................................139

232


GPR based slope stability study of Korapani Landslide, Jammu HimalayaR. P. Singh, Dericks P. Shukla, Chandra S. Dubey, B. K. Mishra and T. Bhatnagar ..........................................140

Engineering geological and geotechnical studies of Budhi Gandaki Hydroelectric Project, central NepalRabindra Prasad Dhakal, Prakash Chandra Adhikary, Jayandra Man Tamrakar and Matrika Prasad Koirala ..... 143

Lithostratigraphy of metasedimentary succession of Nepal Lesser Himalaya: A revision of standardizationRam Bahadur Sah ................................................................................................................................................144

Towards green economy through community ‘Gegran’ benefi ciary goup: A case of Lothar Khola watershed, Chitwan, central NepalRamesh M. Tuladhar ............................................................................................................................................146

Ground motion records from the accelerometer network of National seismological centre, Nepal R. Pandey, M. Bhattarai, C. Timsina, S. N. Sapkota, U. Gautam, L. B. Adhikari, M. Jha, T. Kandel, P. Shrestha, B. P. Koirala, C. Gourraud, V. Boutin and L. Bollinger .....................................................................................147

Quaternary architecture of the Tangtse valley, Ladakh, NW Transhimalaya: Implications to tectonics, landform evolution and climateRandheer Singh, Binita Phartiyal, Girish Ch. Kothyari and Anupam Sharma ..................................................148

An overview of landslide science in the Nepal HimalayaRanjan Kumar Dahal ...........................................................................................................................................149

Long-term growth of the Himalaya inferred from interseismic InSAR measurementRaphae Grandin, Marie-Pierre Doin, Laurent Bollinger, Bé atrice Pinel-Puyssé gur, Gabriel Ducret, Romain Jolivet and Soma Nath Sapkota ...........................................................................................................................150

Petrology of the Middle Triassic volcaniclstic rocks from Balochistan, Pakistan and its relationship with the break-up of GondwanaRehanul Haq Siddiqui, M. Qasim Jan, Asif Hanif Chaudhry and Sikandar Ali Baig .........................................151

Tectonometamorphic evolution of the upper Likhu Khola region, east-central NepalRichard From, Kyle Larson and John Cottle .......................................................................................................153

Reconstruction of paleomonsoon record in the Kathmandu Valley during the last 700 kyr: Approach from pollen and charcoal analysesRie Fujii, Misa Sugimoto, Takeshi Maki and Harutaka Sakai .............................................................................154

Geomorphology, paleoseismology and slip rate of the Main Frontal Thrust between the Charnath and Devdhar Khola, Eastern NepalRizza Magali, Sapkota Soma Nath, Tapponnier Paul, Bollinger Laurent, Etchebes Marie, Klinger Yann, Pandey Ramesh and Kali Elise ........................................................................................................................................155

Geological mapping in Nepal Himalaya: Importance and challenges for underground structuresS. C. Sunuwar .......................................................................................................................................................156

Probabilistic seismic hazard analysis of Kathmandu ValleyS. Rajaure and G. K. Bhattarai ...........................................................................................................................157

233


Structural, metamorphic and geochronologic constrains of a ductile shear zone within the core of Higher Himalayan Crystallines in western Nepal: The Mangri Shear ZoneSalvatore Iaccarino, Carosi Rodolfo, Chiara Montomoli, Antonio Langone and Dario Visonà ........................158

Cause, mechanism and impact of the Seti Flood of 5th May 2012, Western NepalShreekamal Dwivedi and Yojana Neupane ..........................................................................................................160

Role of mega-landslides in valley development in the Nepal HimalayaShuichi Hasegawa and Ranjan Kumar Dahal ....................................................................................................162

Enclaves in Tirit granitoids, Nubra Valley, Northern Ladakh: Evidence of sub-volcanic emplacement and partial assimilation Sita Bora, Santosh Kumar, Brajesh Singh and Umesh K. Sharma ......................................................................163

Hunting of past earthquake along the Main Frontal Thrust using recent geomorphic feature in the area between the Mahara Khola to Dharan in central and eastern NepalSoma Nath sapkota, Paul Tapponnier, Laurent Bollinger, Yann Klinger, Indira Siwakoti and D. R. Tiwari ......164

Glacier basal conditions inferred from seismic dataStefano Picotti, Flavio Accaino and Franco Pettenati .......................................................................................165

Importance of continental subductions for the growth of the Tibetan plateauStéphane Guillot and Anne Replumaz ..................................................................................................................167

Spatial and temporal erosion variability and its drivers in the Arun valley, eastern Nepalese HiamalayaStephanie Olen, Bodo Bookhagen and Manfred Strecker ...................................................................................169

Runoff modeling of glacierized watersheds of Koshi basin in NepalSubash Tuladhar, Narendra Man Shakya and Maheswor Shrestha ....................................................................170

Nature of deformation of the frontal wedge of Darjeeling-Sikkim Himalayas, IndiaSubhajit Ghosh, Puspendu Saha, Rwiti Basu, Sujoy Dasgupta, S.K.Acharyya, Nibir Mandal and Santanu Bose ........................................................................................................................................................171

Natural disaster in Nepal and its projection in the context of climate changeSubodh Dhakal .....................................................................................................................................................175

Is the fault that carries the Kathmandu klippe the Main Central Thrust or an intra-Greater Himalayan thrust?Subodha Khanal and Delores M. Robinson .........................................................................................................176

Study of recharge zone and potential area of groundwater recharge in the Kathmandu valleySwostik Kumar Adhikari¹, Dinesh Pathak¹ and Nir Shakya² ...............................................................................177

Evidence of fault activity recorded in the Pleistocene fl uvio-lacustrine succession in Kathmandu Valley, NepalT. Sakai, A. P. Gajurel, H. Tabata, N. Ooi and B. N. Upreti ...............................................................................178

Flood in Gangapur Village, Banke District: An example of climate-induced disaster in NepalTara Nidhi Bhattarai and Rabindra Osti .............................................................................................................179

Lateral variability of crustal geometry in the Himalayas from west Nepal to BhutanThéo Berthet,*György Hetényi, Rodolphe Cattin, Cédric Champollion, Jamyang Chophel, Erik Doerfl inger, Dowchu Drukpa, Paul Hammer, Sarah Lechmann, Nicolas Lemoigne, Som Sapkota .......................................181

234


Convergence rate across the Nepal Himalaya and interseismic coupling on the Main Hi-malayan Thrust: Implications for seismic hazardThomas Ader, Jean-Philippe Avouac, Jing Liu-Zeng, Helene Lyon-Caen, Laurent Bollinger, John Galetzka, JeGenrich,Marion Thomas, Kristel Chanard, Soma Nath Sapkota, Sudhir Rajaure, Prithvi Shrestha, Lin Ding and Mireille Flouzat .............................................................................................................................................183

2D lithospheric structure of Himalaya collision zone from geophysical and petrological dataTunini Lavinia, Jiménez-Munt Ivone and Fernàndez Manel ...............................................................................184

Greater India extent at its western edge: First palaeomagnetic constraints Ursina Liebke, Erwin Appel and Alberto Resentini ............................................................................................186

Carbon and oxygen isotopic ratios of the Manipur Ophiolitic Melange zone carbonate facies of Indo-Myanmar orogenic belt, NE India Vinod C. Tewari, A. K. Singh, A. N. Sial and N. Ibotombi Singh ........................................................................187

Groundwater storage in the Kathmandu Valley: Potentials and challengesVishnu Prasad Pandey and Futaba Kazama........................................................................................................189

The timing of exhumation of the Lesser HimalayaY. Najman, G. Foster, I. Millar, R. Parrish, M. Bickle, D. Mark, L. Reisberg, R. Mckenzie and R. Rhiede .......190

Glacial retreat and its impact in Tibetan Plateau under global warmingYao Tandong .........................................................................................................................................................192

U-Pb zircon geochronology along the Arun River, eastern Nepal: Consistency of ~1.8 Ga ages from the Main Boundary Thrust to the Ama Drime Antiform in southern Tibet Yaron Katzir, Itai Haviv, Jean-Philippe Avouac, Matthew A. Coble and Tzahi Golan ......................................194

Lithological mapping in the central segment of the Yarlung Zangbo suture zone using ASTER dataYoshiki Ninomiya and Bihong Fu ........................................................................................................................195

Tectonic escape model during Indo-Asia collision: new insights from the relationship between vertical and horizontal shear zones in SE TibetZhiqin Xu, Zhihui Cai,Huaqi Li, Guanwei Li and Hui Cao .................................................................................197

Orogen-parallel extension and exhumation of the Greater Himalaya in the late Oligocene and MioceneZhiqin Xu, Qin Wang, Arnaud Pêcher, Fenghua Liang, Xuexiang Qi, Lingsen Zeng, Huaqi LI Zhihui Cai and Hui Cao ...............................................................................................................................................................198

Flat versus steep subduction: Contrasting modes for the formation and exhumation of high- to ultrahigh-pressure rocks in continental collision zonesZhonghai Li, Zhiqin Xu and Taras Gerya ..........................................................................................................199

Early Mesozoic orogenesis newly discovered in the Lhasa terrane, south TibetLi Hua-Qi and Xu Zhi-Qin ...................................................................................................................................200

Lumla window, Eastern Himalaya – stratigraphy, structure, and implications for extra-peninsular Proterozoic basins in IndiaDilip Saha, Saheli Sanyal and Tapos Goswami ...................................................................................................202

235


Temporal and Spatial Changes in Himalayan Glaciers - Impact of Climate VariabilityK. Kesarwani, B. Pratap, M. Mehta, R. Bhambri, R. and D. P. Dobhal ...........................................................205

Late Quaternary uplit-erosion of the Dhauladhar range and formation of Kangra intermontane basin and Ravi river terraces pull-apart basin, northwest Himalaya-Climate-tectonic linkageV. C. Thakur and M. Joshi ....................................................................................................................................205

Regional-extensive Mg-Al metasomatism in the Main Central Thrust Zone of eastern NepalElena Dalla Fontana, Chiara Groppo, Simona Ferrando1, Franco Rolfo ..........................................................207

Hazard zoning of liquefaction potential at sedimentary deposits Rama Mohan Pokhrel ..........................................................................................................................................208

Erosion assessment in the Middle Kali Gandaki (Nepal): a sediment budget approach Monique Fort, Etienne Cossart ...........................................................................................................................209

~1,800 years record of climatic variation from the Indian Himalaya: Speleothem study.Jaishri Sanwal, B. S. Kotlia, S. M. Ahmad,

C. P. Rajendran1 and Kusala Rajendran ........................................210

Timing of Asia-India collision evident from Zircon U-Pb Chronology and Lu-Hf Isotopes of granitoids and xenolith of Ladakh Batholith, Northwestern Indian HimalayaSantosh Kumar, Brajesh Singh, Fu-Yuan Wu, Wei-Qiang Ji ................................................................................ 211

Was the exhumation of the Greater Himalayan Sequence in central Himalayas totally driven by STD and MCT?R. Carosi, C. Montomoli C, S. Iaccarino, D. Rubatto D and Visonà ...................................................................212

1


The South Tibet detachment (STD) spans the length of the Himalayan orogen and separates the crystalline core below from a (meta-) sedimentary sequence of Tethyan rocks above. It is considered the lynchpin structure in models for the assembly of the major Himalayan tectonic units and emplacement of the crystalline core. This status refl ects the interpretation of this structure as a low-angle normal fault system that accommodated large magnitude slip parallel to the main shortening direction. Such a structure represents a signifi cant anomaly within one of Earth’s great contractional orogens. In recent years, this structure has been alternatively interpreted as a backthrust. Two fi ndings in support of the alternative hypothesis are (1) growing recognition that the STD is sub-horizontal, with a consistent right-way-up thermal signature, for ~200 km south to north across the Himalaya (e.g., Yin 2006; Webb et al. 2011a; Kellet and Grujic 2012); and (2) recently presented evidence that the southern limit of the STD merges with the Main Central thrust, i.e., the Himalayan sole thrust during STD activity, forming a triangle zone geometry at the leading edge of the crystalline core (Yin 2006; Webb et al. 2007; 2011a; 2011b). Here we introduce new data supporting the backthrust hypothesis from the western, central, and eastern Himalaya and propose a new synthesis of the Himalayan structural geometry. In the Zanskar region of the northwest India Himalaya, new fi eld mapping across the Tethyan sequence-crystalline core boundary documents occurrence of the STD from the well-recognized northwest-trending trace of the Zanskar shear zone to the southwest, towards a merger with the Main Central Thrust. In the Himachal region of the northwest India Himalaya, a new study of the regional pattern of metamorphic fi eld gradients is compared with metamorphic predictions of STD normal fault and backthrust models. Current normal fault models cannot explain the right-way-up metamorphic fi eld gradient observed across the southern Main Central Thrust hanging wall, but this is consistent with predictions of backthrust models. New mapping, microstructural, and geochronologic studies across the northern margins of frontal Main Central Thrust (MCT) klippen across southern Nepal demonstrate the presence of the STD here, and of its southwards merger with the Main Central Thrust. This work is presented by He et al. (this volume). The southwards convergence of the STD and MCT have long been recognized in the eastern Himalaya: in southern Bhutan they are locally exposed ~2 km apart (e.g., Grujic et

al. 2002). A recent two-stage model developed in this region shows the STD active with backthrust kinematics (Kellett and Grujic 2012), followed by a brittle STD reactivation. The model reactivation is normal faulting restricted to the range crest. However, new fi eld mapping along the range crest here documents an exclusively ductile STD, indicating that only the fi rst stage of the model is viable. The new results bolster the STD backthrust interpretation, primarily by offering rich new data sets that demonstrate southwards convergence and merging of the STD and the MCT. We integrate new and existing constraints on the STD morphology to update the structural geometry of the Himalaya. The trace of the STD-MCT merger, or “branch line,” trends sub-parallel to the arc of the orogen. The branch line is largely preserved (buried) in the western Himalaya, largely eroded but locally preserved across the central Himalaya, and potentially completely eroded across the eastern Himalaya.

REFERENCES

Grujic, D., Hollister, L. S. and Parrish, R. R., 2002, Himalayan metamorphic sequence as an orogenic channel: insight from Bhutan: Earth and Planetary Science Letters, v. 198 (1-2), pp. 177-191.

He, D., Webb, A. A. G., Larson, K. L., Schmitt, A. K., New fi ndings from crystalline rocks of the frontal klippen, Nepal Himalaya, demonstrate mountain-building via underplating. This volume.

Kellett, D. A., and Grujic, D., 2012, New insight into the South Tibetan detachment system: Not a single progressive deformation. Tectonics, v. 31 doi:10.1029/2011TC002957.

Webb, A. A. G., Yin, A., Harrison, T. M., Célérier, J., and Burgess, W. P., 2007, The leading edge of the Greater Himalayan Crystallines revealed in the NW Indian Himalaya: Implications for the evolution of the Himalayan Orogen: Geology, v. 35 (10), pp. 955-958.

Webb, A. A. G., Schmitt, A. K., He, D., Weigand, E. L., 2011a, Structural and geochronological evidence for the leading edge of the Greater Himalayan Crystalline complex in the central Nepal Himalaya. Earth and Planetary Science Letters, v. 304, pp. 483-495.

Webb, A. A. G., Yin, A., Harrison, T. M., Célérier, J., Gehrels, G. E., Manning, C. E., Grove, M., 2011b, Cenozoic tectonic history of the Himachal Himalaya (northwestern India) and its constraints on the formation mechanism of the Himalayan orogen. Geosphere, v. 7, pp. 1013-1061.

Yin, A., 2006, Cenozoic Tectonic Evolution of the Himalayan Orogen as constrained by along-strike variation of structural geometry, exhumation history, and foreland sedimentation: Earth Science Reviews, v. 76, pp. 1-131.

The South Tibet Detachment is a backthrust: New evidence from studies along the length of the Himalayan orogen

*A. Alexander G. Webb and Dian HeDepartment of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, USA

(*Email: [email protected])

2


Extensive crustal deformation and metamorphism of the Himalayan Metamorphic Belt (HMB), also known as the Great Himalayan Series (GHS) in Bhutan, have recently been modeled in an orogenic channel. This channel is delimited by the Main Central Thrust (MCT) along the base and the South Tibetan Detachment Zone (STDZ) along the upper margin of 15 to 20 km thick and northerly gently-dipping slab. Two sections with well-preserved structures and migmatite, one in Central Bhutan in extreme south near the MCT, and another in the Dhauli Ganga Valley of Uttarakhand in the core of the HHC near the STDZ are discussed in this presentation.

In Central Bhutan along the Mangde Chu (river), the GHS contains deformed and sheared porphyroclastic gneiss and schist. The HHC is thrust over the Lesser Himalayan Shumar/Buxa Group rocks along the MCT, and overlain by the detached and eroded outliers of the low grade metasedimentary sequences of the Chekha and Maneting formations belonging to the Tethyan Sedimentary Zone, having a distinct sharp contact.

Within the 500-m MCT zone, augen-bearing gneiss and schist contain penetrative quartzo-feldspathic concordant bands to give it a migmatite appearance. These stromatic-type migmatites are marked by numerous structures along which locally-generated melt is concentrated, besides its presence as the migmatite bands. Structures with melt are:

(1) Concordant gneissosity within the migmatite with numerous melt-controlled bands, thus producing stromatic migmatite.

(2) Post-stromatic migmatitic randomly-oriented structureless migmatite pods in the initial stages.

(3) Melt-rich ductile shear zones, both dextral and sinistral types and marked by melt-generated domains.

(4) Foliation boudins, having in situ quartzo-feldspathic melt along zones of decompression within their necks along the boudins axes. In such zones, main migmatitic foliation gets totally destroyed, where granite exhibits typical granular igneous textures to have grown during post-tectonic environment. These are also indicative of generation of granitic melt during decompression.

In the NW Himalaya along the Dhauli Ganga valley, the Vaikrita Group of the HHC is bound by the MCT at the base and the SDTZ –the Malari Fault at its top. It reveals small-scale asymmetric deformational structures, e.g. S-C and S-C’ fabrics, σ– and δ–structures, asymmetric folds, boudins, pinch and swells, mineral fi shes, mantled porphyroclasts, small-scale duplexes, shear zones and faults. Two phases of ductile deformation were observed in the HHC: (i) an early top-to-south (to SW) phase, superposed by (ii) a later phase of top-to-north (to NE) deformation.

In the uppermost parts of the sequence near the SDZ in the highest grade of the HHC, original and oldest migmatite fabric (Me1) parallels the existing foliation in schist and gneiss as layers or bands of leucocratic melt (stromatite). Other varieties of migmatite (Me2, Me4) and leucogranite reveal later in situ melting phases, whereas Me3 stage migmatites show evidence of melt migration.

Presence of deformational structures and in situ melt formation and accumulation are the unequivocal evidences that the Himalayan deformation and metamorphism has taken place in an orogenic channel, which been transported over the Lesser Himalayan sedimentary zone along the MCT in the extreme southernmost parts of the Himalaya in Central Bhutan.

Structurally-controlled melt formation and accumulation: Evidence for channel fl ow in the Himalaya

*A. K. Jain1, Sandeep Singh2, Sushmita2, Puneet Seth2 and Mrinal Shreshtha2

1Cental Building Research Institute, Roorkee-247667, India2Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee-247667-India


3


Alluvial fans developed at the southern base of the Shillong Plateau, Bangladesh have been mapped with the help of various remote sensing data. Objective of the study includes examination of the infl uence of neotectonics on the development of alluvial fans in a tectonically active and tropical humid region of the world. A series of alluvial fans have been developed in an E-W stretched area. Sixteen such alluvial fans have been identifi ed in an area of about 160 km long, but fans are also present beyond the study area. Several evidences of neotectonic activities have been identifi ed on the geomorphology and geology of the alluvial fans. Signifi cant evidences are paired terrace, downward shifting of stream confl uences, bending of consecutive streams along a certain line, very recent change in river fl ow, change in sinuosity of small streams, multi-level channel bars, abrupt but small widening in small consecutive streams, sag pond,

differential development of soil profi le etc. On the basis of these evidences this stretch can be divided into two domains - western and eastern. Western fans are comparatively larger in size and lie at a higher elevation than those of the east. Frequent channel shifting is observed in the eastern fans whereas channels are restricted within their valleys forming terraces in some cases in the western fans. Boundary between the alluvial fan and the adjacent fl oodplain shows also different characteristics-abrupt for western fans and gradual for eastern fans. Study results show that fans of the two domains are not equally developed, and the sediments on the fans are not of the same age although all of them are of Holocene age. It can be concluded that neotectonics operating in the region controls the development of the fans, sediment distribution pattern, and occurrence of natural hazards.

Neotectonic control on the alluvial fan development south of the Shillong Plateau, Bangladesh

*A. K. M. Khorshed Alam1 and Md. Badrul Islam2

1Geological Survey of Bangladesh, Dhaka 1000, Bangladesh and 2Department of Geology & Mining, University of Rajshahi, Rajshahi 6205, Bangladesh


4


The Sikkim Himalaya is a tectonically complex and seismically active region within the Himalayan collision belt. We present the results of a broadband MT survey along a 200-km-long profi le cutting across its major tectonic zones. The profi le starts from the Ganga Foreland Basin (GFB) and ends close to South Tibetan Detachment System in north Sikkim at ~5 km altitude. The data were acquired at average station spacings of 5-6 km and after data quality check transfer functions of 33 sites in the frequency range of 100 – 0.001 Hz have been used for 2D joint inversion of TE and TM modes. The decomposition analysis yields a regional geoelectric strike of N5˚E for the entire profi le, although there are variations in the dominant strikes of different geological sub-domains. The delineated crustal geoelectric structure brings out several interesting features. The GFB consists of a 4-6 km thick sedimentary layer overlying the basement (top of the Indian plate). The basement appears to be displaced downward by about 15 km beneath the Main Frontal Thrust/ Main Boundary Thrust, forming a ramp structure. The high conductivity dipping zone within the Lesser Himalayan Domain (LHD) is inferred to represent another major thrust

fault in the region, the surface location of which correlates with the Ramgarh Thrust along which Gondwana rocks are exposed in the Rangit Window. In Sikkim, the Main Central Thrust (MCT) is not well demarcated but has been mapped as an intense deformation zone named as Main Central Thrust Zone (MCTZ). This zone is seen in the geoelectric section as a resistive nearly vertical block bounded by two thrust planes. The High Himalayan Crystallines north of MCTZ also reveal complex subsurface structures and the presence of conductive blocks. A major inference of the present work is that the inferred fault within the LHD, rather than the MBT as suggested earlier, could be the main seismogenic fault causing recurrent seismicity in the region. The presence of a high conductivity zone in the lower crust of the Indian plate at the southern end of the profi le is enigmatic. Based on other geophysical studies in the Bengal Basin further south, it could be related to the Rajmahal volcanics and, thus, can have signifi cant tectonic implications. However, the present profi le needs to be extended further south to map the extent of this conductive zone for a more defi nitive correlation.

Crustal geoelectric structure of the Sikkim Himalaya and adjoining Ganga foreland basin

*A. Manglik1, G. Pavankumar1,2 and S. Thiagarajan1

1CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad-500007, India2Institute of Seismological Research, Raisan, Gandhinagar-382009, India


5


Nearly about six hundred meter tunnel has been deformed out of seven kilometer long tunnel in Chameliya Hydro-Electric Project located in far western Nepal of Darchula District. It was found that when tunnel excavation is goes on, the back chainage undergoes slight deformation about 10-12 meters later on and continues to the forward excavation with specifi ed gap with the tunnel face. At the deformation area, bed rock was disturbed by a local fault. Deformation of the tunnel is found continuously at the invert, at the tunnel wall and on the tunnel roof. Bed rock condition of the deformed area is talc and dolomite, talc and phyllite inter bedded. Orientation of the bed rock and the tunnel

alignment is just about the 10-12° variation at the deformed section. If the talc bed or phyllite bed found in the tunnel wall there the deformation found at the wall area if this rock association found at the crown it will be the at the crown or invert. Back chainage of the supported area, previously the lattice girder could not bear the weight and deformation found. In state of the lattice girder replaced by Steel rib and the problem remain same place. Spacing of the Steel Rib Support was reduced by 3 times less than designed spacing but could not solve the problem. Time to time convergence measurement has been taken at the deformed area.

Tunnel deformation in Chameliya Hydro–Electric Project: A case study

A. S. MaharaNepal Electricity Authority, Kathmandu, Nepal

6


The fossil remains of family Cervidae are poorly known from the sub-Himalayan Siwalik Group of Indo-Pakistan. Hitherto the Siwalik Group yielded the fossil remains of tribe Cervini only from the Plio-Pleistocene times but from China and south east Europe the fossil remains

of Mio-Pliocene tribe Cervini along with Pliocervini and Megacervini are being described. This paper focuses on the paleobiogeography of family Cervidae from the sub-Continent India with the evaluation of new fossil materials with stratigraphic analysis from this region.

Comments on paleobiogeography of family Cervidae from the Sub-Himalayan Siwalik Group of Pakistan

Abdul GhaffarDepartment of Meteorology, COMSATS Institute of Information Technology (CIIT), Islamabad

(E-mail: [email protected])

7


The long-standing convergence between Eurasia and Gondwanian-derived continental blocks since the end of the Paleozoic (Pubellier et al., 2008) is responsible for the present-day structure of the Central Asia region. The current geodynamics of the whole region is dominated by two major collision zones: (1) the Arabia-Eurasia collision forming the Zagros orogen since the late Eocene/early Miocene and which is also reactivating far-fi eld domains as the Alborz or the Kopet Dagh, and (2) the early Eocene India-Eurasia collision across the Himalaya which is responsible of the surrection of the Tibetan Plateau. The Tibetan Plateau is the most remarkable topographic structure of Central Asia and it presents heterogeneous crustal thicknesses (Kind et al. 2002; Miessner et al. 2004; Nabelek et al. 2009; Zhao et al. 2011) despite a relatively low relief. Major disagreements persist concerning the lithospheric structures as for example for the northern part of the Tibetan plateau where some authors propose a lithospheric delamination (Jimenez-Munt et al. 2008) whereas other authors propose that the lithosphere is thick (Zhao et al. 2011).

During the last decade, the Arabia/Eurasia and India/Eurasia collision zones have been the target of numerous geophysical surveys to unravel their crustal and lithospheric structures. However, some other areas of Central Asia suffer from an important lack of data and this study is carried out to image the crust and lithospheric mantle structures over the whole Central Asia region. We will fi rst present a complete compilation of crustal and lithospheric thicknesses obtained mostly from seismologial studies (receiver function method, deep seismic imaging, tomography data).

In order to obtain crustal and lithospheric maps over the whole area, we apply the method defi ned by Fullea et al. (2007) based on the combination of elevation and geoid data (Fig. 1) together with thermal fi eld to map crustal and lithospheric thickness. In this approach, we assume local isostasy and consider a four-layered model composed of crust and lithospheric mantle plus the sea water and the asthenosphere.

In this study, we will present the modelling results that best fi t the previous published data (fi gure 2).

Crustal and lithospheric mantle structures in central Asia derived from geoid, elevation and thermal analysis

*Alexandra Robert, Ivone Jiménez-Munt, Manel Fernàndez and Jaume VergésGroup of Dynamics of the Lithosphere (GDL), Institute of Earth Sciences Jaume Almera,

CSIC, Lluís Solé i Sabaris s/n, 08028 Barcelona, Spain(*Email: [email protected])

Fig. 1: Input data used in this study a) ETOPO1 data for the topography and bathymetry b) Filtered geoid anomaly from EGM2008 (until degree and order 11 of spherical harmonics).

8


Preliminary results (Fig. 2) indicate that crustal thickness appears to be directly correlated with high elevation region. In fact a thickened crust is observed underneath the Tibetan plateau (up to 75km thick), the Tien Shan belt, as well as underneath the Zagros, the Caucasus, the Alborz and the Kopet Dagh belts. However, our results indicate that the lithosphere is very thick underneath the Tibetan Plateau (up to 280km thick in the northern part of the plateau), the Tarim basin and the Tien Shan belt whereas it appears to be thinner underneath the Iranian plateau and the Anatolian plateau. This fi rst order information highlight major differences between (1) the India/Eurasia collision zone where the presence of a very thick lithosphere could be the result of underplating processes, and (2) the Arabia/Eurasia collision zone where the lithosphere is thinner further to the North-East of the Zagros orogen where we propose that subduction processes associated with a high thermal regime dominate.

REFERENCES

Fullea, J., Fernandez, M., Zeyen, H. and Vergès, J., 2007, A rapid method to map the crustal and lithospheric thickness using elevation, geoid anomaly and thermal analysis. Application to the Gibraltar Arc System, Atlas Mountains and adjacent zones, Tectonophysics, v. 430, pp. 97-117.

Jiménez-Munt, I., Fernàndez, M., Vergés, J. and Plat, J. P., 2008,

Lithosphere structure underneath the Tibetan Plateau inferred from elevation, gravity and geoid anomalies, Earth and Planetary Science Letters, v. 267.

Kind, R., Yuan, X., Saul, J., Nelson,D., Sobolev, S. V., Mechie, J., Zhao, W., Kosarev, G., Ni, J., Achauer, U., and Jiang, M., 2002, Seismic Images of Crust and Upper Mantle Beneath Tibet: Evidence for Eurasian Plate Subdution, Science, v. 298, pp. 1219.

Nabelek J., Hetenyi, G., Vergne, J., Sapkota, S., Kafl e, B., Jiang, M., Su, HChen, ., J., Huang,B. and the Hi-CLINB Team, 2009, Underplating in the Himalaya-Tibet collision zone revealed by the Hi-CLIMB experiment. Science v. 325.

Pubellier, M., Chamot-Rooke, N., Ego, F., Guezou, J., Konstantinovskaya, E., Rabaute, A. and Ringenbach, J., 2008, Structural map of eastern Eurasia. Commission for the geological map of the World.

Kind, R., Yuan, X., Saul, J., Nelson, D., Sobolev, S.V., Mechie, J., Zhao, W., Kosarev, G., Ni, J., Achauer, U., Jiang, M., 2002, Seismic images of crust and upper mantle beneath Tibet: evidence for Eurasian plate subduction. Science, v. 298, pp. 1219–1221.

Meissner, R., Tilmann, F., Haines, S., 2004. About the lithospheric structure of central Tibet, based on seismic data from the INDEPTH III profi le. Tectonophysics, v. 380, pp. 1–25.

Zhao, W., Kumar P., Mechie, J., Kind, R., Meissner, R., Wu, Z., Shi, D., Su, H., Xue, G., Karplus, M. and Tilmann F., 2011, Tibetan plate overriding the Asian plate in central and northern Tibet, Nature Geoscience.

Fig. 2: Preliminary maps of the crustal (on the left) and lithospheric (on the right) thicknesses obtained from elevation, geoid and thermal analysis following the method presented in Fullea et al. (2007).

9


H and O isotopic compositions (δD and δ18O) of precipitations are important tracers for hydrological studies as well as paleo-environmental and paleo-elevation studies. Nevertheless only few direct precipitation data exist over the Himalayan arc and, to the exception of Kathmandu, are onlylocated in the Northern fl ank of the Himalaya as analogue for glacier record interpretation. Here we present a set of data, mostly from the southern Himalayan fl ank,including daily sampling of precipitation in Narayanghat, Kathmandu, and Khudias well as river water data.

At a given location, data are marked by strong seasonalcontrast (e.g. Zhang et al. 2001; Gajurel et al. 2006). Seasonal variation is typically 80‰ for δD resulting from the change in origin of moisture and processes of precipitation. Dry season precipitations originate from recycled Central Asia and India water and are strongly enriched in 18O and D including for some snow samples in high elevations. Common compositions are above that of seawater (i.e.>0‰). Theseunusual signatures are is likely due to re-evaporation of droplets during precipitation. Immediately at the onset of the summer monsoon, δD of precipitations drop by 50 to 60‰, refl ecting water masses formed over the Arabian sea and the Bay of Bengal. Precipitations display clear depletion in 18O and D with typical composition of -11‰ and -80‰ respectively. Such compositions are due to massive precipitation of clouds that were only slightly depleted in heavy isotopes throughout their transit toward Himalaya (amount effect). Throughout the monsoon, precipitations are progressively more depleted in heavy isotopes. Similar depletion is observed in different stations of the Indo-Gangetic fl ood plain and results in complex effects of changes in distance of moisture sources and addition of depleted moisture from fl oodplain and local evaporation (Breitenbach et al. 2010).

The relationship between elevation and isotopic composition is very different whether considering south fl ank precipitation or north fl ank precipitation. South fl ank

data display limited effect of elevation. Direct precipitation data between 200 and 2700 m show no signifi cant change and have average δD around -80‰. On the contrary, north fl ank data from Langtang and Mustang show signifi cant depletion down to -130%-150‰. Combined with low elevation South fl ank data, they indicate D depletion around -25‰/1000m for δD (Garzione et al. 2000). This difference refl ects different processes between both sides of the Himalaya. South fl ank precipitations show no elevation effect principally because monsoon rain occurs massively from clouds with comparable compositions. On the contrary, North fl ank precipitations are supplied by the remaining moisture crossing the Himalayan orographic barrier and are depleted in heavy isotopes by distillation effect.

This datasetshow that both the seasonal contrast and the N-S contrast are potential hydrological tracers for river water. Application in the domain of paleo-elevation study is less straightforward and cannot be applied for fl oodplain sedimentary record such as the Siwaliks.

REFERENCES

Breitenbach, S. F. M., Adkins, J. F., Meyer, H., Marwan,N., Kumar, K., K. and Haug, G. H., 2010, Strong infl uence of water vapor source dynamics on stable isotopes in precipitationobserved in Southern Meghalaya, NE India. Earth Planet. Sci. Lett., v. 292, pp. 212-220.

Gajurel, A., France-Lanord, C., Huyghe, P., Guilmette, C. and Gurung, D., 2006, C and O isotope compositions of modern fresh-water mollusc shellsand river waters from the Himalaya and Ganga plain. Chemical Geology, v. 233,pp. 156–183.

Garzione, C. N., Quade, J., DeCelles, P. G., and English, N. B., 2000, Predictingpalaeoelevation of Tibet and the Himalaya from δ18Ovs. altitude gradients in meteoric waters across the NepalHimalaya. Earth Planet. Sci. Lett., v. 183, pp. 215–229

Zhang, X., Nakawo, M., Fujita, K., Tandong, Y., and Jiankang, H., 2001, Variation of precipitation δ18Oin Langtang Valley, Himalayas.Science in China v. 44, pp.769-778.

Stable isotope composition of precipitation across central Nepal Himalaya

*Ananta Gajurel1, Christian France-Lanord2 and Jérôme Lavé2

1Department of Geology, Tri-Chandra College, Tribhuvan University, Kathmandu, Nepal2Centre de Recherches Pétrographiqueset Géochimiques-CNRS, Nancy, France


10


The Central Sector of the Himalayas encompasses the region of Himachal- Kumauan-Garhwal(INDIA) and Nepal. Tectonically, this region is the classical example of thrust tectonics and plate movement. Classical research was done by eminent geologists to establish the thrust movements after the study in Alps.Following the geologists of Geological Survey of India, the subsequent work was completed by geologists of Nepalese, Swiss,French,Austrian and Japanese schools.

The Himalayan arc extends about 2,500 km from northwest to southeast and includes from west to east the highest peaks, viz., Nanga Parbat(8,125 m), Everest (8,848 m), and Namcha Barwa (7,755 m).The width of the belt varies from 250-350 km. The mighty Himalayas and the Karakoram, embodying the largest concentration of lithospheric mass, grew south of the Pamir. The Himalayas contain a fascinating geological record of Precambrian to present and terminate both east and west with spectacular syntaxial bends. The sector of the Central Himalayas covers the Foot hills, Lesser Himalayas, Greater Himalayas and Higher Tibetan-Tethyan Zone. Each Zone has its own tectonic framework.

The collision of India with Asia is one of the most geologically facinating event to have occurred in the past 100Ma. It is responsible for uplift of the Himalayas and Tibet and rejuvenating the tectonic architecture of Karakoram and Kun Lun. Resulting changes in the Earth's orography and consequent climate change are directly tied to this ongoing collisional event. This collisional event has long been argued to be responsible for geological, geochemical and climatological consequenses of global extent. The uplifting process is still going on with the approximate rate of one cm. per year with continued erosion and denudation. The eroded material from its rugged topography is regularly shed into different depositional settings within the Himalayas, Bay of Bengal and Arabian Sea by young river system

The rapid recession of Himalayan glaciers due to global warming is a serious matter of concern for the survival of human civilization in the Indo-Gangetic plain. In this region, the stress and strain caused due from plate motion is responsible for frequent earthquakes enormous loss of human life. Flash-fl oods, landslides and irregular mining have been responsible for frequent natural disasters. Deforestation and road construction have been responsible for landslides.

The central Himalayan tectonic framework, fragile ecological balance and natural disaster

Anshu Kumar SinhaB 602, Vigyan Vihar,Sector 56, GURGAON(NCR DELHI) 122011 , India


11


The Neogene Thakkhola-Mustang Graben lies north of the Dhaulagiri-Annapurna ranges and south of the Yarlung-Tsangpo Suture Zone. The basement of Thakkhola-Mustang Graben is composed of Tibetan-Tethyan sedimentary rocks of Paleozoic and Mesozoic ages, which are unconformably overlain by continental debris (more than 850 m) of Neogene to Quaternary age. Stratigraphically, the Thakkhola-Mustang Graben sediments have been divided into fi ve formations namely the Tetang Formation, the Thakkhola Formation, the Sammargaon Formation, the Marpha Formation and the Kaligandaki Formation. In this study, we mainly focused on sedimentological and palynological studies of the Thakkhola-Mustang Graben, which provides a basis for discussing the paleo-environmental evolution of the southern continental margin of the Tibetan Plateau towards the end of the Miocene. Detailed fi eld mapping, profi le logging, stable carbon and oxygen isotope analysis, and palynological studies were carried out to understand the depositional environment and the paleoclimate. Pollen samples were processed in the laboratory and were studied under the light microscope

(LM) and scanning electron microscope (SEM) using single grain technique. Different sedimentary environments are recognized including alluvial fan, lacustrine, braided river and glacio-fl uvial. Graben sediments are composed of braided fl uvial deposits with lacustrine deposits in different level of the succession. Lacustrine layers in the Tetang and Thakkhola formations are enriched with pollen. Pollen analysis shows that the sediments contain dominant alpine trees Abies, Pinus, Keteleeria, Picea Tsuga and Quercus with some steppe elements such as Artemisia, Compositae, Chenopodiaceae, Plantago and Poaceae. The results show that during this period, the southern part of Tibet was covered mainly by steppe vegetation, indicating dry climate. Organic plant material from the Thakkhola and Tetang formations yielded stable carbon isotope (d13C) values between -21.87 to -26.64 permil, indicating the presence of C3 vegetation. However, the d13C values from the carbonates range between -0.62 to 11.08 permil, which shows the mix vegetation of C3 and C4 plants. It is presumed that the paleoclimate during the sediment deposition time of the Thakkhola-Mustang Graben was signifi cantly warmer than the present-day climate.

Paleoclimate analysis of the Neogene Thakkhola-Mustang Graben (central Nepal)

*B. R. Adhikari1, M. Wagreich2, Khum N. Paudayal3 and Ilse Draxler4

1 Department of Civil Engineering, Pulchowk Campus, Tribhuvan University, Nepal2Department of geodynamics and sedimentology, University of Vienna, Austria

3 Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal4Department of Paleontology, Geological Survey of Austria


12


U/Th chronology, δ18O and δ13C isotopes, mineralogy, gray color, luminescence and variations in petrography along the central growth axis of two cave stalagmites provide 750 year long annual to decadal-resolution record of paleoenvironmental changes from the Indian Lesser Himalaya. Both the caves have minimal evaporation effect. Our results are based on the following observations; (1) lighter stalagmite δ18O values refl ect higher precipitation and vice versa (2) long-term δ18O variations may also refl ect the temperature variation with the lower temperatures generally correspond to the higher rainfall and more negative δ18O and wetter climatic conditions (3) gray color and luminescence of the speleothems show positive correlation with estimates of changes in the northern Hemisphere temperature, with whiter color and stronger luminescence corresponding to the higher temperatures, while the darker color and reduced luminescence to the lower temperatures.

The multi-proxy results indicate that the climate during the last 750 years can be divided into three stages, (a) a dry phase from 1250 to 1480 AD during which the intense aragonite deposited, (b) a wet phase from 1480 to 1850 AD during the Little Ice Age (LIA), and (c) a comparatively drier phase during the post-LIA after 1850 AD. The δ18O data imply a drying trend in the post-LIA which is consistent with the instrumental records. However, on decadal time scales, there are some mis-matches between drought/fl ood

events and our δ18O anomalies, which may be related to uncertainties in the age model. However, our records also document the minor dry events during LIA and wet episodes in the post-LIA. Four prominent periods of weaker rainfall activity at 1590-1595 AD, 1725-1730 AD, 1800 AD and 1840-1850 AD within the wetter LIA are recorded and the 1800 AD event may probably be correlated with the Dalton period of sunspot minimum. Within the age uncertainty, the dry spells during the LIA are linked with the historical drought events in the Indian subcontinent and similar latitudes.

Obtained for the fi rst time from the Indian Lesser Himalaya, our data are consistent with a number of previous studies in the areas infl uenced by the Westerlies but confl icting to the regions, dominated by the Indian Summer Monsoon (ISM). This may be due to the possible changes in the strength of Westerlies in the study area and added by negative anomaly of North Atlantic Oscillation (NAO) during the LIA. We propose that during the LIA, the Lesser Himalaya and the nearby regions were humid, whereas the areas under the sole infl uence of the ISM were dry and suggest that the enhanced Westerlies may have produced higher than normal precipitation during this period in north India. We believe that the hydrological conditions during the LIA may have varied signifi cantly under various precipitation regimes as well as in different latitudes.

Climatic fl uctuations in the last 750 years from Indian Lesser Himalaya as inferred from speleothems: Evidence of a wetter Little Ice Age (LIA)

*B. S. Kotlia1, F. Liang2, G. A. Brook2, S. M. Ahmad3, Jian-Xin Zhao4, L. B. Railsback2, Waseem Raza3, K. D. Collerson4, L. M. Joshi1 and Jaishri Sanwal5

1Centre of Advanced Study in Geology, Kumaun University, Nainital, 263 002, India2Department of Geography, University of Georgia, Athens, GA 30602, USA

3National Geophysical Research Institute, CSIR, Uppal Road, Hyderabad, 500 007, India4Centre for Microscopy and Microanalysis, School of Earth Sciences, University of Queensland, Australia

5Centre for Earth Sciences, Indian Institute of Science, Bangalore, 560 12, India(*Email: [email protected])

13


On 28-29 October 2008, within 12h, two similar Mw6.4 strike slip earthquakes occurred within the Balochistan Range (Pakistan), generating a complex and poorly located seismic sequence. These shallow earthquakes mostly affected Pishin and Ziarat districts, an area where several active faults have previously been identifi ed. To establish the relationship between these 2 earthquakes, fi rst considered as seismic doublets, we computed a large number of radar interferograms. A total of four descending and seven ascending Envisat interferograms, complemented by ALOS ascending interferograms, reveal the surface displacement fi eld generated by the seismic crisis. These interferograms testify that the main active strike slip faults previously recognised in the region, and therefore suspected to be potential sources, were not activated during the earthquake sequence. Instead, the surface displacement measured by InSAR appears consistent with sources in the vicinity of the Ziarat anticline, situated in the core of the Sibi syntaxis between the Kirthar and Sulaiman range. This structure is a large-scale active fold constricted by both dextral and sinistral active strike slip faults on its western termination. All these faults appear as potential sources to the seismic events.

However, because the second earthquake occurred at short distance from the fi rst, the coseismic interferograms are complex, preventing a straightforward interpretation of the surface deformation. In order to determine which faults were activated during the seismic sequence, we perform multiple source models, consistent with the moment tensor

solutions involving either a NE-SW sinistral faults or NW-SE dextral faults as well as combinations of both. We then apply a dedicated methodology to compare all the models with the measurements using the Earth Mover’s Distance (EMD), a content-based distance used in image retrieval that does not require the prior knowledge of precise fault location.

The models composed of sequential segments rupturing along a single fault trend or pure doublets solutions are discarded in favour of scenarios involving conjugate faulting. We conclude that two ~ 10 km-long nearly abutting conjugate strike-slip faults are involved in the sequence. A least-squares inversion of the displacement on both faults is then performed. The inverted NW-SE dextral fault strike-slip (resp. dip-slip) displacement is 0.90 m (resp. 0.28 m). The inverted NE-SW sinistral fault strike-slip (resp. dip-slip) displacement is 1.26 m (resp. -0.34 m). Both estimates are consistent with the coseismic moment release. The analysis of the residuals demonstrates that several secondary fault segments in the vicinity also localised some deformation. Further west, another NE-SW shallow sinistral strike-slip fault accommodated 3.5 cm along a 20 km NE trending fault segment. Three shocks on 09/12/2008 affected the western termination of the NE-SW sinistral fault with a displacement of about 70 cm. In addition to extrusion, the seismic sequence is fi nally shown to induce a subtle block rotation through a bookshelf faulting component. These processes participate to rigid block rotations and structure migrations within the tectonic syntaxis over a time interval of a few days.

Extrusion and bookshelf faulting revealed by InSAR in the Sulaiman range syntaxis (Pakistan)

*Béatrice Pinel-Puysségur, Laurent Bollinger and Christelle BaudryDASE, F-91297 Arpajon, France


14


The Kashmir valley is a bowl-shaped valley, about 140 Kms. long and 40-50 Kms. wide, and lies in the North West of India, having co-ordinates 32°17’ N to 37° 6/’N latitude and 73°6’ E to 800 30’ E longitudes and average height of 1800m amsl. It occupies the depression formed by the bifurcation of Great Himalayan Range whose South Western arm is known as the Pir Panjal Range and the North Eastern arm as the main Himalayan Range. At the Northern limit of the valley is the Qazi Nag Range. These mountainous ranges comprise metamorphosed Paleozoic and Mesozoic marine sediments and effusive rocks. On the periphery mountain ranges of Kashmir Valley, rocks ranging in age from Precambrian to Cretaceous are exposed. Kashmir valley is drained mainly by Jehlum River which meanders from South-West to North-West through the Centre of the valley and leaves the valley through Baramulla gorge, fl owing to the great plains of Punjab (Pakistan). Terrigenous sediments of the Plio-Pleistocene age called Karewas are exposed throughout the valley and also extend for some distance on the eastern fl ank of the Pir Panjal Range.

The Karewas were originally regarded as of lacustrine origin. The term “Karewa” meaning “plateau” (Wadur in local language) was fi rst introduced in the geological literature by Godwin Austin in 1864. The Karewa beds are extensively developed over a length of 140 Km Karewas

form the Quaternary deposits of Kashmir Valley which is the one of the most seismically active region of the world. Large earthquakes (usually M≥6) have produced the seismically induced soft sediment deformation structures (Seismites) in the loosely consolidated and water saturated sandy and silty sediments of the Karewas of Kashmir Valley which acts as the Paleoseismic signatures. The Paleoseismic signatures in the form of seismites are usually formed by the process of liquefaction which usually occurs at the shallow depths (< 10 M). The phenomenon of liquefaction results in the formation of seismites in the form of dikes, sills and sand lenses at the sites of liquefaction which can be further evaluated to estimate the magnitude of the pre-instrumental earthquakes (i.e., “back-analysis”).The cyclic stress method is widely used for evaluating liquefaction. In the cyclic stress method the capacity of the soil (or liquefaction resistance) is quantifi ed in terms of cyclic resistance ratio (CRR). The soil's CRR is usually correlated to an in-situ parameter such as SPT blow count (number of blows per foot).SPT blow counts are affected by a number of procedural details (rod lengths, hammer energy, sampler details, borehole size) and by effective overburden stress. The duration of ground shaking is typically correlated to earthquake magnitude via magnitude scaling factors (MSF). MSF are inversely proportional to the square root of duration of strong motion and are presented in reference to M 7.5 events.

Paleoseismic signatures in the Karewas of Kashmir Valley (India) N/W Himalaya: Determination of magnitude of paleoearthquakes

Bikram Singh and Rais Ahmad KhanDepartment of Geology and Geophysics, University of Kashmir, Srinagar, India

15


The Indus River is the backbone of the NW Trans-Himalayan Ladakh region. Its tributaries Shyok, Nubra and Tangtse rivers are in themselves major drainage patterns and all have played a major role in shaping the geomorphology of the this region. These rivers follow courses of the major tectonic fault/thrust lines viz Indus-Indus Suture Zone (ISZ), Shyok- Shyok Suture Zone (SSZ) and Nubra and Tangtse- Karakoroum fault (KF) and the area is in a tectonically active zone between the ISZ and KF. Ladakh is a part of the rain shadow area exhibiting cold desert environment. Most of the region is dry and barren and receives an annual rainfall of ~30 mm. The morpho-sedimentary records of this area can be used as proxy to global scale climatic shift and regional tectonism as such regions are sensitive to even a slight environmental change. A small perturbation in the climatic factor leads to massive sediment production, erosion and sedimentation, resulting in a dynamic evolution of the landform.

The river valleys have enormous Quaternary deposits of glacial, lacustrine, palaeo-lacustrine, fl uvial and aeolian origin. The main source of water is the glacial and ice melted water, which feeds these rivers. The major geomorphic landforms are U-shaped glacial valleys, gorges, glacial moraines, fi ll terraces, strath terrace, alluvial fans, fan toe cutting by river/stream, debris cone, lacustrine deposits, varves, defl ected stream courses, scree and talus cone, fossil valleys, abandoned channels, waterfalls and rapids etc.

These sedimentary records represent the changes in melt water and rainfall related hydrology of the river.

Studies suggest that occupied parts of these river valleys at 20-30 ka BP, 17-14 ka BP and 12-3 ka BP. Lying in the vicinity of the major fault lines tectonic disturbances is also evident in deformed lacustrine sediments and moreover these lakes are formed due to the damming of the rivers by different landslides (either due to seismic disturbance or abrupt monsoon year’s). In the Indus valley, the initial onset of climate change at the end of the glacial event seems to be marked by a period from ca. 17500 -~14000 yrs BP with a lake record at Saspol-Uley tokpo. This deposit shows no signs of tectonic activity (absence of seismites, tilt in lake beds etc.,) and indicative of a warmer period. A longer phase of fl uvio lacustrine sediment deposition at Spituk-Gupuk from ca. 11,000–1000 yrs BP possibly represents the strengthened southwest monsoon system and marks the transition into the Holocene. This lake was formed after the YD by a blockade downstream possibly triggered by a tectonic activity or even a abrupt monsoon event. In the Shyok valley thick Quaternary deposits are exposed along Pharkatokpo stream and date to pre LGM times. In the Tangtse valley the lacustrine deposits are ~ 50 m thick. Thus, trans-Himalayas hold a rich repository as far as Quaternary sedimentation is concerned which would answer questions of tectonic and climatic disturbances and perturbations.

Late Quaternary sedimentation along the river valleys in Ladakh region of NW Trans-Himalayan range: A climate-tectonic perspective

*Binita Phartiyal1, Anupam Sharma2 and Girish Ch. Kothari3

1 Birbal Sahni Institute of Palaeobotany, 53-University Road, Lucknow-226007, UP., India2School of Earth & Environmental Sciences, Central University of Himachal Pradesh, PO Box 21, Dharamshala, District

Kangra, Himachal Pradesh 176 215, India3 Institute of Seismological Research, Raisan, Gandhinagar, 382 009, Gujarat, India

(*Email: binita phartiyal @gmail.com)

16


The role of large scale detachment fault systems is of crucial importance in the understanding the evolution of orogenic systems. The South Tibetan Detachment System (STDS; Burchfi eld et al 1992; Carosi et al. 1998) represents, in the Himalayan chain, one of the most spectacular example, dividing the low-grade-metamorphic rocks of the Tibetan Sedimentary Sequence in the hanging-wall, from the high-grade-metamorphic rocks of the High Himalayan Crystallines (HHC) from the footwall.

Several competing tectonic models, regarding the exhumation and extrusion of the high grade metamorphic rocks of the HHC are nowadays objects of debates. In these models the STDS, joined with the partly coeval lower Main Central Thrust (Godin et al. 2006), played a crucial role. The knowledge of the thermal and structural activity of the STDS can give a fundamental contribution to discriminate among the different proposed tectonic models.

In addition most of the structural and thermal studies focused on the kinematic and thermal profi les of the footwall rocks (Jessup et al. 2008; Cottle et al. 2011) and only few studies have been concentrated on the hanging-wall rocks (Cottle et al. 2007; Montomoli et al. 2008; Kellet et al. 2011).

Anomalous thermal gradients and telescoping of metamorphic isograds have been highlighted in the upper part of the HHC, approaching the ductile portion of the STDS (Cottle et al. 2011; Law et al. 2011) and have been interpreted to be the result of a progressive up-section migration of shear zone boundaries through space and time

During this work we focused on two sections of the STDS cropping out east of the Ama Drime range (Dingyee area, Southern Tibet) and west of the Annapurna massif (Kaligandaki valley, central Nepal). Here we concentrated on the hanging-wall rocks of the STDS represented by Ordovician limestone in the fi rst transect and by impure marbles and quartzites in the second one.

Meso and microstructural studies have been accompanied by illite crystallinity analyses, calcite-dolomite geothermometer and stable isotope analyses on selected samples. Microfabric analysis of calcite shows shape and

lattice preferred orientations as well as grain size reduction within layers of cm-thickness.

Moving upward in the sequences, primary sedimentary structures are still well recognizable and there is a sharp transition to very-low grade deformation mechanism where pressure solution is predominant. In the more strained portions of the shear zone post-kinematic porphyroblasts of biotite are abundant, overprinting the mylonitic foliation.

Vorticity kinematic analysis point out a high component of pure shear acting during non-coaxial deformation of the STDS.

Calcite- dolomite geothermometers, stable isotopes on calcite and quartz , analyses of deformation mechanisms highlight an apparent abnormal geothermal gradients of ~300°C/km. Several factors can be invoked to explain such apparent anomalous thermal gradients but a strong infl uence can be attributed to the strong vertical shortening derived from the combination of pure and simple shear components during deformation. Moreover deformation was likely accompanied by heating linked to the exhuming high-grade of the underlying HHC (T ~700-750°C) coupling with the colder TSS rocks (Carosi et al. 2007). Shearing with an important component of vertical fl attening contemporaneous with a regional-contact heating effect from the hot rocks below could explain the observed abnormal geothermal gradient observed along the STDS.

REFERENCES

Burchfi el, B. C., Zhiliang, C., Hodges, K. V., Yuping, L. Royden, L. H., Changrong, D. and Jiene, X.,1992, The South Tibetan Detachment System, Himalayan Orogen: extension contemporaneous with and parallel to shortening in a collisional mountain belt. Geological Society of America Special Paper, v. 269, 41 p.

Carosi R., Lombardo, B., Molli, G. Musumeci G., Pertusati P. C., 1998, The South Tibetan Detachment System in the Rongbuk valley, Everest region. Deformation and geological implications., Journal of Asian Earth Science, v. 16, pp. 299-311.

Anomalous thermal gradients in the South Tibetan Detachment System: Strain and heating in decoupling Tibetan Sedimentary Sequence and

Higher Himalayan Crystallines

*C. Montomoli1, R. Carosi2 and C. Visonà3

1Dipartimento Scienze della Terra, via Santa Maria 53, 56126 Pisa (University of Pisa), 2Dipartimento di Scienze della Terra, via Valperga Caluso, 35 10125, Torino, Italy

3Dipartimento di Geoscienze, Università di Padova Via Gradenigo, 6 35131, Padova, Italy(*Email: [email protected])

17


Carosi, R., Montomoli, C., and Visonà, D., 2002, “Is there any detachment in the Lower Dolpo (Western Nepal)?”. Comptes Rendues Geoscience, v. 334, pp. 933-940.

Carosi, R., Montomoli, C., and Visonà’, D., 2007, A structural transect in the Lower Dolpo: Insights on the tectonic evolution of Western Nepal. Journal of Asian Earth Sciences, Volume 29, Issue 2-3, pp. 407-423.

Cottle, J., Jessup, M., Newell, D., Searle, M., Law, R. and Horstwood, M., 2011, Structural insight into the early stages of exhumation along an froge-scale detachment: the South Tibetan Detachment System, Dzakaa Chu section, Eastern Himalaya, J. Structural geol., v. 29, pp. 1781-1797

Cottle, J., Waters, D., Riley, D., Beyssac, O. & Jessup, M. 2011, Metamorphic history of the South Tibetan Detachment System, Mt. Everest region, revealed by RSCM thermometry and phase equilibria modelling, J. of Metamorphic geol.29, 561-582.

Godin, L., Grujic, D. R., Law, D., and Searle, M.P., 2006. Channel fl ow, ductile extrusion and exhumation in continental collision zones: an introduction. In:., Channel fl ow, Extrusion, and Exhumation in Continental Collision Zones, (R.D. Law, M. P Searle, and L.Godin, eds),Geological Society Spec. Publ., v. 268, pp. 1-23.

Jessup, M. J., Cottle, J. M., Searle, M. P., Law, R. D., Newell, D. L., Tracy, R. J., and Waters, D. J., 2008, P-T-t-D paths of Everest Series schist, Nepal. J. Metamorphic Geol., v. 26, pp. 717-739.

Kellet , D. And Grujic, D., 2012., New insight into the South Tibetan Detachment system: not a single progressive deformation, Tectonics, 31.

Law, R., Jessup, M., Searle, M., Francsis, M., Waters, D. and Cottle J., 2011, Telescoping of isothrems beneath the South Tibetan Detachment System, Mount Everest Massif, J. of Structural geol., v. 33, pp. 1569-1594.

18


The last 200 years have witnessed several large and great earthquakes in the Himalaya. The geodetic models imply signifi cant slip defi cit and impending great earthquakes in the central Himalaya and Kashmir Himalaya Evaluation of the historic and geologic data from the Himalaya suggests that the region experienced many signifi cant earthquakes in the past. Despite the some paleoseismological wotk many questions remain on the pattern of earthquake recurrence, style of deformation and causative structures. A major question is when the last great great earthquake in the central Himalaya was. While the renewal time of earthquakes originating on the detachment fault might match the expectations of the seismic gap models, the subsidiary faults within the wedge may localize strain leading to earthquakes events that need not maintain any temporal relation with the plate boundary breaking earthquakes and leading to surface slip due to the favorable geometry of the ramps. Observed temporal and spatial clustering of earthquakes along the Himalaya, nature of surface rupture and the amplifi ed slip reported from geological section associated with the paleo-earthquakes may result from the dual nature of seismic sources along the Himalaya. This fundamental difference in source zones may be the key to understanding the temporal and spatial clustering of earthquakes along the Himalaya. Great earthquakes are known to originate on the basal detachment and none of the historical events are known to have produced surface ruptures, possibly due to rupture termination at the crustal ramps. Whereas, the class of earthquakes originates on the duplex zone propagate vertically on the steeply dipping faults and leading surface ruptures as observed in the 2005 Kashmir earthquake that

showed a peak surface offset of 7 m. Single episodic slips up to 12-17 m observed in trenches excavated in the NW and Nepal Himalaya may be associated with rupture on the crustal ramps and may not be related to plate boundary earthquakes. Our ongoing investigations place the last great earthquake in the central Himalaya sometime between AD 1000 and AD 1290, suggesting that temporal gap in seismicity is real. The traditional tectonic models suggest that all slip on the basal decollement is absorbed on the Himalayan frontal fault (MFT). Our observations on the frequency of earthquakes and modern rate of uplift suggest that high Himalaya range just south of MCT is much higher than what we observe along the HFT. The possible out-sequence-events like the 1803 Garhwal earthquake apparently suggest that the duplex zone south of the MCT is equally, if not more, active and capable of generating large/great earthquakes in the central Himalaya rather than the Himalayan frontal thrusts. Another issue we address in our studies is whether a great plate boundary earthquake had occurred in the central Himalaya in 1505, as suggested by some workers on the basis of earthquake accounts given in Tibetan archives. The preliminary age determinations of the paleoliquefaction features from the alluvial plain in Bihar and Uttar Pradesh suggest that previous great earthquakes in the respective segments may have occurred about 1000 years ago. These dates have some correlation with previous studies on the active faults on the Nepal side. We will present the results of our recent investigations of the geological proxies in the Himalaya and the Gangetic alluvium and discuss our strategy to address some of the outstanding questions on the earthquake recurrence in the Himalaya.

An update on earthquake recurrence in the Himalaya

*C. P. Rajendran and Kusala RajendranCentre for Earth Sciences, Indian Institute of Science, Bangalore 560012, India


19


The National Seismological Network of Department of Mines and Geology, Nepal in collaboration with the Département Analyse, Surveillance, Environnement, (DASE, France) has been monitoring seismic activity around the Nepal Himalaya since 1981. At the moment, this network consists of twenty one short period vertical, one 3-components short period and one 3-components broadband seismic stations covering the whole country and two independent recording centers. The records from the stations in central and eastern Nepal are continuously transmitted to the National Seismological Centre, Kathmandu using radio link and similarly records from stations in western Nepal are telemetered to the Regional Seismological Centre, Surkhet. The main purpose of the network is to locate and evaluate local seismic events around the Nepal Himalaya and alert the authorities of the occurrence of all magnitude greater

than 4 events within the national territory.

In this presentation, we fi rst describe the data acquisition and processing system and its capability. This includes velocity model, location technique and uncertainties associated with location parameters. We further describe the local magnitude estimation in the routine processing and its correlation with moment magnitude determined by different research projects and global agencies. We then describe a 60,000 earthquakes catalog of the Nepal Himalaya, homogeneous in terms of magnitude which is essential for the seismic hazard evaluation. In order to evaluate the variations of the quality of the catalogue, we determine the spatial and temporal variations of its magnitude of completeness (Mc). We fi nally evaluate the variations of a- and b-value along strike and confront both to the major active faults.

Local seismic network and seismicity of the Nepal Himalaya

*C. Timsina1, D. R. Tiwari1, U. Gautam1, R. Pandey1, S. N. Sapkota1, L. B. Adhikari1, P. L. Shrestha1, B. P. Koirala1, M. Bhattarai 1, M. Jha1, T. Kandel1, C. Gourraud1 and L. Bollinger2

1Department of Mines and Geology, Lainchaur, Kathmandu, NEPAL, 2DASE, Bruyères le Châtel 91297 Arpajon, FRANCE


20


The Main Central Thrust (MCT) is a major Himalayan fault which is thought to have accounted for >150 km of movement during the Himalayan orogeny (Schelling and Arita 1991) and plays a pivotal role in tectonic exhumation models such as channel fl ow (Beaumont et al. 2001) and wedge extrusion (Kohn 2008). Unlike thrusts characterised by mainly brittle deformation, such as the Moine Thrust, the deformation associated with the MCT spans several kilometres and is best described as a ductile ‘zone’. Despite its importance in Himalayan tectonic evolution, its precise location remains disputed in many transects (Searle et al. 2008). In this study of the high strain deformation in Sikkim, samples have been collected from the zone of ductile deformation broadly coinciding with the MCT in order to investigate the location and rates of movement of this structure.

Location of the Main Central Thrust

Previously, the term ‘Main Central Thrust’ has been used to refer to two distinct phenomena: 1) a thrust fault and 2) a protolith boundary between the Greater Himalayan Series (GHS) and the Lesser Himalayan Series (LHS). There is general consensus that each of these lithological packages is characterised by distinctive geochronological and chemical signatures. The LHS is a Palaeoproterozoic sequence with an εNd signature of -20 to -25, which has been intruded by ~1.8 Ga granites, whereas the GHS is a Neoproterozoic-Early Palaeozoic sequence, with an εNd signature of -15 to -20, typically intruded by ~500 Ma granites (Parrish and Hodges 1996; Ahmad et al. 2000). The protolith boundary can therefore be ‘mapped’ using isotope geochemical/geochronological data.

This paper presents the fi rst combined U-Pb zircon geochronology and εNd isotopic study in Sikkim. These data determine the provenance of the rocks within the MCT zone in Sikkim, and demonstrate that the Main Central Thrust lies along a boundary roughly corresponding to the fi brolite-in isograd. This boundary coincides with the isotopic break between the GHS and LHS rocks. The GHS in Sikkim has an εNd signature of -17.1 to -12 and a detrital zircon age ranging from ~1.8-0.5 Ga with a Cenozoic overprint, which contrasts with the LHS which has a more negative εNd down to ~ -27 and is intruded by Proterozoic granites of ~1.8 Ga. The MCT therefore represents a lithological, metamorphic and isotopic break, where rocks of one isotopic signature have been thrust over another geochemically distinct package of rocks. The difference between the metamorphic grade in these two packages led to the heating of the LHS and formation of the related zone of inverted Barrovian metamorphism.

Rates of movement on of the Main Central Thrust

The second part of this paper focuses on the newly isotopically defi ned MCT to study its rate of movement. The structural confi guration of the MCT in Sikkim provides the opportunity to look at rates of processes as illustrated in Fig. 1. Information on the timing of monazite growth, in conjunction with evidence of strain and deformation in the rocks, allows determination of the rates and duration of movement on this important structure. Preliminary data indicates that monazite grew between ~22 and 14 Ma in the zone of deformation beneath the MCT, which allows an initial estimate of the thrusting rate to be calculated: around 4 mm a year. This approach yields the fi rst robust quantitative estimate of the rate of displacement on any major structure in the Himalaya.

Using isotope geochemistry to unravel the mysteries of the Main Central Thrust, Sikkim Himalaya

*Catherine M. Mottram1, Nigel B. W. Harris1, Randy. R. Parrish2, Tom W. Argles1 and Clare J. Warren1

1 Department of Environment, Earth and Ecosystems, The Open University, Walton Hall, Milton Keynes, MK7 6AA,2 NERC Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG,


21


REFERENCES

Ahmad, T., Harris, N., Bickle, M., Chapman, H. and Bunbury, J. 2000, Isotopic constraints on the structural relationships between the Lesser Himalayan Series and the High Himalayan Crystalline Series, Garhwal Himalaya: Geological Society of America Bulletin, v. 112, pp. 467-477.

Beaumont, C., Jamieson, R. A., Nguyen, M. H., and Lee, B., 2001, Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled to focused surface denudation: Nature, v. 414, pp. 738-742.

Kohn, M. J., 2008, P-T-t data from central Nepal support critical taper and repudiate large-scale channel fl ow of the Greater

Himalayan Sequence: Geological Society of America Bulletin, v. 120, pp. 259-273.

Parrish, R. R., and Hodges, K. V., 1996, Isotopic constraints on the age and provenance of the Lesser and Greater Himalayan sequences, Nepalese Himalaya: Geological Society of America Bulletin, v. 108, pp. 904-911.

Schelling, D., and Arita, K., 1991, thrust tectonics, crustal shortening, and the structure of the far-eastern Nepal Himalaya: Tectonics, v. 10, pp. 851-862.

Searle, M. P., Law, R. D., Godin, L., Larson, K. P., Streule, M. J., Cottle, J. M. and Jessup, M. J., 2008, Defi ning the Himalayan Main Central Thrust in Nepal: Journal of the Geological Society, v. 165, pp. 523-534.

Fig. 1: a) Structural NS cross section through Sikkim illustrating the geometry of the MCT, deformed by the Teesta dome. 1 and 2 = marker points. b) Hypothetical cross section before formation of the Teesta dome. The marker points 1 and 2 illustrate how, prior to folding, when point 1 was at the surface point 2 would have been at depth. It can therefore be inferred that the age of peak metamorphism at point 2 is likely to be younger than that at point 1.

22


In the eastern Himalaya the structural framework is best displayed in Southeastern Tibet, Sikkim and Bhutan where the OST (Out of Sequence Thrust), MCT (Main Central Thrust), and major lithologic units are tectonically highly active. On a regional scale, the Sikkim Himalaya is tectonically characterized by a domal struc ture which is further evidenced by the seismo-tectonic map. Geomorphic indicators allow the quantitative measurements of landscape shape and development, thus aiding in identifi cation of areas experiencing rapid tectonic deformations. The analysis of tectonic and geometric activity along the main thrusts and faults is based on morphometric parameters, such as sinuosity, drainage basin elongation ratio, volume area ratio, etc. The objective of this study is to investigate the use of numerical geo-morphometric methods for tectonics, geomorphology and critical areas of Sikkim. Nine distinct geomorphic indicators, categorized under linear and areal were identifi ed in the Tista River Basin having 7 independent

(hydrologic) and 7 dependent sub watersheds were calculated. Assessing scale-dependent surface processes can be addressed using remote sensing and geographic information system (GIS) technology. The relation between linear factors and areal factors shows the real time changes in landforms that are caused due to active tectonic in and around Gangtok Sub-basin. There are earthquake activities in the region concentrated mainly along the MCT and OST and are related with thrust faulting. The geo-morphotectonic study using GIS indicates that there is high tectonic activity and uplift in this area especially along MCT III and OST which is the main factor for developing the current landscape morphology, organization and formation of the drainage network. The study demonstrates that remotely sensed data and GIS based approach is easy and accurate than other methods for evaluation and analysis of drainage morphometry and landforms.

Morphometric characteristics as indicators of active tectonics in Sikkim (Tista River, eastern Himalaya): Structural and seismotectonics

constraints

*Chandra S. Dubey1, Mohmmad Tajbakhsh2, Ravindra P. Singh1, Bhupendra K. Mishra1, Dericks P. Shukla1, Tarini Bhatnagar1, Neelratan Singh1, Arnold L. Usham1, Lokrampum Thoithoi1 and Aunshi S.

Ningreichon1

1Department of Geology, University of Delhi, Delhi (India)- 3350632Department of Watershed Management, Birjand University, Iran


23


The northeastern part of Pakistan is known to be a region of extremes, where the highest reliefs and the longest glaciers of the world can be found. In this environment, the multidisciplinary Social, Economic and Environmental Development Project SEED, developed by Ev-K2-CNR and composed of smaller projects focusing on different themes (e.g., glaciology, meteorology, land cover) will permit the characterization, from different points of view, of the Central Karakoram National Park area. One of the themes is focused on improving the knowledge of the territory through the analysis of geological hazards; the output of the project can be an important tool for a future rational territorial planning. In fact, the project has the general aim to promote the sustainable development of the local communities of the Gilgit-Baltistan Region. In this context, an inventory of landslide bodies and a map of landslide- or rock fall-prone areas is useful to identify the areas where human settlements

must be avoided and therefore it provides the stakeholders with an important updatable tool for territorial planning, as required by the new management plan for the national park, where zoning system for conservation of the ecosystem, and promotion of tourism is recommended.

The project started one and half year ago mainly focusing on three different areas located inside the park areas (Fig. 1). Bagrot, Haramosh, Chogo Lungma and Biafo valleys were partially surveyed and the main landslides were identifi ed. The fi eld work has been used as validation tool to verify the location of landslides previously identifi ed trough GIS techniques adapting the AHP methodology to the investigated areas. Debris fl ow, rotational and translational (Fig. 2) landslides and rock falls were outlined and the fi rst cadastre for the Central Karakoram National Park was initiated.

First landslide inventory in the Karakoram National Park: The Chogo Lungma glacial valley

*Chiara Calligaris1, Giorgio Poretti1 and Shahina Tariq2

1Department of Mathematics and Geosciences, University of Trieste, Via Weiss 2, 34128 - Trieste, Italy, 2COMSAT, University of Science and Technology, Park Road, Chak Shahzad - Islamabad, Pakistan


Fig. 1: The Central Karakoram National Park is located in the northern part of Pakistan in a region named Northern Areas. Inside the ellipses, the areas of interests.

24


Acknowledgments

This research was developed in the framework of SEED (Social Economic and Environmental Development in the

CKNP Region, Northern Areas, Pakistan) Project, funded by Government of Italy and Pakistan in collaboration with Ev-K2-CNR Committee and Karakoram International University.

Fig. 2: One of the transational landslides identifi ed during the fi eld survey of June 2012.

25


In the eastern Himalaya, partial melting is widely documented in the Higher Himalayan Crystallines (HHC), a high-grade, several km thick lithotectonic unit located at the higher structural levels of the Himalayan belt (e.g. Goscombe et al. 2006; Searle et al. 2008). In the lower structural levels of the HHC, anatexis occurred at medium to high-P (8-12 kbar) and is recorded in kyanite-bearing granulite (Barun Gneiss and Jannu-Kangchenjunga Gneiss; Groppo et al. 2012a). Toward the structurally upper levels of the HHC, peak-P signifi cantly decreases down to 4-5 kbar, as revealed by the widespread occurrence of cordierite-bearing and kyanite-free gneiss (e.g. Imayama et al. 2010; Streule et al. 2010; Mosca et al. 2011), locally named the Namche Migmatite and Black Gneiss (e.g. Bordet 1961; Lombardo et al. 1993).

This paper focuses on the cordierite-bearing lithologies occurring at the higher structural levels of the HHC by describing in detail three cordierite-bearing gneisses from different geological transects in Eastern Nepal ,from mount Everest to Kangchenjunga. The studied samples differ in terms of bulk composition, likely refl ecting different sedimentary protoliths. However, they all consist of quartz, K-feldspar, plagioclase, biotite, cordierite and sillimanite in different modal percentages. In all the studied samples, cordierite is spectacularly well preserved.

A detailed petrographic study allowsfor the recognition and interpretation of microstructures related to melt production and/or melt consumption and the distinction between peritectic and cotectic cordierite. The fi rst type is poikiloblastic and includes those minerals which are the reactants in the cordierite-forming reaction (quartz, sillimanite, plagioclase and biotite); the second type is subhedral, inclusion-free and shows a lower XMg than the coexisting peritectic variety.

The melt productivity of different prograde assemblages (from two-micas metapelite/metagreywacke to biotite-metapelite) has been investigated at low pressure conditions, evaluating the effects of muscovite vs. biotite de-hydration melting on both mineral assemblages and microstructures. The results of thermodynamic modeling suggest that the

abundance and type of the micaceous minerals in the prograde assemblage is an essential parameter controlling the melt productivity at low-P conditions, the two-mica protoliths are signifi cantly more fertile at any given temperature than biotite gneisses over the same temperature range (Groppo et al. 2012b). Furthermore, the cordierite preservation resulted to be promoted by melt crystallization at a dry solidus and by exhumation along P-T paths with a peculiar dP/dT slopes of about 15-18 bar/°C.

The P-T evolution of the studied samples, reconstructed by combining microstructural observations, mineral chemical data, and pseudosection modeling, is discussed in the framework of the “channel fl ow” model, which is one of the most popular paradigms to explain the tectonometamorphic evolution and the main geologic features of the Himalayan-Tibetan orogen. In this context, the cordierite-bearing migmatites likely represent the source rocks for the Miocene andalusite-bearing leucogranites occurring at the upper structural levels of the Himalayan belt (e.g. Visonà and Lombardo, 2002). Low-P isobaric heating rather than decompression melting is therefore the trigger process of the peculiar peraluminous magmatism (e.g. Visonà et al. 2012).

REFERENCES

Bordet, P., 1961, Recherches géologiques dans l’Himalaya du Népal, région du Makalu, Editions du Centre National de la Recherche Scientifi que, Paris, 275 p.

Goscombe, B., Gray, D. and Hand, M., 2006, Crustal architecture of the Himalayan metamorphic front in eastern Nepal, Gondwana Research, v. 10, pp. 232–255.

Groppo, C., Rolfo, F. and Indares A., 2012a, Partial melting in the Higher Himalayan Crystallines of Eastern Nepal: the effect of decompression and implications for the “channel fl ow” model, Journal of Petrology, v. 53, pp. 1057-1088.

Groppo, C., Rolfo, F. and Mosca, P., 2012b, The cordierite-bearing anatectic rocks of the Higher Himalayan Crystallines (eastern Nepal): low-pressure anatexis, melt-productivity, melt loss and the preservation of cordierite, Journal of Metamorphic Geology, in press.

Imayama, T., Takeshita, T. and Arita, K., 2010, Metamorphic P-T profi le and P-T path discontinuity across the far-eastern Nepal Himalaya: investigation of channel fl ow models, , Journal of

Low-pressure anatexis in the Higher Himalayan Crystallines of eastern Nepal revealed by cordierite-bearing lithologies

*Chiara Groppo1, Franco Rolfo1,2 and Pietro Mosca2

1Department of Earth Sciences, University of Torino, Torino, I-10125, Italy,2IGG – CNR, Torino, I-10125, Italy(*Email: [email protected])

26


Metamorphic Geology, v. 28, pp. 527–549.Lombardo, B., Pertusati, P. and Borghi, A., 1993, Geology and

tectono-magmatic evolution of the eastern Himalaya along the Chomolungma-Makalu transect, In: Treloar, P.J. and Searle, M.P. (eds.) Himalayan Tectonics. Geological Society of London, Special Publication, v. 74, pp. 341–355.

Mosca, P., Groppo, C. and Rolfo, F., 2011, Geological and structural architecture of the Kangchenjunga region in Eastern Nepal, Journal of Nepal Geological Society (in press).

Searle, M. P., Law, R. D., Godin, L., Larson, K. P., Streule, M. J., Cottle, J. M. and Jessup, M. J., 2008, Defi ning the Himalayan Main Central Thrust in Nepal, Journal of Geological Society of London, v. 165, pp. 523–534.

Streule, M. J., Searle, M. P., Waters, D. J. and Horstwood, M. S. A., 2010, Metamorphism, melting and channel fl ow in the Greater Himalaya Sequence and Makalu leucogranite: constraints from thermobarometry, metamorphic modelling and U-Pb geochronology, Tectonics, v. 29, TC5011.

Visonà, D. and Lombardo, B., 2002, Two mica- and tormaline leucogranites from the Everest-Makalu region (Nepal-Tibet): Himalayan leucogranite genesis by isobaric heating? Lithos, v. 62, pp. 125–150.

Visonà, D., Carosi, R., Montomoli, C., Tiepolo, M. and Peruzzo, L., 2012, Miocene andalusite leucogranite in central-east Himalaya (Everest-Masang Kang area): low-pressure melting during heating, Lithos, v. 144, pp. 194-208.

27


Himalaya is regarded as the classic example of continental collision belt. Two main features are distinctive in this mountain belt. The fi rst one is the presence of a extensional detachment, the South Tibetan Detachment System, STDS, (Burg et al. 1983) active during a syn-contractional regime. The second one is the spectacular lateral continuity along 2500 km of the tectono-stratigraphic units and of the tectonic discontinuity (Hodges 2000).

Among these tectono-stratigraphic units, the Greater Himalayan Sequences (GHS) made by medium to high grade metamorphic rocks, is one of the most investigated in order to penetrate inside the evolution of deep seated crystalline rocks. The structural thickness of GHS is not constant along the Himalayan range, varying from a minimum of < 3 km in the Central Dolpo Region (Carosi et al. 2010) to a maximum > 30 km in the far Western Nepal (Carosi et al. 2010) and in Bhutan (Davidson et al. 1997). The most striking features of this unit are the presence of an inverse metamorphism (i.e. metamorphic grade increase structurally upward from chlorite to sillimanite + kfeldspar) and the fact that it is bounded by two faults with opposite kinematics active in the same span of time, a basal thrust (Main Central Thrust) and a normal fault at the top (STDS). The GHS is classically (e.g. Le Fort 1975) subdivided in three formations or units: (i) “unit I” made by micaschists, paragneiss and subordinate marbles, (ii) “unit II” formed by calcsilicate rocks and (iii) “unit III” which includes augen gneiss and migmatites with rare intercalations of marbles and metapelites. These units are in stratigraphic contact and so GHS represents a coherent slab. Almost all the discontinuities within GHS have been regarded as out of sequences thrusts (e.g. Vannay and Hodges 1996).

Mugu Karnali river crosscuts all the tectonic units of the Himalaya. Due to this confi guration its transect is a perfect fi eld laboratory to investigate the Himalayan structures. The Mugu Karnali transect presents nearly 30 km of crustal section of GHS, bounded from the lower Lesser Himalayan Sequences (LHS) and Main Central Thrust Zone (MCTZ) to the upper contact with Tibetan Sedimentary Sequences (TSS).

The lower part of the transect, from Rara Lake to Gamgadhi village, consisting of low-grade quartzite still preserving primary structures, phyllites and impure marbles.

Metabasites with Epidote-Amphibolite facies (Ep, Pl, Am, Qtz, Chl) are also present. The MCTZ is located between the Gamgadhi and Lumla villages. Top-to-South shearing affected low-grade quartzite, Ullery-type orthogneiss and mylonitic micaschists. A zone of inverse metamorphism (0.5-1 km) has been recognized from the chlorite zone to the kyanite zone. In order to constrain the timing of shearing and of metamorphism accessories phases geochronology have been investigated in selected samples, coupled with structural and metamorphic characterization. Lower rocks (i.e. Ullery-type othogneiss) have allanite (Aln) as major accessory mineral along mylonitic foliation, with subordinate apatite, huttonite and very rare monazite (Mnz). This Aln is zoned with a core composition depleted in Th and a rim Th-enriched. Structurally upward, Mnz became the major accessory phase, as St zone is reached (Rubatto et al. 2001). Mnz occurs in different textural settings. Mnz coexisting with xenotime in garnet (Grt) core is very tiny and is Y rich. Mnz inside St grains is larger and Y depleted. Mnz along mylonitic foliation is present in large crystals, strongly zoned, with Y poor cores and Y enriched rims. In this samples garnet is texturally composed of a inclusion rich core, often drawing crystal faces and it chemically zoned with a prograde feature. Structurally upward, in Ky zone, Aln appears again, probably due to higher Ca content in the bulk composition of the rocks (Spear 2010). Aln is inside the Grt along the internal foliation and is also aligned along external foliation and shows, especially the latter, clear LREE zoning with a LREE rich core and a LREE poor rim (more close to clinozoisite composition). Grt in this sample still preserves memory of prograde growth.

Close to the Sill-in isograd, just after the Mangri village a wide (3–4 km) ductile shear zone is present with a top-to-South sense of shear, called Mangri Shear Zone (MSZ). In order to constrain its timing and P-T evolution classic geothermobarometry and P-T pseudosections were used for P-T estimates coupled with Mnz geochronology. P-T estimates with the two methods are broadly the same and highlight at least 2 kbar of pressure gap between footwall and hanging-wall rocks, while geochronology brackets MSZ shearing between 25-17 Ma.

Structurally upward is observed an increase of migmatites and leucogranites intrusion, until in the Puwa Khola valley, Crd- (±And) bearing gneiss with no indication

Tectono-metamorphic characterization of Higher Himalayan Crystallines in the Mugu-Karnali valley (Western Nepal): Preliminary

data

Chiara Montomoli1, *Salvatore Iaccarino1, Carosi Rodolfo2 and Dario Visonà3

1Dipartimento di Scienze della Terra, University of Pisa, Pisa, Italy 2Dipartimento di Scienze della Terra, University of Torino, Torino, Italy

3Dipartimento di Geoscienze, University of Padova, Padova, Italy(*Email: [email protected])

28


of partial melting are encountered. The mineral assemblage (M1, HP stage) is characterized by St, Ky and Grt, with a late M2 (HT-LP) overprint by Crd rimming St and Grt, with rare And coexisting. These rocks are presently correlated with Everest Schist of Jessup et al. (2008). Low-grade marble of the TSS were recognized above Everest Schist.

Preliminary fi eld work highlights no brittle fault between the upper TSS and the lower HHC, and only the ductile portion of the STDS can be followed.

REFERENCES

Burg, J. P., Brunel, M., Gapais, D., Cheng, G. M., and Liu G. H., 1984, Deformation of leucogranites of the rystalline Main Central Sheet in southern Tibet (China), Journal of Structural Geology, v. 6, pp. 535–542.

Carosi, R., Montomoli, C., Rubatto, D., and Visonà, D., 2010, Late Oligocene high-temperature shear zones in the core of the Higher Himalayan Crystallines (Lower Dolpo, Western Nepal), Tectonics, v. 29, TC4029, doi: 10.1029/2008TC002400

Davidson, C., Grujic, D., Hollister, L., Schmid, S. M.,1997, Metmorphic reactions related to decompressionand

synkinematic intrusion of leucogranite, High Himalayan Crystallines, Bhutan, Journal of Metamorphic Geology, v. 15, pp. 593-612.

Hodges, K. V., 2000, Tectonics of the Himalaya and southern Tibet from two perspectives. Geological Society of America Bulletin, v. 112, pp. 324−350.

Jessup, M. J., Cottle, M. J., Searle, M. P., Law, R. D., Newell, D. L., Tracy, R. J., Waters, D. J., 2008, P–T–t–D paths of Everest Series schist, Nepal, Journal of Metamorphic Geology, v. 26, pp. 717–739.

Le Fort, P., 1975, Himalayas: The Collided Range. Present Knowledge of the Continetal Arc, American Journal of Science, v. 275, pp. 1–44.

Rubatto, D., Williams, I. S., Buick, I.S., 2001, Zircon and monazite response to prograde metamorphism in the Reynolds Range, central Australia, Contribution Mineralalogy Petrology, v. 140, pp. 458-468.

Spear, F. S., 2010, Monazite-allanite phase relations in metapelites, Chemical Geology, v. 279, pp. 55–62.

Vannay, J. C., Hodges, K. V., 1996, Tectonometamorphic evolution of the Himalayan metamorphic core beeteen the Annapurna and Dhaulaghiri, Cental Nepal. Journal of Metamorphic Geology, v. 14, pp. 635–656.

29


A large massif (10 x 50 km) of continental High Pressure (HP) rocks is evidenced in the Atbashi Range (South Tian Shan, Kyrgyzstan). Its structure and metamorphic history are investigated to reconstruct the geodynamic evolution of the northern rim of Tarim basin in the Upper Paleozoic. This study gives insights into the crustal-scale structure of this mountain belt, currently intensely reactivated by the India-Asia collision.

Metamorphic units exhibit blueschist to eclogite facies conditions. Evidence for eclogite facies in both acidic and mafi c lithologies and geological structure are in agreement with a previously thinned continental margin. Prograde stage (I) begins in blue-schist/eclogite facies transition at

520±30°-17±1 kbar. Conditions of peak metamorphism (II) in eclogite facies range from 550±30°C-18.5±1 kbar to 540-595°C-21 kbar. Retrograde stage (III) condition is also in the eclogite facies conditions at 515± 30°C-16.7±1 kbar.

Subduction of this thinned COT (Continent-Ocean Transition) occurred by slab pull in a south-dipping subduction zone, while another north-dipping subduction was active below Middle Tian Shan. Final stacking of Middle and South Tian Shan occurred at 320-310 Ma. These antithetic subduction zones are still refl ected in the main structures of Tian Shan. Reactivation of the South-dipping structures since 30 Ma is ascribed to explain the current TianShan intra-continental slab inferred form seismology.

Geodynamic signifi cance of HP metamorphism in Atbashi Range (South Tianshan, Kyrgyzstan) and inferences for crustal-scale structure of

north Tarim-Tibet orogenic system

*Chloé Loury1, Yann Rolland1, Stéphane Guillot2, Dmitriy V. Alexeiev3 and Alexander V. Mikolaichuk4

1Géoazur UMR, Observatoire de la Côte d’Azur, Univerité de Nice Sophia-Antipolis, Faculté des Sciences, Parc Valrose, 06108 Nice, France

2ISTerre, University of Grenoble 1, CNRS, 1381 rue de la Piscine, 38041 Grenoble, France3Geological Institute, Russian Academy of Sciences, Pyzhevskiy 7, 119017, Moscow, Russia

4Institute of Geology, National Academy of Sciences, 30 Erkindyk Av., Bishkek 720481, Kyrgyzstan(*Email: chloé[email protected])

30


Within the scope of German governmental development cooperation (fi nancial and technical) the majority of geoscientifi c- and mining-related projects are mainly implemented by the Federal Institute for Geosciences and Natural Resources (BGR), Hannover (Germany), commissioned by the Federal Ministry for Economic Cooperation and Development (BMZ).

For more than 50 years, this highly-professionalized scientifi c-technical authority and their partner organizations have jointly realized projects around the world focusing on the exploration of groundwater and raw materials, in the fi elds of mining and environmental geology, among others.

Triggered by unprecedented natural disasters (e.g. Hurrican Mitch 1998) causing daunting tangible and non-tangible losses, BMZ responded to such serious development-inhibiting events by incorporating Disaster Risk Reduction (DRR) policy issues into the German development cooperation policy framework. According to that, German project implementation organizations, such as BGR, have been mandated for more than ten years to implement technical cooperation projects dealing with all spheres of disaster risk and risk management. With regard to these DRR activities, BGR is currently involved in two technical cooperation projects, one in Indonesia and another one in Pakistan. Respective partners are the Geological Surveys of the countries mentioned.

Based on its own geoscientifi c expertise, BGR is largely accountable to foster the personnel capacity of scientifi c-technical counterpart authorities in terms of assessing both the geohazardous potentials (e.g. seismic hazard, landslide and land subsidence susceptibility) and the resulting risk (exposure). This is aimed at the enhancement of the advisory capacity of the project partners pertaining to risk-sensitive spatial planning activities that should exemplarily and

commonly be rendered within particular pilot areas.

With regard to the personnel capacity development, a recurrent and signifi cant issue of all previous and current DRR-related BGR-projects needs to be addressed is the assessment of the regional landslide susceptibility. However, project experiences have shown that the partners have not fully internalized the landslide susceptibility assessment as a consecutive process of several working steps, yet. For that reason, BGR developed a reasoned, modular workfl ow (i.e. a ‘Standard Operating Procedure’) illuminating all mandatory assessment steps taking into account best-practice approaches. This integrated workfl ow broaches following main topics: 1) Field survey activities, e.g. applying a newly designed standardized landslide survey data sheet to establish a landslide inventory; 2) Activities focusing on the digital data capture of fi eld inventory information in a landslide inventory database; 3) GIS-based inventory mapping applying the digital inventory information; 4) GIS-based probabilistic and deterministic landslide susceptibility assessment and mapping incorporating the digital inventory information.

According to technical cooperation project specifi cations, all four steps have been comprehensively underpinned by the needs-based design of IT-applications, by the elaboration of user-friendly guidelines and manuals, by carrying out on-the-job trainings as well as by jointly organized fi eld trips to practice landslide survey techniques. Based on this impartial, all-inclusive landslide susceptibility assessment package, BGR is now able to transfer and to apply this workfl ow package to each landslide prone region or country in the context of DRR-related technical cooperation projects. The presentation will give an insight into the workfl ow products designed and shares lessons learned from the application of this workfl ow in the two projects countries mentioned above.

An integrated landslide susceptibility assessment approach within DRR-related technical cooperation projects of the BGR

D. Balzer, M. Fuchs, D. Kuhn and J. TorizinFederal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany

31


The Intergovernmental Panel on Climate Change (IPCC) concluded in 2007 that evidence of global warming is “unequivocal”, that a human infl uence on global and regional climate has emerged, and that further global warming of several degrees Celsius is likely during this century. IPCC (2007a; 2007b) and other reports (Bierbaum et al. 2007) have projected varieties of adverse impacts of future climate change, some already demonstrably underway. Recent understanding on climate change emphasizes that while reducing greenhouse gas emissions (“mitigation”) must continue as an international priority, action on minimizing the adverse effects of the changes on societies and ecosystems (“adaptation”) is also critical.

In Nepal, the rate of climate change has been among the highest in the world, with high elevation sites warming the most. Analysis of recent climate data reveals a signifi cant warming trend with more than 1oC average maximum temperature rise in the last 30 years. It is twice as fast as the average warming for the mid-latitudinal Northern Hemisphere (24 to 40oN) over the same time period, and illustrates the high sensitivity of mountain regions to climate change. Over 350 deaths have occurred annually due to extreme weather events, and this rate is increasing. There is growing evidence of widespread glacial retreat, water resource depletion, changes in weather pattern and monsoon timing, losses in crop yield and biodiversity, disruption in ecosystem services, increase in disease outbreak etc. These stresses are already affecting economic performance and human well-being. The agriculture and water resource sectors, crucial to the wellbeing of people, are particularly sensitive to fl uctuations in weather and climate.

The recently developed climate change scenarios for Nepal across multiple general circulation models show considerable convergence on continued warming, with country averaged mean temperature increase of 1.4°C, 2.8°C and 4.7°C projected by 2030s, 2060s and 2090s, respectively. Future impacts associated with the projected temperature rise are likely to be signifi cant to make things more diffi cult because of the complexity of Nepal’s interconnected physical and social environments and its limited human, fi nancial and institutional and technological resources. This paper gives an overview of the observed and projected climate change and the associated impacts in the Nepal Himalaya, and discusses adaptation challenges.

REFERENCES

Bierbaum, R., Holdren, J. P., MacCracken, M., Moss, R. H. and Raven, P. H., 2007, Confronting climate change: Avoiding the unmanageable and managing the unavoidable. Scientifi c Expert Group Report on Climate change and Sustainable development, prepared for the 15th Session of the Commission on Sustainable Development. UN Foundation-Sigma XI

Intergovernmental Panel on Climate Change (IPCC), 2007a, Climate Change 2007: The Physical Basis: Summary for Policy Makers, Contribution of Working Group1 to the Fourth Assessment Report of the Inter Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom, and New York, NY. Available at: http://www.ipc.ch/WG1_SPM_17Apr07.pdf

Intergovernmental Panel on Climate Change (IPCC), 2007b, Climate Change 2007: The Physical Basis, Contribution of Working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom, and New York, NY. Available at: http://ipcc-wg1.ucar.edu/wg1/wg1-report.html

Climate change in the Nepal Himalaya: Observations, projections and adaptation challenges

Danda Pani AdhikariDepartment of Geology, Tri-Chandra Campus, Tribhuvan University, Kathmandu, Nepal

(Email: [email protected])

32


A structural and thermochronologic study of the Central Pamir Gneiss Domes and their cover in the Central Pamir is presented. The work is based on the Soviet 1:200,000 geologic maps and fi eldwork of the TIPAGE (Tien-Shan-Pamir Geodynamic Program) group from 1993 to 2011.

The structure of the Central Pamir is dominated by Cenozoic deformation related to the India-Asia collision. Only few structures of the Phanerozoic amalgamation of the Pamir were not reactivated. The Cenozoic structural development of the Central Pamir can be simplifi ed into three phases:

(1) Between initial collision of India and Asia and ≤20 Ma, emplacement of large thrust sheets led to strong north-south shortening; in the eastern Central Pamir, the major thrust sheet has a minimum displacement of 35 km. Its stratigraphic thickness is about 7 km but its internal structure and thus the true thickness is weakly constrained by the available data. Klippen of Early Paleozoic strata of the thrust sheet south of the Central Pamir Muskol and Shatput domes (compare fi gure 1) that lie on Carboniferous to Triassic strata of the footwall can be linked to the Akbaital nappe previously mapped by Russian authors north of the domes. In the Saksasu valley of the Muskol dome, the thrust sheet is intruded by a ~36 Ma granodiorite (U-Pb zircon).

(2) This crustal imbricate stack is cut by east-west trending normal faults and shear zones that defi ne the Central

Pamir Gneiss Domes. Normal shear is concentrated along the northern margin of the domes and was the main process associated with exhumation of the Central Pamir gneiss domes from ~30 km depth at 20-15 Ma (Ar-Ar and fi ssion-track geo-thermochronology). Intrusion of granites (one dated) around 34.8 Ma (U-Pb zircon) preceded exhumation while leucocratic dykes (e.g. 18 Ma U-Pb monazite) are coeval with fast exhumation. Detrital U-Pb zircon ages indicate that the protoliths of the domes are Paleozoic; thus, these amphibolite-facies meta-sedimentary rocks are likely equivalents of the Paleozoic to early Mesozoic strata of the footwall of the thrust sheets. This indicates that the upper crust thickened to ~ 30 km.

(3) Neogene shortening is bi-vergent: top-to-south back-thrusting north of the Central Pamir domes opposes top-to-north thrusting in the south. Neogene deformation affects ~18 Ma (Ar-Ar geochronology) coarse fl uvial and alluvial fan strata with basaltic dikes and fl ows south of the dome; restoration of these strata yields up to 40% shortening.

Total shortening by thrusting of the Central Pamir is at least 40% in the Shatput-Muskol area with a minimal total shortening of 70 km; internal deformation with recumbent north-vergent folds within the domes and its cover indicate much higher values.

Miocene gneiss-domes in the central Pamir: Burial and exhumation

*Daniel Rutte1, Mike Stearns,2 Lothar Ratschbacher1 and Bradley Hacker2

1Geologie, TU Bergakademie Freiberg, Freiberg, Germany2Geological Sciences, UCSB, California, USA


33


REFERENCES

Russian Ministry of Geology, 1986, Geological map of the Tadjik SSR, scale 1:200.000, St. Petersburg.

Schwab, M., Ratschbacher, L., Siebel, W., McWilliams, M., Minaev, V., Lutkov., V., Chen, F., Stanek, K., Nelson, B. and Wooden, J. L., 2004, Assembly of the Pamir: Age and origin

of magmatic belts from the southern Tien Shan to the southern Pamir and their relation to Tibet, TECTONICS, v. 23, TC4002.

Vlasov, N. G., Yu. A. Dyakov, and E. S. Cherev (Eds.), 1991, Geological map of the Tajik SSR and adjacent territories, 1:500,000, Vsesojuznoi Geol. Inst. Leningrad, Saint Petersburg.

Fig. 1: Simplifi ed geologic map of the Tadjik Pamir south of the Main Pamir thrust. Emphasis is laid on the magmatic arcs, domal occurrences of high grade rocks and structural units of the Central Pamir. Only the major structures relevant for the division of the Pamir are shown. Triangles on faults are on the hanging wall side of thrusts, squares on the hanging wall side of normal faults. Faults representing sutures are in the color of their corresponding magmatic belt. The Northern (Asia) and Central (Cimmeria) Pamir are separated by the Paleotethys Suture. The terms Kunlun and Tanymas Suture are used in the Russian literature but do not represent oceanic sutures in the modern understanding because they are drawn on top of their corresponding accretionary wedge. Simplifi ed from Russian Geology Ministry (1986), Schwab et al. (2004) and Vlasov et al. (1991).

34


Explaining crustal movements around the eastern Himalayan Syntaxis (EHS) is key in creating models of Tibetan Plateau evolution. Actually, two end-member models are widely considered: the classic escape model, which calls for large-scale displacement of lithospheric blocks and crustal fl ow with a combination of topographic loading and Poiseuille-type channel fl ow, driven by long-term monsoon-dependent high erosion and gravitational potential energy of the Tibetan Plateau. A change in surface-velocity vectors from northward convergence to eastward motion of material north of the EHS is revealed by GPS measurements across the India-Asia collision zone. Western Yunnan is one of the key areas for tracing crustal fl ow around the EHS and deciphering its mechanism. In this area GPS data indicate clockwise rotation continuing south to ~26°N, where the direction of surface movement is partitioned to the west into western Yunnan and Burma and to the southeast, south of the Sichuan basin.

In our study, we present new paleomagnetic data on ~30

Ma mafi c dykes from the Gaoligong Shan in western Yunnan in order to detect block rotations around the EHS. These dykes are ~1m to ~6m wide. They intruded into granites of the Gaoligong Shan and reveal a sharp contact. Results from rock magnetic studies, refl ected light microscopy, and SEM/EDX analysis identify Ti-rich titanomagnetite as the main magnetic remanence carrier co-existing with magnetite and hematite in different proportions. This indicates a primary magnetization but also a relatively high degree of alteration. Alternating fi eld demagnetization reveals good grouping remanence directions. The distribution of the in situ site means is D/I=63°/26° (α95=22°, k=7), which indicates a clockwise rotation around the Eastern Syntaxis. The difference vector of the overall site mean and the expected direction at ~30 Ma, calculated from apparent polar wander paths (D/I=7°/48.5°), yields a clockwise rotation of 56°±24° around the Eastern Syntaxis accumulated since ~30 Ma. This matches with present GPS velocities (expected to accumulate to ~30°-60° clockwise since ~30 Ma based on the present day rotation rates of 1°/Myr to 2°/Myr).

Block rotations around the eastern Himalayan Syntaxis: Paleomagnetic investigations in the Gaoligong Shan

*Daniela Kornfeld1, Sabine Eckert1, Erwin Appel1, Lin Ding2 and Deliang Liu2

1Department of Geosciences, University of Tübingen, 72074 Tübingen, Germany, 2 Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China


35


In central Nepal, the rock exposed at the surface between the Main Central thrust and the Main Boundary thrust is the Lesser Himalayan rock. In other regions of Nepal, Lesser Himalayan rock is not exposed but buried by klippen of Greater Himalayan rock. Thus, central Nepal along the ModiKhola, south through the Kali Gandaki River is one location where the entire thrust belt in Lesser Himalayan rock is exposed. This location is critical to determining the kinematics of thrust belt. Recent work has suggested over 2000 km of shortening in the Himalayan thrust belt. The largest amount of minimum shortening found in thrust belt is approximately 1000 km in far western Nepal. The purpose of this study is to determine the structural architecture of central Nepal through the collected structural data, incorporating available age data, and drawing and balancing cross sections. Because of assumptions in the stratigraphy, two cross sections are balanced through the same location of the ModiKhola south through the Kali Gandaki River. Each cross section has different underlying assumptions and decisions made during the construction. One motivation for this study was to test whether making cross sections using different assumptions affected the amount of shortening in the cross sections. We tested whether major changes in the stratigraphy and simplifi cations regarding the evolution of the LH duplex affected the amount of shortening.

Cross section A has a shortening estimate from the Main Central thrust to the Main Boundary thrust, including motion on the Main Central thrust, of 359 km or 77.8%. Cross section B has a shortening estimate of 371 km or 78.4% over the same region. These shortening estimates do not include meso-scale and micro-scale shortening in the Lesser Himalayan and Greater Himalayan rocks nor do they include possible intra-Greater Himalayan faults. The percentage of shortening between the two cross sections is the same and the amount of shortening is not signifi cantly different. These are striking outcomes given the different choices made when constructing the cross sections especially with regards t o the stratigraphy. This suggests that the different choices made when drawing a cross section may be irrelevant for the estimate of shortening amount and percentage of shortening. In addition, in these particular cross sections, the established Ramgarh/Munsiari thrust is not present in the footwall of the Main Central thrust. Because this thrust is present at least from Himachal, India to east Bhutan, we are certain that this thrust must also be present in central Nepal. Thus, the Ramgarh/Munsiari thrust must have been faulted out at the surface. The thrust in the footwall of the Main Central thrust is the next thrust below the Ramgarh/Munsiari thrust called the Trishuli thrust.

Testing variations in shortening estimates in central Nepal along the Modi and Kali Gandaki Rivers

*Delores M. Robinson1 and Aaron J. Martin2

1Department of Geological Sciences, The University of Alabama, USA, Tuscaloosa, AL 35487 USA2Department of Geology, University of Maryland, College Park, USA


36


The Himalayas comprise one of the largest collections of glaciers outside the polar regions, with glacier coverage of ~33,000 km2 (Dyurgerov and Meier 1997). The rivers of the Himalayas are of glacial origin and are thus perennial. Since the mid of last century many large glaciers in Himalayas have disintegrated to smaller glaciers primarily due to global warming (Kulkarni et al. 2007; Shrestha et al. 2012). During this glacier melt, several glacial lakes form up in the vicinity of retreating glaciers or from their melt water (Jain et al. 2012). These glacial lakes are mostly situated in elevation between 3000-5000 m elevations and are formed in unstable regions. During Glacial lake outburst fl oods (GLOF), they can produce discharge rates of 30,000 m3 sec−1 which can cover over 200 km in downstream region (Richardson 2000). Thus, a detailed approach is required to mark out these potential risky lakes before they begin to get into severe conditions. An extreme rainfall event coupled with them having vulnerable lithology and slopes could trigger a fl ash fl ood event in the area. This study investigates the possibility of a glacial lake outburst fl ood in Sikkim, which has a massive topography and extensive annual precipitation. Based on the analysis of geomorphic, climatic, and tectonic processes in Sikkim, a vulnerable glacial lake were identifi ed.

Various datasets such as Aster GDEM (http://www.gdem.aster.ersdac.or.jp/feature.jsp), Landsat Satellite (http://www.landcover.org/data/landsat/), Rain-gauge enhanced 0.25 degree daily satellite grid precipitation product viz. APHRODITE (http://www.chikyu.ac.jp/precip) and TRMM (http://disc2.nascom.nasa.gov/Giovanni/tovas/) for Sikkim area were collected coupled with fi eld data. These datasets were processed and analysed using remote sensing and GIS softwares like ERDAS 9.2, Arc GIS 9.3, ILWIS and GrADS. Nearly 219 glacial lakes, clustering in three zones as shown in Fig. 1, were identifi ed using International Centre for Integrated Mountain Development (ICIMOD) and Glacier atlas of India (Geological survey of India) on glaciers and glacial lakes data (http://www.rrcap.unep.org/issues/glof/glof/India/Tista/reports/annex/annex_II/glacial_Main.htm). The relationship of glacial lakes in terms of its regional orography, geomorphology and geology was analyzed using the inventory.

The primary weightage was given to slope, precipitation

and geological structures, while secondary weightages were given to aspect, drainage and area of the lakes to demarcate the vulnerable lakes. The regions that have high slopes coupled with heavy precipitation and are tectonically active were given the highest vulnerability rating. Ultimately, vulnerable lakes were identifi ed using these specifi ed parameters, from which sites of potential fl ash fl oods were determined. Hence the glacial lakes, which lie in the heavy monsoon reaches areas of eastern Sikkim and western Sikkim region of Kanchenjunga have higher potential of creating hazardous event through fl ash fl oods and landslides. The lakes that had high precipitation and high sloping angle were given very high chances of bursting.

Out of 219 lakes, majority (101) fall in Eastern Sikkim region, while 98 lakes are found in the Northern and 20 lakes are present in Western Sikkim region. In all, 8 glacial lakes fall under very high vulnerability category (class I), while 12 lakes were identifi ed that were in high vulnerability zone (class-II). Eastern Sikkim had the highest number of glacial lakes, not surprisingly it had the highest number (14) of hazardous lakes too, followed by the Northern region which has 8 hazardous lakes. The Western region has the least number (2) of hazardous lakes.

In the northern region 4 lakes fall under moderate category followed by 3 lakes in high while mere 1 lake falls in very high category. A lake in North Sikkim region right in the vicinity of Gurudongmar Lake was found to be highly hazardous. There are 2 lakes, one each in high and very high hazardous category. These lakes though less in number but cover quite a large area and so posing a risk in the immediate downstream region. In eastern Sikkim region 6 very highly hazardous and 8 hazardous lakes were found and some of the lakes are situated right on the road networks within the proximity of densely populated areas. The region becomes most active amongst all three and the possibility of a hazardous event here becomes very high. Every year several landslide and fl ash fl oods occur in Sikkim during the summer monsoon season. Therefore, the areas around Gangtok in the Eastern Sikkim having highest density of glacial lakes are most susceptible to GLOFs. Hence detail study of glacial lakes in Eastern Sikkim is needed for proper management and prevention from such natural hazards.

GLOF susceptibility of Sikkim Himalayas

*Dericks P. Shukla1, Chandra S. Dubey1, R. P. Singh1, B. K. Mishra1 and T. Luthra2

1Department of Geology, Centre for Advanced Studies, University of Delhi, Delhi-110007, India.2Department of Geosciences, College of Earth and Mineral Sciences, Penn State University, 16802-PA, USA


37


REFERENCES

Dyurgerov, M. B., Meier, M., 1997, Mass balance of mountain and subpolar glaciers: a new global assessment for 1961–1990. Arctic and Alpine Research, v. 29, pp. 379- 91.

Jain, S. K., Lohani, A. K., Singh, R. D., Chaudhary, A., and Thakural, L. N., 2012, Glacial lakes and glacial lake outburst fl ood in a Himalayan basin using remote sensing and GIS. Natural Hazards, v. 62, pp. 3887-899.

Kulkarni, A. V., Bahuguna, I. M., Rathore, B. P.,Singh, S. K., Randhawa, S. S., Sood, R. K. and Dhar, S., 2007, Glacial

retreat in Himalayas using Indian remote sensing satellite data. Current Science, v. 92, pp. 69–74.

Richardson, D. S. and Reynolds, J. M., 2000, An overview of glacial hazards in the Himalayas. Quaternary International Volumes, v. 65-66, pp. 31-47.

Shrestha, B. B., Nakagawa, H., Kawaike, K., Yasuyuki B., and Zhang, H., 2012, Glacial hazards in the Rolwaling valley of Nepal and numerical approach to predict potential outburst fl ood from glacial lake. Landslides, DOI: 10.1007/s10346-012-0327-7.

Fig. 1: Geological and Structural Map of Sikkim showing distribution of glacial lakes in 3 clusters.

38


On May 5, 2012 an outburst fl ood on the Seti River resulted to the loss of life and property and has left terror that a similar catastrophe could occur at any time in Pokhara. Local people and government agencies want a scientifi c explanation of this event; in the absence of detailed scientifi c studies, speculations have been made by scientists in the course of normal hypothesis-making. The following key questions must be addressed. 1. What was the cause of the Seti river disaster? 2. Is another similar fl ood likely? 3. What role might imprudent habitation have played in raising the death toll? 4. What other types and magnitudes (e.g., peak fl ows) of fl oods are possible in the future? 5. How large a population remains vulnerable? The major objectives of this paper are to share the hypotheses evolving fi rst from a brief helicopter-borne survey a few weeks after the disaster, then from preliminary ground-based fi eld observations in November 2012; to discuss and share the ideas of the scientifi c community during a “town-hall” type of workshop aimed at public dissemination of knowledge; and to establish a fi rm basis for producing fi nal answers to the fi ve questions as best we are able.

Following a brief helicopter-borne survey a few weeks after the disaster, but before this latest ground-based study, we had concluded preliminarily:

a. It was not a normal GLOF! The fl ood could not have been a usual type of GLOF (Glacier Lake Outburst Flood), because no such precursor lake existed in the basin.

b. Rockfall-impounded lake: not only that, either! It was observed from satellite repeat imaging, that a modest rockfall occurred into the Seti gorge between 2002 and 2008, and was reactivated a few weeks prior to the disaster. However, quantitatively this explanation appeared, after the fi rst helicopter-borne survey, to fall short, because the gorge was thought to lack the impounded volume needed to explain the fl ood.

c. Working hypothesis # 1: The karst model. The rockfall dam outburst model was soon modifi ed, and included the possibility that not only the gorge could have contained a lake, but possibly karst caverns in those same rocks could have been water fi lled and may have been dammed and then undammed by the rockfall.

d. Rock avalanche/landslide trigger. Another wrinkle and clue to the mystery of the disaster’s causes emerged. On the morning of the disaster just an hour or two before, a tour plane operator observed visually and captured on wing-tip cameras a huge brown avalanche cloud several kilometers up the Seti valley (Annapurna Range) from where he was fl ying. In blog postings and to us personally, the operator (Mr. Maximov) stated that the brown cloud was both vastly larger and much dirtier/browner than any snow avalanche he had ever witnessed.

e. Working hypothesis # 2: All-of-the-above (multiple sources). It was felt, after the initial helicopter-borne survey, that a composite model might work best. Supraglacial and englacial water, wet snow, water produced by frictional melting of avalanche snow and ice, and water stored in the rockfall-dammed gorge lake and perhaps in karst each might have contributed to the fl ood. The process-chain of mass movements then was triggered by the large avalanche/landslide.

To test the above hypotheses, a ground survey was carried out in the upper Seti Basin from Nov. 5 to 10, 2012. The more recent ground survey has resulted in some fundamental fi ndings, some of which support earlier ideas and others introducing new process linkages and emphasizing the involvement of impounded water in the gorge more than other sources of water.

The investigation team, having completed this initial round of fi eldwork, has initiated a detailed analysis of the fi eld results and lab investigations of collected samples.

Investigation of the Seti River disaster (May 5, 2012) and assessment of past and future mountain hazards facing Pokhara, Nepal and upstream

communities

*Dhananjay Regmi1, Jeffrey Kargel2, Lalu P. Paudel3, Khagendra R. Poudel4, Gregory Leonard2, Bhabana Thapa5 and Anusha Sharma3

1Himalayan Research Institute, Kathmandu, Nepal2 Department of Hydrology and Water Resources, The University of Arizona, USA

3Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal4Department of Geography, Prithivi Narayan Campus, Tribhuvan University, Pokhara, Nepal

5Central Department of Geography, Tribhuvan University, Kirtipur, Kathmandu, Nepal(*Email: [email protected])

39


Here we offer a summary of preliminary fi ndings. Chief among our results:

It was not a glacier lake outburst fl ood; the largest water source was probably a natural rockfall-impounded reservoir in the gorge.

We have confi rmed that a large avalanche starting from over 7000 m elevation on Annapurna IV on May 5, 2012 triggered the disaster of that same day.

(3) Large rockslides into a deep gorge in the years and weeks prior to the disaster conditioned the system for the disaster due to impoundment of the upper Seti River in the gorge.

(4) The gorge is far deeper than anyone had previously supposed; a minimum measured depth of 226 m and a total depth possibly in the 500-600 m range in places.

(5) The bottom elevation of the gorge tends to ascend upward in the valley more gradually than does the elevation at the top of the gorge; hence, the gorge becomes generally deeper to the north.

(6) The possible contained volume of water due to the impounding rockslides is far greater than previously supposed due to a somewhat greater width and the greater depth and lower bottom gradient.

(7) The contained water volume in the natural reservoir is probably suffi cient all by itself to account for the fl ood disaster. (However, this conclusion still rests on comprehensive 3-D mapping of the gorge and sediment deposits left by the impoundment lake.)

(8) The triggering mechanism for the fl ood disaster was, as our earlier speculations had suggested, an intense avalanche wind sustained and aggravated by ingestion of enormous amounts of ancient sediments from the newly defi ned Annapurna Formation.

(9) The avalanche wind and dust cloud deposited a massive sheet of mud (now 1-5 cm thick of fi ne white powder) across much of the upper Seti Basin.

(10) The Annapurna Formation, made of unconsolidated and poorly consolidated/weakly lithifi ed glacial deposits and glacial lake deposits, was the source for the massive outfl ows of sediment and fl oods that formed the terraces and valley bottom of Pokhara Valley (that event is usually assigned an age of about 750 years).

(11) Evidence of previous large-scale mass movements—probably suffi cient to have had effects on the populated parts

of Pokhara Valley—are abundant in the upper Seti Basin; these include massive rockslides and terraces indicative of large and possibly simultaneous debris fl ows.

(12) In general, the largest scale of possible mass movements, such as those that buried the whole Pokhara Valley 750 years ago, are improbable and in fact are not likely ever to occur again, because a huge lake that once appears to have existed in the upper Seti River basin (and which was responsible for depositing the Annaourna Formation) no longer exists and will not reform. However, mass movements or fl oods much greater than the May 5, 2012 event are possible. Many scenarios for fl ooding may potentially involve larger fl ood volumes than on 5 May 2012. Most concerning, enormous amounts of unconsolidated ancient lake sediment still exists and could become fl uidized during an abnormally wet monsoon and an earthquake, for one hypothetical instance. Furthermore, small supraglacial ponds exist on the glaciers; though not a hazard now, their likely future growth must be monitored.

We have tracked down the likely sequence of events, which, in brief, consisted of a rockslide into a gorge and formation of an impounded lake in the gorge; then a huge rock and ice avalanche off Annapurna IV, which violently swept debris into the impounded lake and caused the rupture of the gorge dam, and thus unleashing of the fl ood. Additional sources of water may have been incorporated into the avalanche mass movement, including small supraglacial ponds, subglacial water bodies, wet snow, and frictional melting of snow and ice. The ingestion of ancient lake sediments, and especially powder-like silt, added much mass to the avalanche fl ows and is what caused the high sediment content of the fl oodwaters. Increasing habitation along the riverbank and lowest terrace is the biggest cause for continuing concern; minor fl oods that probably happened before with little impact may now happen again on similar scales and cause devastation and sorrow. The possibility of fl oods and debris fl ows larger than the 5 May 2012 event cannot be discounted. Our ground-based is preliminary and needs to be followed by very detailed fi eldwork; fl ood modeling; and other analysis; and attention to the demographic relationships with terrain along the river’s edge and socioeconomic investigation of why people are living in such dangerous places. Besides fi nding a solution to the problem of imprudent habitation, we fi nd that a cost-effective warning system must be emplaced; this probably would involve resident involvement and use of modern telecommunications now available to most residents.

40


Models of Himalayan mountain-building are generally dominated by one of two end-member processes: extrusion and underplating. Extrusion requires exhumation of mid-crustal material between surface-breaching faults: a thrust fault below and a normal fault above. Underplating involves mid-crustal accretion of material from underthrusting India to the over-riding Himalayan orogen. There is a key structure in the Himalaya for differentiating the models: the South Tibet detachment (STD), a fault system bounding the top of the Himalayan crystalline core. The gently north-dipping, top-north STD is recognized as a normal fault that controls the extrusion of the crystalline core in extrusion models, such as wedge extrusion and channel fl ow coupled with orographically-focused denudation (e.g., Burchfi el and Royden 1985; Beaumont et al. 2001). In contrast, the STD is interpreted as a backthrust that constrains the emplacement of the crystalline core at depth in underplating models such as tectonic wedging (e.g., Webb et al. 2007). The two end-member models have different predictions in terms of the leading edge of the crystalline core. Extrusion requires that the leading edge has been eroded away, whereas the leading edge could be preserved if the crystalline core was emplaced at depth by underplating. Thus fi nding the leading edge of the crystalline core is able to distinguish the two models.

Specifi c features of the synclinal frontal klippen of southern Nepal suggest that the leading edge of the crystalline core may be preserved along the northern margins of the klippen. The base of the klippen is defi ned by the Main Central thrust (MCT), which bounds the base of the crystalline core across most of the Himalaya. However, the core of the klippen syncline is commonly occupied by Early Paleozoic Tethyan rocks which are universally associated with the STD hanging wall. A depositional contact separates these Tethyan rocks from the underlying Bhimphedi metasedimentary sequence. The Bhimphedi rocks share features with basal Tethyan rocks to the west and east (i.e., the Haimanta and Chekha rocks): (1) these units consist of Late Proterozoic siliciclastic (meta-)sedimentary sequences intruded by Early Paleozoic granites, and (2) these units have a right-way-up metamorphic sequence from

~200-300 °C down to ~550-650 °C. The MCT occurs at the base of the Bhimphedi sequence except along the northern margin of relatively northern klippen, where a wedge of gneisses (with peak metamorphic temperatures of ~650-750 °C) separates the thrust from the Bhimphedi sequence. This wedge pinches out to the south. Webb et al. (2011) documented an Early Miocene ~200m thick top-north shear zone in one location along the gneiss – Bhimphedi sequence contact. They proposed that this shear zone is the STD, such that the southward-terminating gneiss wedge is the leading edge of the crystalline core, and the STD merges with the MCT to the south. In this study, we examine the northern margins of the Kathmandu nappe and Dadeldhura klippe to test this model.

We conducted fi eld mapping combined with microstructural, quartz c-axis fabric, and geochronological studies to analyze transects across these two regions. Along the north margin of the Kathmandu nappe, our structural mapping shows a continuous top-north shear zone, termed the Galchi shear zone, separating gneiss to the north from the Bhimphedi sequence to the south. Gneisses between the Galchi shear zone and MCT pinch out toward the south. Quartz c-axis fabrics from the Galchi shear zone indicate uniformly top-north motion. A crosscutting leucogranite from Lapsephedi and a weakly-deformed leucogranite from Kakani along the Galchi shear zone yield zircon U-Pb age clusters for rims ranging ~27-14 Ma and ~35-24 Ma, respectively. These ages constrain the motion of the Galchi shear zone to the Early and Middle Miocene.

Across the northeastern margin of the Dadeldhura klippe, our structural mapping reveals a ~0.7 km thick, top-north shear zone, along the Tila river, termed the Tila shear zone,. Gneisses between the Tila shear zone and MCT pinch out laterally along the trace of the MCT. The asymmetric quartz c-axis fabrics of rocks from the Tila shear zone indicate top-north shearing. Quartz microstructures and opening angles of quartz c-axis fabrics indicate deformation temperatures of ~650 -350 °C from the base to the immediate hanging wall of the Tila shear zone. Zircon from two crosscutting

New fi ndings from crystalline rocks of the frontal klippen, Nepal Himalaya, demonstrate mountain-building via underplating

*Dian He1, A. Alexander G. Webb1, Kyle P. Larson2 and Axel K. Schmitt3

1Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, USA, 2Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

3Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095, USA(*Email: [email protected])

41


leucogranites in the shear zone yields U-Pb age clusters for rims spanning from ~30 to 17 Ma. The zircon ages constrain the timing of top-north motion of the Tila shear zone as the Early Miocene.

All characteristics of the Galchi and Tila shear zones including the sense of shear, structural position, metamorphic fi eld gradient, and timing of motion are consistent with those of the STD shear zone. Therefore we interpret these shear zones as southern occurrences of the STD and the gneisses as the crystalline core. The pinch-out of the gneisses to the south indicates that the MCT-STD branch line bounds the leading edge of the crystalline core. We interpret the STD as a sub-horizontal fault on the basis of its multiple exposures that extend for >200 km from the frontal klippen in the south, to major traces along the range crest in the north, and even further north to the Northern Himalayan gneiss domes (e.g., Wagner et al. 2010). The MCT-STD branch line precludes extrusion models such as wedge extrusion and channel fl ow-focused denudation, but supports underplating models such as tectonic wedging. The presence of the MCT-STD branch line requires that the STD is a backthrust. Sparse work suggests that the crystalline core may have been constructed via underplating and duplexing of multiple mid-crustal horses (Reddy et al. 1993; Corrie and Kohn 2011). These fi ndings are synthesized in a reconstruction showing that the Himalayan orogen has built up via underplating processes.

REFERENCES:

Beaumont, C., Jamieson, R. A., Nguyen, M. H. and Lee, B., 2001, Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled to focused surface denudation. Nature, v. 414, pp. 738-742.

Burchfi el, B. C. and Royden, L. H., 1985, North–south extension within the convergent Himalayan region. Geology, v. 13, pp. 679-682.

Corrie S. L. and Kohn M. J., 2011, Metamorphic history of the central Himalaya, Annapurna region, Nepal, and implications for tectonic models. Geol. Soc. Am. Bull., v. 123, pp. 1863-1879.

Reddy S. M., Searle M. P. and Massey J. A., 1993, Structural evolution of the High Himalayan Gneiss sequence, Langtang Valley, Nepal. In Treloar P. J. and Searle M. P. (eds), Himalayan Tectonics: Geol. Soc. Special Publication, v. 74, pp. 375-389.

Wagner, T., Lee, J., Hacker, B. R. and Seward, G., 2010, Kinamtics and vorticity in Kangmar Dome, southern Tibet: Testing midcrustal channel-fl ow models for the Himalaya. Tectonics, v. 29, TC6011.

Webb, A. A. G., Yin, A., Harrison, T. M., Célérier, J. and Burgess, W. P., 2007, The leading edge of the Greater Himalayan Crystallines revealed in the NW Indian Himalaya: Implications for the evolution of the Himalayan Orogen: Geology, v. 35, pp. 955-958.

Webb, A. A. G., Schmitt, A. K., He, D. and Weigand, E. L., 2011, Structural and geochronological evidence for the leading edge of the Greater Himalayan Crystalline complex in the central Nepal Himalaya. Earth Planet. Sci. Lett. V. 304, pp. 483-495.

42


Different authors grouped the crystalline rocks of Higher Himalaya of Nepal into different classes and divisions. Among them, Le Fort (1975) grouped the Higher Himalayan Geology into three Formations: Formation I, II, and III (from bottom to top). Along the Marsyangdi River section rocks of Formation I begin in between Thakanbesi and Sange. In Formation I, the Kyanite bearing gneisses exposed at immediate upstream of Sange waterfall and about 300 m upstream from Tallo Jagat. Lithology of Formation I exposed up to Tal Village. Upstream from Siran Tal the rocks of Formation II begin and continued up to Timang area. On the way from Thanchowk to Chame augen gneiss of Formation III are exposed. In this study, the petrographical study was carried of rock samples collected from Khotro to Bagarchapp along right bank of the Marsyangdi River. Rocks of this particular section consists alteration of amphibole, pyroxene bearing calcareous gneisses and siliceous marble, with subordinate bedding of garnet-biotite bearing banded and granitic gneisses. According to Le fort (1975), the characteristic lithology belongs to the rock of Formation II.

Mineralogical analysis was carried of 18 thin sections representing different rock samples. Based on the results,

calcareous silicate gneisses dominate other rock typ e in the vicinity. These rock type constitutes the minerals as quartz (30-36 %), feldspar (13-30%), Calcite (15-20%), biotite (4-13%), Amphiboles 10%, pyroxenes 8-16 % and few others minerals in minor constituents. Similarly, next common rock types of the area are gneissic rock containing varied mineral constituent. The chief mineral found is quartz (35-53%), feldspar (25-47%), biotite 15-25% and other additional minerals as muscovite 3-7%, sericite 1-4%, chlorite 3-5%, garnet 1-3%. The next rock types found in the vicinity are medium to coarse grained silicious marble. These rock contain calcite as major constituent (58-60%), feldspar (10-18)%, quartz <5%, few micas, amphibole (16%), pyroxene (5-11%). The most common mineral among all rock type is quartz followed by feldspar with index minerals like biotite and garnet.

REFERENCES

Le Fort, P., 1975. Himalayas: the collided range, present knowledge of the continental arc. American Journal of Science, v. 275A, pp. 1-44.

Petrographical analysis of crystalline rocks of the Higher Himalaya along the Marsyangdi Valley

*Diwakar Khadka1, Naresh Kaji Tamrakar2 and Prakriti Raj Joshi3

1Hydro Consult PVT LTD, Nepal2Centre Department of Geology, Tribhuvan University, Nepal

3Soil, Rock and Concrete Laboratory, Nepal Electricity Authority(*Email: [email protected])

43


The seismogenic setting of Bhutan is unusual due to its lower-than-average 20th century seismic moment release (Drukpa et al. 2006), its absence of a reliable historical record, and its unusual location near the Shillong plateau where a great earthquake in 1897 resulted in ≈10 m of N/S shortening of the Indian plate to its south (Gahalaut et al. 2011). Despite these indicators that lower than normal convergence velocities should currently prevail, the GPS velocity between Shillong and Lhasa suggests that convergence in Sikkim and Bhutan occurs at velocities exceeding 20 mm/yr. GPS points between the Greater Himalaya and the Shillong Plateau measured in 2003, 2006 and 2012 permit us to quantify Bhutan's seismogenic potential.

Sikkim GPS data (Mukul et al. 2008; Mullick et al. 2009) and new data presented here can be explained by a convergence velocity of 22 mm/yr with a locking line at 20 km depth. No evidence for creep is manifest south of the

locking line. Our preferred solutions suggest 7°N dip similar to the centroid solution for a 2009 Mw=6.1 earthquake in E. Bhutan.

Given the foregoing values for velocity, dip and depth we searched for the probable northern limit of the locking line, and hence the down-dip width of the Himalayan décollement in Sikkim and Bhutan (Table 1). In E. Bhutan we use the 2009 earthquake as a proxy for the locking line. Our inferred locations for the locking line approximately follow the 3.5 km contour (Avouac 2003).

We next proceed to determine the maximum magnitude earthquake that could occur in the Bhutan Himalaya at the present day assuming that a historical earthquake with 18 m of slip may have occurred c.1100 as recorded in trenches at 88.8°E and 92.8°E (Kumar et al. 2011), or in 1713 (Ambraseys and Jackson 2003) as recorded in Tibetan histories.

GPS constraints on Indo-Asian convergence in the Bhutan Himalaya: Segmentation and potential for a 8.2<Mw<8.8 earthquake

Dowchu Drukpa1, Phuntsho Pelgay1, Anjan Bhattacharya2, Phillipe Vernant3, Walter Szeliga4 and *Roser Bilham5

1Seismology and Geophysics Division, Department of Geology and Mines, Thimphu, Bhutan2Dept. Mathematical Sciences, University of Tezpur, Napaam 784028, India

3Géosciences Université Montpellier, Cedex 34095, Montpellier, France4Dept. of Geol. Sci, Central Washington University, Ellensberg, Wa, 98926, USA

5Dept. of Geol. Sci, University of Colorado, Boulder, CO 80309-0399, USA (*Email: [email protected])

Fig.1: GPS points in Sikkim, Bhutan, Shillong and southern Tibet, and rupture segments A, B and C discussed in the text. Grey line is the inferred locking line south of which great ruptures propagate.

44


The Sikkim-Bhutan Himalaya is bounded by prominent along-arc changes of strike that we invoke to suggest favorable locations for rupture termination or initiation (King and Nabelik 1985). In the west, at 87°, a 10° change in strike of the Himalaya occurs between the 1934 rupture zone (Feldl 2005) and the almost east-west 500-km-long Sikkim-Bhutan segment (A-B-C). An abrupt 20° change in strike of the Himalayan arc occurs in 91.7°E in eastern Bhutan at the start of the 400-km-long, N70°E striking, Aranuchal Pradesh segment close to the intersection of the inferred Kopilli fault.

Between these major segment boundaries we identify A) the E.Nepal-Sikkim segment west of the Gish fault (Mukul et al., 2008), Yadong rift and Kishinganj Fault (Ni and Barazangi, 1984). The west end of the Shillong plateau is invoked to separate segments B) and C) on the basis that the 1897 earthquake may have reduced stress in segment C (Bilham and England 2001; Gahalaut et al. 2011) and there is weak evidence to suggest a slightly narrower décollement there (Table 1).

Table 1: Décollement widths, depths and anticipated maximum Mw earthquakes in Sikkim and Bhutan inferred from GPS convergence rates assuming no rupture since 1713, or c. 1100.

E. Nepal/ Sikkim

W. and Central Bhutan *E.Bhutan

latitude locking line 27.65°N 27.6°N 27.33°Nwidth décollement 94 km 99 km 67 kmalong-arc rupture 150 km 150 km 150 km

1713 & 6 m of slip Mw=8.3 Mw=8.3 Mw=8.2c.1100 & 18 m slip Mw=8.5 Mw=8.5 Mw=8.418 m segments A,

B&C Mw=8.5 Mw=8.7

18 m segments AB&C 8.8<Mw<8.9

* constrained by the epicenter of the 21/9/2009 Bhutan Mw=6.1 earthquake

We conclude that if no great earthquake has ruptured this entire region since 1100 AD a cumulative slip defi cit of ≈18 m could be released in single 8.8<Mw<8.9 earthquake. The current 18 m slip defi cit is disconcertingly similar to slip estimated to have occurred in paleoseismic trenches near Bhutan (Kumar et al, 2011), suggesting that the failure all or part of the Bhutan décollement soon would

not be unexpected. An alternative interpretation based on a possible intervening great earthquake in 1713 (for which we have no paleoseismic evidence) suggests that a Mw≈8.2 earthquake, similar to the 1934 event could repeat at the present time in any of the segments we have identifi ed. The apparent absence of creep suggests that, given our current state of knowledge, a future great earthquake is inescapable.

REFERENCES

Ambraseys, N. and Jackson, D., 2003, A note on early earthquakes in northern India and southern Tibet. Current Science, v. 84, pp. 570-582.

Avouac, J. P. Mountain Building, Erosion, and the Seismic Cycle in the Nepal Himalaya. Advances in Geophysics, v. 46, pp. 1-80.

Bilham, R. and P. England, (2001) Plateau pop-up during the great 1897 Assam earthquake. Nature, 410, 806 - 809

Drukpa, D., Velasco, A. A. and Doser, D. I., 2006, Seismicity in the Kingdom of Bhutan (1937–2003): Evidence for crustal transcurrent deformation. J. Geophys. Res., v. 111, B06301, doi:10.1029/2004JB003087

Feldl, N., 2005, Crustal Deformation Across the Himalaya of Eastern and Central Nepal, M.S. Thesis,. University of Colorado. http://ebookbrowse.com/gdoc.php?id=102764884&url=13bb017c54ff10416d87321563811b66

Gahalaut,V.K., Rajput, S. and Kundu, B., 2011, Low seismicity in the Bhutan Himalaya and the stress shadow of the 1897 Shillong Plateau earthquake. Phys. Earth Planet. Int., v. 186, pp. 97–102.

King, G., and Nabelek , N. 1985, Role of Fault Bends in the initiation and termination of earthquake rupture. Science, v. 228(4702), pp. 984-987.

Kumar, S., et al., 2010, Paleoseismological evidence of surface faulting along the northeastern Himalayan front, India: Timing, size, and spatial extent of great earthquakes, J. Geophys. Res., v. 115, doi:10.1029/2009JB006789.

Mukul, M., Jade, S., Matin, A., 2008. Active Deformation in the Darjiling-Sikkim Himalaya based on 2000-2004 Geodetic Global Positioning System Measurements. In Recent Advances in Earth Science: Indian Statistical Institute Platinum Jubilee Volumes, P.Ghosh & S. Bandyopadhyay (eds.), World Scientifi c Publisher, Singapore. 1-28.

Mullick, M., F. Riguzzi, and D. Mukhopadhyay (2009), Estimates of motion and strain rates across active faults in the frontal part of eastern Himalayas in North Bengal from GPS measurements, Terra Nova, 21, 410–415.

Ni, J., and M. Barazangi (1984), Seismotectonics of the Himalayan Collision Zone: Geometry of the Underthrusting Indian Plate Beneath the Himalaya, J. Geophys. Res., 89(B2), 1147–1163, doi:10.1029/JB089iB02p01147.

45


The problem of the relationship between society and the environment exists from the time of the fi rst civilizations. Human impact on the environment can be quantifi ed. On other hand is the infl uence of geological and geographical environment on the formation of culture and history. In the formation of ancient civilizations such infl uence was very signifi cant at all stages of its development. Human society, its development form a complex system in which not only interact with the social, political, economic and technological, but also natural processes, presented by climate change and geodynamic events. The impact of these systems, the natural processes of varying complexity had a decisive infl uence on the human species, the formation of the generating economy, the development of civilization processes in the Alpine-Himalayan orogenic belt from Greece and the Black Sea to Nepal, India and Central Asia, and Europe part of Russia. Natural geodynamic processes that are associated with the internal activity of the Earth, directly or indirectly determine the nature of human societies. Among them are studies of serious short-term catastrophic natural exposure - earthquakes, tsunamis, landslides, fl oods, etc. They were enshrined such a thing as natural disasters. But other aspects of the geodynamic processes that appear not so obvious, but for a long time, and their integral human exposure study is much worse.

To developing strategy for social behavior in anticipation of natural disasters it is important to bear in mind that along with almost instant disasters such as earthquakes, tsunamis or fl oods, there are hidden disaster - natural phenomena, developing slowly and lead to catastrophic events through the decades and centuries. Among the hidden disasters are glaciers, rises (transgressions) and falling (regression) of sea level and large lakes, desertifi cation, water logging, erosion and abrasion, smooth tectonic movements. Requires some critical episodes - the imposition of more frequent fl uctuations in natural phenomena (such as the imposition of the dry season on developing long-term drying) to hide the disaster became apparent. Another long intervals of time necessary to investigate and to determine the frequency of earthquakes in active areas (seismotectonic cycles), the average frequency of events or periods of frequent earthquakes.

The need for a historical approach is determined by the fact that the variations of geodynamic parameters of the medium had on the lives of people not only negative but also positive effects. Realize their value can again only in a historical context. Timeframes include the characterization of the natural conditions led to the emergence of man, his evolution to the formation of phenomena of civilization and the fi nal stage of the history of Homo sapiens, characterized by the development of the economy and generating corresponding to the geology of the concept of the Holocene (the last 10 thousand years). But even in the restricted framework, we further restrict the range of historical comparisons of only a few developments of importance in the development of civilizations and left a deep imprint in the memory of mankind.

A person can exist in an extremely narrow, in terms of physics and chemistry, the parameters of temperature, pressure, chemical composition of air, water and food, and it depends on minor changes to it, as well as mechanical stress and changes in geophysical fi elds. Geoecological conditions of human existence is made up of natural background conditions, which we have adapted, and their changes. The latter may be the result of a natural evolution of the environment and human impacts on it, and often a combination of both. Environment settings affect people both directly and indirectly through changes in the objects of its social and economic activities. It is these effects we mean when we talk about the deteriorating environmental situation and its improvement in the noosphere conception.

The dominant number of publications and discussions of geoecological problems for the negative impacts of human activities on the environment and reverse the impacts there by transformed the environment on humans. Paying tribute to these aspects, it should be noted that often the reevaluation of such impacts, as well as in previous years, the dominant strategy for large-scale alteration of nature - manifestation of anthropocentric point of view.Any society there, alive and growing in specifi c environmental conditions and the problem of the relationship between society and the environment exists from the time of the fi rst civilizations. In the fi eld of professional deep-focused research is not enough, though for good reason.

Infl uence of geodynamic processes on social development

E. NesterovHerzen State Pedagogical University of Russia, Saint-Petersburg, Russia


46


The infl uence of geodynamic processes most clearly evident in the early stages of development of society and is manifested to the present. The presence of overt and covert disasters and the importance of assessing patterns of occurrence of catastrophic events require to consider geo-ecological problems in historical perspective. Without such research areas, it is impossible to understand the role of geo-ecological factors in modern life and to make any reliable predictions in this area.

Analysis of the effects of strong earthquakes Alpine-Himalayan region shows that the single earthquake, however strong they may be, rarely are the cause of major historical change. In the era of political instability or excessive economic strain extreme natural event can disrupt the delicate balance, and all at once or over time lead to irreversible consequences. Perhaps it is a role for the Minoan Great Powers played a Minoan-eruption earthquake. Natural disaster has undermined the power of Minoan power, which, although able to partially reverse its effects and to continue the former policy, after 50 years, was defeated and conquered Achaeans became strong. Thus, when determining the infl uence of environmental factors had gone into oblivion one of the fi rst powerful civilizations. The current state of

science does not allow a proper quantifi cation of the degree of infl uence of environmental factors on the emergence and evolution of man, though a crucial infl uence for us, no doubt. The unique geo-ecological conditions that existed in the Alpine-Himalayan fold belt of Late Cretaceous time, created in different periods of geological history of the opportunities for the emergence and evolution of man and ancient civilizations.

REFERENCES

Berberian, M., 1994, Natural hazards and the fi rst earthquake catalogue of Iran. Vol. 1: Historical hazards in Iran prior to 1900.Tehran: IIEES Publ., 604 p.

Frodeman, R., 1995, Geological reasoning: Geology as an interpretive and historical science: Geological Society of America Bulletin, v. 107, pp. 960-968.

McKenzie, D., 1978, Active tectonics of the Alpine-Himalayan belt: the Aegean Sea and surrounding regions // Geophys. J. Roy. Astron. Soc., v. 55. pp. 217-254.

Nesterov E. M. and Solomin , V. P., 2010, Interrelations between philosophy and Earth science // Journal of International Scientifi c Publications: Educational Alternatives (www.science-journals.eu), Bulgaria. v. 8. Part 1, pp. 76-89.

47


The East Himalayan syntaxis remains a puzzle. Active faults are poorly mapped, and slip-rates, uncertain, partly due to regional partitioning. Controversy persists on the exact sources of two of the greatest continental earthquakes ever recorded (12/06/1897, M≈8.5, Shillong; 15/08/1950, Mw=8.7, Assam), which reportedly produced no primary surface ruptures. By combining fi eldwork with high-resolution satellite image interpretation, we revisited the tectonic geomorphology of the main range-fronts in NE India and Bangladesh and identifi ed, from their surface signature, the most active thrusts.

In Arunachal-Pradesh, we found outstanding tectonic escarpments 8 to 30 m high along the Himalayan and Mishmi foothills. Near Wakro and Roing, steep scarps cutting proximal terrace deposits and fl uvial risers unambiguously result from co-seismic faulting. Most likely, they formed during the 1950 earthquake and previous comparable events. On the footwall of the high cumulative scarp near Tezu, beheaded tree stumps encrusted with gravels attest to burial by massive 1950 debris fl ows. Near Pasighat, the Main Frontal Thrust lifts progressively older terraces of the Siang River up to higher and higher levels westwards. Dating of terrace deposits and surfaces is in progress to constrain the timing of deposition and uplift with complementary techniques (cosmogenic isotopes, 14C, OSL).

Overall, the Shillong plateau tilts northwards, with a marked contrast between its northern and southern edge. To the north, its gently sloping surface, which abrades Proterozoic basement, is incised only a few hundred meters

by the Brahmaputra and tributaries. Uplifted Proterozoic inselbergs protrude far north of the river, towards the Himalayan range-front, which precludes the existence of a large, recent, south-dipping thrust along the north side of the plateau. To the south, by contrast, the plateau towers 1200-1500m above the Bangladesh plain and deep Surma basin. It is sharply truncated by an abrupt fl exure dented by the steep canyons of headward-retreating catchments. At the foot of the fl exure, the spectacular escarpment of the active South Shillong Thrust (SST) follows the Dauki Fault in the east and Chokpot Thrust in the west. It separates fl exed Eocene Limestones from steeply south-dipping marine Miocene shales. West of Chokpot, one young, ≈ 6m-high scarp, of probable seismic origin, was found along this thrust. All geological and geomorphic indicators thus concur at different scales to suggest the SST was the most likely source of the 1897 earthquake.

In Bangladesh, we confi rmed the presence of emergent thrusts along the topographic front of the Chittagong-Sylhet foldbelt. The clearest one, near Shazibazar, follows the prominent scarp truncating the west limb of the broad, asymmetric Raghunandan Hills anticline. Linear tectonic scarps similarly cut gently east-dipping Quaternary sandstone monoclines along the west sides of the Lalmai and Tarap Hills. Such cumulative escarpments, whose heights reach tens of meters, likely grow through co-seismic rupture of the plate-boundary mega-thrust beneath the fold-belt, as it ramps up to the surface along the west side of the Meghna river basin.

Tectonic geomorphology and active megathrust traces in the East-Himalayan Syntaxis

*Elise Kali1,2, Paul Tapponnier1, Jérôme van der Woerd2, Swapnamita Choudhury 3, Saurabh Baruah4, A. K. M. Khorshed Alam 5, Aktarul Ahsan5, Catherine Dorbath2, Laurent Bollinger6 and Paramesh Banerjee1

1Earth Observatory of Singapore, Nanyang Technological University 2Institut de Physique du Globe, Strasbourg, France

3Wadia Institute, Dehra Dun, India4North-East Institute of Science and Technology, Jorhat, India;

5Geological Survey of Bangladesh, Dhaka, Bangladesh6CEA-DASE, Bruyeres le Chatel, France


48


The present period of the Earth sciences development shows particular attention to investigation of the planet deep structures, which is caused by necessity to solve theoretical problems of geodynamics, forecast deeply lying mineral deposits sites more effectively, study issues of seismic danger, predict and lessen natural disasters damage, especially caused by earthquakes and volcanic eruptions, and also to research environment protection problems. Continuous and complex geological evolution of the Asiatic continent in such folded regions, as Himalaya has been under way for practically all the Earth history. Different regions of the continent have common patterns both in forming tectonic structures and mineral deposits location.

The studies are carried out either by way of geological and geophysical constructions or by formal processing of gravimetric data. In some cases data received by method of double crossing refl ected earthquake waves was used as a basis for gravity anomalies calculations. The difference in the assumed earth's crust models, methods of geophysical data interpretation and scopes of used geophysical and geological materials predetermined signifi cant differences between descriptions of deep structures made by different authors.

This work has been carried out on the basis of the present regional petrophysical, gravimetric, partly aeromagnetic data as well as the author fi eld observations. The research methods are based on theoretical and practical considerations mentioned in a number of works. Comparing the resulting picture of the deep structure with the REWM profi les showed a near resembleness of the refl ecting horizon position with the roof of basalt layer. Width comparison of over-basalt sections of the earth's crust has not shown any accurate correlation between width of volcanogenous-sedimentary and other layers.

The analysis of correlations between location of copper, polymetals, rare metals and ore deposits and the earth's crust deep structure, which were brought to light as a result of small-scale geological and geophysical works, showed broad possibilities of the depth research for solution of metallogenic problems. Dependance of deposits location on width and structural peculiarities of different earth's crust layers are basis not only for prognosis when searching deeply lying mineral deposits, but also for bringing out sources of ore material, defi ning the roles of each crust

layer in ore genesis and solving a lot more issues. Studying interrelations between depth structures and ore deposits led also to evaluation of the practicability of deep geological research depending on its detailed character. In particular, it was determined that a high degree of the earth's crust partition and detailed mapping of mass dispersion for each layer sharply raise prognostic searching and metallogenic informational ability of deep structures. On the contrary, reducing deep structures to schematic images of consolidated crust as non-layered or two-layer body makes them of little value and even detrimental for solutions of theoretical tasks of regional and genetic metallogeny. This conclusion made long ago and fi nding more proof in petrophysical data is a theoretical basis of metallogenic studies on deep-geological ground. It evolves possibility and necessity to divide the earth's crust into geological bodies of different structure. In spite of increasing importance to study structures of over-basalt layer of the crust activity of work in this fi eld is very little. That is why both usage of received prognostic-searching indications and further attempts of solving metallogenic problems on the ground of deep geological-geophysical data are rather diffi cult. In this respect, more accurate defi nition of previously found correlations between deposits and crust structure based on fi ner crust division is thought to be of interest.

It follows from the above description of dependencies between copper, lead and zinc deposits locations and width of different crust sections that all mentioned deposits are correlated with the widths of volcanogenous-sedimentary, granite, granodiorite layers. The increasing number of deposits with lessening layers thickness means that all layers play the part of ore-containing environment in ore genesis. It is stressed by the high quotients of correlation (m) for a small number of deposits located in places where volcanogenous-sedimentary and granite layers are absent. At the same time the correlation between deposits and granodiorite layer show another relation. In fact, deposits "avoid" placement in this layer preferring volcanogenous-sedimentary and granite layers to it. This fact probably means that the rocks of granodiorite layer are not favorable for copper, lead and zinc ore deposits. This is probably the reason why a considerable part of lead and zinc deposits lies on the plots with comparably big widths (up to 6 km). The deviation from Puasson distribution with copper and polymetallic deposits regarding the granodiorite layer can be explained partly by

Patterns of mineral’s distribution in the folded regions

Evgeny M. NesterovThe Herzen State Pedagogical University of Russia, St. Petersburg, Russia

49


the presence of genetic relation of copper with the rocks of the mentioned layer. But in no lesser degree this could have been conditioned by tough term of ore concretion. The latter assumption seems to us more probable. Distribution of copper and polymetallic deposits relative to the total width of granite and granodiorite layers do not refl ect the genetic nature. At the same time such relations for gabbro-diorite layer are established most vividly. Actually, the number of deposits and correlation intensity increase with increasing of layer width i.e. with increasing of ore generating mass.

Deposits decrease at widths bigger than modal ones is predetermined by their remoteness from ore mobilizing hotbed.

REFERENCES

Nesterov, E. M., 1992, Metallogenic relations between copper, lead and zinc in Zaisan folded system and depth structure of the earth's crust. Vestnik LGU, v. 24, pp. 62-68.

Nesterov, E. M., 2008, Depth structure of Ural-Okhotsk belt and regularities of mineral deposits location / Tectonics of East Asia. pp. 13-25.

50


Slope failures and landslides are the most important process of hillslope erosion in non-glaciated active orogens. Beside tectonic activity, climate forcing, in particular daily and cumulated rainfall, have been pointed out as critical for triggering landslides, but large questions remain open relative to slope dynamics and climate infl uence.

To address the question of hillslope erosion in active orogens, we are currently implementing different methodological approaches to measure erosion rates and document erosion processes in the central Himalaya. We present a focused study on the Khudi Khola valley (southern Annapurnas region). This 136-km2-wide catchment has previously been monitored in 1999-2004 to document climatic dynamics and fl uxes of suspended sediment. Those fl uxes indicate an average modern erosion rate of 2-3mm/yr, well above erosion rates in surrounding High Himalayan catchments.

From fi eld study and aerial photos, a zone of large landslides in the upper part of the valley was identifi ed as a major potential source for those sediments. On the long-range, comparison of satellite images from 1974 to 2011 indicates indeed that the landslide has been very active, his scar moving up by 400 m, providing the source for the very high sediment production. Using relationships linking the area and the volume of a landslide, the volume of material produced by the slide between 1996 and 2011 was founded to be 5.2 to 5.8x106 m3. This represents an average mobilization rate of 2.3 to 2.8mm/yr, which is consistent

with previous results.

To better document the short-term behaviour of this landslide, a specifi c study has been carried out during 2010 to 2012 monsoons on the landslide and on the Khudi watershed.

Ten kilometres downstream from the landslide, suspended sediment concentration was measured every day and sediment samples were analyzed. Major elements data showed constant values during monsoon and a geochemical signature similar to the landslide samples, which is consistent with a predominant contribution of the landslide to the fi nal sediment exported by the river all over the monsoon.

In parallel, in order to follow the motions at the heart of the landslide, cameras were installed on the edges of the scar, taking one picture every thirty minutes during daytime. From these pictures, we were able to measure displacement vectors, using the iterative PIV plug-in for ImageJ software. Preliminary results show continuous displacements from the end of June to November within the landslide. In addition, we observe a good temporal correlation between major slope creeping and geomorphic activity and daily rainfall peaks. We also observe a major infl uence of cumulated rainfall on the magnitude of displacement vectors. Nevertheless, further downstream, we only observe high sediment concentration values during the fi rst weeks of the monsoon, although the rainfall and the landslide activity are still important until the middle of September. On-going work is focused on answering such apparent paradox.

Hillslope erosion and landslide dynamics in the central Himalayas

Florian Gallo1, Jérôme Lavé 1, Guillaume Morin 1, Christian France-Lanord 1, and Ananta Prasad Gajurel2

1Centre de Recherches Pétrographiques et Géochimiques, CNRS, Vandoeuvre-lès-Nancy, France2Department of Geology, Tri-Chandra College, Tribhuvan University, Kathmandu, Nepal

51


According to the intensities available, the M8 1934 Nepal/Bihar earthquake hit mainly the SE part of Nepal. Chen and Molnar (1977), by means of long-period surface waves, relocated the epicentre approximately 10 km south-west of Mount Everest, west of Arun River (see the star in Fig. 1), whereas Singh and Gupta (1980) using the entire wave fi eld place it on the southern Himalayan frontal thrust close to the India/Nepal border (large black dot in Fig. 1). No surface ruptures were reported, co- and post-seismic geodetic data and aftershock recordings are scarce and, thus, the fault is not well-constrained. Hough and Bilham (2008) adopted the epicentre by Chen and Molnar (1977) and a 150x85km2 source, hypothesizing W-ward directivity.

We performed the automatic inversion of the macroseismic data of Ambraseys and Douglas (2004) (isoseismal lines in Figure 1), using the KF model and a genetic algorithm with niching (NGA) (Sirovich and Pettenati, 2004; Pettenati and Sirovich 2007) and retrieved 11 source parametres. Isoseismal lines are plotted using the Natural Neighbour n-n technique; let us recall that the n-n isolines (Sirovich et al. 2002) are obtained without any explicit or implicit assumption about the observed phenomenon and thus strictly honour the data. As we know, our inversions have an intrinsic ambiguity of ±180° in the rake angle; the available signs of the available recordings let us solve this ambiguity.

Our preliminary epicentres are two, about 30 and 50 km SW of that by Chen and Molnar, 1977, with M=7.9. The inversion identifi es two solutions with almost the same quality: the fi rst fault source with strike angle 15º, dip 79º, rake 71º±180º, parallel to the Arun River, the second 256º, 21º, 149º±180º (Fig. 2). The frame in Figure 2 compares our result (grey colour) with the Singh and Gupta (1980) mechanism (thin black line). The fi lled circles indicate compression, whereas open circles show dilatation. The instrumental mechanism is constrained by few data. We would like to draw your attention on the fact that the fault plane of Singh and Gupta (1980), striking E-W, dips south in an area where the frontal thrust dips north. In the same area, Chen and Molnar (1977) quote the earthquake mechanisms by Fitch (1970) and Molnar et al. (1973) and recognise low angle mechanisms; instead, strike-slips mechanisms ESE-

WNW oriented, from old studies, are discarded. In the frame on the right of Fig. 2, the only dilatation is in the correct sector of our inversion, 5 compressions out of 7 are also in the correct sector (the 2 on the wrong side are close to the NNE-SSW plane, however). We can therefore suggest that the 1934 mechanism was transpressive (dextral); the 256° strike of one solution is compatible with the principal Alpidic thrust, whereas the other (15°) is anti-Alpidic. The nucleations of the two solutions are in between the epicentres by Chen and Molnar (1977) and Singh and Gupta (1980). Our preferred solution, striking 256°, has W-ward directivity; the one striking 15° is almost symmetric.

Levelling studies of the India-Nepal border zone could help in understanding the geodynamics; then, the correction of intensities for the site effects would perhaps improve the inversions.

The M8 Jan. 15th, 1934 Bihar earthquake: Intensity inversion and source update with instrumental data

*Franco Pettenati, Livio Sirovich and Stefano Picotti1OGS (The National Institute of Oceanography and Experimental Geophysics), Trieste, IT 34010, Italy,


Fig. 1: N-n isoseismals of the M8 Jan. 15th, 1934 earthquake (data by Ambraseys and Douglas, 2004). The star is the Chen and Molnar (1977) epicentre, the large black dot is the Singh and Gupta (1980) one.

52


REFERENCES

Ambraseys, N. N. and Douglas, J., 2004, Magnitude calibration of north Indian earthquakes, Geophys. J. Int., v. 159, pp. 165-206.

Chen, W. P. and Molnar, P., 1977, Seismic moments of majors earthquakes and the average rate of slip in Central Asia, J. of Geophys. Res., v. 82, pp. 2945-2969.

Fitch, T. J., 1970, Earthquake Mechanisms in the Himalayan, Burmese, and Andaman Regions and Continental Tectonics in Central Asia, J. of Geophys. Res., v. 75, pp. 2699-2709.

Hough, S. and Bilham, R., 2008, Site response of the Ganges basin inferred from re-evaluated macroseismic observations from the 1897 Shillong, 1905 Kangra, and 1934 Nepal earthquakes, J. Earth Syst. Sci., v. 117, pp. 773-782.

Molnar, P., Fitch T. J. and Wu F. T., 1973, Fault plane solutions of shallow earthquake and contemporary tectonics in Asia, Earth Planet. Sci Lett., v. 19, pp. 101-112.

Pettenati, F. Sirovich, L., 2007, Validation of the Intensity-Based Source Inversions of Three Destructive California Earthquakes, Bull. Seism. Soc. Am., v. 97, No. 5, pp. 1587-1606, doi:10.1785/0120060169.

Sirovich, L. Pettenati, F. Cavallini, F. and Bobbio, M., 2002, Natural-Neighbor Isoseismals, Bull. Seismol. Soc. Am., v. 92, pp. 1933-1940.

Sirovich, L. and Pettenati, F., 2004, A new Automatic Source Inversion Technique of Intensity Patterns of Earthquakes; Validation on a Destructive Shock of 1936 in NE Italy, Journal of Geophysical Research, v. 109, B10309, doi: 10.1029/2003JB002919, 2004, pp.16.

Singh, D. D. and Gupta, H. K., 1980, Source dynamics of two great earthquakes of the Indian subcontinent: the Bihar-Nepal earthquake of January 15, 1934 and the Quetta earthquake of May 30, 1935, Bull. Seismol. Soc. Am., v. 702, pp. 757-773.

Fig. 2: The synthetic best fi tting n-n isoseismals of the two solutions of our KF inversion. The white boxes are the surface projections of the source faults. The frame on the right compares the KF result striking 258° (in grey) with the fault-plane solution by Singh and Gupta (1980; thin black lines). The solution on the left, striking 15°, is close to the auxiliary plane of the solution striking 256° shown in the frame.

53


Mountain ranges have strong impact on the long-term (i.e., >1 Ma) global carbon cycle because metamorphic degassing from active collisional orogens may supply a signifi cant fraction of CO2 to the atmosphere (Evans 2011).

The Himalayan belt is a major collisional orogen on Earth still active today, and is a likely candidate for the production of a large amount of metamorphic CO2 that may have caused long-term changes in climate of the past, present and near future (Gaillardet and Galy 2008). Large metamorphic CO2 fl uxes are facilitated by rapid prograde metamorphism of big volumes of impure carbonate rocks coupled with facile escape of CO2 to the Earth’s surface. The nature and magnitude of metamorphic CO2 cycle in Himalaya, however, is poorly known, highly debated and diffi cult to be quantifi ed.

This study, recently integrated in the Ev-K2-CNR SHARE (Stations at High Altitude for Research on the Environment: http://www.evk2cnr.org/cms/en/research/integrated_programs/share) Project, will focus on the

metamorphic decarbonation processes occurred (and still occurring) during the Himalayan collision.

We aim to clarify: (1) abundance and types of CO2 source rocks; (2) nature and rate of decarbonation reactions; (3) nature and distribution of the CO2 escape-paths toward the Earth’s surface; (4) chronology of metamorphic decarbonation processes at different structural levels and at different times; (5) present-day CO2 degassing in tectonically active areas.

Our results will most likely lead to a deeper understanding of the infl uence exerted by the orogenic processes on climatic changes at global scale.

REFERENCES

Evans, K., 2011, Metamorphic carbon fl uxes: how much and how fast? Geology, v. 39, pp. 95-96.

Gaillardet, J. and Galy, A., 2008, Himalaya: carbon sink or source? Science, v. 320, pp. 1727-1728.

Looking for metamorphic CO2 degassing in the active Himalayan orogen

*Franco Rolfo1,2, Chiara Groppo1, Pietro Mosca2, Simona Ferrando1, Emanuele Costa1 and Krishna P. Kaphle3

1Department of Earth Sciences, University of Torino, Torino, I-10125, Italy 2 IGG-CNR, Torino, I-10125, Italy3Nepal Geological Society, Kathmandu, Nepal


54


The metamorphic architecture of eastern Nepal Himalaya is characterized by a well-documented inverted metamorphism (Bordet 1961; Brunel and Kienast 1986; Goscombe et al. 2006; Searle et al. 2008), with metamorphic grade increasing northward from lower (Lesser Himalayan Sequence: LHS) to higher structural levels (Higher Himalayan Crystallines: HHC) across the Main Central Thrust Zone (MCTZ). Peak metamorphic conditions experienced by metamorphic units at different structural levels have been the subject of extensive research (e.g. Pognante and Benna 1993; Goscombe and Hand 2000; Jessup et al. 2008; Imayama et al. 2010), but their P-T-(t) evolution is still poorly constrained except for a few notable exceptions (e.g. Goscombe and Hand 2000).

A synthesis of our recent petrological studies in eastern Nepal is reported in this contribution, based on a number of geotraverses across the Dudh Kosi, Arun and Taplejung tectonic windows, where the LHS is exposed beneath the MCTZ and the HHC. In order to defi ne the whole P-T evolution experienced by lithotectonic units, detailed petrological investigations were mainly focused on metapelites. In these lithologies metamorphic assemblages range from the low–grade chlorite and garnet zones (LHS), to the medium–grade garnet-biotite, staurolite and kyanite zones (lower MCTZ), up to the sillimanite zone and a further zone of incipient partial melting with breakdown of muscovite and formation of K-feldspar (upper MCTZ). Structurally above the MCTZ, anatexis is widespread in the HHC and is recorded by granulite-facies kyanite-bearing metapelite (Barun Gneiss of Bordet 1961) at the lowermost structural levels (lower HHC) and at structurally upper levels (upper HHC) by cordierite-bearing, kyanite-free gneiss (i.e. Namche Migmatite and Black Gneiss of Lombardo et al. (1993).

The P-T trajectories followed by the different lithotectonic units have been constrained combining microstructural observations, mineral chemistry and

pseudosection modeling. The uniformity of the approach applied on all samples from different structural levels is a robust method to quantitatively compare the resulting P-T paths. From the lower to the upper structural levels, the P-T trajectories we obtained are as follows:

(1) LHS: prograde increase in both P and T, up to peak conditions of 500-550 °C and 7-8 kbar (Groppo et al. 2009; Mosca et al. 2012);

(2) Lower MCTZ: (i) prograde heating and decompression up to peak conditions of 600-650°C, 8-9 kbar, followed by cooling and decompression. Structurally upward, (ii) lack of a preserved prograde metamorphic history, with peak metamorphic conditions of 650-700 °C, 7-8 kbar and subsequent cooling and decompression (Groppo et al. 2009; Mosca et al. 2012);

(3) Upper MCTZ: peak-T of 750-800 °C at relatively high-P of 10-12 kbar, followed by decompression and cooling mainly in the kyanite stability fi eld (Groppo et al. 2009, 2010; Mosca et al. 2012);

(4) Lower HHC: (i) heating during decompression in the kyanite stability fi eld and, structurally upward, (ii) nearly isobaric heating in the sillimanite stability fi eld. Peak conditions are of about 800 °C, 8-10 kbar and are followed by nearly isothermal decompression down to 6.5-7.5 kbar (Groppo et al. 2012a);

(5) Upper HHC: nearly isobaric heating up to peak-T of 750-800 °C at a relatively low-P of 4-5 kbar, followed by cooling and decompression (Groppo et al. 2012b).

These P-T paths are compared with the petrologic predictions of the “channel fl ow” model (Beaumont et al. 2001; Jamieson et al. 2004), maybe currently the most popular paradigm to explain the tectonometamorphic evolution and the fi rst-order geologic features of the Himalayan-Tibetan orogen. The overall geometries of the P-T paths match very well the predictions of the numerical model, thus suggesting

From low-grade metamorphism to anatexis: a petrologic journey across the eastern Nepal Himalaya and implications for the “channel fl ow”

model

*Franco Rolfo1,2, Chiara Groppo1, Pietro Mosca2 and Bruno Lombardo2

1Department of Earth Sciences, University of Torino, Torino, I-10125, Italy,2IGG-CNR, Torino, I-10125, Italy(*Email: [email protected])

55


that “channel fl ow” is fully compatible from a petrologic point of view, as the main process operating during the exhumation of the eastern Himalayan metamorphic units.

REFERENCES

Beaumont, C., Jamieson, R. A., Nguyen, M. H. and Lee, B., 2001, Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled to focused surface denudation, Nature, v. 414, pp. 738-742.

Bordet, P., 1961, Recherches géologiques dans l’Himalaya du Népal, région du Makalu, Editions du Centre National de la Recherche Scientifi que, Paris, 275 p.

Brunel, M. and Kienast, J. R., 1986, Etude pétro-structurale des chevauchements ductiles himalayens sur la transversale de l’Everest-Makalu (Népal oriental). Canadian Journal of Earth Sciences, v. 23, pp. 1117–1137.

Goscombe, B. and Hand, M., 2000, Contrasting P–T paths in the Eastern Himalaya, Nepal: inverted isograds in a paired metamorphic mountain belt, Journal of Petrology, v. 41, pp. 1673-1719.


Groppo, C., Rolfo, F. and Lombardo, B., 2009, P-T evolution across the Main Central Thrust Zone (Eastern Nepal): hidden discontinuities revealed by petrology, Journal of Petrology, v. 50, pp. 1149-1180.

Groppo, C., Rubatto, D., Rolfo, F. and Lombardo, B., 2010. Early Oligocene partial melting in the Main Central Thrust Zone (Arun Valley, eastern Nepal Himalaya), Lithos, v. 118, pp. 287-301.

Groppo, C., Rolfo, F. and Indares A., 2012a, Partial melting in the Higher Himalayan Crystallines of Eastern Nepal: the effect of decompression and implications for the “channel fl ow” model, Journal of Petrology, v. 53, pp. 1057-1088.

Groppo, C., Rolfo, F. and Mosca, P., 2012b, The cordierite-bearing

anatectic rocks of the Higher Himalayan Crystallines (eastern Nepal): low-pressure anatexis, melt-productivity, melt loss and the preservation of cordierite, Journal of Metamorphic Geology, in press.

Imayama, T., Takeshita, T. and Arita, K., 2010, Metamorphic P-T profi le and P-T path discontinuity across the far-eastern Nepal Himalaya: investigation of channel fl ow models, Journal of Metamorphic Geology, 28, 527–549.

Jamieson, R.A., Beaumont, C., Medvedev, S. and Nguyen, M.H., 2004, Crustal channel fl ows: 2. Numerical models with implications for metamorphism in the Himalayan-Tibetan orogen, Journal of Geophysical Research, 109, B06407.

Jessup, M. J., Cottle, J. M., Searle, M. P., Law, R. D., Newell, D. L., Tracy, R. J. and Waters, D. J., 2008, P-T-t-D paths of Everest Series schist, Nepal, Journal of Metamorphic Geology, v. 26, pp. 717-739.

Le Fort, P., 1975, Himalaya: the collided range. Present knowledge of the continental arc, American Journal of Science, v. 275A, pp. 1–44.

Lombardo, B., Pertusati, P. and Borghi, A., 1993, Geology and tectono-magmatic evolution of the eastern Himalaya along the Chomolungma-Makalu transect. In: Treloar, P.J. & Searle M.P. (eds.) Himalayan Tectonics. Geological Society of London, Special Publication, v. 74, pp. 341–355.

Mosca, P., Groppo, C. and Rolfo, F., 2012, Structural and metamorphic features of the Main Central Thrust Zone and its contiguous domains in the eastern Nepalese Himalaya, Journal of Virtual Explorer, in press.

Pognante, U. and Benna, P., 1993, Metamorphic zonation, migmatization, and leucogranites along the Everest transect (eastern Nepal and Tibet): record of an exhumation history, In: Treloar, P.J. and Searle, M.P. (eds.) Himalayan Tectonics. Geological Society of London, Special Publication, v. 74, pp. 323–340.

Searle, M. P., Law, R. D., Godin, L., Larson, K. P., Streule, M. J., Cottle, J.M. and Jessup, M. J., 2008, Defi ning the Himalayan Main Central Thrust in Nepal, Journal of Geological Society of London, v. 165, pp. 523–534.

56


In the eastern Nepal Himalaya, calc-silicate rocks are widespread in the medium and upper structural levels of the Greater Himalayan Sequence (Goscombe et al. 2006), but they have received so far little attention. We present the results of a preliminary petrographic study of several calc-silicate rocks from different structural levels and from different geological transects in eastern Nepal.

In the upper portion of the Main Central Thrust Zone, calc-silicate rocks generally occur as decimetre to metre-thick levels or boudins within medium- to high-grade, locally anatectic, metapelites (Groppo et al. 2009; Mosca et al. 2012). Structurally upward, calc-silicate rocks are hosted in the anatectic kyanite-sillimanite-bearing gneisses of the lower portion of the Higher Himalayan Crystallines (Barun Gneiss of Groppo et al. 2012) and often occur as tens of meter thick, folded or boudinaged, levels occasionally associated to layers of impure marbles. The studied samples have a granofelsic structure, although they sometimes show the evidence of a brittle to ductile deformation resulting in a local grain size reduction.

The transition between the hosting paragneiss and the calc-silicate granofels is generally gradual and is characterized by the progressive disappearance of biotite, the appearance of diopsidic clinopyroxene and the modal increase of plagioclase. A banded structure is locally observed in the calc-silicate rocks, defi ned by the different modal proportion of the rock-forming minerals in adjacent layers. These evidences suggest that the calc-silicate rocks were derived from former marly intercalations within a thick sedimentary (mostly pelitic, with minor limestones) sequence.

The equilibrium assemblages consist of Ca-rich plagioclase, diopsidic clinopyroxene and quartz in different proportions, with the local addition of garnet, zoisite, K-feldsapar, scapolite, and/or calcite. The existence of a systematic variation in the mineral assemblages as a function of the structural level was recognized. More in detail:

(1) Garnet and zoisite only occur in the calc-silicate rocks from the lowermost structural levels (i.e. MCTZ and lower HHC). Garnet is locally very abundant and it is often intergrown with quartz, whereas zoisite is systematically included in garnet and/or clinopyroxene.

(2) On the contrary, K-feldspar and scapolite only occur in the calc-silicate rocks from the uppermost structural levels (i.e. upper HHC).

(3) Interestingly, in all the studied samples from the upper structural levels, clinopyroxene is partially replaced by green amphibole, which is completely absent in the samples from the lower structural levels.

(4) As concerning the accessory phases, titanite is ubiquitous, whereas allanite is only present in the upper HHC samples.

(5) Garnet-bearing samples from the lower structural levels always contain graphite, locally very abundant and coarse-grained. Graphite is always absent in the garnet-free samples from the upper structural levels, which locally contain calcite.

Following this preliminary petrographic study, petrological investigations will clarify if these systematic variations in mineral assemblages are related to: (1) primary protolith differences; (2) different peak metamorphic conditions; (3) different fl uids circulated at different structural levels during metamorphic evolution, or (4) a combination of these factors.

REFERENCES


Groppo, C., Rolfo, F. and Indares A., 2012, Partial melting in the Higher Himalayan Crystallines of Eastern Nepal: the effect of decompression and implications for the “channel fl ow” model. Journal of Petrology, v. 53, pp. pp. 1057-1088.


Calc-silicate rocks from different structural levels of the Greater Himalayan Sequence (eastern Nepal): Garnet-bearing vs. garnet-absent

assemblages

*Giulia Rapa1, *Chiara Groppo1, Simona Ferrando1 and Franco Rolfo1,2

1Department of Earth Sciences, University of Torino, Torino, I-10125, Italy 2IGG – CNR, Torino, I-10125, Italy(*Email: [email protected])

57


Surkhet Valley is a tectonic valley consisting of fl uvio-lacustrine deposit such as boulders, cobbles gravels, sands, silts and clays brought up by the rivers from the surrounding hills. The northern hill slopes of the valley are moderate to steep consisting of lesser Himalayan rocks and Lower Siwalik rocks while southern hill slopes are low to moderate consisting of Lower Siwalik and Middle Siwalik rocks. Based on geological mapping and study of engineering properties of valley sediments, they are classifi ed into seven different deposit types.

The study shows that some areas in the central and southern part of the valley have low bearing capacity

while the northern part of the valley has moderate to high bearing capacity and is thus suitable for the construction of infrastructure and for the development of human settlement. Whereas the southern part of the valley is prone to liquefaction hazard in case of large earthquake.

Various methods such as auger drilling, standard penetration test and laboratory analysis of soil samples were carried out in order to complete the study. Similarly, a number of traverses were carried out along the rivers, tributaries, trails and roads to assess geo-hazard like landslide, fl ooding, riverbank cutting, pollution, waste disposal sites and solid waste managements.

Engineering geological mapping and geo-hazard and geo-environmental studies of Quaternary deposits of Birendranagar Municipality and its

surrounding area, Surkhet Valley, Rapti Zone

*Gyani Raja Chitrakar1, Birendra Piya2, Dinesh Nepali2 and Surya Prakash Manandhar2

1461-Ranibari Chowk, Samakhusi, Kathmandu, Nepal2Department of Mines and Geology, Kathmandu, Nepal


58


Multichronological study was performed for weakly metamorphosed early Miocene fl uvial Dumri Formation and overlying the Kuncha and Lesser Himalayan Crystalline nappes in order to clarify the timing and heat sauce of metamorphism, and emplacement and cooling history of the nappes. The results provide evidence of thermal imprint of the Dumri Formation at 11~10 Ma. U-Pb ages of the same detrital zircons show bi-modal distribution having peaks at ~1 Ga and 500-600 Ma. On the other hand, the overlying quartzite of the Kuncha Formation shows a reset age of detrital zircons at 9.5 Ma though they have U-Pb age older than 1.7 Ga. Difference of U-Pb age of detrital zircon in between the Dumri and Kuncha Formation suggests that the Kunchanappe had never exposed on the ground during the early Miocene when the Dumri Formation was deposited. Two mica garnet schist of the MCT zone shows FT age of

detrital zircon at 7.8 Ma, and 40Ar - 39Ar age of muscovite at 19 Ma, though the detrital zircons have U-Pb ages older than 600 Ma. It is certain that the heat sauce of metamorphism of the Dumri Formation could be ascribed to the overlying nappe. Timing of thermal imprint on the Dumri Formation indicates that the metamorphic nappe reached present position before at least ~10 Ma.

The ParajulKhola granite in the core of augen gneiss distributed in the frontal zone of Kunchanappe has 1. 89 Ga zircon U-Pb age. It has undergone early Miocene thermal event and cooled down below 250°C at 14.7 Ma and below 120°C at 10.3 Ma. These thermochronological data suggest that frontal part of the Kunchanappe was exposed on the ground at 15~14 Ma and cooled down immediately, but inner part of nappe kept hot condition during the emplacement.

Emplacement of hot metamorphic nappe during 15-10 Ma and thermal imprint on the underlying early Miocene fl uvial Dumri

Formation in Jumla-Surkhet area, western Nepal

*Harutaka Sakai1, Hideki Iwano2, Tohru Danhara2, Takafumi Hirata1 and Yutaka Takigami3

1Department of Geology and Mineralogy, Kyoto University, Kyoto 606-8502, Japan 2Kyoto Fission-Track Co. Ltd, Kyoto 603-8832, Japan

3Kanto GakuenUniversity, Ohta-shi, Gunma 373-8515, Japan(*Email: [email protected])

Fig. 1: Iron model of metamorphism imprinted in the Dumri Formation caused by emplacement of hot Kuncha nappe and Lesser Himalayan Crystalline nappe. Cooling rate of the nappe is after Sakai et al. (2012).

59


REFERENCES

Sakai H., Iwano H., Danhara T., Takigami Y Rai, S. M., Upreti, B. N., Hirata, T., 2012a. Emplacement of hot metamorphic nappe during 15-10 Ma, and thermal imprint on the underlying early Miocene fl uvial DumriFormation. Island Arc 21.

Sakai H., Iwano H., Danhara T., Takigami Y., Rai, S. M., Upreti, B. N., Hirata, T., 2012b. Rift-related origin of the Paleoproterozoic Kuncha Formation, and cooling history of the Kuncha nappe and Taplejung granites, eastern Nepal Lesser Himalaya – a multichronological approach. Island Arc 21.

60


In order to decipher the origin and tectonothermal history of the Kunchha nappe, we undertook geological investigation in the Taplejung window in eastern Nepal, and carried out multichronological analyses of zircon, apatite and mica of the Kunchha Formation and Taplejung granites. Three granite bodies that intrude into the Kunchha Formation show fi ssion-track (FT) ages of zircon to be 6.2 to 4.8 Ma and apatite ages to be 2.9 to 2.2 Ma, though the granites yielded zircon U-Pb ages of 1846±21 Ma and 1875±15 Ma, and muscovite 40Ar-39Ar ages of c. 1650 Ma. The U-Pb intercept age of detrital zircons from the Kunchha schist of Kunchha Formation is 1888±12 Ma, and this age represents a probable depositional age of the lower part of the Kunchha Formation. The FT ages of zircon and apatite from the same Kunchha schist are found to be 5.4 and 2.5 Ma, respectively. No detrital zircon younger than 1.6 Ga was identifi ed from any of these samples. It means that the Kunchha nappe has never undergone thermal events after 1.6 Ga till the Himalayan orogeny in Miocene. The Kunchha Formation and overlying Kali Gandaki Supergroup as well as the Taplejung granites can be correlated with the Coronation Supergroup and the Hepburn intrusives in the Wopmay orogen, northwest Canada (Fig. 1). They are interpreted to be deposits in the basins of continental rift system and subsequent passive-margin settings. All the FT age data of zircon and apatite provide evidence that both Kunchha nappe and overlying Crystalline nappe seem to have cooled down laterally from the nappe front to northward. The FT ages of zircon from the nappe front to central part of the nappe in Taplejung suggest that isotherm of 250°C, closure temperature of zircon FT, retreated toward north at c.10 mm/yr during the middle to late Miocene and Pliocene time.

Fig. 1: A possible model of tectonic setting of the Kali Gandaki Supergroup in the Nepal Lesser Himalaya and its relationship to the Coronation Supergroup, northwest Canada (Sakai et al., 2012a, b). Both are interpreted to be deposits in the initial rift and passive continental margin originated from a mantle plume. Paleogeographic reconstruction of three continental blocks is after Hou et al. (2008).

REFERENCES

Sakai H., Iwano H., Danhara T., Takigami, Y., Rai, S. M., Upreti, B. N., Hirata, T., 2012a, Emplacement of hot metamorphic nappe during 15-10 Ma, and thermal imprint on the underlying early Miocene fl uvial Dumri Formation. Island Arc 21.

Sakai H., Iwano H., Danhara T., Takigami Y., Rai, S.M., Upreti, B.N., Hirata T. 2012b. Rift-related origin of the Paleoproterozoic Kunchha Formation, and cooling history of the Kunchha nappe and Taplejung granites, eastern Nepal Lesser Himalaya – a multichronological approach. Island Arc 21.

Rift-related origin of the Paleoproterozoic Kunchha Formation and cooling history of the Kunchha nappe and Taplejung Granites, eastern

Nepal Lesser Himalaya: A multichronological approach

*Harutaka Sakai1, Hideki Iwano,2 Tohru Danhara,2 Yutaka Takigami3 , Santa Man Rai4, Bishal Nath Upreti4 and Takafumi Hirata1

1Department of Geology and Mineralogy, Kyoto University, Kyoto 606-8502, Japan, 2Kyoto Fission-Track Co. Ltd, Ohmiyaminami Tajiri,Kyoto 603-8832, Japan

3Kanto Gakuen University, Ohta-shi, Gunma 373-8515, Japan4Department of Geology, Tri-Chandra Campus, Tribhuvan University, Kathmandu, Nepal


61


Ongoing growth of the Himalayan fold-thrust belt since the Middle Miocene is mostly accomplished by the deformation of the Lesser Himalayan Sequence (a deformed package of rocks which dominates the southern half of the Himalaya). However, the fi rst-order kinematic evolution of this process remains unclear. Four end-member models are proposed: frontal accretion through forward-propagation of a basal thrust (e.g., Schelling and Arita 1991); discrete underplating of thrust horses from the downgoing plate to the fold-thrust belt (e.g., Bollinger et al. 2004); expansion of the orogen via incremental accretion along the basal shear zone (e.g., Searle et al. 2008); and out-of-sequence faulting (e.g., Harrison et al. 1997). Both the underplating and out-of-sequence models can explain the rapid uplift and exhumation observed along the central belt of the Himalaya. We test

these models by determining the relationship between major thrust faults within the western Lesser Himalayan Sequence: the Berinag thrust and Tons thrust. Map geometries require >40 km and >80 km displacements along the Berinag and the Tons thrusts, respectively. Those two thrusts have no known intersection in most parts of western Himalaya, except along the lower Pabbar River in the Tons valley, a poorly explored area where those two thrusts must intersect each other. Three proposed geometries are: (A) the Tons thrust terminates along the Berinag thrust; (B) the Berinag thrust terminates along the Tons thrust; (C) the Berinag thrust and Tons thrust are a single structure, such that the distinct hanging wall rocks are separated by a depositional contact (Fig. 1). The fi rst two possible geometric relationships can be accomplished by out-of-sequence faulting or underplating (Webb et al. 2011).

Assembly of the Lesser Himalayan duplex along the Tons Valley, northwestern India

*Hongjiao Yu1 and A. Alexander G. Webb1

1 Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA(*Email: [email protected])

Fig. 2: Geological map of the lower Pabbar river area and cross section. The thick dashed line indicates the leading edge of the Berinag group. The map pattern indicates the Pabbar thrust developed fi rst, followed by underplating of the Berinag sheet to the Pabbar thrust. Continued motion along the new sole thrust toward the foreland becomes the brittle-ductile Tons and Berinag thrusts, operating as a single structure.

62


Field mapping the Lesser Himalayan Sequence along the Tons Valley and the lower Pabbar valley reveals a new fi rst-order thrust fault, which we term the Pabbar thrust (Fig. 2). The Pabbar thrust separates the hanging wall of the Tons thrust (the Outer Lesser Himalayan Sequence) above from the hanging wall of the Berinag thrust (the Berinag Group) below. It is a ~300 m thick ductile shear zone marked by S-C fabrics, mylonitic fabrics, and sheath folds, demonstrating southwest-directed thrusting. Sheath folds, with hinges parallel to the stretching lineations defi ned by strongly elongated quartz grains in NE-SW direction, developed at cm to m scale of wavelength and amplitude within the shear zone. The Berinag and Tons thrust zones (Fig. 2) display both brittle features and ductile shear fabrics including southwest-directed brittle faults, southwest verging tight to open folds, and week southwest-trending stretching lineations. The map pattern shows the Tons thrust hanging wall directly overlaying the Berinag thrust hanging wall along a thrust contact. This pattern can be accomplished by out-of-sequence faulting along the Tons thrust, or by underplating of the Berinag sheet to the Tons thrust hanging wall (Fig. 1B). The ductile nature of the Pabbar thrust and the brittle-ductile nature of both the Berinag thrust and Tons thrust suggest that the Pabbar thrust developed fi rst, followed by underplating of the Berinag sheet to the Pabbar thrust. Continued motion along the new sole thrust toward the foreland becomes the brittle-ductile Tons and Berinag thrusts, operating as a single structure (Fig. 2).

The kinematic history of the Pabbar thrust and the Berinag-Tons thrust suggests that the ongoing growth of the Himalayan fold-thrust belt since the Middle Miocene most likely occurred through the discrete underplating of thrust horses from the downgoing plate, not by out-of-sequence faulting. Expansion of the orogen by incremental accretion model is also invalid here since the expected pervasive shear features through the LHS are not observed in the fi eld. Instead, shear is only concentrated in discrete fault zones.

REFERENCES

Bollinger, L., Avouac, J. P., Beyssac, O., Catlos, E. J., Harrison, T. M., Grove, M., Goffé, B., and Sapkota, S., 2004, Thermal structure and exhumation history of the Lesser Himalaya in central Nepal. Tectonics, v. 23, TC5015, doi: 10.1029/2003TC001564.

Harrison T. M., Ryerson F. J., Le Fort P, Yin A., Lovera O. M., and Catlos E.J., 1997a. A Late Miocene-Pliocene origin for the Central Himalayan inverted metamorphism. Earth Planet. Sci. Lett. v. 14, pp. 1–8

Searle, M. P., Law, R. D., Godin, L., Larson, K. P., Struele, M. J., Cottle, J.M., and Jessup, M.J., 2008, Defining the Himalayan main central thrust in Nepal: Journal of the Geological Society, London, v. 165, p. 523–534.

Schelling, D., Arita, K., 1991, Thrust tectonics, crustal shortening, and the structure of the far-eastern Nepal. Himalaya: Tectonics, v. 10, pp. 851–862.

Webb A. A. G., Yin A., Harrison T. M., Célérier J., Gehrels G.E., Manning C.E. and Grove M., 2011, Cenozoic tectonic history of the Himachal Himalaya (northwestern India) and its constraints on the formation mechanism of the Himalayan orogeny. Geosphere, v. 7, pp. 1013–1061

Fig. 1: Possible geometric/kinematic relationships of Tons and Berinag thrusts, modifi ed from Webb et al. 2011

63


Long-term localization of tectonic strain in response to erosion by surface processes is an intriguing hypothesis with implications ranging from fl exural isostasy and river anticlines to tectonic aneurysm and channel fl ow. We examine geomorphic indices and thermochronologic constraints along the Barun River in Eastern Nepal fl owing entirely within the High Himalaya and perpendicular to the orogenic convergence, from Mt. Everest and Mt. Makalu in the west, to the confl uence with the Arun River gorge in the east.

Apatite (U-Th)/He valley bottom ages decrease from ~2 Ma at the Makalu base camp to ~0.75 Ma at the Arun gorge. Along the same transect Zircon (U-Th)/He ages decrease from ~4 Ma to ~1.8 Ma. This data together with a sub-vertical age-elevation transect along the slopes of Mt. Makalu, suggest that exhumation rates near Mt. Makalu are about half of those near the Arun River.

Previously published AFT data from the peak of Mt. Everest suggests that less than 3-5 km of rock were removed at the peak setting over the last 14 Ma, while our own (U-Th)/He data from the Everest base camp in Tibet supports <3 km of valley bottom exhumation over the last 10 Ma.

Using 3D thermo-kinematic modeling we estimate the exhumation rates in the Everest and Makalu area over the last ~10 Myr at about 0.3-1 mm/yr, signifi cantly lower than the rates of 1.5-2 mm/yr in the Arun gorge. In addition, we discuss stratigraphic and thermochronologic observations which suggest that other prominent Himalaya peaks such as Shisha Pangma, Annapurna and Manaslu have also experienced long-term exhumation rates which are much lower than those of adjacent valleys. Along strike, lateral variations of the topography along the Himalaya of Nepal thus primarily refl ect lateral variations in exhumation rate, with high peaks corresponding to relatively low exhumation rates. This fi nding contradicts the notion that high peaks should correlate with higher uplift and exhumation rates.

Differential exhumation rates in the High Himalaya perpendicular to the orogenic convergence: From Mt. Everest to the Arun River gorge

*Itai Haviv1,2, Jean-Philippe Avouac3, Ken A. Farley3, Mark T. Harrison4, Prabhat Neupane5 and Matt Heizler6

1Division of Geology and Planetary Sciences, California Institute of Technology, USA2 Department of Geology and Environmental Sciences, Ben-Gurion University, Israel

3 Division of Geology and Planetary Sciences, California Institute of Technology, USA4Department of Earth and Space Sciences, UCLA, USA

5Earth and Environmental Sciences, University of New Orleans, USA6New Mexico Bureau of Geology and Mineral Resources, NM Tech, USA


64


Since 2004, the Tectonics Observatory at Caltech (USA) and the National Seismological Centre (Ministry of Industry, Nepal) have established a network of continuously monitoring GPS stations in Nepal expanding on a earlier network of 3 stations which had been deployed in 1997 by the Department Analyse et Suveillance de l’Environnement (CEA, France). This network was designed to monitor slow strain build up in preparation of future earthquakes as well as transient geodetic deformation due to earthquakes, slow slip events and other sources of transient deformation.

The network currently comprises 33 active sites that cover the entire country. Dual frequency code and phase observations are recorded with Trimble NetRS and NetR8 receivers. Measurements at sampling

intervals of 1 and 15 sec are stored internally while the high rate data is also backed up on external serial ring buffers. The majority of stations is manually downloaded at regular intervals. A wireless internet link connects currently 4 sites to the NSC offi ce in Kathmandu. Near-term telemetry plans call for wireless connectivity of a large number of additional sites. The challenging topography demands a combination of various methods, including satellite, cellular, and long range spread spectrum based systems. We review station design and operation and address current challenges. Including data from the three DASE-NSC sites and from nearby IGS stations we calculate time series of positions for all stations and present an updated velocity fi eld.

Contemporary crustal deformation measured by the Caltech-NSC-DASE Nepal cGPS Network

*J. Genrich1, J. Galetzka1, F. Chowdhury1, K. Chanard1, T. Ader1, J.-P. Avouac1, M. Flouzat2, S. Sapkota3 and the NSC Team3

1Tectonics Observatory, California Institute of Technology, Pasadena, CA 91125, USA, 2CEA, DAM, DIF, F-91297 Arpajon, France

3National Seismological Centre, Department of Mines and Geology, Ministry of Industry, Lainchaur, Kathmandu, Nepal


65


The Himalayan orogen represents the archetype of mountain building in a continental collision setting. Its primary features are now understood, but the details of its seismotectonic behaviour and seismic hazards are still only partially documented. To expand on a former pioneering study led in the sub-Himalaya of central Nepal, south of Kathmandu (Lavé and Avouac 2000), we analyzed geomorphic evidences of recent crustal deformation in the sub-Himalaya across the portion of the Main Frontal Thrust fault (MFT) located along the Himalayan arc of Nepal. Active faulting and folding at the MFT is quantifi ed from structural geology and deformed fl uvial terraces along ten rivers from west to east. Those Holocene fl uvial terraces were dated using 14C on charcoals within sandy/silty material, or by measuring 10-Be cosmogenic nuclides in boulders on top of the terraces or in exposed strath terraces.

The dated terraces and deformation profi les, complemented by paleoseismic trenches, indicate that the structural style of folding may largely vary along the MFT. If rock uplift profi les are found to express fault bend folding for mature folds, more complex relationships between uplift and structural section are observed for nascent folds or MFT step over regions with uplift rates locally exceeding 20 mm/yr close to MFT surface expression.

For most profi les, except one along Sapt Kosi, thrusting along the MFT has absorbed around 20 mm/yr of N-S shortening on average over the Holocene period, which is slightly more than modern GPS shortening rates across the whole Himalayan range. At the scale of Nepal, the MFT is defi nitively the most active Himalayan structure during the Holocene.

Along most of the Himalayan arc of Nepal, despite disparities in Siwaliks geometry, microseismicity distribution, and topography of the range, it appears that the seismotectonic model proposed by Lavé and Avouac (2000) can be generalized. The interseismic elastic strain accumulation beneath the High Himalaya, due to Main Himalayan Thrust (MHT) locking ~100 km north of the MFT, is fully released by large (Mw~8) to very large (Mw > 8.5) earthquakes with seismic ruptures breaking the MHT up to the surface or the near surface at the MFT. Those conclusions are fully consistent with the evidences of recent, very large surface ruptures at the MFT all along the Himalayan arc.

REFERENCES

Lavé J., and J. P. Avouac, 2000. Active folding of fl uvial terraces across the Siwalik Hills Himalaya of central Nepal, J. Geophys. Res., v. 105, pp. 5735-5770.

Shortening rates and seismotectonic model along the Himalayan arc of Nepal

J. Lavé1, D. Yule2 and S. Sapkota3

1CRPG, UPR 2300, CNRS-Université de Lorraine, 15 rue Notre Dame des Pauvres, 54501 Vandoeuvre les Nancy, Cedex, France

2Department of Geological Sciences, California State University, Northridge, CA 91330-8266, USA3Seismolab, Department of Mines and Geology, Kathmandu, Nepal

66


Landslides are a widespread phenomenon in the Three-Gorges Area of P. R. of China. More than 3,000 landslides are known in the Three-Gorges-Reservoir area. About the same number is expected to be found in the anabranches of the Yangtze River. Rapid water level changes of The Yangtze reservoir with up to 30 m difference in the damming height can cause reactivation of already existing landslides, and in some cases they can cause the generation of new landslides. Mapping of landslides in the Xiangxi river area, a northern anabranche of the Yangtze river, on large scale maps delivered the fi rst information about their distribution pattern. Most landslides are situated in the vicinity of the Xiangxi River. Jurassic and Silurian strata are found to be most suitable for landslides.

In a second step an analysis was performed with ArcGIS-methods and with Artifi cial Neural Networks in order to fi nd areas with high susceptibility for landslides. Both methods were found to be suitable to fi nd areas with high susceptibility for landslides on a medium scale. The most important features in controlling landslides are found to be morphological factors, lithology, and distance to rivers. In some areas, up to 80 percent of the already existing landslides were correctly located in areas classifi ed as highly susceptible for landslides. However, the performance of these classifi cation methods for landslide recognition can be enhanced in future when better digital elevation models and more detailed lithological maps will be accessible.

Landslide recognition and analysis: A case study in the Three-Gorges Area, China

J. Rohn1, R. Bi1, M. Schleier1, C. Dumperth1, D. Ehret2 and W. Xiang3

1Friedrich-Alexander University Erlangen-Nuremberg/Germany2 Regional Board Freiburg/Germany

3China University of Geosciences Wuhan/P. R. China

67


Landslide-dammed lakes are commonly short-lived and are often eroded within a few days or weeks after their formation (Costa and Schuster, 1988). However, larger ones may also remain constant in size for years, like Hattian Slide in Kashmir (Schneider 2008; Konagai and Sattar 2012) or centuries like Lake Sarez in Pamir (Schuster and Alford 2004). The lake development refl ects the state of the landslide dam shape and composition in relation to the water resources in the study area on the one hand and determines the level of lake outburst and fl ooding hazards on the other hand.

Seepage through the dam or retrogressive erosion caused by uncontrolled overfl ow of the dam are the main causes of the dam breaching. Also new Earthquakes or new large mass movements in to the lake impounded behind the dam are common causes of dam failure. The most used stabilization method of these dams has been the construction of a protected (lined) spillway. Also lake drainage by means of siphons, pumping, tunnels outlets and diversions have been used. In a few cases, blasting to open new stream channels were successful.

The Attabad landslide in Hunza valley, northern Pakistan occurred early January, 2010, and blocked Hunza river to a height of 120 m. Similar historical landslide dams collapsed further south (Hewitt 1982), which suggested a fast erosion of the new dam, which created a lake, 21 km long, inundating several settlements and parts of the Karakoram Highway. Different fl ood wave scenarios were modeled and up to 40,000 persons evacuated, but the lake level reached the unlined artifi cial spillway without dam breaching end of May 2010. Stepwise damming to excavate deeper and consecutive blasting to lower the lake level is

still going on. The stability of the Gneiss matrix of the dam was underestimated and resists natural erosion. It is essential to lower the saddle of the dam to decrease the outburst risk and to let the fl ooded Karakoram Highway emerge.

Early April 2012, a rock/ice avalanche, entraining a lateral moraine, originating from a northern side glacier below Bilafond Glacier in Gayari Valley, Siachen Region in Jammu Kashmir, Pakistan engulfed a camp, burying over 120 people. The compacted debris cone started to dam a lake, which during snow melt could have failed, resulting in a possible outburst. Flood wave simulations showed the risk of fl ooding further settlements downstream, therefore excavating of a channel was started immediately to lower the risk and to enable the rescuers to dig for remaining bodies. This excavation was successful, even though the debris matrix formed of morainic material and ice was soaked with glacier melt water.

REFERENCES

Costa, J. E., Schuster, R. L., 1988, The formation and failure of natural dams. Geological Society of America Bulletin, v. 100, pp. 1054-1068.

Hewitt, K., 1982, Natural dams and outburst fl oods in the Karakorum Himalaya. In: Glen J. W., (ed.): Hydrological aspects of alpine and high-mountain areas. IAHS Publication, v. 138, pp. 259–269.

Konagai, K., Sattar, A., 2012, Partial breaching of Hattian Bala Landslide Dam formed in the 8th October 2005 Kashmir Earthquake, Pakistan, Landslides, v. 9, pp.1–11.

Schneider, J. F., 2008, Seismically reactivated Hattian slide in Kashmir, Northern Pakistan, J SEISMOLOGY, DOI 10.1007/s10950-0, 00; ISSN 1383-4649.

Schuster, R. L., Alford, D., 2004, Usoi Landslide Dam and Lake Sarez, Pamir Mountains, Tajikistan. Environmental and Engineering Geoscience, v. 10(2), pp. 151–168.

Landslide dams in the western Himalayan range and mitigation measures

Jean F. SchneiderInstitute of Applied Geology, BOKU University of Natural Resources and Life Sciences, 1190 Vienna, Austria


68


In this presentation I will give an overview of what has been learned from monitoring geodetic strain and seismicity in the Himalaya as a result of the long-lived collaborative effort between the National Seismic Centre (DMG, Nepal), the DépartementAnalyse et Surveillance de l’Environnement (CEA, France) and the Tectonics Observatory at the California Institute of Technology (USA). The geodetic and seismological data collected have brought important information on the spatial distribution and rate of elastic

strain which is building up to be released by future large earthquakes. These data also bring information on the sensitivity of the Himalayan seismicity to small stress perturbations induced by Earth tides and surface hydrology. These data can be used, in addition to past historical seismicity, to validate and calibrate physics-based models of the seismic cycle which might be used to assess the characteristics (location, magnitude) and probability of occurrence of large earthquakes in the Himalaya.

Seismic hazard in the Himalaya of Nepal: Recent progress and perspectives

Jean-Philippe AvouacCalifornia Institute of Technology

69


The fl ood disaster of May 5th, 2012 in Pokhara Valley, Nepal, which took the life of at least 72 people, is explained by a so-called sturzstrom with subsequent debris fl ow. The same processes have formed the smooth terrace landform of Pokhara Valley: at least two gigantic debris-fl ow events about 12,000 and 750 years ago, both times marked by global warming phases. In both cases, the whole valley was covered by 3-5 km3 of debris transported from the same

huge depression where the recent sturzstrom came from. A new catastrophe of similar size would be apocalyptic: today about half a million people live in the valley. The very urgent need is obvious of a detailed investigation into the circumstances of the disaster of May 5th, especially the possible infl uence of global warming, as well as a reliable forecast of a potential recurrence of similar or possibly much greater events.

The May 5th fl ood disaster in Pokhara Nepal: A last warning sign sent by nature?

Jörg Hanisch1, Achyuata Koirala2 and Netra Prakash Bhandary3

1Jorge Consult, H anover; Germany 2ICIMOD, Kathmandu, Nepal

3Ehime University, Matsuyama, Japan

70


The East Asian and Indian Summer Monsoons belong to the most distinctive climatic phenomena on Earth, affecting directly or indirectly almost half of the world’s human population. Over the last decade, the climatic evolution of the Tibetan Plateau and the adjoining high mountain regions have gained increasing attention due to their signifi cant role in modifying the dynamics of the Indian and East Asian Summer Monsoons. Through complex interactions with, and impacts on, the global atmospheric circulation, these regions are latterly merged to the “Third Pole Environment (TPE)”, which is regarded as one of the forthcoming hot spots on environmental research in the world. Changes in extent and variability of the summer monsoons have had and will have large-scale effects on the high mountain environment. In addition, the social and economic development in the surrounding regions of China, India, Nepal, and farther countries in South-East Asia is highly dependent on the stability of climate and environments. As a result, understanding the controls and variability of past and present monsoon circulation is essential to estimate how environments will respond to future climate changes. Due to the lack of longer instrumental climate records and a sparse spatial distribution of meteorological stations, the survey and use of proxy datasets are needed to support reliable climate change scenarios.

Stable isotopes of various elements (mainly13C, 8O, 2H = D) are used in different natural archives like ice cores, lake sediments, speleothems, peat bogs, soils, and wood to derive palaeoclimate information. The spatial resolution of 18O and D composition in meteoric water is a good indication for summer monsoon activity on the southern part of the Tibetan plateau (Araguás-Araguás et al. 1998; Aggarwal et al. 2004; Johnson and Ingram 2004; Tian et al. 2001a and b; Tian et al. 2003). The study area in southern Tibet is situated in an important transition zone (approximately parallel to the 100°E), between the air masses of the Southwest Asian (Indian) monsoon, the East Asian monsoon and the Westerlies. Johnson and Ingram (2004) were able to assign the variations of D and 18O in present precipitation over China to regional functions of temperature and precipitation amount. They emphasize

the implications that isotope time series from palaeoclimate proxy records have for the reconstruction of past monsoon variability. Therefore, networks of isotope time series from the Asian Summer Monsoon realm seem a promising approach to capture the spatial and temporal variations of isotope ratios in palaeoprecipitation and to assign these patterns to fl uctuations in monsoon intensity and changes in dominant circulation patterns. So far, very few studies on stable isotopes in tree rings have been carried out on the Tibetan plateau and adjacent high mountain regions (e.g. Liu et al. 2003; Liu et al. 2004; Bräuning and Grießinger 2006; Grießinger et al. 2011). Within this study we present annually resolved stable carbon (13C) and stable oxygen 18O) tree-ring time series from different sites in south-eastern Tibet.

REFERENCES

Aggarwal, P. K, Fröhlich, K., Kulkarni, K. M., Gourcy, L. L., 2004, Stable isotope evidence for moisture sources in the Asian summer monsoon under present and past climate regimes. Geophysical Research Letters, v. 31 (8), pp. L08203, 10.1029/2004GL019911

Araguás-Araguás, L., Fröhlich, K., Rozanski, K., 1998, Stable isotope composition of precipitation over southeast Asia. Journal of Geophysical Research, v. 103, pp. 28,741-28,742.

Bräuning, A., Grießinger, J., 2006, Late Holocene variations in monsoon intensity in the Tibetan-Himalayan region-evidence from tree-rings. Journal of the Geological Society of India, v. 68 (3), pp. 485-493.

Griessinger, J., Bräuning, A., Helle, G., Thomas, A. and G.H. Schleser, 2011. Late Holocene Asian summer monsoon variability refl ected by δ18O in tree�rings from Tibetan junipers. Geophysical Research Letters, v. 38, L03701, doi:10.1029/2010GL045988, 2011.

Johnson, K. R. and Ingram, B. I., 2004, Spatial and temporal variability in the stable isotope systematics of modern precipitation in China: implications for paleoclimate reconstructions. Earth and Planetary Science Letters, v. 220, pp. 635-377.

Tian, L., Yao, T., Schuster, P. F., White, J. W. C., Ichiyanagi, K., Pendall, E., Pu, J. and Yu, W., 2003, Oxygen-18 concentrations in recent precipitation and ice cores on the Tibetan Plateau. Journal of Geophysical Research, v. 108 (D9) doi: 10.1029/2002JD002173.

Asian summer monsoon history in southern Tibet for the late Holocene: Results from a network of tree-ring isotope chronologies

*Jussi Griessinger and A. BräuningFriedrich-Alexander-University of Erlangen-Nuremberg, Institute of Geography, D-91054 Erlangen, Germany


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Tian, L., Yao, T., Sun, W., Stievenard, M., Jouzel, J. (2001a): Relationship between D and 18O in precipitation on north and south of the Tibetan Plateau and moisture recycling. Science in China (Series D), v. 44 (9), pp. 789-796.

Tian, L., Masson-Delmotte, V., Stievenard, M., Yao, T., Jouzel, J., 2001b, Tibetan Plateau summer monsoon northward extent revealed by measurements of water stable isotopes. Journal of Geophysical Research, v. 106, pp. 28,081-28,088.

Liu, X., Qin, D., Shao. X., Chen. T. and Ren, J., 2003, Climatic signifi cance of stable carbon isotope in tree rings of Abies spectabilis in southeastern Tibet. Chinese Science Bulletin, v. 48 (18), pp. 2000-2004.

Liu, Y., Ma, L., Leavitt, S. W., Cai, Q. and Liu, W., 2004, A preliminary seasonal precipitation reconstruction from tree-ring stable isotopes at Mt. Helan Shan, China, since AD 1804. Global and Planetary Change, v. 41, pp. 229-239.

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The Tripura-Mizoram accretionary belt is the southern extension of the Surma Basin, an outer arc basin lying within the greater Bengal Basin (Mannan 2002; Rahman and Faupl 2003). The basin contains an excellent record of the Neogene period, represented by the Surma Group exposed in Mizoram area as the Bhuban and Bokabil Formations. The Bhuban Formation is divisible into Lower, Middle, and Upper units composed of alternating arenaceous and argillaceous sequences. The main lithofacies exposed in area sandstone, siltstone, shale and its admixtures in various proportions with occasional pockets of shell limestone, calcareous sandstone, and intra-formational conglomerates. (Tiwari and Kachhara 2003). Palaeontological data in the form of invertebrate biota and vertebrate fossil fi sh published in last few years have provided broad ages for these sequences (Tiwari, 2001; 2006; Tiwari and Bannikov 2001; Tiwari and Kachhara 2000; 2003; Tiwari and Mehrotra 2000; 2002; Tiwari et al. 1997; 1998; Ralte et al. 2011). Limited foraminiferal data has also been provided (Jauhri et al. 2003; Lokho and Raju 2007; Lalmuankimi 2010) from few horizons, but precise dates for several mapped sections of practically fossil-devoid huge thicknesses are needed to correlate these repetitive cycles of rocks. The broad Lower, Middle, and Upper units of the Bhuban Formation need to be constrained with modern chronostratigraphic divisions.

Though most of these rocks are arenaceous sandstones, intermittent calcareous argillaceous units have provided moderately preserved calcareous nannofossils. It has been possible to precisely date several nannofossil bearing levels from widely separated sections. There is marked representation of grey and buff coloured sandstones in all three units of Bhuban Formation, which are highly bioturbated.

The Ruata quarry (23°45’143” N : 92°40’631”E) is located ca. 12km west of Aizwal city on the right side of the Aizawl-Sakawrtuichhun road, and is exposed in the western limb of the Aizwal anticline. Two fossiliferous beds of lower 4.9m and upper 3.1m thicknesses displaying grey silty sandstone and brown silty sandstone, respectively are delineated by a ca. 1m thick bed of sandstone – shale alteration which contains intra-formational calcareous

conglomeratic bands. Two samples lying at the base and one at the top of this conglomeratic level have yielded nannofossils. The lower samples have yielded Late Burdigalian-Early Langhian (Early-Middle Miocene) age nannofossils of NN2-NN4 zones, whereas the upper sample has given rise to Messinian age nannofossils (Late Miocene) of NN11B Zone. The said conglomerate horizon is actually hard ground in which several zones are mixed.

The samples from the Turial Bungalow and Turial Prayer sections exposed as part of Aizwal – Turial section have given rise to datable nannofossils. The 1,618m thick Turial section shows increase of buff sandstone upwards.

Two samples from Turial Bungalow section, one at the base and the other ca. 0.75 m above, have yielded nannofossils of Aquitanianian-Early Serravalian age, i.e., belonging to NN1-NN6 zones of Middle Miocene time slice. The upper sample has yielded nannofossils of NN11B-NN12 zones belonging to latest Tortonian / Messinain (Miocene/ Pliocene) boundary.

Only one productive sample from the Turial Prayer point section (23°44’06.7” N : 92°45’56.7” E) has yielded nannofossils and has a constrained time slice from Late Burdigalian – Early Langhian, i. e., Early- Middle Miocene of NN11B nannofossil zone.

Following nannofossil species are recorded from Ruata quarry section, Turial Prayer point and Turial Bungalow sections representing the Bhuban Formation: Amaurolithus ampliphicus (Bukry and Percival 1971; Gartner and Bukry 1975); A. delicatus (Gartner and Bukry 1975); A. primus (Bukry and Percival 1971; Gartner and Bukry 1975);Angulolithina arca (Bukry 1973b); Catinaster sp.; Ceratolithus acutus (Gartner and Bukry 1974); Coccolithus miopelagicus (Bukry 1971); Umbilicosphaera jafari (Müller 1974);Catinaster coalitus (Martini and Bramlette 1963);

Nannofossil biostratigraphy from Bhuban Fomation, Mizoram, norheastern India and its palaeoenvironmental interpretations

*Jyotsana Rai1, J. Malsawma2, C. Lalrinchhana, 2 Lalchawimawii2 and V. Z. Ralte2

1Birbal Sahni Institute of Palaeobotany, Lucknow- 226007 2Department of Geology, Mizoram University, Aizawl- 796 004


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Helicosphaera ampliaperta (Bramlette and Wilcoxon 1967); H. carteri (Wallich 1877; Kamptner 1954); H. paleocarteri (Theodoridis 1984); H. californiana (Bukry 1981a); H. intermedia (Martini 1965); H. minuta (Müller 1981); H. perch-nielseniae (Haq 1971; Jafar and Martini 1975); H. walbersdorfensis (Müller 1974b); Gephyrocapsa sp.1; Gephyrocapsa sp.2; Pyrocyclus orangensis (Hay and Towe 1962); Reteculofenestra minuta (Roth 1970); Sphenolithus conicus (Bukry 1971); S. delphix (Bukry 1973); S. heteromorphus (Defl andre 1953); Triquetrorhabdulus milowii (Bukry 1971); Tetralithoides symeonidesii (Theodoridis 1984); and calcareous dinofl agellate Thoracosphaera tuberosa (Kamptner 1963).

The moderately preserved and reasonably diversifi ed nannofossil assemblage from Bhuban Formation is signifi cant as several species of horseshoe shaped Amaurolithus and Ceratolithus are recorded that are very good Neogene stratigraphic markers of low latitude open sea sections (Perch- Nielsen 1985). H. ampliaperta has been used as Early Miocene zonal marker by Martini (1971) and Bukry (1973) and has been very rarely preserved in open ocean areas. Presence of several species of Heicosphaera probably suggests their preference for upwelling area.

REFERENCES

Bukry, D., 1973, Low latitude coccolith biostratigraphic zonation, Initial Reports of the DSDP, v. 15, pp. 685-703.

Jauhari A. K., Mandaokar, B. D., Mehrotra, R. C., Tiwari, R. P. and Singh, P., 2003, Corals and foraminifera from the Miocene Upper Bhuban Formation of Mizoram, India, Journal of Palaeontological Society of India, v. 48, pp. 12-20.

Lalmuankimi, C., Tiwari, R. P., Jauhri, A. K. and Ralte, V. Z., 2010, Foraminifera from the Bhuban Formation of Mizoram. Journal of Palaeontological Society of India, v. 55 (1), pp. 71-75.

Lokho, K. and Raju, D. S. N., 2007, Langhian(early Middle Miocene) Foraminiferal Assemblage from Bhuban Formation, Mizoram, NE India, Journal of the Geological Society of India, v. 70, pp. 933-938.

Mannan, A., 2002, Stratigraphic evolution and geochemistry of the Neogene Surma Group, Surma Basin, Sylhet, Bangladesh. Academic dissertation, University of Oulu, Linnanmaa.

Martini, E., 1971, Standard Tertiary and Quaternary calcareous nannoplankton zonation, in Proceedings of the Second Planktonic Conference Roma 1970, (ed. A. Farinacci), Edizioni Technoscienza, Rome, v. 2, pp. 739-785.

Perch- Nielsen, K., 1985, Cenozoic calcareous nannofossils, in Plankton Stratigraphy (eds. H.N. Bolli; J.B. Saunders& K. Perch- Nielsen), Cambridge University Press, pp. 427-554.

Rahman, M. J. J. & Faupl, P., 2003, The composition of the subsurface Neogene shales of the Surma group from the Sylhet Trough, Bengal Basin, Bangladesh, Sedimentary Geology, 155, 407-417.

Ralte, V. Z., Tiwari, R. P., Lalchawimawii and Malsawma, J., 2011, Selachian fi shes from Bhuban Formation, Surma Group, Aizawl, Mizoram, Journal of The Geological Society of India, v. 77, pp. 328-348.

Tiwari, R. P., 2001, Neogene palaeontology of the Surma Group, Mizoram, India. The Arcoida (Mollusca:Bivalvia), Journal of Palaeontological Society of India, v. 46, pp.147-160.

Tiwari, R. P., 2006, Neogene Palaeontology of the Surma Group, Mizoram, India, The Tellinoidea (Mollusca: Bivalvia). Journal of Palaeontological Society of India, v. 51(1), pp. 33-42.

Tiwari, R. P. and Bannikov, A. F., 2001, Early Miocene marine fi shes from the Surma Group, Mizoram India, Bollettino del Museo Civico di Storia Naturale diVerona, Geologia Paleontologia Preistoria, v. 25, pp. 11-26.

Tiwari, R.P. and Kachhara, R.P., 2000, Two new species of Apolymetis (Bivalvia:Tellinidae) from the Miocene of Mizoram, India, Tertiary Research, v. 20(1-4), pp. 79-84.

Tiwari, R. P. & Kachhara, R. P., 2003, Molluscan biostratigraphy of the Tertiary sediments of the Mizoram, India, Journal of the Palaeontological Society of India, v. 48, pp. 59-82.

Tiwari, R. P. and Mehrotra, R. C., 2000, Fossil woods from the Tipam Group of Mizoram, India, Tertiary Research, v. 20(1-4), pp. 85-94.

Tiwari, R. P. and Mehrotra, R. C., 2002, Plant Impressions from the Barail Group of Champhai-Aizawl Road section, Mizoram, India, Phytomorphology, v. 52(1), pp. 69-76.

Tiwari, R. P., Barman, G. and Satsangi, P. P., 1997, Miocene crabs from Mizoram, India, Journal of Palaeontological Society of India, v. 42, pp. 27-132.

Tiwari, R. P., Mishra, V. P. and Lyngdoh, B. C., 1998, Lower Miocene fi sh teeth from Mizoram, India, Geoscience Journal, v. 19(1), pp. 9-17.

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A large number of thrust sheets, small to large in size, have been mapped by several geo-scientists in Lesser Himalaya (Auden 1935; Heim and Gansser 1935; Gansser 1964; Hagen 1969; Stőcklin and Bhattarai 1977; Stőcklin 1980; Valdiya 1980; 1988; Sakai 1985 etc.). Well known crystalline nappes in the Nepal Himalaya are the Kathmandu, Jajarkot, Bajhang and the Dadeldhura Nappes from east to west.

A small thrust sheet is located at Kahun of Tanahu District, central Nepal. It occupies the position between the Kathmandu Nappe in the east and Jajarkot Nappe in the west. The Klippe is shown in both the geological maps of central Nepal (published by DMG, without date) and the geological map of Nepal (Amatya et.al., 1996). Besides this, there is no more information about this klippe. Geologically, the location of the thrust sheet is very important with the view point of tectonics to understand the root zone problems of Lesser Himalayan thrust sheets (Upreti, et.al., 1999).

In the present study detailed geological mapping was carried out in 1:25,000 scales to understand the stratigraphy, structure and metamorphism of the Klippe and its foot wall. The lithological succession of the Klippe can be divided into three formations as the Gwaslung Formation, the Musimaran Formation and the Shivpur Schist from bottom to top respectively. The Gwaslung Formation forms the basal part of the Klippe overlying the thrust contact with the Benighat Slates of the Upper Nawakot Group. It consists of a succession of intercalation of grey, saccrroidal marble, white calcareous, fi ne-grained quartzite and greenish-grey, fi ne-grained schist. It transitionally passes to the Musimaran Formation which consists of the intercalation of faintly laminated dirty grey quartzite and grey medium-grained garnetiferous schist with average thickness about 400 m. The Shivpur Schist occupies the topmost part of the Klippe. It consists of monotonous succession of garnetiferous schist. The contact of this formation with underlying Musimaran Formation is also transitional.

The Kahun Klippe forms the core of a large synclinorium whose axis passes through the Kahun Shivapur area. Mesoscopic and microscopic structures such as z-type folds, S-C fabric and spiral inclusions in garnet indicate top to the south sense of shearing in the thrust sheet. Present study shows

that the Shivpur Schist (uppermost unit of the thrust sheet) is comparable to the Raduwa Formation of the Kathmandu Nappe. The Gwaslung Formation and the Musimaran Formation are believed to the units older than the Raduwa Formation, which are missing in the Kathmandu area.

The tectonic position, lithology and microstructures indicate that the Kahun Klippe is the westward continuation of the Kathmandu Nappe. Most probably the Kathmandu Nappe covered entire central Nepal serving as the roof thrust of the Lesser Himalayan duplex structure. Later it was extensively eroded in the Tanahu-Pokhara area and the Kahun Klippe remained as an erosional remnant of the Kathmandu Nappe in this part of the Lesser Himalaya.

REFERENCES

Amatya, K. M., Jnawali, B. M., 1996, Geological map of Nepal: Kathmandu, Department of Mines and Geology, (DMG).

Auden, J. B., 1935, Traverses in the Himalaya: Geological Survey of India Records, v. 69, pp.123-167.

Gansser, A., 1964. Geology of the Himalayas. Interscience, London, p. 289.

Hagen, T., 1969, Report on the Geological Survey of Nepal, Preliminary Reconnaissance. Zurich, Memoirs de la Soc. Helvetique des sci. Naturelles.

Heim, A., Gansser, A., 1939. Central Himalaya: Geological observations of the Swiss expedition 1936. Mem. Soc. Helv. Sci. Nat., v. 73 (1), pp. 1-245.

Hagen, T., 1969. Report on the geological survey of Nepal Preliminary reconnaissance. Zurich Memoires de la Societe Helvetique des Sciences Naturelles, LXXXVI/1, 185p.

Sakai, H., 1985, Geology of the Kali Gandaki Supergroup of the Lesser Himalaya in Nepal. Memoirs of Facility of Science, Kyushu University, Ser. D. (Geology, v. 25 93), pp. 337-397.

Stőcklin, J; Bhattarai, K.D., 1977. In: Himalaya Report Geology of Kathmandu Area and Central Mahabharat Range Nepal. Department of Mines and Geology Kathmandu, Nepal, 86 p.

Stöcklin, J., 1980, Geology of the Nepal and its Regional Frame: Jour. Geol. Soc. London, v. 137, pp. 1-34.

Upreti, B. N., Le Fort, P., 1999, Lesser Himalayan crystalline nappes of Nepal: problem of their origin. In: Macfarlane, A., Quade, J., Sorkhabi, R. (Eds.), Geological Society of America Special paper, vol. v. 328, pp. 225-238.

Valdiya, K. S., 1980, The two intracrustal boundary thrusts of the Himalaya. Tectonophysics 66, 323-348.

Valdiya, K. S., 1988. Tectonics and evolution of the central sector of the Himalaya. Philosophical Transactios of the Royal Society of London, v. A326, pp. 151-175.

The Kahun Crystalline Klippe, Tanahu, central Nepal: Westward continuation of the Kathmandu Nappe?* Kabi Raj Paudyal, Roshan Koirala and Lalu P. Paudel

Central Department of Geology, Tribhuvan University, Kathmandu, Nepal(*Email: [email protected])

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Soil formation is strongly infl uenced by its surrounding environment. Sediments are playing a major role as parent materials in this context as they cover about 80% of the earth’s terrestrial surface. Soils on the other hand represent the interface of any kind of processes induced by terrestrial eco-subsystems, again affecting the parent materials before or after (re-)distribution. In this context time is an important factor of soil development, and soils might therefore preserve information about landscape and environmental fl uctuations especially since the late Quaternary. The reconstruction of environmental fl uctuations in turn is a major task with respect to forecasting man or naturally-induced changes.

Soils developed in fl uvial deposits of the Chamkhar Chhu river system in Eastern Bhutan were studied for verifi cation the above mentioned assumptions. The deposits represent 25 fl uvial terraces up to more than 260 m above the recent river level.

The common complexity of soils nature is converged by a combined methodical approach covering physical and

chemical processes to avoid misinterpretations. It holds especially for high mountain areas, and it includes the concurrent use of different methods, the study of the total solum, and comparatively simple methods to cover large numbers of soil samples. The soil physical and chemical analyses were maintained by numerical age dating of fossil A horizons.

The results indicate that soils can be used as proxies of the history of landscape and climate. Local as well as global climate fl uctuations are well preserved in the soils despite slope processes inducing reverse-tended soil formation in fl uvial deposits of Late Pleistocene origin and older, while soils on fl uvial deposits of Holocene age indicate distinct chronosequences (Tshering Dorji et al. 2009).

REFERENCES

Tshering Dorji, Caspari T., Bäumler R., Veldkamp A., Jongmans A., Kado Tshering, Tsheten Dorji and Baillie, I., 2009, Soil development on late Quaternary river terraces in a montane valley in Eastern Bhutan. Catena, v. 78(1), pp. 48-59.

Soils as proxies of the history of landscape and climate: Examples from eastern Bhutan

Karma D. Dorji1 and *Rupert Bäumler2

1National Soil Services Centre (NSSC), Ministry of Agriculture & Forests, Thimphu, Bhutan2Institute of Geography, University of Erlangen, D-91054 Erlangen, Germany,


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Micro (pollen) and macro plant remains (seed, fruit and leaves) from the Late Quaternary sediments in the Kathmandu Basin have been used to quantify the climatic parameters. The Besigaon section belonging to the Gokarna Formation has yielded a signifi cant amount of plant fossil remains for this investigation. The radiocarbon date of a

seed from Corylus ferox from this section is 53,570±820. Applying the co-existence approach the Mean Annual Temperature (MAP) at this time was 13.8-17ºC. Similarly the mean annual precipitation (MAP) was 1065-1682 mm. The temperatures at the warmest month (WMT) and the coldest month (CMT) were 25-26.2 ºC and 1.8-10.3 ºC respectively.

Vegetation and climate during 50 kyr BP in the Kathmandu basin

*Khum N. Paudayal1, Sudarshan Bhandari1,2 and Arata Momohara3

1Central Department of Geology, Tribhuvan University, Nepal 2Paleo-Labo Company, Saitama, Japan

3Faculty of Horticulture, Chiba University, Japan (*Email: [email protected])

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The viscoelastic structure underneath the Tibetan Plateau is a controversial topic of impor tance with regard to the long term evolution and topography of the Himalaya and Tibet Plateau. It has been proposed that the Tibet plateau owes its relatively uniform elevation to a low crustal viscosity and that the High Himalaya has resulted from the extrusion of a 10-15 km thick channel with a low viscosity (of the order of 1017-1018 Pa.s.). We show that the Earth's response to variations of hydrological surface loading, recorded over thousands of years by paleo-shorelines and over the last decade by geodetic measurements can be used to place direct constraints on crustal rheology and test those ideas. In the

fi rst case load variations can be estimated from the dating and present elevation of the numerous paleo-shorelines fringing most Tibetan basins. The viscoelastic response should in principle have induced vertical deformation of the shorelines. In the second case, it is the seasonal variations of elevation induced by seasonal variation of continental water storage which can be used to probe crustal visco-elastic properties. In that case the time evolution of surface load is estimated from the satellite dataset provided by the Gravity Recovery and Climate Experiment (GRACE). In both approaches, the viscoelastic response is computed using the code RELAX.

.

Constrains on the visco-elastic structure of the Tibetan Plateau from deformation induced by variations in hydrological surface loading over

multiple time scales

*Kristel Chanard1, Sylvain Barbot12, Jean-Philippe Avouac1 and William Amidon3

1Division of Geology and Planetary Sciences, California Institute of Technology, Pasadena, USA2Earth Observatory of Singapore, Nanyang Technological University, Singapore

3Middlebury College, Middlebury, USA(*Email: [email protected])

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The Gonnga Shan granite, a Cenozoic intrusive body southwest of the Longmen Shan range, remains a poorly understood feature of the eastern margin of the Tibetan Plateau. U-Pb zircon ages from throughout the granite suggest that it was emplaced in several phases between ~35 and ~10 Ma, and thermochronology data throughout the granite body and the surrounding region indicate that the granite has been exhumed more rapidly than the surrounding rocks. Zircon fi ssion track ages from within the granite range from 2 to 8.4 Ma, in contrast with rates in the units to either side, which generally range from ~12 to ~30 Ma (Xu and Kamp, 2000). The cooling ages do not vary systematically from north to south within the granite, and suggest relatively rapid exhumation at rates on the order of 1-2 km/My. In contrast to the consistency of the thermochronology data, the topography of the granite region is highly variable. The southern section of the granite contains extremely high relief and steep slopes, while the central section of the gr anite contains gentle slopes and low relief. The northern section of the granite contains a single high peak, but otherwise intermediate topography. Despite the difference

in exhumation rates between the granite and the surrounding rocks suggested by the thermochronology data, there is not a clear topographic signature of a difference in uplift rates. Preliminary cosmogenic 10Be basin wide erosion rates suggest that the short-term exhumation rates vary by an order of magnitude between the southern and central segments, and that erosion rates are in line with the topographic variations. In the southern section, erosion rates as high as 1.8 mm/yr are consistent with thermochronology-based exhumation rates; however, in the central section, erosion rates of 0.15 and 0.11 mm/yr are an order of magnitude slower than long-term exhumation rates. This requires a signifi cant slow-down of erosion rates and likely an associated reduction in relief and hillslope steepness in this section of the granite.

REFERENCES

Xu, G. Q., and Kamp, P. J. J., 2000, Tectonics and denudation adjacent to the Xianshuihe fault, eastern Tibetan Plateau: Constraints from fi ssion track thermochronology: JGR–SolidEarth, v. 105, pp. 19,231–19,251, doi: 10.1029/ 2000JB900159.

Disequilibrium between short term and long term exhumation rates in the Gongga granite, western Sichuan

*Kristen L. Cook1, Yuan-his Lee2 and Arjun Heimsath3

1Department of Geosciences, National Taiwan University, Taipei, Taiwan2Department of Earth and Environmental Sciences, National Chung-Cheng University, Taiwan

3School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA(*Email: [email protected])

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Debate over the viability of different mechanisms responsible for the tectonometamorphic evolution of the Himalayan mid-crust has been a focal point for much of the recent literature published on the region. While the majority of the studies published pertaining to mid-crustal convergence accommodation processes tend to favour one endmember model or the other (i.e. some type of wedge taper or mid-crustal fl ow) the perceived endmembers may actually constitute a false dichotomy (Beaumont and Jamieson 2010; Larson et al. 2011). In support of this hypothesis, recent geologic investigations in the Budhi Gandaki region of Nepal reveal a transition in the exhumed midcrustal core of the Himalaya from deep, hinterland-style midcrustal fl ow-type deformation to shallower, foreland-style wedge taper-type deformation (Larson et al. 2010). The same transition has been inferred in the upper Tama Kosi region of east-central Nepal (Larson 2012).

This study presents three P-T-t-D paths derived from three different structural levels within the upper Tama Kosi region. From low to high, these structural levels correspond to the approximate positions of the staurolite-, kyanite-, and sillimanite-in isograds. In situ Th-Pb monazite dating and concomitant REE measurement provide control on the temporal evolution of P-T paths determined through phase equilibria modeling. Monazite grains yield ages of 10-8 Ma in the staurolite-grade specimen. These are interpreted to have grown synkinematically with the staurolite-in reaction along a burial path indicating deformation and prograde metamorphism were synchronous in the late Miocene. Monazite grains in the kyanite-grade specimen yield distinct age groups with characteristic REE patterns. The oldest age group, at ~21.2 Ma, is associated with relatively low Y values and high Gd/Yb ratios. This may be attributable to concomitant garnet growth and refl ects the minimum age of peak metamorphism. The younger monazite ages show an inverse relationship between Y concentration and age, and range between ~18.5 and ~14.6 Ma. This pattern is consistent with garnet breakdown releasing Y to be taken up by new monazite growth. Two of the analyses from the

younger group are from monazite included in kyanite, which is predicted by phase equilibria models to form during initial garnet breakdown. This indicates the rock reached kyanite stable conditions in the early Miocene along a heating and decompression path. The sillimanite-bearing specimen yields a P-T-t path similar to that determined for the kyanite-grade specimen but with more pronounced decompression. The minimum age of peak metamorphism is constrained to ~ 22 Ma followed by monazite growth and garnet breakdown during decompression between ~22 Ma and ~15 Ma.

These P-T-t data demonstrate that the middle and upper portion of the exhumed mid-crust in the Tama Kosi region were coupled by ~22 Ma, and that kyanite growth occurred in the early Miocene. They also imply that the isograds observed are not part of a single Barrovian-style metamorphic episode as the staurolite in the staurolite-bearing specimen grew ~10 Myr after the formation of the kyanite isograd, at a time when the rocks in the upper portion of the mid-crust were undergoing rapid cooling and decompression. The stark distinction between the structurally lowest specimen and the middle and upper specimens is consistent with a transition from early mid-crustal fl ow recorded in the middle and upper structural levels to later wedge taper in the lower structural level.

REFERENCES

Beaumont, C. and Jamieson, R., 2010, Himalaya-Tibetan Orogeny: Channel Flow versus (Critical) Wedge Models, a False Dichotomy? USGS Open-File Report 2010-1099.

Larson, K. P., Godin, L. and Price, R. A., 2010, Relationships between displacement and distortion in orogens: Linking the Himalayan foreland and hinterland in central Nepal, Geological Society of America Bulletin, v. 122, pp. 1116–1134.

Larson, K. P., Cottle, J. M. and Godin, L., 2011, Petrochronologic record of metamorphism and melting in the upper Greater Himalayan sequence, Manaslu-Himal Chuli Himalaya, west-central Nepal. Lithosphere, v. 3(6), pp. 379-392.

Larson, K. P., 2012, The geology of the Tama Kosi and Rolwaling valley region, East-Central Nepal. Geosphere, v. 8(2), pp. 507–517.

Tectonic Insight from P-T-t paths, upper Tama Kosi region, Nepal

*Kyle P. Larson1, Felix Gervais2 and Dawn A. Kellett3

1Earth and Environmental Sciences, IKBSAS, University of British Columbia Okanagan, 3333 University Way, Kelowna, BC, V1V 1V7, Canada

2Département des Génies Civil, Géologique et des Mines, École Polytechnique de Montréal, Montréal, QC H3T 1J4, Canada

3Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8, Canada(*Email: [email protected])

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Detailed geomorphic mapping along the Main Frontal Thrust (MFT) in the macroseismic area of the 15/01/1934, Mw ≈8.1, Bihar-Nepal earthquake suggests that several of its strands ruptured recently. We found particularly well-preserved evidences of recent faulting in the Sir Khola valley, where the river crosses the Patu thrust. We used Total-Station leveling and Terrestrial Lidar Scanning to survey the tectonic/fl uvial geomorphology and log the structure of cleaned sections. Refreshing 50 m of a cliff at the base of a ≈ 26 m-high cumulative thrust escarpment along the river’s eastern bank exposed four north-dipping thrusts outlined by dark gouge. Three of them (F1, F3, F4 from south to north) truncate ≈ 2m-thick gravel/pebble layers. The main slope-break near the base of the escarpment coincides with the emergence of F3, which emplaces sheared Siwaliks on a wedge of soft fl uvial deposits and colluvium whose proximal part contains collapsed Siwalik blocks. The emergence of F4 corresponds to local steepening of the escarpment slope, and that of F1 to an eroded scarplet, down-slope across the low-level footwall terrace T2. This F1 thrust zone emplaces a toe of folded Siwalik sandstones upon several units of conglomerates, whose fl uvial origin is clear from pebbles imbricated by south-directed water-fl ow. The hanging wall strath terrace T2, which now stands 4-5 m above the river-bed, was uplifted by ≈3 m of co-seismic slip during an earthquake (E1) on the uppermost F1 splay, which is only sealed by the young fi ll of a still active rill channel at the foot of the eroded scarplet. Faults F1 and F3 are also exposed in a 43 m-long trench excavated at the base

of the main escarpment on the river east bank. The trench confi rms, and complements, the relationships of F1 and F3 with similar, and additional, fl uvial and colluvial deposits. In the trench, the wedge of soft overbank and colluvial wash observed along the river-cut tops an older collapse wedge capping F3, implying the occurrence of a more ancient event (E2) on that thrust splay.

The calibrated 14C ages of 25 detrital charcoal samples collected along the river-cut and in the trench constrain the chronology of deposition, and place limits on the dates of E1 and E2. Six sample ages indicate that the unconsolidated T2 conglomerates offset by E1 were emplaced by the river in the period spanning the 16th to early 20th centuries, while the channel fi ll sealing F1 is modern. In the trench, 11 charcoal ages constrain the date of E2 on F3 to postdate fl uvial conglomerates emplaced around AD 570-665 and to predate the colluvial wedge that collapsed above F3 in the 13th-16th centuries, with a preferred age in the mid 13th century. Oxcal tests, using Bayesian models, of more refi ned depositional scenarios based on robust stratigraphic inferences concur to support a simple surface faulting scenario, in which E2 and E1 are the AD 1255 and 1934 earthquakes, respectively. These results bring evidences that the 15/01/1934, Mw ≈ 8.1, Bihar-Nepal earthquake was not a blind event. They also suggest it might have been a repeat of the catastrophic, AD 7/06/1255 historical event that devastated Kathmandu and mortally wounded the King, implying a recurrence time of ≈680 yrs for great MFT earthquakes in eastern Nepal.

Earthquakes surface ruptures in the Sir Khola valley: Implications for the recurrence time of great Himalayan earthquakes

*L. Bollinger1, S. Sapkota2, P. Tapponnier3, Y. Klinger4, Y. Gaudemer4 and D. Tiwari2

1CEA/DAM/DIF, Arpajon, France2Department of Mines and Geology, National Seismic Center, Kathmandu, Nepal.3Earth Observatory of Singapore, Nanyang Technological University, Singapore

4Institut de Physique du Globe de Paris, CNRS, Paris, France(*Email: [email protected])

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The Dharan-Mulghat area can be divided into three tectonic units: the Higher Himalayan Crystallines, the Lesser Himalayan sequence and the Siwaliks separated by the Main Central Thrust and the Main Boundary Thrust respectively. The Lesser Himalayan sequence is divided into ten formations, grouped into two groups and one individual formation. The Bhedetar Group includes the Raguwa Formation, the Phalametar Quartzite, the Churibas Formation, the Sangure Quartzite and the Karkichhap Formation; followed by the Ukhudanda Formation, the Mulghat Formation, the Okhre Formation and the Patigau Formation, as the Dada Bajar Group of rocks; and the Bhorleni Formation as an individual formation.

The Main Central Thrust (MCT), the Main Boundary

Thrust (MBT), the Chimra Thrust (CT) and the Chhotimorang Thrust (CMT) are the major faults in the Dharan−Mulghat area. The Chimra Thrust separates the Dada Bajar Group of rocks from the Bhedetar Group. The Chhotimorang Thrust separates the Bhedetar Group of rocks from the Bhorleni Formation. The Leutiphedi Anticline and the Malbase Syncline are the major folds in the study area plunging towards east.

The microstructure study reveals that the rocks of the Lesser Himalayan sequence are highly deformed in comparison to the Higher Himalayan Crystallines. The strain analysis of quartz and feldspar grains shows a simple shear component in the hanging wall of the MCT and pure shear Component in the hanging wall of the CT.

Geology of Dharan-Mulghat area in east Nepal with special reference to microstructure and strain analysis

Lalit Kumar Rai, Kamala Kant Acharya and Megh Raj DhitalCentral Department of Geology, Tribhuvan University, Kathmandu, Nepal

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Stratigraphic classifi cation of the Nawakot Complex rocks in the Kathmandu area by Stöcklin (1980) is one of the best and widely accepted classifi cations till the date. This classifi cation has been regarded as the basis for correlation and tectonic interpretation in all other sections of Nepal and even adjacent areas of Indian Lesser Himalaya. However, present studies in the Mugling-Damauli section of central Nepal showed several discrepancies in his classifi cation and a modifi cation of the classifi cation is necessary. In this

paper we point out the problems in the classifi cation of Stöcklin (1980) as evidenced from the fi eld investigation and propose a modifi ed stratigraphic classifi cation for the Lesser Himalaya in central Nepal.

REFERENCES

Stőcklin, J., 1980, Geology of the Nepal and its Regional Frame. Journal of the Geological Society of London, v. 137, pp. 1-34.

Stratigraphic classifi cation of the central Nepal Lesser Himalaya by Stöcklin (1980): Does it need modifi cation?

*Lalu P. Paudel1, Kabi Raj Paudyal1, Sujan Devkota2, Tara Pokhrel3, Naresh Maharjan2, Deo Kumar Limbu1, Roshan Koirala1 and Pramod Pandey1

1Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal2 Department of Mines and Geology, Lainchaur, Kathmandu, Nepal

3Melamchi Hydropower Project, Kathmandu, Nepal(*Email: [email protected])

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Rutile, the most common polymorph of TiO2, is a widely distributed accessory mineral in medium– to high–grade metamorphic rocks and to a lesser extent in igneous rocks. Due to its chemical and physical stability during the sedimentary cycle, rutile is also commonly found in the heavy mineral suite of detrital rocks and can therefore provide important information about its source rocks. Zr–in–rutile is used as a geothermometer (Zack et al. 2004a) and the trace element content of rutile can help to discriminate between different source lithologies in provenance studies (e.g. Zack et al. 2004b; Meinhold et al. 2008).

Similarly to zircon and other U–bearing minerals, rutile can be dated by the U–Pb method (e.g., Mezger et al. 1989). However, it has so far received less attention because it usually has lower U and lower relative radiogenic Pb content compared to zircon and because of the lack of abundant rutile U–Pb reference materials, with the exception of e.g. rutile R10 and R19 (Luvizotto et al. 2009; Zack et al. 2011). A further complication to U–Pb dating is that rutile can contain a relatively large proportion of common (non radiogenic) Pb. Compared to zircon, rutile is characterized by a lower closure T for Pb diffusion (around 500ºC, although there is not yet agreement on closure temperature estimates) and hence rutile U–Pb dates primarily indicate the time since the last signifi cant metamorphism or cooling below ~500ºC. Rutile can therefore be used as a thermochronometer in a variety of studies aimed at determining the minimum age of metamorphism or constraining cooling histories of metamorphic terranes. Growing interest is being paid to U–Pb chronology of detrital rutile as applied to sedimentary provenance. Rutile has indeed the potential to become a key provenance tracer, as it adds an important lower temperature complement to zircon and with zircon comprises a much more unique isotopic fi ngerprint of the source region, allowing more confi dent identifi cation of source areas or reconstruction of basin depositional histories.

In this study we have applied LA–MC–ICP–MS (laser ablation multi–collector inductively coupled plasma mass spectrometry), a technique with high spatial resolution and analytical throughput, to the rapid U–Pb dating of single grains of rutile. We introduce the use of two new natural rutile materials, Sugluk–4 and PCA–S207, as primary and secondary reference materials during the analysis, for which new high precision ID–TIMS (isotope dilution thermal ionization mass spectrometry) U–Pb dates have also been determined.

We have determined the age of rutile grains from modern rivers draining the Bhutan Himalayas (Grujic et al., 2002) and compared these results to detrital zircon U–Pb data from the same sample, in order to show the power of rutile in the interpretation of sediment provenance. These results show that drainages with bedrock predominantly comprised of high grade GHS yield rutile U–Pb ages of 10–20 Ma, whereas zircons from these sample are primarily >480 Ma, with only a few grains or metamorphic rims refl ecting the Himalayan Miocene metamorphism. The contrast between zircon and rutile signatures is very dramatic and as such provides important complementary information about the events within the orogen.

REFERENCES

Grujic, D., Hollister, L.S., Parrish, R.R., 2002, Himalayan metamorphic sequence as an orogenic channel: insight from Bhutan, Earth and Planetary Science Letters, v. 198(1–2), pp. 177–191.

Luvizotto, G.L. et al., 2009, Rutile crystals as potential trace element and isotope mineral standards for microanalysis, Chemical Geology, v. 261(3–4), pp. 346–369.

Meinhold, G., Anders, B., Kostopoulos, D., Reischmann, T., 2008, Rutile chemistry and thermometry as provenance indicator: An example from Chios Island, Greece, Sedimentary Geology, v. 203(1–2), pp. 98–111.

Mezger, K., Hanson, G.N., Bohlen, S.R., 1989, High–precision UPb ages of metamorphic rutile: application to the cooling

Detrital rutile U–Pb geochronology by LA–MC–ICP–MS: New approach, reference materials and applications to sedimentary

provenance in the Bhutan Himalayas

Laura Bracciali1,2, Randall R. Parrish1,3, Daniel J. Condon2, Matthew S.A. Horstwood1, *Yani Najman2

1NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottingham, UK2Lancaster Environment Centre, Lancaster University, Lancaster, UK,

3Department of Geology, University of Leicester, UK(*Email: [email protected])

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history of high–grade terranes, Earth and Planetary Science Letters, v. 96(1–2), 106–118.

Zack, T., Moraes, R., Kronz, A., 2004a, Temperature dependence of Zr in rutile: empirical calibration of a rutile thermometer, Contributions to Mineralogy and Petrology, v. 148(4), pp. 471–488.

Zack, T., von Eynatten, H., Kronz, A., 2004b, Rutile geochemistry and its potential use in quantitative provenance studies, Sedimentary Geology, v. 171(1–4), pp. 37–58.

Zack, T. et al., 2011, In situ U–Pb rutile dating by LA–ICP–MS: 208Pb correction and prospects for geological applications, Contributions to Mineralogy and Petrology, v. 162(3), pp. 515–530.

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It has been established that the Tibetan Plateau and adjacent mountain ranges infl uence the atmospheric circulation of the Asian monsoons and the Westerlies. On the other hand, the dynamics of the precipitation on which a billion people depend are not well understood. The Tibetan Plateau features numerous lakes as well as the headwaters of major south-east Asian rivers that have sustained civilizations since the mid-Holocene. Studying palaeo-moisture availability over the plateau may help to evaluate meteorological data and thus scrutinize modern precipitation trends in respect of long-term development and adjust scenarios of future moisture availability accordingly. Archives that record high resolution palaeo-moisture signals are scarce on the Tibetan Plateau and mainly restricted to few areas.

Taft et al. (2012) have shown that the shells of the pulmonate freshwater gastropod Radix may represent suitable archives. The stable isotope patterns provide valuable information for characterizing lake systems and large as well as regional scale climate conditions. Living Radix is widely distributed on the plateau, and fossil Radix has been reported from a number of geological sections. Radix preferably dwells in shallow water and during the formation of the aragonitic shell the mineralization is directly infl uenced by the environment. It lives long enough to archive the annual hydrological cycle of a selected habitat. The shells continue growing during winter and are suffi ciently large that they can be sub-sampled in sub-seasonal resolution.

We here present δ18O and δ13C isotope compositions from modern Radix shells from nine lakes across the Tibetan Plateau to the Pamirs. We hope to extend the knowledge of

ecosystem specifi c differences or similarities as a basis for proper interpretation of palaeo-environments. From each shell, c. 15-30 sub-samples were taken in one millimeter steps along the ontogenetic spiral of growth, and δ18O and δ13C isotope compositions were analyzed. The oxygen isotope patterns exhibit increasing infl uence of precipitation and decreasing infl uence of evaporation, from west to east on the plateau. δ18O values of shells from lakes on the eastern and central plateau mirror monsoon signals, indicated by more negative values and higher variability compared to the more western lakes. The δ13C compositions are dependent on different carbon sources and biological activity within the particular habitats. General climatic differences of the lake regions due to the different regional settings are clearly mirrored in the isotope compositions of the shells, without noticeable dependence on the particular lake system. In comparison to other climate archives from the Tibetan Plateau, the isotope patterns in Radix shells mirror general climatic differences between the different regions as well as intra-annual and even sub-seasonal changes. The fossil record of Radix sp. on the Tibetan Plateau reaches back to the Miocene and thus opens a long-time window for understanding the dynamics of moisture availability at different temporal scales. Our approach is currently applied to Late Holocene fossil Radix shells from Lake Karakul (Pamirs) sediments and preliminary results will be presented along with the data from modern shells.

REFERENCES

Taft, L., Wiechert, U., Riedel, F., Weynell, M. and Zhang, H. C., 2012, Sub-seasonal oxygen and carbon isotope variations in shells of modern Radix sp. (Gastropoda) from the Tibetan Plateau: potential of a new archive for palaeoclimatic studies, Quaternary Science Reviews, v. 34, pp. 44-56.

Stable isotope compositions in modern gastropod shells from the Tibetan Plateau and the Pamirs mirror hydrologic and climatic signals in sub-

seasonal resolution

*Linda Taft1, Uwe Wiechert1, Hucai Zhang2, Steffen Mischke1,3, Birgit Plessen4, Marc Weynell1, Andreas Winkler1 and Frank Riedel1

1Freie Universität Berlin, Department of Earth Sciences, Malteserstr. 74-100, 12249 Berlin, German2Yunnan Normal University, Key Laboratory of Plateau Lake Ecology and Global Change, College of Tourism and

Geography, Kunming, Chenggong 650500, China3University of Potsdam, Institute of Earth and Environmental Science, Karl-Liebknecht-Str. 24-25, 14476 Potsdam,

Germany4Helmholtz-Zentrum Potsdam, Deutsches GeoForschungsZentrum (GFZ), Telegrafenberg C 327, 14473 Potsdam, Germany


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Recent studies indicate that the Himalayan orogen have commonly experienced >30 Ma episodes of high temperature metamorphism and partial melting that resulted in the formation of migmatite complexes and different types of granite (Lee and Whitehouse 2007; Zeng et al. 2009; Gao et al. 2009a and b). Characterizing the geochemical nature of and mechanisms for these anatectic events is important for understanding the geochemical and tectonophysical effects of melting processes in large collision belts. The Yardoi gneiss dome is located to the east of the Northern Himalayan gneiss dome (NHGD) and consists of two-mica granite and leucogranite in the core, surrounded by high grade metapelite and metabasite in the margin. Leucogranites occur either as a relatively large pluton in the core or as dikes of various sizes in the marginal areas. Further south of the Yardoi gneiss dome, there are two relatively large two-mica granite plutons: the Dala to the north and the Quedang to the south. SHRIMP zircon U/Pb dating indicates that (1) the leucogranites formed at 35.3 ± 1.1 Ma (Zeng et al. 2009); (2) two-mica granites from the core of Yardoi gneiss dome and from the Quedang pluton formed at 42.6±1.1 Ma and 42.8±0.6 Ma, respectively, similar to those from the Dala pluton (Qi et al. 2008; Aikman et al. 2008). Both suites of granite are Na-rich peraluminous (Na2O/K2O>1.0, A/CNK>0.99 and up to 1.42). Some of the 35.3 Ma leucogranites have an adakite-like geochemistry. All the two-mica granites have similar Sr, Nd and other element geochemistry, characterized by (1) high SiO2(>68 wt%) and Al2O3 (>15 wt% and up to 17 wt%) but low FeO and MgO, high Na2O/K2O (>1.0 and up to 1.3) and A/CNK (>1.0) ratios; (2) enrichment in Sr and LREE, but depletion in HREE and Y; (3) high Sr/Y (>37.5) and La/Yb (>29.3) ratios; (4) no or very weak negative Eu anomalies; (5) relatively elevated Rb and Rb/Sr ratios as compared to those in typical adakitic granites; (6) low 87Sr/86(i) (<0.7190) and unradiogenic Nd (Nd(i) = -9.2~-15.0) isotope compositions, similar to those in the 35.3 Ma leucogranites and amphibolites, but signifi cantly different from those in the younger (<30 Ma) leucogranites and metasedimentary wall rocks. These granites are located within the adakite fi eld in either Sr/Y-Y or La/Yb-Yb diagram. Our new data suggest that these two-mica granites with diluted adakite geochemistries resulted from partial

melting of an amphibolite source at overthickened crustal conditions.

Combing our data with those from the literature, there are three trends in the Rb-Sr systematics for the granites from the Himalaya (Fig. 1). The fi rst trend (Trend-A), defi ned by the >40 Ma granites is characterised by elevated Sr concentrations by at least a factor of 2 as compared to typical younger K-rich leucogranites at similar Rb concentrations. The second trend (Trend-B) defi ned by 30-40 Ma granites has subdued Sr concentrations that one substantially different from those in the typical K-rich leucogranites. The third trend (Trend-C) defi ned by the typical 30-10 Ma leucogranites, has low Sr but relatively high and variable Rb concentrations. Trend-A (overthickened melting) represents those amphibolite-derived melts formed in the garnet stable fi eld (e.g. overthickened crustal conditions) and diluted to various degrees by metasediment-derived melts. This process can account for the relatively weak but still observable adakitic nature of these Na-rich peraluminous granitic melts from the Yardoi area. These melting events, dominated by amphibolite partial melting at overthickened crust conditions at the early stage of tectonic evolution of the Himalayan orogen, could be a common feature to large-scale collision belts. Such melting events could be a major factor leading to the transition from compressional overthickening to extensional collapse of the southern Tibet prior to 30 Ma. The melting events could aslso be responsible for the formation of trend-B granites. Trend-B (transitional melting) represents combined effects of amphibolite and metasediment melting during the transition from compressional overthickening to the onset of extensional collapse in the Himalayan orogen. Trend-C (decompressional melting), however represents melts predominantly derived from metasediment partial melting during the

Coupling of tectonics and crustal anatexis and the formation of Cenozoic granites in the Himalayan collisional orogenic belt

*Lingsen Zeng1, Li-E Gao1, Jing Liu2, Kejia Xie2 and Guyue Hu1

1 Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China, 2 Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085


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rapid exhumation of the Himalayan high grade rocks. Our data demonstrate a strong coupling between the tectonic processes and granitic magma generation in the evolution of large-scale collisional orogenic belts.

REFERENCES

Aikman, A. B., Harrison, T. M. and Ding, L., 2008, Evidence for Early (>44 Ma) Himalayan Crustal Thickening, Tethyan Himalaya, southeastern Tibet. Earth and Planetary Science Letters, v. 274, pp. 14-23.

Gao, L-E., Zeng, L. S., Liu, J. and Xie, K. J., 2009a, Pre-35 Ma Na-rich magmatic events in the Yardoi area, southern Tibet. Geochimica et Cosmochimica Acta, v. 73(13), A414.

Gao, L-E, Zeng, L. S., Liu-Zeng, J., and Xie, K. J., 2009b, Early Oligocene Na-rich peraluminous leucogranites in the Yardoi gneiss dome, southern Tibet: Formation mechanism and tectonic implications. Acta Petrologica Sinica, v.25, pp. 2289-2302.

Inger, S. and Harris, N.,1993, Geochemical Constraints on Leucogranite Magmatism in the Langtang Valley, Nepal Himalaya. Journal of Petrology, v. 34, pp. 345–368.

Lee, J., and Whitehouse, M. J., 2007, Onset of mid-crustal extensional fl ow in southern Tibet: Evidence from U/Pb zircon ages. Geology, v. 35, pp. 45-48.

Qi, X. X., Zeng, L. S., Meng, X. J., Xu, ZQ., and Li, T. F., 2008, Zircon SHRIMP U-Pb dating for Dala granite in the Tethyan Himalaya and its geological implication. Acta Petrologica Sinica, v. 24, pp. 1501-1508.

Searle, M. P., Parrish, R. R., Hodges, K. V., Hurford, A., Ayres, M. W. and Whitehouse, M. J., 1997, Shisha Pangma leucogranite, south Tibetan Himalaya: fi eld relations, geochemistry, age, origin, and emplacement. Journal of Geology, v. 105, pp. 295–317.

Zeng, L. S., Liu, J., Gao, L-E., Xie, K. J., and Wen, L., 2009, Early Oligocene crustal anatexis in the Yardoi gneiss dome, southern Tibet and geological implications. Chinese Science Bulletin, v. 54, pp. 104-112.

Zhang, H., Harris, N., Parrish, R., Kelley, S., Zhang, L., Rogers, N., Argles, T., and King, J., 2004. Causes and consequences of protracted melting of the mid-crust exposed in the North Himalayan antiform. Earth and Planetary Science Letters, v. 228, pp. 195–212.

Fig. 1: Rb-Sr systematics for the Cenozoic Himalayan granites. Two-mica granites include those from the Yardoi area, Cuobu and Malashan; Leucogranites include those from the NHGD (Zhang et al., 2004), and the High Himalaya (Inger and Harris 1993; Searle et al. 1997; Zeng et al. unpublished data). Trend A, B, and C schematically show the general trend for each suite of granites. Transition in the melting conditions from ~45 Ma (overthickened melting) via ~30-40 Ma (transitional melting) to ~30-10 Ma (decompressional melting) is strongly coupled with the tectonic evolution in the Himalaya belt.

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Placing timing constraints on how metamorphism in the Greater Himalayan Series (GHS) progresses is critical in determining the mechanism and rate of exhumation of this high grade unit, which is essential to our understanding of the details of India-Asia collision. The mode of exhumation is as yet unresolved; proposed models which may be tested using metamorphic chronology include channel fl ow (e.g. Jamieson et al. 2004), critical taper (e.g. Kohn 2008) and tectonic wedging (Webb et al. 2007). Numerous studies have attempted to constrain the age and duration of metamorphism in the GHS, but in many cases the timing constraints are derived from accessory phases whose exact textural relationships to the main metamorphic minerals are poorly known. This study combines geochemical analysis of trace elements in monazite with in situ U-Th-Pb geochronology to reveal greater detail in the tectonometamorphic history of the GHS in the eastern Himalaya.

Bhutan provides a broad expanse of exposed GHS rocks, including metapelites that are ideally suited to metamorphic investigation. Bhutan’s geology is unique across the Himalayan orogen due to its many klippen of Tethyan sediments and out-of-sequence thrust fault (Kakhtang thrust) within the GHS. Samples for this study were taken throughout the GHS, below the Kakhtang thrust. Fortunately, the accessory mineral monazite is common to most pelitic samples from the GHS in Bhutan, further

enhancing their suitability for this kind of integrated study.

Samples from different levels of the GHS in Bhutan were collected during fi eldwork in 2009 and 2010, and subjected to rigorous petrographic analysis to determine the best metamorphic assemblages for in situ geochronology. Texturally distinct monazite grains in these samples were identifi ed by petrography, and variations in their geochemistry characterized by X-ray mapping. The results of U-Th-Pb dating of monazite grains in situ using laser ablation on the Attom at the NERC Isotope Geochemistry Laboratory provide constraints on (i) the timing of peak metamorphism across the GHS and (ii) the age and duration of prograde mineral growth, bracketed by monazite ages from both included and matrix grains (exemplifi ed in Fig. 1.). Integration of the textural and geochemical data suggests that geochemically distinct populations of monazite grew during a period of decompression (between 19 and 13.5 Ma for the sample in Fig. 1). In situ U-Th-Pb ages obtained from this population of monazites determine the duration of this period of decompression, and how that duration varies at different levels in the GHS. Dating discrete phases of the metamorphic cycle (prograde, peak and decompression) in such detail forges powerful links between metamorphic studies and large-scale tectonic processes, and provides a basis for testing models of orogenic exhumation.

Detailed monazite chronology of Greater Himalayan Series metapelites from Bhutan

*Lucy V. Greenwood1, Tom W. Argles1, Randall R. Parrish2,3, Nicholas M.W. Roberts2, Clare Warren1 and Nigel B.W. Harris1

1Department of Earth, Environment and Ecosystems, The Open University, Gass Building, Walton Hall, Milton Keynes, Buckinghamshire, UK

2NERC Isotope Geochemistry Laboratories, Keyworth, Nottingham, UK3Department of Geology, University of Leicester, University Road, Leicester, UK


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REFERENCES

Jamieson, R. A., Beaumont, C., Medvedev, S., and Nguyen, M. H., 2004, Crustal channel fl ows: 2. Numerical models with implications for metamorphism in the Himalayan-Tibetan orogen: Journal of Geophysical Research, v. 109, p. 1–24.

Kohn, M. J., 2008, PTt data from central Nepal support critical taper and repudiate large-scale channel fl ow of the Greater Himalayan Sequence: Geological Society of America Bulletin, v. 120, pp. 259-273.

Stacey, J. S., and Kramers, J. D., 1975, Approximation of terrestrial lead isotope evolution by a two-stage model: Earth and Planetary Science Letters, v. 26, pp. 207-221.

Webb, A. A. G., Yin, A., Harrison, T. M., Célérier, J., and Burgess, W. P., 2007, The leading edge of the Greater Himalayan Crystalline complex revealed in the NW Indian Himalaya: Implications for the evolution of the Himalayan orogen: Geology, v. 35, pp. 955.

Fig. 1: Tera-Wasserburg diagram of monazite populations from a sample taken from the GHS in Bhutan. Monazite populations are divided by textural context and Y content distinguished by grey tone. Dashed lines are extended through data to an intercept age and anchored to a common lead value of 0.83 ± 0.02 (Stacey and Kramers, 1975). The data show that a distinct group of monazite included in garnet and kyanite, along with low Y monazite cores from the matrix, grew at approximately 21 Ma. The age population of monazite analyses of high Y rims ranges from approximately 19 to 13.5 Ma.

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On 11 August 1931, a Ms 7.9 earthquake ruptured the NNW-striking Fuyun fault in Northwest China. This event ranks among the largest continental strike-slip earthquakes of the past century. Surface breaks were mapped over a length of 160 km with an average co-seismic right-lateral slip of 6.3±1.2 m. The earthquake hypocenter was located about midway along the fault, beneath the Karaxingar Mountain, a 1900 m-high push-up ridge.

On the upper east side of the mountain crest lies a NW-trending extensional basin with tens of meters high normal fault scarps cutting bedrock and intersecting one another at high angle. This basin has usually been interpreted as a pull-apart or a collapse/landslide feature. However, such interpretations are not consistent with the topography and regional stress–fi eld. High resolution geomorphic mapping of the basin, using a Terrestrial Lidar Scanner (TLS), yields new insight into the relative chronology of the scarps. It

suggests instead that they may have been the combined result of both the August 11 main shock and of a large aftershock on August 18 (M≈7).

The western foothills of the Karaxingar push-up ridge are bounded by a shallow-dipping thrust with a spectacular escarpment showing evidence of growth through multiple co-seismic events. From a TLS topographic survey, and age constraints from the 10Be/26Al cosmogenic exposure ages (between 56±3 and 76±2 ka) of two uplifted fans, we estimate a vertical throw rate of only 0.09±0.02 mm/yr, about 1/10th of the dextral slip-rate on the main Fuyun fault. Accurate TLS DEM profi les across the thrust indicate that the maximum uplift of the fan surfaces may have accrued in as many as 8 seismic events, each with a co-seismic throw of ≈1 m. Such measurements imply characteristic slip behavior, as observed along the main strike-slip segments of the Fuyun fault.

Characteristic vertical throw and slow Late-Quaternary uplift rate on the Karaxingar Push-up Thrust, Xinjiang, China

M. Etchebes1, P. Tapponnier1, Y. Klinger2, J. Van Der Woerd, Xu Xiwei, Sun Xinzhe, Tan Xibin, M. Rizza and Tsang Lok Hang

1Earth Observatory of Singapore, Nanyang Technological University, Singapore2Institut de Physique du Globe, Paris, France

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A severe earthquake of magnitude Mw=6.9 (MLNSC=6.8) struck Sikkim and eastern Nepal in the evening of September 18, 2011 at UTC 12:40 (NST 6:25 PM). The event recorded at all NSC seismic stations triggered the Seismic Alert System. It was then located in the vicinity of the Kanchanjangha sanctuary, near the Sikkim–Nepal border, lying out of the seismic network. The seismic records that allowed NSC analysts to locate 136 aftershocks within the fi rst 24 hours of the crisis.

Within the very next few days, NSC prepared a post seismic campaign. Three temporary accelerometers were deployed in eastern Nepal at Tumlingtar, Ilam and Taplejung, four broadband seismic stations at Dhankuta, Jhapa, Ilam

and Taplejung and few more campaign GPS site in the area. These temporary stations were dismantled after 3 months in January 2012.

This paper will present an overview of the data acquired by NSC during the seismic crisis that followed the 18/09/2011 earthquake. It will then focus on the spatial and temporal structure of the more than 800 aftershocks localized using both permanent short-period stations and temporary 3-components broadband stations’ seismic networks.

T he spatial pattern of the aftershocks, located along a 80 km-long SE trending zone, will fi nally be confronted to the complex-2 patches rupture model deduced from teleseismic waveform inversion.

Seismological overview of 18th September Mw=6.9 earthquake at the Sikkim-Nepal border

*M. Jha1, D. R. Tiwari1, S. N. Sapkota1, L. Bollinger2, R. Pandey1, C. Timsina1, U. Gautam1, P. Shrestha1, B. P. Koirala1, L. B. Adhikari1, M. Bhattarai1, T. Kandel1 and C. Gourraud1

1DMG, Lainchaur, Kathmandu, Nepal2DASE, Bruyères le Châtel 91297 Arpajon, France


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The Himalayan range represents the archetype of mountain building in continental collision setting. It is also considered in many studies as the locus of intense interactions between climate, erosion and tectonics. A better understanding of these interactions requires detailed knowledge of the distribution of the erosion across the range as well average erosion rates. The products of central Himalayan erosion are exported to the Bengal fan by a major river system: the Ganga watershed. This river provides the opportunity to quantify the recent Himalayan erosion rates as its watersheds integrates a large part of the Himalayan arc and is insensitive to the stochastic nature of the erosion events in the headwater like landslide or debris fl ow events.

Here we present the results of two complementary approaches to measure erosion rates: decadal sediments fl uxes measured through ADCP, suspended load sampling and semi-empirical model at Harding Bridge in Bangladesh, and, at the scale of the Late Holocene, mean erosion rates derived from 10-Be cosmogenic nuclides in river sediments of the Ganga and of its major tributaries. In order to derive the erosion in the mountainous part of the Ganga watershed, the effects of 500 to 1000 km fl oodplain transfer on the sedimentary signal has been fi rst evaluated. The gauged

sediment fl ux is mainly biased by the sequestration of sediments in the fl oodplain. But based on geochemical budget, sequestration is limited to ca. 10 % of the eroded sediment fl ux. Cosmogenically derived denudation rates in Bangladesh may also be biased by the accumulation of nuclides during sediment transfer in the fl oodplain. The comparison of the 10-Be concentration of sediments in the main Himalayan Rivers, upstream of the fl oodplain with sediments in Bangladesh and the use of modelling approaches suggests that this effect has also a limited impact on the 10-Be concentration in sediments. After corrections of those reduced fl oodplain transfer effects, gauged sediment fl uxes and 10-Be in sediments yield very similar denudation rates for central Himalaya: 0.8 and 1.0 mm/yr respectively (20% uncertainties), suggesting relatively constant erosion rates during the last millennium.

Combined with complementary data of geochemical/mineralogical provenance, 10-Be in sediment, sediment gauging or fl uvial incision rates derived fl uvial shear stress within the central Himalayan range, those results indicate that recent or Late Holocene erosion rates are maximum in the High Himalaya in association with high rainfall and uplift above a mid-crustal ramp, and reach there on average 3 mm/yr.

Modern and Late Holocene average erosion rates of the central Himalayan arc

M. Lupker, J. Lavé, C. France-Lanord and P. H. BlardCRPG, UPR 2300, CNRS-Université de Lorraine, 15 rue Notre Dame des Pauvres, 54501 Vandoeuvre les Nancy, Cedex,

France

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The Nagar Parkar igneous complex occurs along the junction of the Thar Desert and the Rann of Kutch (71o05’N, 24o25’E). It comprises stocks, bosses and dykes of Late Proterozoic A-type granitoids emplaced in a basement of peneplained amphibolitic rocks (Jan et al., 1994). These have been intruded by steeply dipping mafi c dykes that are locally in swarms of parallel sheets or networks. Individual dykes are generally no more than a 5 m in thickness and 300 m in length, but some are larger and up to 2 km in length. The age of the makfi c dykes is not known, but they may also be Late Proterozoic; local intrusions of granitic dykes in them lead to assume that the latest phases (s) of the granitic magmatism overlapped with the mafi c magmatism. In some places the dmafi c dykes are composite and intimately associated with parallel sheets of rhyolite/trachyte and aplite/microgranite, leading to assume the occurrence of bimodal magmatism.

The mafi c dykes may have chilled margins, and show considerable modal and textural variations. They are fi ne- to medium-grained and holocrystalline to hypocrystalline; many are porphyritic (up to 8 cm plagioclase phenocrysts in rare cases) and some display fl ow alignment in phenocysts. They can be divided into two groups on the basis of the principal mafi c mineral: amphibole-bearing and (titanian?) augite-bearing. Both contain zoned plagioclase (labradorite-andesine, commonly sausurritized), opaque oxide, sphene, apaptite and secondary minerals. Some of the augite-bearing rocks also contain olivine. Field relations are not clear, but the amphibole-bearing dykes appear to be older than the augite-bearing ones.

The two groups of dykes are quite similar in major element geochemistry (Laghari, 2004). Analyzed rocks are alkaline and characterized by high TiO2 and Na2O+K2O contents, and their Mg # are too low (generally <40) to represent primary magma. Fourteen representative analyses are olivine-normative, with six also being nephelene-normative. Trace element and REE analyses of two pyroxene-bearing and one amphibole-bearing dykes show that the latter is enriched in all the trace and RE elements. However, their mantle normalized trace element and chondrite normalized REE patterns are similar and slope towards HFS and HRE elements. Normalized trace element spidergrams for the two are characterized by Ba, K, Ta, and P spikes, and Th and Nb troughs, however, Rb, La and Sr show opposite relations. Normalized REE show depressions on Ce and Dy, and humps on Nd and Ho. The normalized trace element patterns of the Nagar Parkar mafi c dykes share more characteristics, especially the distinct Nb trough, with subduction zone lavas and contaminated volcanics than with within plate alkali basalts. Figure 1 shows the close similarity in the TrE patterns of the mafi c dykes and the most contaminated Rio Grande Rift lava (cf. Wilson, 1989, Fig. 11.22c, p. 357). Similarity in geochemistry in the two groups of the mafi c dykes and their close association in space and time may have resulted from either (1) partial melting of heterogeneous mantle, (2) two-stage partial melting of the same mantle source, 3) low-P fractionation of the Pxn-type magma, or (3) zoned magma chamber with Hbl-type occupying the upper/outer part.

Petrogenesis of alkaline mafi c dykes in the Nagar Parkar igneous complex, southeastern Sindh, Pakistan

*M. Qasim Jan1, Amanullah Laghari2, M. Asif Khan1 and M. Hassan Agheem2

1National Centre of Excellence in Geology, University of Peshawar, Peshawar, Pakistan, 2Centre for Pure and Applied Geology, University of Sindh, Jamshoro, Pakistan


94


REFERENCES

Jan, M. Q., Laghari, A. and Khan, M. A., 1997, Petrography of the Nagar Parkar igneous complex, Tharparkar, southeastern Sindh. Geological Bulletin, University of Peshawar, v. 30, pp. 227-249.

Laghari, A., 2004, Petrology of the Nagar Parkar granites and associated basic rocks, Thar district, Sindh, Pakistan. Unpublished PhD thesis, University of Peshawar.

Wilson, M., 1989, Igneous Petrogenesis. Unwin Hyman, London.

Fig. 1: Comparison between the Chondrite normalized trace elements (except K, P and Ti which are normalized to primordial mantle) between the Pxn-bearing (triangles), Hbl-bearing (large dots) and most contaminated Rio Grande Lava (small dots).

95


Presently, multi layered energy-balance snow schemes are included in a few hydrological models for studying the cold region processes; however, an effort is needed in the fi eld of cryospheric modeling for the application of such models in wider region of hydroclimatic variabilities in simulating open and forest snow processes and glacier melt runoff simultaneously in a distributed framework. This research is motivated towards an improved snow and glacier melt modeling in a distributed hydrological framework with the development of multilayer energy balance based snow and glacier melt model (WEBDHM-S) for accurate simulation of snow/ice cover area, snow/ice melt runoff, glacier mass balances in distributed biosphere hydrological framework and application of the model at the Narayani river basin (about area of 32000 km2) of Central Nepal Himalaya.

The elevation of the basin ranges from 180m to 8200m with tropical to arctic climatic environment. The simulations are carried out at hourly time steps and at 1 km spatial resolution for the three hydrological years (2002-2004) with the use of Global Land Data Assimilation System (GLDAS)

atmospheric forcing (except observed temperature and precipitation). The spatial distribution of seasonal snow and glacier cover, snow and glacier melt runoff along with rainfed runoff, and glacier mass balances are simulated. The qualitative pixel-to-pixel comparisons for the snow-free and snow-covered grids in the region reveal that the simulations agree well with the Moderate Resolution Imaging Spectroradiometer (MODIS) eight-day maximum snow-cover extent data (MOD10A2) with an accuracy of 85% and a bias of 3 %. The state of snow and glaciers at each model grid are simulated prognostically and thus the distributed net annual mass balances are estimated. River discharge is satisfactorily simulated with Nash effi ciency of 0.90. In addition, the hypsography analysis for the equilibrium line altitude (ELA) suggests that the average ELA in this region is about 5400-5500 m, despite of variability of ELA in each glacier and region. This study shows potential for applicability of WEB-DHM-S model in simulating cryospheric processes to entire Hindukush Himalaya and Karakoram region.

Towards improved snow and glacier melt simulation in a distributed hydrological framework: Application at Narayani river basin of central

Nepal Himalaya

*Maheswor Shrestha1, Lei Wang2, Toshio Koike3, Yongkang Xue4 andYukiko Hirabayashi5

1Department of Electricity Development, Ministry of Energy, Kathmandu, Nepal2Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China

3Department of Civil Engineering, the University of Tokyo, Tokyo, Japan4Department of Geography and Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles,

USA5Institute of Engineering Innovation, The University of Tokyo, Tokyo, Japan


96


Northward subduction of the leading edge of the Indian continental margin to depths greater than 100 km during the early Eocene resulted in high-pressure (HP) quartz-eclogite to ultrahigh-pressure (UHP) coesite-eclogite metamorphism at Tso Morari, Ladakh Himalaya, India. Integrated pressure (P)-temperature (T)-time (t) determinations within petrographically well-constrained settings for zircon- and/or monazite-bearing assemblages in mafi c eclogite boudins and host aluminous gneisses at Tso Morari uniquely document segments of both the prograde burial and retrograde exhumation path for UHP units in this portion of the western Himalaya.

Poikiloblastic cores and inclusion-poor rims of compositionally-zoned garnets in mafi c eclogite were utilized with entrapped inclusions and matrix mineral phases for thermobarometric calculations and isochemical phase diagram construction, the latter thermodynamic modelling performed with and without the consideration of cation fractionation into garnet during prograde metamorphism. Calculations were performed in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 (NCKFMASHTO) system using THERMOCALC v3.33 and the most up-to-date thermodynamic dataset available at the time of study (tc-ds55) (Powell and Holland, 1988; Holland and Powell 1998, updated to August, 2004). Analysis of the garnet cores document (M1) conditions of 21.5±1.5 kbar and 535±15°C during early garnet growth and re-equilibration. Zircon inclusions in garnet cores yield a maximum age determination of 58.0±2.2 Ma for M1 (Rayner et al. 2012). Peak HP/UHP (M2) conditions are constrained at 25.5–27.5 kbar and 630–645°C using the assemblage garnet rim–omphacite–rutile–phengite–lawsonite–talc–quartz (coesite), with mineral compositional data and regional considerations consistent with the upper P–T bracket. An age determination of 50.8±1.4 Ma for HP/UHP metamorphism is given by (M2) zircons that are enchased in the garnet rim and were analysed in the eclogitic matrix (Rayner et al. 2012).

Two garnet-bearing assemblages from the Puga gneiss (host to the mafi c eclogites) were utilized to constrain the subsequent decompression path for the massif at the same sample locality. A non-fractionated isochemical phase diagram for the assemblage phengite–garnet–biotite–plagioclase–quartz–granodioritic (plagioclase+quartz+K-feldspar) melt was constructed in the model system MnO–CaO–Na2O–K2O–FeO–MgO–Al2O3–SiO2–H2O (MnCNKFMASH) utilizing the DOMINO computational software and the same thermodynamic dataset as above (Holland and Powell 1998). Garnet compositional data constrains the (M3) assemblage to a restricted pressure-temperature stability fi eld centred on 12.5±0.5 kbar and 690±25°C. A second non-fractionated isochemical phase diagram calculated for the lower-pressure assemblage garnet–cordierite–sillimanite–biotite–plagioclase–quartz–granodioritic (plagioclase+quartz+K-feldspar) melt (M4) documents a narrow pressure-temperature stability fi eld ranging between 7–8.4 kbar and 705–755°C, which is consistent with independent multi-equilibria P–T determinations. Dating of monazite cores surrounded by allanite rims constrain the timing of the (M4) re-equilibration to 45.3±1.1 Ma (Rayner et al. 2012).

Coherently linking metamorphic conditions with petrographically-constrained ages at Tso Morari provides an integrated context within which previously published petrological or geochronological results can be understood. In addition, the change in path morphology from (M2) to (M4) suggests that the base of the continental crust may have acted as a transit point for eclogitized continental crust, effectively separating an initially rapid exhumation stage driven by a large density contrast between ultramafi c mantle and subducted felsic crust (buoyant exhumation; Beaumont et al. 2009), from a stage of markedly slower decompression due to a drop in buoyancy (e.g. Walsh and Hacker 2004) thus providing the required thermobarometric context for amphibolite-facies re-equilibration in both retrogressed eclogites and their host rocks.

Integrated pressure-temperature-time constraints for the Tso Morari dome (Northwest India) Part II: Implications for the burial and

exhumation path of UHP units in the western Himalaya

*Marc R. St-Onge1, Nicole Rayner1, Richard M. Palin2, Michael P. Searle2 and Dave J. Waters2

1Geological Survey of Canada, 601 Booth St., Ottawa, Ontario, Canada, K1A 0E8 2, Department of Geological Sciences, University of Oxford, Parks Road, Oxford, UK, OX1 3PR


97


REFERENCES

Beaumont, C., Jamieson, R. A., Butler, J. P., and Warren, C. J., 2009, Crustal structure: A key constraint on the mechanism of ultra-high-pressure rock exhumation. Earth and Planetary Science Letters, v. 287, pp. 116-129.

Holland, T. J. B., and Powell, R., 1998, An internally–consistent thermodynamic dataset for phases of petrological interest. Journal of Metamorphic Geology, v.16, pp. 309-344.

Powell, R., and Holland, T. J. B., 1988, An internally consistent thermodynamic dataset with uncertainties and correlations: 3. Application to geobarometry, worked examples and a

computer program. Journal of Metamorphic Geology, v. 6, pp. 173-204.

Rayner, N., St-Onge, M. R., Palin, R. M., Searle, M. P., and Waters, D.J. 2012, Integrated pressure-temperature-time constraints for the Tso Morari dome (Northwest India) Part I: In situ U-Pb geochronology of monazite and zircon. Journal of the Nepalese Geological Society, this issue.

Walsh, E. O., and Hacker, B. R., 2004, The fate of subducted continental margins: Two-stage exhumation of the high-pressure to ultrahigh-pressure Western Gneiss complex, Norway. Journal of Metamorphic Geology, v. 22, pp. 671-689.

98


The high-mountain areas of Central Asia have experienced pronounced environmental dynamics during the past decades, most likely caused by climate change. These dynamics include both permafrost retreat and the retreat of glaciers. Whilst the degree and the spatio-temporal patterns of permafrost retreat remain largely unknown due to the lack of detailed studies, glacier changes can be mapped from satellite imagery. The trends of glacial retreat in Central Asia are clear in general, but unbalanced and complex in detail (Mergili et al. 2012). Glacier and permafrost changes disturb the dynamic equilibrium of the high-mountain geomorphic systems, leading to the increased occurrence of rapid mass relocation processes (Huggel 2004). Such can constitute hazards for the population in the valleys. In contrast to small-scale "local" geohazards occurring at high frequencies, which are well-known to the communities, so-called "remote" geohazards with the source high up in the mountains and long travel distances down to the populated areas occur at low frequencies. Therefore the communities are not adequately prepared and events may lead to disasters.

The research presented concentrates on the analysis of evolving glacial and periglacial hazards in the Pamir of Tajikistan. A multi-scale approach is used, the regional-scale investigations largely build on medium-scale satellite imagery (ASTER, Landsat) and DEMs (ASTER GDEM, SRTM V4), the local-scale investigations are supported by WorldView-1 imagery and the derived DEMs.

Based on extensive multi-temporal mapping, the spatio-temporal development of potentially hazardous lakes in the forefi elds of the retreating glaciers is explored. Many of the several hundred glacial lakes in the area have newly developed or grown substantially since the late 1960s (declassifi ed Corona images are used to identify glacial lakes in this period; Fig. 1). Most of them are located between 4200 and 4900 m a.s.l., and it is observed that the emergence and growth of glacial lakes has been shifting towards more elevated catchments in the last decade. Depending on the condition of the dam, possible mass movements into the lake and lake size and evolution, glacial lakes are more or less susceptible to sudden drainage which can lead to major fl ows of debris, mud and water (Glacial Lake Outburst Floods or GLOFs). At least two signifi cant events of this

type have occurred in the Pamir since 2002, one of which was catastrophic.

Furthermore, glaciers retreating over steep rock cliffs possibly producing rock/ice avalanches are identifi ed. Particular attention is paid to areas susceptible to melting permafrost. A solar radiation model is used to determine permafrost areas under the current conditions and under projected conditions in the future. Particularly in the western Pamir, glacierized areas with steep slopes will become susceptible to melting permafrost and therefore mass movements during the next decades.

A multi-hazard regional-scale analysis framework for high-mountain geohazards, based on the Open Source Geographic Information System GRASS GIS, is developed and used. The susceptibility of glacial lakes to produce GLOFs is determined, based on an exactly defi ned scheme taking into account the characteristics of the lake and the dam, but also of the catchment of the lake (e.g. possible landslides into the lake; Fig. 2; Mergili et al. 2011). The susceptibility to rock/ice avalanches is determined in an analogous way. In a further step, the impact areas of possible lake outburst fl oods and rock/ice avalanches are delineated. For this purpose, various empirical-statistical model approaches are combined in order to come up with robust estimates (see Fig. 2; Mergili et al. 2011). The validity of the regional-scale model framework is evaluated for selected areas where high-resolution satellite imagery (mainly WorldView-1) and DEMs are available: (1) The regional-scale models are run with the high resolution datasets in order to fi gure out the infl uence of raster resolution; (2) local-scale models for the motion of mass movements are used; (3) observed events are used as reference. Based on the fi ndings from the evaluation, the parameters of the regional-scale models are adapted and the uncertainty of the results is determined.

The further development of the model framework will aim at the inclusion of datasets of populated zones and of local geohazards. The major task will be (1) to prioritize areas for mitigation measures and (2) to facilitate the identifi cation of safe places. One major challenge of these tasks will be to appropriately account for the spatial inaccuracies immanent to regional-scale models.

High-mountain geohazards in the Pamir (Tajikistan) induced by climate change

*Martin Mergili, Fabian E. Gruber, Johannes P. Mueller and Jean F. SchneiderInstitute of Applied Geology, BOKU University of Natural Resources and Life Sciences, 1190 Vienna, Austria


99


Fig. 1. Two growing glacial lakes in the Palmer.

100


REFERENCES

Huggel, C., 2004, Assessment of Glacial Hazards based on Remote Sensing and GIS Modeling. Dissertation at the University of Zurich, Schriftenreihe Physische Geographie Glaziologie und Geomorphodynamik, 88.

Mergili, M. and Schneider, J. F., 2011, Regional-scale analysis of lake outburst hazards in the southwestern Pamir, Tajikistan,

based on remote sensing and GIS, Natural Hazards and Earth System Sciences, v. 11, pp. 1447-1462, doi:10.5194/nhess-11-1447-2011

Mergili, M., Kopf, C., Müllebner, B. and Schneider, J. F., 2012, Changes of the cryosphere in the high-mountain areas of Tajikistan and Austria: a comparison, Geografi ska Annaler, Series A, v. 94(1), pp. 79-96, doi:10.1111/j.1468-0459.2011.00450.x

Fig. 2. Hazard indication map for lake outburst fl oods in the southwestern Pamir (lake outburst susceptibility and possible impact areas; glacial and non-glacial lakes are included).

101


In the central and southeastern parts of the Himalayas, the High Himalayan Crystalline (HHC) high-grade rocks are mainly exhumed in the frontal part of the range, as a consequence of a tectonic exhumation controlled by combined thrusting along the Main Central Thrust (MCT) and extension along the South Tibetan Detachment System (STDS). In the NW Himalaya, however, the hanging wall of the MCT in the frontal part of the range consists mainly of low- to medium grade metasediments, whereas most of the amphibolite facies to migmatitic paragneisses of the HHC of Zanskar are exposed in a more internal part of the orogen as a large scale dome structure referred to as the Gianbul dome. This Gianbul dome is cored by migmatitic paragneisses formed at peak conditions of 800°C and 8 kbar. This migmatitic core is symmetrically surrounded by rocks of the sillimanite, kyanite±staurolite, garnet, biotite, and chlorite mineral zones. The structural data from the Miyar-Gianbul Valley section reveal that the Gianbul dome is bounded by two major converging thrust zones, the Miyar Thrust Zone and the Zanskar Thrust Zone, which were reactivated as ductile zones of extension referred to as the Khanjar Shear Zone (KSZ) and the Zanskar Shear Zone (ZSZ) respectively. Structural and metamorphic data indicate that the Barrovian metamorphism observed in the northern limb of the dome results from the northwestward underthrusting of the HHC of Zanskar beneath the sedimentary series of the Tethyan Himalayan occurring between 35 and 28 Ma (Vance and Harris 1999; Walker et al 1999). Geochronological data across the ZSZ reveal that this extensional structure was active during early Miocene (Dèzes et al. 1999). In contrast with the tight constraints on the timing of the tectonometamorphic evolution of the NE half of the Gianbul dome, the timing of the crustal thickening and subsequent extension on the southern limb of the dome is poorly constrained. Located on the southern limb of the dome, the Miyar Valley represents a natural cross-section through the southern border of the HHCZ of Zanskar. Moving upsection along the valley, from the village of Udaipur to the Gumba glacier upstream, the metapelites of the HHCZ preserve a typical Barrovian metamorphic fi eld gradient characterized by a gradual succession of chlorite, biotite, garnet, kyanite + staurolite, sillimanite and migmatite zones (Fig. 1).

The main tectonic structure in the Miyar valley corresponds to the SW-dipping Miyar Thrust Zone. Sheath

folds testify to an intense ductile deformation in these shear zone, and a clear top-to-the-NE shear sense is indicated by sigma clasts and shear bands in the orthogneiss, as well as by sigmoidal inclusion trails in syntectonic garnet porphyroblast in the amphibolite facies paragneiss. Across the Miyar Thrust Zone, the contractional structures are superposed by SW-dipping extensional shear bands and sigma clasts indicating a top-to-the SW sense of shear along the main schistosity. These observations reveal that the Miyar Thrust Zone was reactivated as a ductile zone of extension referred to as the Khanjar Shear Zone (Steck et al. 1999; Robyr et al. 2002)

One of the major features of the tectonometamorphic evolution of the HHC in the southern limb of the Gianbul dome is that the metamorphism and tectonism in this portion of the Himalaya relates to NE-directed thrusting. In order to bring geochronological constraints on the regional metamorphism observed on the southern limb of the dome, the prograde sequence of allanite and monazite has been investigated in detail.

Along the Miyar Valley section, allanite appears to be the LREE-stable accessory phase at greenschist facies conditions. Its fi rst occurrence coincides with the stability fi eld of biotite suggesting a temperature of 430–450 °C for its growth. Moving upsection, the fi rst metamorphic monazite forms at amphibolite facies conditions at the staurolite- in isograd. At these P-T conditions, allanite is preserved only as inclusion in garnet and staurolite porphyroblasts indicating that allanite is replaced by monazite at ca.610-640°C. In situ LA-ICPMS U-Th-Pb dating of the fi rst metamorphic monazite occurring within the upper structural level of the staurolite-kyanite zone gives ages ranging between 42 and 37 Ma. These data indicate that the upper structural level of the staurolite-kyanite zone realized temperature conditions of 610-640°C during the middle Eocene. In contrast dating of monazites collected in the lower structural level of the staurolite-kyanite as well as in the structurally lower sillimanite zone provides ages ranging from 27-30 Ma. Coexisting allanite and monazite preserved in garnet porphyroblasts of the sillimanite zone give ages between 35 and 39 Ma for the allanites and between 29 and 30 Ma for the monazites. These data reveal a leap of about ten million years between monazite growth across the Miyar shear zone indicating that the Miyar thrust

Timing of prograde metamorphism in the High Himalaya of NW Lahul (NW India)

*Martin Robyr1, Sriparna Banerjee1 and Afi fé El Korh1

Institut für Geologie, Universität Bern, Baltzerstrasse 1+3, CH-3012 Bern, Switzerland(*Email: [email protected])

102


zone was active between 40 and 30 Ma. Furthermore these new data constrains the time elapsed between of 430–450°C and 610-640°C which implies an average heating rate of ca 25 °C/m.y. Combined with geochronological data from the migmatite zone (monazite, 26 Ma; Robyr et al. 2006) and from undeformed leucogranitic dykes in the centre of the dome, (monazite, 22-19 Ma; Robyr et al. 2006) the new data provided by this study allow the entire reconstruction of the tectonometamorphic evolution of the Gianbul dome.

REFERENCES

Dèzes, P., Vannay, J.-C., Steck, A., Bussy, F. and Cosca, M., 1999, Synorogenic extension: quantitative constraints on the age and displacement of the Zanskar Shear Zone (NW Himalayas), Geol. Soc. Am. Bull., v. 111, pp. 364-374.

Robyr, M., Vannay, J. C., Epard, J.-L. and Steck, A., 2002, Thrusting, extension and doming during the polyphase tectonometamorphic evolution of the High Himalayan Crystalline Sequence in NW India. Journal of Asian Earth Sciences, v. 21, pp. 221-239.

Robyr, M., Hacker, B. R. and Mattinson, J., 2006, Doming in compressional orogenic settings: New geochronological constraints from the NW Himalaya. Tectonics, v. 25, TC2007, doi:10.1029/2004TC001774

Steck, A., Epard, J.-L. and Robyr, M., 1999, The NE-directed Shikar Beh Nappe - a major structure of the Higher Himalaya. Eclogae Geologicae Helvetiae, v. 92, pp. 239-250.

Vance, D. and Harris, N., 1999, Timing of prograde metamorphism in the Zanskar Himalaya. Geology, v. 27, pp. 395-398.

Walker, J. D., Martin, M. W., Bowring, S. A., Searle, M. P., Waters, D. J. and Hodges, K. V. (1999), Metamorphism, melting, and extension : age constraints from the High Himalayan Slab of southeast Zanskar and northwest Lahul, J. Geol., v. 107, pp. 473-495.

Fig. 1: Cross section along the Miyar Valley on the southern limb of the Gianbul dome showing the sequence of mineral isograds and weighted mean Th-Pb ages for monazite and allanite.

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The Global Geopark Network supported by UNESCO intends not only to highlight beautiful examples of geoscientifi c exposures, but also to utilize them for the welfare of local people. The Himalaya extends mostly over low-income countries and thus the attempt to form the geopark program is considered suitable for Nepal. After having conducted geotours and forming geoguidebook series in the Himalaya since 2004 (Yoshida et al. 2011; Yoshida et al. 2012a), we realized that it will be better to started a project of forming geoparks in the Nepal Himalaya including the Everest, Lang Tang valley, and Kaligandaki areas (Fig. 1).

The fi rst trial is identifi ed to be done for the Kaligandaki valley in west-central Nepal, which, among others, is considered most suitable for the global geopark in Nepal (Yoshida et al. 2012b).

The Kaligandaki valley is the deepest valley in the world, cutting across the main Himalayan range between two 8000 m peaks of Annapuna and Dhaulagiri. The valley crosses all major three geologic zones, the Tethys Himalayan, Higher Himalayan, and Lesser Himalayan zones from the north to the south. Eleven geosites along the trekking course in the middle-upper reaches of the valley from Tatopani to Muktinath have been identifi ed (Figs. 1, 2). They include beautiful and interesting geological outcrops and topographic sceneries, as well as natural hazards (Upreti and Yoshida, 2005). Further, the area provides the Tamang cultural and ethnic characteristics. In the presentation, highlights of these geosites from all the above areas are introduced along with a series of geoguidebooks from the area (Upreti and Yoshida 2005; Yoshida et al. 2009; 2011; 2012b).

Forming global geoparks in the Nepal Himalaya

*Masaru Yoshida1, Khem Raj Nepal2 and Bishal Nath Upreti3

1Gondwana Institute for Geology and Environment, Hashimoto, Japan 2Dilibazar Height Marg, Kathmandu, Nepal

3Department of Geology, Tri-Chandra Campus, Tribhuvan University, Kathmandu, (*Email: [email protected])

Fig. 1: Geologic outline and schematic cross-section of the Nepal Himalaya (modifi ed after Upreti and Le Fort 1999).

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REFERENCES

Upreti, B.N. and Yoshida, M. (eds), 2005, Geology and Natural Hazards along the Kaliganaki Valley, Nepal, Guidebook for Himalayan Trekkers Ser. 1, Department of Geology, Tri-Chandra Campus, Tribhuvan University, Kathmandu, 165 pages.

Upreti, B.N. and Le Fort, P. 1999. Lesser Himalayan Crystalline Nappes of Nepal: Problems of their origin. Geol. Soc. Am. Bulletin, Special Issue. No.328, pp. 225-238.

Yoshida, M., Upreti, B.N., Rai, S.M.., 2011, Himalayan Guidebooks for Eco-trekking -Observing Geology and Nature in the Field-.

GRG/GIGE Miscl. Pub. 24 (E-book), 25 pages. Field Science Publishers, Hashimoto, Distributed by Amazon Kindle Self Publishing Co.

Yoshida, M. Upreti, B.N., Rai, S.M.., 2012a, Geotours and Geoguidebooks of the Himalaya. In: Yoshida, M. et al. (Eds), Geotours, Geoparks and Earth Science Olympiad: Enjoy Earth Sciences! (in Japanese). E-book, in preparation, Geological Society of Japan, pp. 41-76.

Yoshida, M.,Nepal, K.R., Upreti, B.N., 2012b, The project of proposing a global geopark in the Nepal Himalaya. In: Yoshida, M. et al. (Eds), Geotours, Geoparks and Geo-Olympic: Enjoy Earth Sciences! (in Japanese). E-book, in preparation, Geological Society of Japan, pp. 173-194.

Fig. 2: Geological outline of the Kaligandaki valley area showing the proposed geosites (red circle with GS numbers) and geopark area (delineated with white dashed line).

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Numerical Simulation is a powerful tool to analyze the deep crustal processes and can provide an insight into the deformation of the basement. Direct observations and geophysical observations only are not suffi cient to analyze the deep crustal processes. Many numerical methods like fi nite element, fi nite difference and potential fi eld etc are popular in Earth Science. The Himalaya and Tibet provide an ample opportunity to examine the complex deformation process in the compressive stress regime.

This paper is an attempt to analyze the state of stress and deep crustal process and their relation to this orogenic system. Many interesting fi ndings were obtained during the INDEPTH geophysical surveys but the results of these surveys were not suffi cient to explore the deep crustal relations among the Himalayan Mega Thrust, crustal ramp and mid crustal melt. In this study, 2-D fi nite element method is used to analyze the state of stress and deep crustal process and their relation on the stress fi eld and velocity vector. Elasto-plastic, plane strain model constrained by the northward convergent displacement boundary condition is used to simulate the stress fi led. Young’s modulus, density, Poisson’s ratio, yield strength and strain hardening are used to constrain the material properties of different layers. General values for these parameters are selected from the available published literature and best fi t values from previous studies. Modelling result reveal that thrust/fault geometry, their deep crustal relations and how do they terminate has effect on the stress fi eld and displacement vector and exhumation. The lateral variation of the stress orientation and surface exposure of fault/thrust and lithologic units may be the expression of the deep crustal relations between the major structure their geometry and how do they terminate at the depth. So the along strike variation in the Himalaya may be the manifestation of structural geometry and their deep

crustal relationships.

In general the Himalaya is in a compressive state of stress. The magnitude of the stress and orientation depend on the layer properties. Tensional stress fi eld is obtained just above the Main Central Thrust (MCT) duplex structure in the Tethys Sediments and in the frontal part of the Himalaya in the Indogangetic Sediments, Main Frontal Thrust (MFT), Siwaliks and Main Boundary Thrust (MBT). The tensional stress concentration shows normal fault also co-exists with the southward propagating thrust fault. The modeling results show that Sync-orogenic extensional features are the characteristic feature in the region of general regional shortening and crustal thickening. Their distribution depends on the rheology, structures and structural geometry. Probably these sync-orogenic extensional structures are decoupled from the underlying system dominated by convergence as the extensional stresses are observed only on the surface. The South Tibetan Detachemnt (STD) may be initiated as thrust faults as the tensional stress are only observed at the surface of the fault. Modelling results reveal that stronger physical properties for the mafi c lower crust and Indian crust and weaker physical properties for the partially molten middle crust can produce the reasonable stress fi eld in the Himalaya and southern Tibet provided general physical properties are used for the other layers and fault zones. Modeling results reveal that formation of the Higher Himalayan dome is enhanced by the partially molten middle crust. Probably, the fl atness of the Tibetan Plateau is also related to the mid crustal partially molten melt. The concentration of the high shear stress in front of the Main Himalayan Thrust (MHT) decollement is responsible for the deformation in the Himalayan front and the partially molten melt below the southern Tibet is responsible for the formation of the rift system in the Tibetan Plateau.

Elasto-plastic fi nite element modeling along the Project INDEPTH profi le: Implication for the Himalayan tectonics

*Matrika Prasad Koirala1 and Daigoro Hayashi 2

1Department of Electricity Development, Ministry of Energy, Government of Nepal, 576 Bhakti Thapa Sadak (4), Kathmandu, Nepal

2Simulation Tectonics Laboratory, Faculty of Science, University of the Ryukyus, Okinawa, 903-0213, Japan(*Email: [email protected])

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Conventionally it is believed that the Main Frontal Thrust (MFT) and Main Boundary Thrust (MBT) continue throughout the Himalaya as two sub-parallel faults. However, detailed fi led studies, analysis of satellite imageries, and investigation of SRTM data clearly indicate that the situation is more complicated. The imbricate frontal faults in the Nepal Himalaya are generally sub-parallel, they trend NW–SE, and extend for tens of kilometres. Each fault in this fault swarm terminates in either a fold or another fault. In the latter case, the fault towards the foreland terminates frequently at the fault extending from the hinterland.

The Lesser Himalayan and Siwalik rocks constitute imbricate slices and duplexes. Consequently, there are outliers of the Lesser Himalayan rocks in the Siwaliks of east Nepal in the vicinity of the Marin Khola, Katari, Bagpati, and

Kampughat. Hence, the defi nition that the MBT separates the Lesser Himalayan and Siwalik rocks becomes invalid. A closer look at the Siwaliks reveals that there are a number of independent and discontinuous faults at the foreland front. They too cannot be classifi ed as a single fault. Generally, about 20 to 30 km long tight folds extend from the fault tips, and there are extensive areas where the Siwalik rocks are overturned. There are also a number of backthrusts in the Siwaliks as well as in the Lesser Himalaya.

An active fault runs very close to the “MBT” between the Mahakali River and Budar as well as in the area between Surkhet and Dang. Steeply inclined recent gravel beds are observed in the Siwaliks of the Mahakali area in far-west Nepal and near Barphalyang in the Ilam district of east Nepal. Such features clearly indicate that the entire frontal fault system is tectonically active.

Distribution of frontal faults in Nepal Himalaya

Megh Raj DhitalCentral Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal


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After the complete closure of the Iapetus Ocean during Late Silurian times (Caledonian orogeny) the continents of Baltica, Avalonia, and Laurentia formed the continent of Laurussia. The Caledonian orogeny and collision of Gondwana and Laurentia was related to the formation of the large Early Devonian supercontinent Oldredia (Golonka et al. 2006). The Early Devonian transgression occupied peri-Gondwanan regions and most probably has been connected with initial rifting of the selected terranes from Gondwana (e.g. Sibumasu) and origin of the Paleotethys Ocean which expanded during Carboniferous times. The collision of the North China plate and closure of Solonker Ocean during Permian times concluded the orogenic process. From the paleobiogeographical point of view (brachiopods, foraminifera, corals, cephalopods etc.) several terranes have been separated in this time from Gondwana and belonged to cold/temperate/cool-water and/or warm-water of Cimmerian (Transitional)/Marginal Cathaysian biogeographical provinces, especially of the eastern part of the Cimmeria-Qiangtang, Tengchong, Baoschan, Sibumasu (Shan-Thai) terranes, and Indochina block including Vietnam (Metcalfe 2002; Golonka et al. 2006; Ueno 2006 with literature therein) which were separated from Gondwana by young Neotethys Ocean. On the other hand the Permian paleogeography of East and Northeast Asia is still matter of discussion. The latest Permian and earliest Triassic quick rifting of this ocean and drifting of several Gondwana-derived blocks caused strong Indosinian orogeny during Triassic times. This orogeny was the result collision of Indochina with both Sibumasu and South China blocks, which closed part of the Paleotethys Ocean. The time of new break-up of northernmost part of the Gondwanan Pangea is controversial and still enigmatic (Ueno 2006). An especially relationship between Qiangtang and Lhasa blocks in space and time causes a lot of controversies. This break-up most probably took place during earliest Jurassic times, indicated especially by separation of the Lhasa Block from Gondwana. This block very quickly drifted northwards. Paleogeographical

position of the Lhasa Block during Mesozoic times is hardly disputable. Separation of the Cimmerian Continent [Iran (Alborz)-Qiangtang-Malaysia-Sibumasu] from this part of Pangea during latest Carboniferous–earliest Permian times by rifting and drifting event originated Neothethyan Ocean and therefore the Lhasa Block belonged to the southern margin of this new ocean. Northwards migration of the Cimmerian Continent took place during Permian-Triassic times causing wide opening of the Neotethys and closing of the Paleotethys Ocean. The Late Triassic Indosinian Orogeny has been one of the most spectacular geotectonic event refl ect collision of this continent (mainly Sibumasu part) with Indochina block. The world-wide distribution of Pliensbachian-Early Toarcian large bivalves of the so-called Lithiotis-facies (dominated by Lithiotis, Cochlearites, Litioperna genus) indicates very rapid expansion of such type of bivalves. Himalayan (Nepal-Garzanti and Frette, 1991) and Tibetan (Nyalam area –Yin Jiarun and Wan Xiaoqiao 1998) occurrences of Lithiotis and/or Cochlearites bivalves could help to reconstruct of Early Jurassic position of the Lhasa Block. Occurrence of Lithiotis-type bivalves from southern Europe (Spain, Italy, Croatia, Slovenia, Greece, Albania and Romania where these type of bivalves have been recently discovered-Lazar et al., in preparation), westernmost Asia/Arabia (eastern Turkey, Iran, Iraq, Kuwait, Oman) to central Asia in this time suggested migration path from western Tethys trough Panthalassa Ocean up to western margin of North and South America (USA, Peru). These bivalves during larval-stage episodes could use the numerous terranes within Panthalassa Ocean as „stepping-stones” allowing free migration eastward from the Alpine Tethyan Ocean to Himalayan/Tibetan one. The later history of geotectonic movements of the Lhasa Block towards the Asia continent took place during the Early Cretaceous time up to the Paleogene docking. By this event the geotectonic reconfi guration of the Neotethys during Early Cretaceous produced wider opening of this Ocean with full connection with Panthalassa Ocean.

Late Paleozoic and Mesozoic evolution of the Peri-Gondwanan plates and paleobiogeographical evidences of the Early Jurassic position of the

Lhasa Block

Michal Krobicki1,2, Jan Golonka2 and *Iuliana Lazar3

1Upper Silesian Branch, Polish Geological Institute – National Research Institute; 41-200 Sosnowiec, Krolowej Jadwigi 1; Poland

2Department of General Geology and Geotourism, AGH University of Science & Technology; 30-059 Krakow, Mickiewicza 30; Poland

3Department of Geology, University of Bucharest, 010041 Bucharest, 1-N. Balcescu, Romania (*Email: [email protected])

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REFERENCES

Garzanti, E. and Pagni, F. M., 1991. Stratigraphic succession of the Thakkhola region (Central Nepal) – comparison with the northwestern Tethys Himalaya, Rivista Italiana di Paleontologia e Stratigrafi a, v. 97, pp. 3-26.

Golonka, J., Krobicki, M., Pająk, J, Nguyen Van Giang and Zuchiewicz, W., 2006. Global plate tectonics and paleogeography of Southeast Asia. Faculty of Geology, Geophysics and Environmental Protection, AGH University of Science and Technology; Arkadia, pp. 1-128.

Metcalfe, I., 2002. Permian tectonic framework and palaeogeography of SE Asia. Journal of Asian Earth Sciences, v. 20, pp. 551-566.

Ueno, K., 2006. The Permian antitropical fusulinoidean genus Monodiexodina: distribution, taxonomy, paleobiogeography and paleoecology. Journal of Asian Earth Sciences, v. 26, pp. 380-404.

Yin, J. and Wan, X., 1998. Discovery of Early Jurassic Lithiotis (Bivalvia) bioherm in Tethyan-Himalaya and its migration. Acta Palaeontologica Sinica, v. 37, pp. 253-256.

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The India-Asia collision resulted in crustal thickening and shortening, metamorphism and partial melting along the 2200 km long Himalayan range. In the core of the Greater Himalaya widespread in situ partial melting in sillimanite + K-feldspar gneisses resulted in formation of migmatites and Ms+Bt+Grt+Tur±Crd±Sil±And leucogranites, mainly by muscovite dehydration melting. Initial melting occurred in the kyanite stability fi eld (c.10-12 kbars) forming Late Eocene-Oligocene kyanite-bearing leucogranites (e.g. Annapurnas), but the bulk of melting occurred at shallow depths (4-6 kbar; 15-20 km depth) in the middle crust, but not in the lower crust during the Miocene resulting in sillimanite, andalusite or cordierite-bearing leucogranites (e.g. Everest, Makalu, Langtang). The channel fl ow hypothesis for the Greater Himalayan Sequence (Searle et al. 2006; 2010) fi ts all known geological and geophysical parameters (Fig. 1). 87Sr/86Sr ratios of leucogranites are very high (0.74-0.79) and heterogeneous, indicating a 100% crustal protolith. Melts were sourced from fertile muscovite-bearing pelites and quartzo-feldspathic gneisses of the Neo-Proterozoic Haimanta-Cheka Formations. Melting was induced through a combination of thermal

relaxation due to crustal thickening and from high internal heat production rates within the Proterozoic source rocks in the middle crust. Himalayan granites have highly radiogenic Pb isotopes and extremely high uranium concentrations. Little or no heat was derived either from the mantle or from shear heating along thrust faults. Mid-crustal melting triggered southward ductile extrusion (channel fl ow) of a mid-crustal layer bounded by a crustal-scale thrust fault and shear zone (Main Central Thrust; MCT) along the base, and a low-angle ductile shear zone and normal fault (South Tibetan Detachment; STD) along the top. Multi-system thermochronology (U-Pb, Sm-Nd, 40Ar-39Ar and fi ssion track dating) show that partial melting triggered mid-crustal fl ow between the simultaneously active shear zones of the MCT and STD. Melts were channeled up via hydraulic fracturing into sheeted sill complexes from the underthrust Indian plate source beneath southern Tibet, and intruded for up to 100 km parallel to the foliation in the host sillimanite gneisses (e.g. Everest-Rongbuk profi le). Crystallization of the leucogranites was immediately followed by rapid exhumation, cooling and enhanced erosion during the Early-Middle Miocene.

Crustal melt granites and migmatites along the Nepal Himalaya: Implications for channel fl ow

*Mike Searle1, John Cottle2, Micah Jessup3, Mike Streule4, Rick Law5 and Dave Waters1

1Department of Earth Sciences, Oxford University, South Parks Road, Oxford, OX13AN, UK. 2Department of Earth Science, University of California, Santa Barbara, CA 93106-9630, USA.

3Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, USA.4Department of Geology, Royal School of Mines, Imperial College, London, UK.

5Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA.(*Email: [email protected])

110


REFERENCES

Searle, M. P., Law, R. D., and Jessup, M. J., 2006. Crustal structure, restoration and evolution of the Greater Himalaya in Nepal-South Tibet: implications for channel fl ow and ductile extrusion of the middle crust. In: Law, R.D., Searle, M.P. & Godin, L. (Eds) Channel Flow, Ductile Extrusion

and Exhumation in Continental collision zones. Geological Society, London, Special Publication, v. 268, pp. 355-378.

Searle, M. P., Cottle, J. M., Streule, M. J. and Waters, D. J., 2010. Crustal melt granites and migmatites along the Himalaya: melt source, segregation, transport and granite emplacement mechanisms. Transactions of the Royal Society of Edinburgh, v. 100, pp. 219-233. Doi:10.1017/S175569100901617X

Fig. 1: Himalayan Channel Flow model for the Everest – Rongbuk profi le, after Searle et al. (2006, 2010). Inset photos (top left) shows the STD profi le at Dzacha chu, north of Everest, in South Tibet. Inset (lower right) shows central part of the channel in the Kangshung valley, east of Everest, in South Tibet. Giant blocks or rafters of gneisses with early leucogranite sills are completely enclosed in Miocene leucogranites.

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The 7.6 magnitude earthquake of 8 October 2005 in the Muzaffarabad area and then 3.8 magnitude Sheikhupura earthquake of 08 August 2010 in NW Himalaya (Fig. 1) caused severe destruction in Kashmir, Punjab and neighboring region of Pakistan. The October 08, 2005 earthquake, worst ever natural disaster in Pakistan, claimed more than 80,000 lives, clearly exposing the poor standards of building construction-a major challenge facing the earthquake-prone developing nations that also happen to be thickly populated. In this paper, we examine variations in the stress fi eld, seismicity patterns, seismic source character, tectonic setting, plate motion velocities, and the geodynamic factors relating to the geometry of the underlying subsurface structure and its role in generation of very large earthquakes. Focal mechanism solutions of the Muzaffarabad earthquake and its aftershocks are found to have steep dip angles that are comparable to the Indian intra-plate shield earthquakes rather than the typical Himalayan earthquakes that are characterized by shallow angle northward dips.

Inversion of focal mechanisms of the Harvard CMT catalogue indicates distinct stress patterns in the Muzaffarabad region, seemingly governed by an overturned

Himalayan thrust belt confi guration that envelops this region, adjoined by the Pamir and Hindukush regions. Recent developments in application of seismological tools, like the receiver function technique have enabled accurate mapping of the dipping trends of the Moho and Lithosphere-Asthenosphere Boundary (LAB) of the Indian lithosphere beneath southern Tibet. These have signifi cantly improved our understanding of the collision process, the mechanism of Himalayan orogeny and uplift of the Tibetan plateau, besides providing vital constraints on the earthquake-related hazard threats posed by the Himalayan seismicity. New ideas have also emerged through macroseismic investigations, seismic hazard assessment. While many researchers suggest that the Himalayan front is already overdue for several 8.0 magnitude earthquakes, some opine that most of the front may not really be capable of sustaining the stress accumulation required for generation of great earthquakes. We propose that the occurrence of great earthquakes like those of 1897 in Shillong and 1950 in Assam have a strong correlation with their proximity to multiple plate junctions conducive for enormous stress build up, like the eastern Himalayan syntaxis comprising the junction of the Indian and Eurasian plates, and the Burma and Sunda micro-plates.

The Muzaffarabad earthquake of 8 October and the 8 August 2012 Sheikhupura earthquake: New insights into Himalayan seismicity and

tectonics

*Monalisa1 and M. Qasim Jan2

1Department of Meteorology, COMSATS Institute of Information Technology (CIIT), Islamabad, Pakistan 2National Center of Excellence in Geology (NCEG), University of Peshawar, Peshawar, Pakistan


112


Fig. 1: Regional tectonic setting of the area showing the location of major earthquakes (M ≥ 5.0) in and around Pakistan, including the Sheikhupura Earthquake (modifi ed from United States Geological Survey web site).

113


Kathmandu Basin-fi ll sediments refl ect fl uvial, lacustrine, lacustrine delta and fl uvial deposits. Among these sediments fl uvial depositional environment was dominated prior to the open lacustrine and after and during the draining stage of the ancient lake. These sediments are distributed within the Tarebhir and Lukundol formation in the southern part of the basin. Fluvio-deltic sediments mainly deposited at the north and east of the basin. These sediments are distributed within the Gokarna and Thimi formations. Lacustrine deltaic sediments were started deposits during the shallow water stage of an ancient lake from southern part of the basin. Sediments of the Sunakothi formation show lacustrine deltaic sediments. Fluvial gravel deposits known as the Terrace gravel (Paudel and Sakai 2009) cover at the top of all these stratigraphic units, which is thicker at the southern margin and gradually thinning toward the center of the basin (Paudel and Sakai 2005; 2008). Fluviolacustrine depositional cycle within the basin-fi ll sediments expressing partial to complete cyclothems within the Sunakothi formation. Nearly all the cycle within the formation initiate with sand that grade to interbedded sand and mud to gray green silty mud and fi nally to gray mud. These patterns of sediments indicate numerous cycles of lake shore facies that grade to central lacustrine facies. These facies change within the Sunakothi formation show ancient lake expansion and contraction during the deposition period of the Sunakothi formation.

On the basis of the facies analysis, Sunakothi formation is divided into the following fi ve facies associations: (a) facies association A: it is composed by muddy rhythmites and silt and laminated to ripple sand bed of the prodeltaic origin (b) Facies association B: it is composed by the cross-stratifi cation, ripple-drift and parallel lamination of the lacustrine delta front like origin (c) facies association C: it is characterized by muddy fl ood-plain and alteration of the fi ne and coarse sediments, which indicates delta-plain like origin (d) facies association D: it is characterized by sandy to silty rhythmites of the marginal shallow lacustrine origin above the delta-plain (e) fl uvial association E: thick gravel deposits of the gravelly braided river origin interbedded former three associations. It indicates that the transition from lacustrine to alluvial environment is characterized by fl uvial

and lacustrine deltaic system in the south. Sedimentological study of the Sunakothi Formation shows these sediments were deposited during rapid lake level rise and fell, indicated by thick fl uvial channel gravel beds within the sandy and muddy sequence. Climatic and basin margin tectonics play key role for lake level change during this period. On the basis of this study, sediments of the Sunakothi formation are the southern counterparts of the deltic Thimi-Gokarna formations distributed in the northern part of the basin.

On the basis of sedimentological study and fi eld survey, Kathmandu basin is evolved by following different phases during different past geological time:

Phase of paleoriver valley development prior to the lacustrine stage: It was occurred before early Pleistocene. Thick fl uvial gravel beds underlie the lacustrine sequence indicate this phase of deposition.

Phase of limnologic development: During the Early to middle Pleistocene pre-existing fl uvial system was blocked by debris from south-east and formed lacustrine body of water that inundated the preexisting fl uvial system. Initially lacustrine body was relatively small and extremely shallow, being concentrated on the southern margin of the basin. Marshes and swamp were formed in nondraining area.

Phase of lacustrine completion: During the late Pleistocene, lacustrine water deepened as the surface area expanded.

Phase of lacustrine deterioration: Since around 45000 year before present, lake water started to drain. Draining stage started from the southern part of the basin. Gradual decline of water level occurred and sedimentation at the center of the basin was gradually replaced by fl uviatile regime. Development of the fl uvial system occurred upon the fl oor of the original lake bed

REFERENCES

Paudel, M. R. and Sakai, H., 2009, Stratigraphy and depositional environment of late Pleistocene Sunakothi formation in Kathmandu Basin, central Nepal, jour, of Nepal Geo. Soc, v. 39. pp 33-44.

Evolution and depositional characteristics of the Late Quaternary Kathmandu basin

Mukunda Raj PaudelDepartment of Geology, Tribhuvan University, Trichandra campus, Ghantaghar, Kathmandu, Nepal


114


Paudel, M. R. and Sakai, H., 2008, Stratigraphy and depositional environment of the basin-fi ll sediments in the southern marginal part of the Kathmandu Valley, central Nepal, Bulletin of the central Department of Geology, Tribhuvan University, Kathmandu, Nepal, v. 11, pp. 61-70

Paudel, M. R. and Sakai, H., 2005, Depositional environment and Stratigraphic position of the Sunakothi Formation, in the southern part of the Kathmandu Valley, Central Nepal. The 112th annual meeting of the Geological society of Japan, Kyoto, Japan, pp. 339.

115


Hydropower has become an important part of energy sources in Nepal. Study of the Himalayan geology and investigation in the intervening rock mass is very much important for the development of hydropower projects in this region. Upper Trishuli-1 Hydropower Project is situated in the upper reaches of Lesser Himalaya in central Nepal. The project is one of the large scale hydro-project with installed capacity of 216 MW in the Lesser Himalayan Crystalline in upper catchment of the Trishuli river basin. The Lesser Himalayan sequence can be divided into seven units namely Kunchha Formation, Ronga Carbonates, Brabal Schist, Syabrubesi Schist, Wangal Quartzite, Syabru Gneiss and Schist and Phenglung Khola Quartzite. In the area normally exposes metamorphic rocks in a wide range and all the project structures aligned on the rock sequence of gneiss and schist. However, the area is very close to the regional thrust, Main Central Thrust (MCT) that runs about 7 km north from the project site. Few local geological structures such as shear zones, small faults and folds can be observed within the project area. The rock types distributed throughout the project area are of mainly two type, quartzitic-schist and gneiss. The quartzite is highly foliated and gneiss is blocky to massive in nature.

The project site has been investigated by surface as well as subsurface investigation methods. The surface investigation comprises regional geological and tectonic mapping as well as engineering geological survey and mapping of the project structure sites. The subsurface investigation comprises 2D Electrical Resistivity Tomography (ERT) survey, exploratory core drilling, in-situ geotechnical testing, laboratory testing in rock core samples and geological drifting. A site of the hydropower project requires a robust understanding of the geological conditions for the optimum design of major engineering facilities. Deterministic geological framework has been addressed on three aspects; rock domains, fracture zones and fracture domains. The identifi cation and description of fracture domains has also provided a basis for the statistical properties of fractures and minor fracture zones. Based on the surface geological investigation, the targets of further investigation for the major facility area (headworks, headrace tunnel, surge tank and powerhouse and tailrace etc.) are established. In total 860 m exploratory core drilling and 11.5 km 2D ERT survey have been carried out to investigate the subsurface condition of the rock and overburden materials in the project area. As a result, the rock mass was found to be fair to good quality.

Engineering geological investigation for hydropower development in the Himalaya: A case study on Upper Trishuli-1 Hydropower Project

*Narayangopal Ghimire1 and Lalu P. Paudel2 and Sangbae Lee3

1Jade Consult, Kathmandu, Nepal 2Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal

3RockInfo Co. Ltd, Busan, South Korea(*Email: [email protected])

116


Ring shear machines are in use for a long time particularly to evaluate residual strength of clayey materials that undergo large deformations or displacements, such as in case of landslides and debris or mud fl ows. As such, residual strength of a clayey material is also often measured in reversal box shear test, but except for a few stress distribution-related shortcomings, the material in a ring shear machine can be sheared for an infi nite amount of deformation to yield a true value of residual internal friction. Previous ring shear tests reveal that the residual strength of a clayey soil is achieved after 5-100 cm of horizontal shear displacement depending on the size of specimen and soil composition in terms of

clay mineralogy. Landslide material in the Himalaya was fi rst tested by Skempton (1964), and he found that the fi eld residual value of the tested landslide material was more or less the same as measured in the laboratory. In this study, we collected some 16 clay samples from different landslide sites along Prithvi Highway, and Narayanghat-Mugling Highway in the mid Nepal Himalaya (Figure 1), and tested them all in a ring shear machine of 8-cm internal diameter, 12-cm external diameter, and 2-cm thick specimen size and about 0.1mm/min of shear rate. At the same time, all collected samples were also evaluated for mineralogical composition in an X-ray diffractometer.

Ring shear strength and mineralogical perspective on large-scale landslides on the mid-Nepal Himalaya

*Netra P. Bhandary1, Ryuichi Yatabe2, Ranjan K. Dahal3, Shuichi Hasegawa4 and Manita Timilsina5

1Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan,2Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan

3Department of Geology, Tri-Chandra Campus, Tribhuvan University, Kathmandu, Nepal3Faculty of Engineering, Kagawa University, Takamatsu, Japan

4Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan(*Email: [email protected])

Fig.1: Location map of the investigation area (Highway sections) and sampling locations

117


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dual

fric

tion

r (de

gree

s)

Range for peak angle ofinternal friction

Range for residual angle ofinternal friction

Fig. 2: Range of peak and residual angles of internal friction for the collected samples

10

15

20

25

30

35

40

0 5 10 15 20 25 30Clay fraction (< 2m), F c (%)

Angl

es o

f int

erna

l fric

tion,

d, r

(deg

rees

)

φd (degree)

φr (degree)

Fig. 3: Variation in angles of internal friction with the amount of clay fraction (<2m)

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As a result of the ring shear and X-ray diffraction tests, we found that the clay mineralization is mostly limited to mica formation (including hydrous mica, i.e., illite) with occasional identifi cation of chlorites, mostly in phyllitic, slate, and shale zones, where the landslide material is found to have an angle of residual internal friction from 20 to 27 degrees (Figure 2 to Figure 4). Except for a couple of locations, where excessive chlorite was found, most landslide sites were found to have greater infl uence of mica formation. From these laboratory evaluations, it is inferred that most landslides of creeping nature in the mid Nepal

Himalaya have 20 to 27 degrees of average slope. Moreover, smectization (i.e., transformation of chlorite and mica-like minerals into smectites) in this part of the Himalaya, unlike most tectonically active areas, is not prevalent, probably because landmass erosion in terms of landslides and slope failures takes place much before the slip surface mineralogy could be converted into smectite-rich composition.

REFERENCE

Skempton, A. W., 1964, Long term stability of clay slopes, In: Geotechnique, v. 14(2), pp. 77-102.

0

10

20

30

40

0 10 20 30 40

Peak intensity ratio {(Ch+Mi)/(Qz+Fel)}

Angl

e of

pea

k/re

sidu

al fr

ictio

n

Angle of peak friction, φdAngle of residual friction, φr

Fig. 4: Variation of internal friction angle with peak intensity ratio of (chlorite+micas) to (quartz+feldspar)

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The Pamir, as the Tibetan Plateau, experienced multiple subduction and accretion cycles during the Paleozoic to Cenozoic, leading to the formation of extremely thickened crust (up to 70 km). For Tibet, several magmatic episodes with distinct compositions have been observed and described. For the Pamir, where magmatic rocks are also abundant, no systematic investigation exists. This study addresses this issue and relates the Tibetan magmatism to that of the Pamir; we investigate the relationships between both orogens as well as similarities in respect to timing, composition, petrogenesis, and geodynamic setting of their magmatism.

Magmatic rocks in the Pamir comprise a wide range of age, spatial distribution, and geochemical composition. The studied samples from the southern and central Pamir cover ages from Cretaceous to Miocene, and are predominantly plutonic (granite to diorite and rare gabbro) and to a lesser extent volcanic. Zircon U-Pb dating revealed that Cretaceous magmatism occurred in two time intervals with peaks at about 102-110 Ma and 67-77 Ma, producing peraluminous (A/CNK: 1.0-1.5), (high-K calc-alkaline diorites, granodiorites and granites. Both Cretaceous magmatic episodes can be traced along the rim of the Shakhdara dome in the southern Pamir and in the western part of the central Pamir. Based on their major and trace elemental composition, there is no signifi cant difference between both age clusters. However, their isotope geochemistry shows a clear distinction. The older Cretaceous sequence features initial εNd values that range from -8.5 to -11.0, corresponding to εNd model ages based on a depleted mantle evolution of 1.3-2.0 Ga. The initial 87Sr/86Sr values are within the range of 0.7099-0.7116. In contrast, the Late Cretaceous sequence features higher initial εNd values from -4.6 to -6.5, with corresponding Nd model ages of 1.2-1.3 Ga. Their initial 87Sr/86Sr values are within the range of 0.7080-0.7097. A general feature of all the granitoid samples is the pronounced negative Nb-Ta-Ti anomaly in a multi trace element variation diagram, expressed by Nb/La ratios of 0.17 to 0.57 and 0.11 to 0.26, for the younger and older suites, respectively.

From the data currently available, it appears that the main episode of Cenozoic magmatism occurred at 14-25 Ma, spatially distributed over the central and southern

Pamir. Four older samples (28-46 Ma) are randomly distributed in the same regions and the two youngest samples (11 Ma) are found in the Dunkeldik region of the easternmost central Pamir. The Cenozoic rocks comprise granodiorite, granite, and leucogranite that are slightly peraluminous to metaluminous (A/CNK: 0.95-1.07), high-K calc-alkaline. They have initial εNd values of -6.4 to -8.3, with the exception of one early Oligocene granodiorite (33 Ma) with an initial εNd value of -2.6. In the Early Miocene, bimodal magmatism was active. The erupted alkali-basalts show slightly negative Nb-Ta-Ti and Eu anomalies, have initial εNd values of -4.2 to -8.3 and initial 87Sr/86Sr values of 0.7064-0.7105. Currently, these rocks have been observed only in the Muskol/Murgab dome region of the central Pamir. The coevally intruded leuco- and biotite-granites are slightly peraluminous to metaluminous (A/CNK: 0.99-1.07) and show overlapping isotopic compositions with initial εNd values of -6.4 and -7.3 and initial 87Sr/86Sr of 0.7073 and 0.7093. However, these have a much wider spatial distribution across the central and southern Pamir.

The overall negative initial εNd values of the analyzed samples indicate that none were derived directly from the (depleted) mantle by multi-stage processes prior to emplacement. Addition of various amounts of preexisting (continental) crustal material, or a direct origin from pre-existing crust is required to explain the isotopic compositions. A remarkable feature is the shift from almost pure continental crustal εNd values, observed in the Mid-Cretaceous granitoids, to higher values in Late Cretaceous granitoids, which suggest a higher degree of a primary mantle component. Overall, this may refl ect a change in the melting regime and/or the source of the granitoids during the Cretaceous. Such a temporal variation is not observed for the Cenozoic granitoids, although their overall variation of initial εNd is larger.

A similar magmatic gap (ca. 100-80 Ma) as described for the Pamir was observed for the Tibetan plateau at 75-60 Ma (Chung et al. 2005). The magmatic activity on the Tibetan Plateau has been ascribed to northward, low-angle subduction beneath southern Tibet before the Indian indentation. The magmatic gap is supposed to be caused by slab roll-back accompanied by southward migration of asthenospheric

Cretaceous-Cenozoic magmatism in the Pamir and a comparison with Tibet

*Nicole Malz1, Jörg A. Pfänder1, Lothar Ratschbacher1and Bradley R. Hacker2

1Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany

2 Earth Sciences, University of California, Santa Barbara, 93106, USA(*Email: [email protected])

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convection, causing the fi nal phase of Gangdese arc magmatism to be dominated by an asthenospheric mantle source component. Similar observations can be made in the Pamir, although their causes are still unclear. The subducting Neotethyan slab was suggested to have detached from Indian continental lithosphere at about 45 Ma, leading to the cessation of Gangdese arc magmatism (Kohn and Parkinson 2002; DeCelles et al. 2002). The episodic and geochemically variable Cenozoic magmatism in the Tibetan Plateau can be closely correlated to the tectonic evolution with ongoing subduction, slab roll-back and extensional regimes (Chung et al., 2005 for summary). Such a variation in Cenozoic

magmatism is a feature that has not yet been observed for the Pamir.

REFERENCES

Chung, S. L. et al., 2005, Tibetan tectonic evolution inferred from spatial and temporal variations in post-collisional magmatism, Earth-Sci. Rev., v. 68, pp. 173-196.

DeCelles, P. G., Robinson, D. M., Zandt, G., 2002, Implication of shortening in the Himalayan fold-thrust belt for uplift of the Tibetan Plateau, Tectonics, v. 21, p. 1062.

Kohn, M. J., Parkinson, C. D., 2002, Petrologic case for Eocene slab breakoff during the Indo-Asian collision, Geology, v. 30, pp. 591-594.

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The burial and exhumation path for the ultra-high pressure units at Tso Morari, eastern Ladakh, have been constrained through the careful integration of petrographic observations, phase diagram calculations and multi-phase geochronological analysis. The Tso Morari Complex is the western-most of about 12 North Himalayan domes that are the northern extension of the Indian plate. Quartzo-feldspathic metamorphic rocks derived from granitoid protoliths, referred to as the Puga gneiss, occur within the core of an elongate domal culmination while eclogite and retrogressed eclogite occur as lenses and boudins widely distributed within the host gneiss. In order to constrain the prograde burial and retrograde exhumation path at Tso Morari in a petrologically-coherent P–T–t context, samples of both the mafi c eclogite boudins and the host Puga gneiss were investigated. The pressure-temperature path at Tso Morari is described fully in St-Onge et al. (this volume) but can be summarized by six distinct stages: (a) early M1 growth and equilibration of eclogitic garnet cores (b) isothermal eclogitic garnet rim growth (c) continued garnet growth concomitant with increasing P and T conditions to peak pressure conditions, (d) HP/UHP M2 metamorphism (e) M3 isothermal decompression, and (f) a late stage increase in temperature during continued decompression to M4 thermal peak conditions.

In order to link P-T conditions to timing constraints, data table phases from both the prograde assemblage in the mafi c eclogite and retrograde assemblages in the Puga gneiss were identifi ed across multiple thin sections using the automated search function of a scanning electron microscope. The best constrained targets were analysed in thin section by SHRIMP ion microprobe to preserve their petrological context. U-Pb SHRIMP analysis of zircon inclusions within eclogitic garnet cores preserve an age of 58.0±2.2 Ma interpreted as the maximum age of M1 metamorphism. Zircon preserved in the matrix of the mafi c eclogite exhibit a consistently low Th/U ratio and low HREE abundances, and yield a mean U-Pb age of 50.8±1.4 Ma. Based on their chemical signature and petrological context (matrix and enchased in the M2 garnet rim), these zircons are interpreted to date peak M2 HP/UHP metamorphism.

The only datable metamorphic phases identifi ed in the host Puga gneiss were rare monazite cores in equilibrium with allanite rims which constrain the timing of the M4 re-equilibration to 45.3±1.1 Ma. While allanite was identifed as large laths in the prograde assemblage of the mafi c eclogite and as retrograde rims after monazite in the Puga gneiss, these were not successfully dated. Progress on the analytical development of allanite standards for ion microprobe will be summarized, and possible pitfalls highlighted.

The integrated thermobarometric and temporal context presented for Tso Morari is consistent with paths published for the Kaghan UHP locality in northern Pakistan (Kaneko et al. 2003; Parrish et al. 2006; Wilke et al. 2010a; b) however key temporal differences emerge. Continental subduction and attainment of UHP conditions at Tso Morari preceded that at Kaghan by c. 3–4 Ma, while both Kaghan and Tso Morari subsequently re-equilibrated at approximately similar times following a period of rapid exhumation.

REFERENCES

Kaneko, Y., et al., 2003, Timing of Himalayan ultrahigh-pressure metamorphism: Sinking rate and subduction angle of the Indian continental crust beneath Asia. Journal of Metamorphic Geology, v. 21, PP. 589–599. doi:10.1046/j.1525-1314.2003.00466.x

Parrish, R. R., Gough, S. J., Searle, M. P. & Waters, D. J., 2006, Plate velocity exhumation of ultrahigh-pressure eclogites in the Pakistan Himalaya. Geology, v. 34, pp. 989–992. doi:10.1130/G22796A.1

St-Onge, M. R., Rayner, N., Palin, R. M., Searle, M. P., and Waters, D. J. 2012, Integrated pressure-temperature-time constraints for the Tso Morari dome (Northwest India) Part II: Implications for the burial and exhumation path of UHP units in the western Himalaya. Journal of the Nepalese Geological Society, this issue.

Wilke, F. D. H., O’Brien, P. J. & Altenberger, U., 2010a, Multi-stage reaction history in different eclogite types from the Pakistan Himalaya and implications for exhumation processes. Lithos, v. 114, pp. 70–85.

Wilke, F. D. H., et al., 2010b, The multistage exhumation history of the Kaghan Valley UHP series, NW Himalaya, Pakistan from U–Pb and 40Ar/39Ar ages. European Journal of Mineralogy, v. 22, pp. 703–719.

Integrated pressure-temperature-time constraints for the Tso Morari dome (Northwest India) Part I: In situ U-Pb geochronology of monazite

and zircon

*Nicole Rayner1, Marc R. St-Onge1, Richard M. Palin2, Michael P. Searle2 and Dave J. Waters2

1Geological Survey of Canada, 601 Booth St., Ottawa, Ontario, Canada2Department of Geological Sciences, University of Oxford, Parks Road, Oxford, UK


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The Indian summer monsoon (ISM) delivers intense rainfall to southern Asia and so affects the survival of many millions of people, yet the underlying causes that determine its variability remain poorly understood. Climate modellers require knowledge of how the distribution and intensity of the ISM has varied across a range of timescales to identify the mechanisms that drive monsoon evolution. Tectonic studies of the Himalayas and Tibet have focused on feedback between climate and plateau elevation over timescales of 106-107 years. However to understand the causes of megadrought and of natural hazards relating to periods of high monsoon intensity it is vital to harness a high-resolution proxy over timescales of 104-105 years. For example, speleothem time series provide annually-resolved records of precipitation isotopes in continental settings. In particular the 18O/16O proxy

has direct links to the surface hydrological cycle, and, now these links are becoming better understood as a result of fi eld monitoring and laboratory calibrations.

The Shillong plateau of NE India captures the early rainout of the ISM air mass moving north from the Bay of Bengal. We have investigated speleothem-rich caves from the southern plateau where we are monitoring the relationships between monsoon timing and intensity and the recording of speleothem climate proxies through instrumental monitoring of the cave environment. Early U-series results identify an annually resolved >3000 yr record (Fig. 1) displaying regular laminae that preserve seasonal variations in 13C and trace elements.

What drives variations in the Indian summer monsoon?*Nigel B. W. Harris1, Dave Mattey2, Peter van Calsteren1, Louise Thomas1 and Talat Ahmad3

1Department of Environment, Earth and Ecosystems, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK2Department of Earth Sciences, Royal Holloway University of London, Egham TW20 OEX, UK

3University of Kashmir, Srinagar 190006, Jammu and Kashmir, India(*Email: [email protected])

Fig. 1: (a) Vertical section through base of a speleothem (UMS10a from Krem Umsynrang, Shillong Plateau) showing regular laminae, 350 microns thick; height of image = 200mm. (b) U-series ages from same speleothem indicating annual growth over

3000 years.

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Preliminary analysis of our dataset suggests that excursions in the 13C and 18O records can be matched with known periods of monsoon failure and associated famine in the historical record from the 7th to the 18th centuries (Fig. 2). Such studies are likely to be pivotal in establishing short-

term controls on monsoon evolution, such as teleconnections between the ISM and ENSO. In contrast, climate-tectonic feedbacks operate over timescales of ~106 years and high-resolution climate records on the timescales of tectonic forcing are entirely lacking.

Fig. 2: Excursions in delta18O (upper plot) and delta13C (lower plot) from UMS10a with major excursions matched to known drought events over the most recent 1500 years.

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The uplift and erosion of the Himalayas has resulted in the accumulation of a vast pile of terrestrial sediments called the Siwalik Group deposited at the frontal deep of the mountains. The Siwalik Group in the study area is divided into the Lower Siwalik, Middle Siwalik A, Middle Siwaliks B and Upper Siwalik stratigraphically upwards. The Lower Siwaliks is represented by an interbedding of red and purple mudstones, shales, and fi ne- to very fi ne-grained sandstones. The Middle Siwaliks A shows a gradual increase of sandstone grain size as well as thickness of beds. The sandstones are calcareous. The mudstones are variegated in lower part and grey-green in upper part. The Middle Siwaliks B is mainly represented by multi-storied, coarse- to very coarse-grained ‘pepper and salt’ sandstones. The Upper Siwaliks comprise compact and hard boulder- and pebble-bearing conglomerates with yellow mudstones in the lower part and loose conglomerates with yellow mudstones in upper part. The sandstones of the study area mostly belong to the litharenites and subordinately to the sublitharenites.

The Siwalik rocks show a coarsening-upward sequence, evidencing a continuous uplift of the Himalaya. However, the individual depositional units show a fi ning-upward sequence refl ecting the fl uvial depositional environment.

The continued movement of the Indian Plate past the Eurasian Plate is the main cause of the formation of the foreland basin into which the Siwaliks rocks were deposited, and it led to the deformation of the Siwalik rocks. This deformation was responsible for the generation of series of thrusts which succeeded one another in both space and time. Due to this thrusting the Siwalik rocks of the study area are repeated three times. The pattern of thrusting in the study area is related to thin-skinned tectonic model.

A balanced cross-section was constructed across the Sub-Himalayan Siwalik Hills of the Chisapani-Dhab section of the study area in order to determine the structural geometry of the region and to calculate tectonic shortening. The Mid-Western Nepal Sub-Himalaya is underlain by a basal detachment fault, the Main Detachment Fault (MDF) which lies at a depth of about 5 km beneath the Sub-Himalaya. The Main Boundary Thrust (MBT), the Bheri Thrust, the Babai Thrust and the Main Frontal Thrust (MFT) are all splay thrusts of the MDF which ramps up-section through the 5 km thick Siwalik sedimentary prism with no major intervening thrust fl ats; the Mid-Western Nepal Sub-Himalaya thus has an emergent imbricate fan geometry. North south shortening across the Chisapani -Dhab section of the study area is approximately 29km (55%) shortening.

Lithostratigraphy and structural pattern of the Siwaliks in Surkhet and Bardiya Districts, mid-western Nepal

Nirmal Kafl e, *Kamalakanta Acharya and Megh Raj DhitalCentral Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal


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The Danba Structural Culmination (DSC) is a tectonic window into the Songpan-Garzê fold belt (SGFB) in E Tibet (Fig. 1a). It comprises a series of doubly-plunging antiforms, which are cored by Neoproterozoic orthogneisses and overlain by a cover sequence of late Neoproterozoic-Triassic metasedimentary rocks, with the two separated by a regional décollement (Fig. 1b). These sedimentary rocks are thought to have undergone kyanite-grade Barrovian-type metamorphism at c. 204-190 Ma, culminating locally in sillimanite-grade crustal anatexis in the northern part of the DSC (Huang et al. 2003a).

The region is of particular interest due to confl icting ages and interpretations pertaining to whether the partial melting was a progressive part of the Barrovian metamorphism or a separate thermal event (Huang et al., 2003b; Wallis et al., 2003). More broadly, the locality provides a rare window into the tectono-thermal history of E Tibet. Finally, it is an excellent opportunity to quantify the structural and petrological evolution of Barrovian metamorphism using modern techniques, namely integrated P-T phase diagram modelling and in-situ SHRIMP U-Pb monazite geochronology.

To explore these aims, the region was extensively sampled, with metapelites acquired from each exposed mineral zone. XRF data was obtained, and a subset of almost isochemical samples from staurolite- to sillimanite-

grade chosen for P-T modeling and U-Pb dating. Using THERMOCALC in the full MnO-Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 system, and incorporating constraints from compositionally zoned garnets and the Henry et al. (2005) Ti-in-biotite thermometer, the array of peak metamorphic conditions show a common metamorphic fi eld gradient (England and Richardson 1977), implying that crustal anatexis was progressive and followed the kyanite-grade metamorphism. This is supported by petrographic observations that show a consistent deformation history for all of the samples, and also by SHRIMP U-Pb geochronology on in-situ monazite, which categorically demonstrates that the sillimanite-grade metamorphism occurred progressively with the kyanite-grade metamorphism at c. 185 Ma. Only the staurolite-grade sample was resolvably different, with a slightly older age of c. 191 Ma.

As well as resolving the relationship between the kyanite- and sillimanite-grade metamorphism, this study has produced a nuanced understanding of the entire Barrovian sequence. This reveals that the P-T path gradients both within and between samples progressively shallow with grade, which agrees well with the classic model of an orogeny evolving from a compressive regime to a period of thermal relaxation. More generally, it reinforces the point that no one rock can characterize a Barrovian event, but rather a suite of rocks is needed from different structural levels to fully characterize the evolving P-T conditions.

Barrovian metamorphism and crustal anatexis in the Danba structural culmination, E Tibet: Was it polymetamorphic?

*Owen Weller1, Marc St-Onge2, David Waters1, Nicole Rayner2, Mike Searle1, Sun-Lin Chung3, Richard Palin1, Yuan-Hsi Lee4 and Xi-Wei Xu5

1Department of Earth Sciences, University of Oxford, Oxford, OX1 3AN, UK, 2Geological Survey of Canada, Ottawa, KIA 0E8, Canada

3Department of Geosciences, National Taiwan University, Taipei 106, Taiwan4Department of Earth and Environmental Sciences, National Chung-Cheng University, Taiwan

5Institute of Geology, China Earthquake Administration, Beijing 100029, China(*Email: [email protected])

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REFERENCES

England, P. and Richardson, S., 1977. The infl uence of erosion upon the mineral facies of rocks from different metamorphic environments. J. Geol. Soc. London, v. 134, pp. 201–213.

Henry, D., Guidotti, C. and Thomson, J., 2005, The Ti-saturation surface for low-to-medium pressure metapelitic biotites: Implications for geothermometry and Ti-substitution mechanisms. Am. Mineral., v. 90, pp. 316-328.

Huang, M., Buick, I., and Hou, L., 2003a, Tectonometamorphic Evolution of the Eastern Tibet Plateau: Evidence from the Central Songpan-Garzê Orogenic Belt, Western China. J. Petrol., v. 44, pp. 255-278.

Huang, M., Maas, R., Buick, I., and Williams, I., 2003b, Crustal response to continental collisions between the Tibet, Indian, South China and North China Blocks: geochronological constraints from the Songpan-Garzê Orogenic Belt, western China. J. Metamorph. Geol., v. 21, pp. 223-240.

Roger, F., Malvieille, J., Leloup, P., Calassou, S., and Xu, Z. 2004,

Timing of granite emplacement and cooling in the Songpan-Garzê Fold Belt (eastern Tibetan Plateau) with tectonic implications. J. Asian Earth Sci., v. 22, pp. 465-481.

Roger, F., Jolivet, M., Malavieille, J., 2010, The tectonic evolution of the Songpan-Garzê (North Tibet) and adjacent areas from Proterozoic to Present: A synthesis. J. Asian Earth Sci., v. 39, pp. 254-269.

Wallis, S., Tsujimori, T., Aoya, M., Kawakami, T., Terada, K., Suzuki, K., and Hyodo, H., 2003, Cenozoic and Mesozoic metamorphism in the Longmenshan orogen: Implications for geodynamic models of eastern Tibet. Geology, v. 31, pp. 745-748.

Yuan, C. et al. 2010. Triassic granitoids in the eastern Songpan Ganzi Fold Belt, SW China: Magmatic response to geodynamics of the deep lithosphere. Earth Plan. Sci. Lett., 290, 481-492.

Zhou, M., Yan, D-P., Kennedy, A., Li, Y., and Ding, J. 2002, SHRIMP U-Pb zircon geochronological and geochemical evidence for Neoproterozoic arc-magmatism along the western margin of the Yangtze Block, South China. Earth Plan. Sci. Lett., v. 196, pp. 51-67.

Fig. 1. (a) Tectonic block map of Asia. Modifi ed from Roger et al. (2010). (b) Geological map showing the stratigraphy and metamorphic isograds of the DSC. Gc: Gongcai complex. Gz: Gezong complex. Granitoid age data: [1] Yuan et al. (2010), [2] Roger et al. (2004), [3] Zhou et al. (2002). Modifi ed from Huang et al. (2003a).

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Single core specimens of siltstone/sandstone from 127 stratigraphic levels collected from the Lower and Middle Siwaliks Group comprising 1.5 km thick sediments in the Sub Himalayan North Belt along the Tinau Khola River have been measured for the low-fi eld magnetic susceptibility and anisotropy (AMS). The magnetic fabric is complex, of both primary sedimentary-compactional and secondary tectonic origins, and can be characterized by: (i) mainly oblate AMS ellipsoids, (ii) low degree of anisotropy (P’ mostly <1.1) and low magnetic susceptibility (< ca. 10-7 m3kg-1) contributed mainly by paramagnetic and diamagnetic minerals, and (iii) WNW-ESE magnetic lineations normal to the direction of paleotectonic compression.

The lower 1120 m section subjected to thermal demagnetization reveals a characteristic remanence of the high unblocking temperature (>600C) carried by hematite. Ratios of remanences at various demagnetization steps allowed the fi rst-order estimation of remanence contributions from magnetic minerals (goethite, maghemite, magnetite, and hematite), and discrimination of rockmagnetic zones correlatable with distinct lithofacies, mapped in detail by Tokuoka et al. (1990) and Ulak amd Nakayama (2001). The magnetic polarity sequence constructed using primary remanences from 77 levels were correlated with the geomagnetic polarity time scale (Lourens et al. 2003) between ca. 13.2 Ma (base of Chron C5AAN, 13.015–13.183 Ma) and the middle of Chron C5n.2n (9.987–11.040 Ma). The sediment accumulation rate for section pre-dating 11.040 Ma is estimated at 25-61 cm kyr-1 (average, 39 cm kyr-1), which is close to 32–50 cm kyr-1 reported from other

Siwaik sections in Nepal. Constraining the base of the Tinau Khola north section to 13.2 Ma (i.e., older than the Tinau Khola south (see Gautam and Rösler 1999) by 1.7 myr) is believed to attract further multidisciplinary and multiproxy research directed at geotectonic, climatic and environmental paleoreconsructions of Himalaya-wide events (Gautam et al., 2012).

REFERENCES

Gautam, P., Ulak, P. D., Paudayal, K. N., Gyawali, B. R. and Bhandari, S., 2012, Magnetostratigraphic dating of the prime-time sedimentary record of Himalayan tectonics and climate: new age constraints (13-10 Ma) from the Siwaliks of the Tinau Khola north section, Nepal. Geophys. J. Int., v. 190(3), pp. 1378-1392 .

Gautam, P. and Rösler, W., 1999, Depositional chronology and fabric of Siwalik Group sediments in central Nepal from magnetostratigraphy and magnetic anisotropy. In: Geology of the Nepal Himalaya: Recent Advances, ed. LeFort, P. & Upreti, B.N., J. Asian Earth Sciences, 17, pp. 659-682.

Lourens, L., Hilgen, F. J., Shackleton, N. J., Laskar, J., Wilson, D., 2004, The Neogene Period. In: A Geological Time Scale 2004, edited by: Gradstein, F.M., Ogg, J.G., Smith, A.G., Cambridge University Press, Cambridge, U. K., pp. 409-440.

Tokuoka, T., Takayasu, K., Hisatomi, K., Yamasaki, H., Tanaka, S., Konomatsu, M., Sah, R.B. and Rai, S. M., 1990, Stratigraphy and geologic structures of the Churia (Siwalik) Group in the Tinau Khola-Binai Khola area, West Central Nepal. Mem. Fac. Sci., Shimane Univ. 24, pp. 71-88.

Ulak, P. D. and Nakayama, K., 2001, Neogene fl uvial systems in the Siwalik Group along the Tinau Khola section, west-central Nepal Himalaya. Jour. Nepal Geol. Soc., v. 25, pp. 111–122.

Precise magnetostratigraphy (13–10 Ma) and rock-magnetic zonation of the Siwaliks from the lower part of Tinau Khola north section, Nepal

*P. Gautam1, P. D. Ulak2, K. N. Paudayal3, B. R. Gyawali3 and S. Bhandari3

1Creative Research Institution (CRIS), Hokkaido University, N21, W10, Kita-ku, Hokkaido 001-0021, Sapporo, Japan.2Department of Geology, Trichandra Campus, Tribhuvan University, Kathmandu, Nepal

3Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal(*Email: [email protected])

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The Pangong range is an 8km wide shear zone corresponding to the exhumed root of the central Karakorum fault zone (KFZ), one of the great continental strike-slip faults of the India-Asia collision zone. Ductile deformation is the most intense in the Tangtse and Muglib strands which bracket the shear zone to the SW and NE, respectively.

Structural and microstructural data show that deformation was at least partly synchronous with partial melting and the intrusion of granitic bodies and dykes. New U/Pb SHRIMPII and LA-ICP-MS ages for 24 zircons populations, from 5 gneiss and mylonites as well as 10 leucocratic dykes, span in age from 105.1±1.1 Ma to 14.2±0.1 Ma. Old ages are inherited from the surrounding Cretaceous Ladakh and Karakorum batholiths, while 13 ages are younger than 25.6 Ma and refl ect Miocene partial melting. The oldest dyke that can be shown to be syntectonic to the KFZ is 18.8±0.4 Ma old, suggesting that strike slip deformation started in the Tangtse strand at least at ~19 Ma. Other published U/Pb ages imply that deformation lasted until at least ~13.5 Ma. The absolute ages of dykes that are deformed or crosscut the foliation demonstrate that deformation was heterogeneous in space and time.

24 new Ar/Ar ages, together with published ones, allow reconstructing the shear zone cooling history. Cooling was diachronic across strike and ductile deformation (~300°C)

stopped earlier in the SW than in the NE: at ~16 Ma in the south Tangtse granite, ~11 Ma in the Tangtse strand, ~9Ma in the Pangong range, and ~8Ma in the Muglib Strand. Deformation thus appears to have migrated/localized from the whole shear zone to the Muglib strand, the only locus showing evidence for brittle deformation and active faulting. Taking into account data previously collected along the KFZ, and a fi nite offset of 200 to 240 km, it appears that the fault has been active for at least 22 Ma, with a slip rate of 0.84 to 1.3 cm/yr in its central section.

Stain rates measured in quartz ribbon with the QSR method from 5 samples across the Tangtse shear zone are higher in the two mylonitic strands than in the surrounding rocks. The corresponding integrated shear rate is in the order of 5.7 E-14 s-1 which would correspond to an integrated fault rate on the order of 1.45 cm yr-1. Such rate is close to, but somewhat higher, than the fault rate deduced from geological constraints.

This study conducted in the frontal part of the Himalayan orogen shows that large continental strike-slip faults can be linked with magmatism and be stable for more than 20 Ma, even in the hottest part of the orogen where strain localization is supposed to be at a minimum. While de fault zone propagates along strike, deformation also migrates across-strike within the ~8km wide shear zone.

Synkinematic magmatism, heterogeneous deformation, and progressive strain localization in a strike-slip shear zone: The case of the right-

lateral Karakorum Fault

*P. H. Leloup1, E. Boutonnet1, N. Arnaud2, J. L. Paquette3, W. J. Davis4 and K. Hattori5

1LGL-TPE Laboratoire de Géologie de Lyon-Terre, Planètes, Environnement, UMR CNRS 5276, Université Claude Bernard Lyon 1 - ENS, France

2Géosciences Montpellier, UMR CNRS 5243, Université de Montpellier 2, France3Laboratoire Magma et Volcans, UMR CNRS 6524, Université Blaise Pascal, Université de Clermont-Ferrand, France

4ESS/GSC-CNCB/GSC-CC/GEOCHRON, Geological Survey of Canada5Department of Earth Sciences, University of Ottawa, Canada


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Most giant earthquakes (Mw≈9) occur offshore, through ruptureof subduction mega-thrusts. Can they alsostrikeonland, within continents? Given its length (2500 km) and shortening rate (≈ 2 cm/yr), the Himalayan megathrust (MHT/MFT) is potentially capable of generating earthquakes of Mw≈8.8 or greater. It has been suggested that two historical events (1505, 1100 AD) might fall in that category. At the same time, the surface ruptures of the last 4 great Himalayan earthquakes (1897, 1905, 1934, 1950), with 8 < Mw< 8.7, have not been described.

We review here some of the uncertainties on the sources of Himalayan earthquakes, in the light of new fi ndings along the range. We argue that many, if not all, the great earthquakes of the 19th and 20th century have broken the surface. The principal diffi culties in fi nding the ruptures and constraining their lengths stem from the exceptionally active, monsoon drivenfl uvial processes that resurface the frontal part of the range on short time-scales. Constraining the recurrence time of large events through trenching is also challenging because of the fairly large amounts of co-seismic

slip and throw (typically ≈ 10 and ≈ 5 m, respectively, for Mw 8+ events).

High river-cut faces seem to provide the most rewarding exposures. Quantifying, with high-resolution Lidar DEMs, multiple episodes of uplift of well-dated surfaces also holds promise. There appearsto be many geomorphically well-preserved fl ights of perched river terraces suggestive of quasi-characteristic throw. Presently, the data at hand makes it diffi cult to demonstrate the existence of giant earthquakes. Most of the youngest hanging-wall terraces stand only a few meters above river beds. We have not found sites with amounts of slip and throw on order of 20 and 10 meters, respectively, that mightunambiguously be attributed to only one event. While it is not yet possible to rule outthe rare occurrence of Mw≈9 events with many hundreds of km-long ruptures that might concatenate shorter segments typical of Mw8+ earthquakes, we suspect that the clustering of such earthquakes, within one hundred years or so, every 600-700 years or so, may dominate the seismic moment release pattern along distinct stretches of the Himalayan range.

Seismic behavior of the Main Himalayan Thrust:Giant events or clustering of great earthquakes?

Paul Tapponnier1, Soma Nath Sapkota2, Laurent Bollinger3 and Yann Klinger4

1NTU, Singapore2DMG, NSC, Nepal

3CEA/DIF/DASE, France

4IPGP, Paris, France

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The Stak massif, located in the NW Himalaya syntax (northern Pakistan), corresponds to a continental eclogitic unit formed during the subduction of the northern margin of the Indian continent. This HP/UHP unit was extensively retrogressed during the Himalayan collision associated with the replacement of eclogite-facies minerals by amphibolite-facies paragenesis. In this contribution we propose a continuous pressure-temperature path calculated using a micro-cartographic approach. This method uses microprobe X-ray compositional maps of a small thin-section area followed by calculations of ~200,000 pressure-temperature estimates using appropriate thermometers and barometers.

This study show that the Stak eclogite underwent prograde metamorphism, increasing from 650°C and 2.4 GPa to the peak conditions of 750°C and 2.5 GPa, then retrogressed to 700–650°C and 1.6-0.9 GPa under amphibolite-facies conditions. The estimated peak metamorphic conditions and PT-path are similar to those of the Kaghan and Tso Morari high- to ultra-high-pressure massifs. We propose that these two massifs and the Stak massif defi ne a large HP to UHP province in NW Himalaya, ~500 km long and 150 km wide. This Himalayan province is comparable to the Dabie-Sulu province in China and the Western Gneiss province in Norway.

Deciphering high-pressure metamorphism in collisional context using microprobe-mapping methods: Application to the Stak eclogitic massif

(NW-Himalaya)

Pierre Lanari1, *Stéphane Guillot1, Nicolas Riel1, Olivier Vidal1, Keiko H. Hattori2, Stéphane Schwartz1 and Arnaud Pêcher1

1ISTerre, University of Grenoble 1, CNRS, 1381 rue de la Piscine, 38041 Grenoble, France2Department of Earth Sciences, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada


131


The Hindu Kush Himalayas (HKH) and the Tibetan Plateau region is one of the most heavily glaciated areas in the world outside the polar region. Climate change has global impacts on natural systems of the earth including the cryosphere which has experienced a global decline of snow and ice, including mountain glaciers. The HKH region is no exception and it has been widely recognized that global climate change is causing the shrinkage or retreat of glaciers in this region. This is leading to the formation and expansion of many glacial lakes, which could lead to an increase in the number of Glacial Lake Outburst Floods (GLOFs). Since the 20th century, at least over 50 GLOF events have occurred in the HKH region which caused catastrophic effects to the downstream region, with serious damages to life, property, forests, farms, and infrastructure. Therefore, it has become imperative to map out systematically and scientifi cally all glacial lakes of the region and conduct GLOF risk assessment.

Thus, ICIMOD embarked upon the mapping of glacial lakes of the HKH region comprehensively and developing a database of glacial lakes in fi ve major river basins of the HKH. The fi ve river basins are Amu Darya, Indus, Ganges, Brahmaputra and Irrawaddy basins. For Amu Darya basin, only Afghanistan part is covered by this inventory. The main

purpose of this study is to derive the fi rsthand knowledge upon the distribution of glacial lakes in various basins of the HKH region which could form the basis for further studies and investigation of glacial lake hazards, their risk assessment and mitigative action against the potential GLOF, e.g., in the development of early warning system, for saving life and property of the people living downstream in various parts of the region.

Mapping and inventorying of glacial lakes of the HKH region has been carried out applying RS/GIS and using mainly Landsat TM/ETM+ images from 2005±3 years. It has ensured the consistent source of data and information. The area of the investigation is limited above 2000 m a.s.l. The present study has resulted into mapping of a total number of 20,485 lakes in those fi ve major river basins of the HKH. Among those lakes, 20,204 lakes are glacial lakes and 296 lakes are non-glacial lakes. The glacial lakes cover a total area of 1955.75 km2. Following mapping and inventory development, GLOF risk assessment becomes imperative. For this, an integrative methodology with a step-wise approach has been developed and applied for GLOF vulnerability and risk assessment in Nepal. It is anticipated that such assessment can be extended to other parts of the HKH.

Glacial lakes mapping in the Hindu Kush Himalayas and risk assessment of their outburst fl oods

*Pradeep K. Mool1, Wu Lizong2, Sharad P. Joshi1, Arun Shrestha1 and Rajendra B. Shrestha1

1International Centre for Integrated Mountain Development (ICIMOD), GPO Box: 3226, Kathmandu, Nepal,2Cold and Arid Regions Environmental and Engineering Research Institute (CAREERI), Chinese Academy of Sciences,

Donggang West Road 320, Lanzhou, Gansu, China 730000(*Email: [email protected])

132


River form and fl uvial process evolve simultaneously and operate through mutual adjustments towards self-stabilization. Channel stability is the ability of the stream, over time, to transport the fl ows and sediment of its watershed in such a manner that the dimension, pattern and profi le of the river is maintained without aggrading or degrading. Dynamics of river is closely related to stability of river, aggrading/degrading potential of channel, channel planform changes, etc. Determining these parameters require extensive fi eldwork and gathering of morphological, hydraulic, and sedimentological data.

The main stem Bagmati River originates at the eastern hill Nagarkot of the Kathmandu Valley is eighth order perennial river that stretches for 206 km with an elongated catchment of area 3761.23 sq km. The river incises through different geological units as- the Kathmandu Valley, the Lesser Himalaya, Sub-Himalaya and the Terai Plain. The river course has been evaluated to understand its dynamism at

different geological units. Seven representative segments characterized with different planform and morphologic characteristics at different geological units were analyzed through detail fi eld survey and investigation. The river segments from upstream to downstream are classifi ed as ‘C2’, ‘F2’, ‘F2’, ‘B2a’, ‘F3’, ‘D4’ and ‘C3’ streams characterized by class supported boulder, cobble and gravel sized substrates. The dimension less shear stress in ‘F2’, ‘B2a’ and ‘F3’ segments exceed critical dimensionless shear stress even at much lower bankfull condition suggests that these streams are competent enough to transport their bed material. Similarly, the existing bankfull depth and existing bankfull water surface slope are higher than the required bankfull mean depth and bankfull water surface slope at these segments. Stream power of segments 1 to 7 is 209.9, 2826.9, 3637.6, 103896.1, 6477.1, 128.9 and 203.5 respectively. The ‘F2’, ‘B2a’ and ‘F3’ stream segments shows greater stream power than ‘C2’, ‘D4’ and ‘C3’ segments. Therefore the ‘F2, ‘B2a’ and ‘F3’ stream segments are potential to degradation.

Dynamics of the Bagmati River in relation to geological terrains, central Nepal Lesser and Sub-Himalayas

*Pramila Shrestha and Naresh Kazi TamrakarCentral Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal


133


With the rapidly growing population, development of human civilization and increasing construction of infrastructures, the demand of aggregate is increasing abruptly day by day. The naturally occurring sand and gravel are not suffi cient to fulfi ll the demand in the Kathmandu Valley and the Kavre area. The river environment can be disturbed by quarrying it. Therefore, the crushed-rock aggregates should be used to meet the requirements. The accessible resources and its quality and quantity for aggregates play an important role in the durability of roads, buildings, projects, many other infrastructures and sustainable development of the country. The negligence of quality of aggregates would be disastrous, nondurable, slippery and degradable. Therefore, being aware of these things, quality of aggregates should be kept at high priority. The search of outcrops from which suitable aggregates may be quarried is required. This study aims at exploring and evaluating the resources and quality of crushed-rock aggregates from the Lesser Himalayan rocks in the Kavre area.

Several lab tests and analyses were made to characterize the physical, mechanical, chemical and petrographic properties of the aggregates. Many kinds of rocks were identifi ed from the outcrop in the study such as quartzite, psammitic schist, calc-quartzite, metasandstone and

metasiltstone. Thirteen representative samples were taken from different lithological formations. The water absorption value (WAV) of samples ranges from 0.302 to 2.393%. Dry density varies from 2.308 to 2.743 gm/cm3 and the uniaxial compressive strength value ranges from 23.62 to 217.92 MPa. In general, these indicate that the aggregates are compact and strong. The aggregate crushing value (ACV) ranges from 19.56 to 35.4% and the aggregate impact value (AIV) ranges from 11.02 to 23.84% showing that the aggregates are resistant against compressive load and strong against impact load. The sodium sulphate soundness value (SSSV) lies between 5.95 to 16.66% and methylene blue absorption values (MBV) in all samples are <1% indicating that the samples are durable and chemically sound. The alkali silica reactive features, swelling and expanding clay minerals like chert, opal, high-quartz, extremely deformed fractured quartz, smectite, and kaolinite are absent. Though some quartz grains are undulosed and fractured, they are mega and low-quartz. Only the clay mineral illite, 1M type is present in very small proportion. All these parameters show that the samples of the Lesser Himalayan rocks from the Kavre area are suitable enough and meet the ASTM standard, BS standard and Nepal standard, and are acceptable for concrete aggregates.

Physical, mechanical and petrographic properties of Lesser Himalayan rocks from Kavre area: An assessment of quality for concrete aggregates

*Prem Nath Paudel and Naresh Kazi TamrakarCentral Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal


134


The present-day convergence of ~5.0 cm/year between the Indian and the Eurasian plates generates both vertical uplift as well as horizontal deformation along the Himalayan arc and southern Tibet. At this collision boundary, about 40% of the total convergence is usually consumed by the subduction of the Indian plate beneath the Eurasian plate, and the rest of about 60% is consumed by the internal deformation of the Eurasian plate. In the present study, we have reinvestigated the isoseismals of ten moderate to great historical damaging earthquakes along the arcuate belt in the central segment between the Himachal and the Darjeeling Himalaya for understanding its geodynamic responses. Analysis was carried out in line with the evidences of ruptures, eccentricities of isoseismals and the changes in Indian plate obliquities. It was noted that the elongated axes of the isoseismals and the strike of the major ruptures for shallow earthquakes are almost parallel with the strike of the Himalayan arc. As estimated, the Indian plate obliquity decreases sharply past the Himachal Himalaya towards east, and reduces to zero near Nepal-Bihar border, and further increases gradually towards east. It was also apparent from the observations of graben structures in the central Himalaya and the regional trends of major thrust sheets or horizontal shearing along the Himalaya arc are well compatible with

the changes in Indian plate obliquities. Ruptures and the trends of major axes of isoseismals for shallow historical damaging earthquakes are clearly conformable with the Indian plate obliquity. An empirical power law relationship between eccentricity and focal depth established under the present study illustrates that the deeper events are more infl uenced by the bending of the penetrating Indian lithosphere and the shallower events are more controlled by the Indian plate obliquity. A positive correlation between eccentricities of isoseismals and Indian plate obliquity also supports this contention. Further, the arc-parallel shorting caused by the deformation processes in Western and Eastern Himalayas is normally compensated, at least in part, for arc-parallel extension along the central portion of the orogen. We thus propose that the observed deformations must have a defi nite role in the rupture processes during the incidences of moderate to great earthquakes at shallower part in the Himalaya and southern Tibet. A wide range of kinematic responses i.e. from rigidity to complete partitioning of the slip to changes in obliquity are recorded all along this curved Himalayan margin. Earlier studies also suggest that the convergence around a curved margin (e.g., Himalaya, Aegean, northern Chili, and Scotia fore arcs) produces three-dimensional deformation of fore arc.

Role of Indian plate obliquity vis-à-vis interplate deformation behind the generation of large earthquakes along the arcuate Himalayan segment

*Prosanta Kumar Khan and Md. Afroz AnsariDepartment of Applied Geophysics, Indian School of Mines, Dhanbad-826 004, India


135


The Mai Khola Hydroelectric Project is 15.6 MW with the design discharge of 16 m3/s and design net head of 112.71 m. It is located at Chisapani, Soyak and Danabari VDCs in Ilam district, Eastern Development Region of Nepal. The study is concerned with geological and engineering geological study of the Mai Khola Hydroelectric Project and also evaluates the support system along the tunnel alignment on the basis of Q system and compares the predicted rock mass and estimated support on the basis of surface mapping with actually encounter rock mass and installed support after excavation.

Geologically, the project area consists of the rocks of the Middle Siwalik Group. The Middle Siwaliks rocks consists of grey colored , medium - to coarse-grained, pepper and salt sandstone, light bluish grey, medium-bedded, fi ne-grained siltstone and brownish grey mudstone. They are interbedded and repeated frequently.

The headworks site seems to be fairly suitable for the Weir structures. Approach canal, settling basin and inlet portal located on fl at alluvial terraces on the left bank of the Mai Khola River. The headrace tunnel is 2192 m long having inverted-D shaped with 4.3 m diameter. Common rock type

along the headrace tunnel is sandstone, siltstone and mudstone. The sandstone proportion predominant in headworks area and decreases towards south and completely absent in surge tank and penstock alignment. The siltstone alternating with thin layer of mudstone is frequently observed throughout the area being more predominant in the southern part. The headrace tunnel outlet portal and surge shaft lie on the hill slope characterized by colluvium deposits. The penstock alignment passes through the highly weathered siltstone and mudstone. The area is moderately steep to gentle. The semi-surface power house lies on the lower alluvial terrace and fl ood plain. The tailrace canal runs through the recent fl ood plain deposits. Main Boundary Thrust (MBT) is the major structure in the study area and observed at about 90 m upstream from the weir axis.

The average Q-value of rock mass along the headrace tunnel surface mapping is 0.062 to 1.33 and after excavation the value is 0.004 to 0.23. An extremely poor to poor relation observed between the rock mass class on surface mapping and exceptionally poor to very poor on excavation. After analyzing the results of the surface and underground study of the rock mass, it is concluded that excess support is required during construction.

Geological, engineering geological and geotechnical study of the Mai Khola Hydroelectric Project, Ilam, Eastern, Nepal

Pusker Raj Joshi1, Kamala Kant Acharya2 and Rabindra Dhakal3

1Central Department of Geology, TU, Kirtipur, Kathmandu 2Central Department of Geology, TU, Kirtipur, Kathmandu

3Himal Hydro and General Construction Limited

136


Large number of Apatite Fission Track (AFT) ages from the Higher Himalayan Crystalline (HHC) have been found to be younger than 5 Ma (Jain et al. 2000; Burbank et al. 2003; Vannay et al. 2004; Blythe et al. 2007; Thiede et al. 2004; 2005, 2009; Patel and Carter 2009; Patel et al. 2011a; 2011b). A recent comparison of AFT data from the NW-Himalaya by Patel et al. (2011a), in the adjacent of the present study area, highlights similar range but linear pattern of AFT ages in the HHC units between the Munsiary/Main Central Thrust (MT/MCT) and South-Tibetan Detachment System (STDS) that experienced rapid exhumation (>1mma-

1) since ~4 Ma. Despite similar range of AFT ages in the NW Himalayas, there is difference in the slope of linear pattern in the different region of the Himalaya (Patel and Carter 2009; Patel et al. 2011a). In spite of similar climate pattern, the difference in the slope of linear age pattern of the HHC is described due to local tectonic factor that signifi cantly infl uence the exhumation pattern (Patel and Carter 2009; Patel et al. 2011a; 2011b) .

On the basis of the study from the central Nepal Himalaya, two competing tectonic mechanisms, namely thrusting along a single major thrust- the Main Himalayan Thrust (MHT) with non-uniform underplating due to duplexing or overthrusting of a major crustal ramp (Bollinger et al. 2006; Robert et al. 2009; Herman et al. 2010) and out-of-sequence (OOS) thrusting in addition to thrusting along the MHT (Wobus et al. 2005; Hodges et al. 2004), have been proposed to describe the kinematics of the Himalaya. In the present work,18 new Apatite Fission Track (AFT) ages of samples collected along a north-south transect cutting across major thrusts namely Vaikrita Thrust (VT), Main Central/Munsiari Thrust (MCT/MT), Berinag Thrust (BT) and the Baijnath nappe in the Kumaon-Garhwal Himalaya, NW-

India have been reported. Ages in the hanging wall of VT which range from 2.1±0.2 to 4.2±0.7 Ma, have been found to be becoming younger linearly with distance from north to the VT. This trend crosses the VT with signifi cant jump in ages. In the south of the VT, ages lying between 1.7±0.4 and 3.9±0.8Ma, and show linear variation with distance from the VT to MT/MCT. Ages (0.3±0.1 to 0.9±0.2Ma) between the MT/MCT and BT are further younger and show similar younging linear trend from MCT/MT to BT.

An AFT age-transect through the Kumaon-Garhwal Himalaya shows a sharp discontinuity in AFT-age centered around the zone between the BT and VT, within the zone of physiographic transition. To the north of the BT, AFT ages (0.3 to 4.2 Ma) are younger than that of the south of it (5 to 7 Ma) within the Baijnath Nappe. North of the VT the ages gradually become older (4.2 Ma at Changuch) (Fig. 1). This contrasting age pattern across the MCT zone can be described due to reactivation of the MCT zone during late Miocene-Pliocene time due to which hanging wall HHC block uplifted rapidly than the footwall LHS.

Step pattern of the AFT ages from the BT to the VT refl ects that the faults were active during post-Mio-Pliocene period but not active synchronously (Fig. 2). The northern most the VT was active earlier before ~3.8Ma followed by activation along the MCT/MT before ~1.7Ma and the BT possibly before ~0.3 Ma. It refl ects sequential uplift and cooling towards the south from the VT to BT which is consistent with an in-sequence style of thrust propagation. Thrusting along the BT at ~0.3 Ma is probably shifted gradually southward and recently movements along a north-dipping (shallow depth, 10–15 km) plane quite different from the MCT.

Plio-Quaternary exhumation history of the Garhwal-Kumaon Himalayas, NW-India: An analysis on low-temperature

thermochronological data

*R. C. Patel, Paramjeet Singh and Nand LalNational Facility on Low-temperature Thermochronology, Department of Geophysics, Kurukshetra University,

Kurukshetra- 136 119, India(*Email: [email protected])

137


Fig. 1. Digital elevation model (DEM) of Kumaon-Garhwal region, NW- Himalaya with main shear zones and Tectonic units, MCT—Main Central Thrust, STDS—South Tibetan Detachment System, LHS—Lesser Himalayan Sequence, HHC—Higher Himalayan Crystalline, TSZ—Tethyan Sedimentary Zone, Locations of the apatite fi ssion track (AFT) ages are shown by circular white dots.

138


REFERENCES

Blythe, A. E., Burbank, D. W. Carter, A. Schmidt, K., Putkonen, J., 2007, Plio-Quaternary exhumation history of the central Himalaya: 1. Apatite and zircon fi ssion-track and apatite [U-Th]/He data. Tectonics, v. 26, TC3002. doi: 10.1029/2006TC001990.

Bollinger, L., Henry, P., Avouac, J. P., 2006, Mountain building in the Nepal Himalaya: thermal and kinematic model. Earth & Planetary Science Letters, v. 244, pp. 58–71.

Burbank, D. W., Blythe, A. E., Putkonen, J. L., Pratt-Situala, B., Gabet, E. J., Oskin, M. E., Barros, A. P., Ohja, T. P., 2003, Decoupling of erosion and precipitation in the Himalaya. Nature, v. 426, pp. 652-655.

Herman, F., Copeland, P., Avouac, J.-P., Bollinger, L., Mahéo, G., Le Fort, P., Rai, S., Foster, D., Pêcher, A., Stüwe, K., Henry, P., 2010, Exhumation, crustal deformation, and thermal structure of the Nepal Himalaya derived from the inversion of thermochronological and thermobarometric data and modeling of the topography. Journal of Geophysical Research, v. 115, B06407, doi:10.1029/2008JB006126

Hodges, K. V., Wobus, C., Ruhl, K., Schildgen, T., Whipple, K., 2004, Quaternary deformation, river steepening and heavy precipitation at the front of Higher Himalayan ranges. Earth and Planetary Science Letters, v. 220, pp. 379-389.

Jain, A. K., Kumar, D., Singh, S., Kumar, 548 A., Lal, N., 2000, Timing, quantifi cation and tectonic modelling of Pliocene-Quaternary movements in the NW Himalaya: evidence from fi ssion track dating. Earth and Planetary Science Letters, v. 179, pp. 437-451.

Patel R. C., Carter, A., 2009, Exhumation history of the Higher Himalayan Crystalline along Dhauliganga-Goriganga River valleys, NW India: New constraints from fi ssion-track analysis. Tectonics, v. 28, doi : 10.1029/ 2008TC002373.

Patel, R. C., Adlakha, V., Lal, N., Singh, P., Kumar, Y., 2011a,

Fig. 2. (a) Schematic cross section through Kumaon-Garhwal Himalaya modifi ed after Célérier et al., (2009) (through A-A’ in Fig. 1extended upto Sub-Himalaya in the south). Numbers correspond to the sample number as shown in the table A1. (b) AFT age transect, plotted as function of distance from the MT.

Spatiotemporal variation in exhumation of the Crystallines in the NW-Himalaya, India: Constraints from Fission Track dating analysis. Tectonophysics, v. 504(1-4), pp. 1-13. doi:10.1016/j.tecto.2010.11.011

Patel, R. C., Adlakha, V., Singh, P., Kumar, Y., Lal, N., 2011b, Geology, structural and exhumation history of the Higher Himalayan Crystallines in Kumaon Himalaya, India. Journal of Geological Society of India, v. 77 (1), pp. 47-72. doi. 10.1007/s12594-011-0008-5.

Robert, X., van der Beek, P., Braun, J., Perry, C., Dubille, M., Mugnier, J.-L., 2009, Assessing Quaternary reactivation of the Main Central thrust zone (central Nepal Himalaya): new thermochronologic data and numerical modeling. Geology, v. 37, pp. 731–734, doi:10.1130/G25736A.1

Thiede, R. C., Bookhagen, B., Arrowsmith, J. R., Sobel, E. R., Strecker, M.R., 2004. Climatic control on areas of rapid exhumation along the Southern Himalayan Front. Earth Planetary Science Letters 222, 791–806.

Thiede, R. C., Arrowsmith, J. R., Bookhagan, B., Mcwilliams, M.O., Sobel, E. R., Strecker, M. R., 2006. Dome formation and extension in the Tethyan Himalaya, Leo Pargil, north west India. Geological Society of America Bulletin 118(5/6), 635–650. doi: 10.1130/B25872.1

Thiede, R. C., Ehlers, T. A., Bookhagen, B., Strecker, M. R., 2009. Erosional variability along the NW Himalaya. Journal of Geophysical Research 114, F01015, doi: 10.1029/2008JF001010.

Vannay, J.-C., Grasemann, B., Rahn, M., Frank, W., Carter, A., Baudraz, V., Cosca, M., 2004, Miocene to Holocene exhumation of metamorphic crustal wedges in the NW Himalaya. Evidence for tectonic extrusion coupled to Xuvial erosion. Tectonics, v. 23, TC1014, doi: 10.1029/2002TC001429.

Wobus, C., Helmsath, A., Whipple, K., Hodges, K. V., 2005, Active out-of-sequence thrust faulting in the central Nepalese Himalaya. Nature, v. 434, pp. 1008-1011.

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A very ennovative technique used to be followed by the Russion Scientists for the exploration of base-metals. The auther had an opportunity to examine this technique and the equipment in 1980 in Ujbekistan of U.S.S.R. The technique involves a large scale electrolysis process which sweeps

the ‘cations’ carrying the base- metals e.g. lead, copper, zinc etc. from the mineralized zone by the help of strong d.c. current passing through the ground. The ‘cations’ are trapped in an array of specially designed ‘cathode’ electrodes.

Electro-chemical technique for base metal exploration

R. C. TalukdarGeological Survey of India

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Landslides are one of the most common natural hazards in many mountain regions of the world. These hazards pose a great threat to both human lives and property and are widely spread in high mountains such as the Himalayas. The western sector of Himalayas encompassing the Kumaun, Garhwal, Himachal and Kashmir regions have suffered a great loss from landslides and slope instability. The slope stability study was carried out near Korapani landslide with the coordinates 33°07’40” N, 75°26’13”E, at 1100 m elevation situated on Batote-Doda area of Jammu and Kashmir in Western Himalaya. The rocks underlying this area belong to the Salkhala series composed of moderately metamorphosed mica schists, carbonaceous phyllites, granites and gneisses. The landslide area is mostly covered with overburden composed of highly sheared and weathered phyllites and schists resting over the hard bedrock. There were 2-3 landslides (Fagla Landslides) on the western part of the as seen in Google Earth images for year 2003 and 2004 (Figure 1), while Korapani landslide itself had not occurred till that time. However, during the fi eld visit of 2012, Korapani landslide had taken place (Figure 2) and the others (Fagla Landslides) had been treated. This indicates that the area is tectonically active and simultaneous landslides have been occurring here.

Since the area is active, the amount of overburden which gets saturated due to precipitation coupled with toe cutting by river catalyzes the process of landsliding. Hence to demarcate the overburden bedrock thickness Ground Penetrating Radar Survey was carried out using different sets of antennae along different road cuts as shown in fi gure 2 and the SIR-20 and RADAN software was used for data acquisition and processing. Data acquired by the 200 MHz antenna has been used for analysis and interpretation. The

overburden-bedrock interface on the landslide in the upslope area was observed to be at 6m depth, which reduced to approximately 5m in middle and this depth decreases to about 4m at the bottom of the slide. So, the thickness of overburden is more in the upslope and less in the downslope portion which indicates that the slope is very unstable and highly susceptible to failure.

Using the GPR Survey, Aster GDEM and Total Survey Station data, cross profi le of the Korapani landslide facing towards North-North west has been prepared. The blue line in the fi gure 3a represents the topography of the hill slope as mapped by the Total Survey Station whereas red dashed line marks the topography obtained through the Aster GDEM data for the year 2010 when the landslide had not occurred on that slope. The yellow dashed line in fi gure 3b, indicates the overburden-bedrock interface obtained through the GPR survey on Road A(1060m), Road B(1080m), Road C(1100m) and Road D(1100m). The upper part of the landslide has agriculture terrace (fi gure2 and 3a) because of which water keeps on percolating into the soil making the slope more prone to failure. Also, towards the lower elevation, we can see that the slope has a little depression because of the intensive erosion caused by the reservoir water of the Baglihar Hydro electric Project dam. The cross sections (Figure 3a and 3b) clearly show the difference between the earlier slope of the hill and the present depression created by the landslide. Further, by computing the area between the different positions of soil-bedrock interface, slope from Aster GDEM data and slope from Total Survey Station in the cross section, the amount of total overburden of the slide, material which has already slided down and the material which may slide down in future can be calculated. Ultimately, the amount of sediment load entering the Chenab River can be quantifi ed.

GPR based slope stability study of Korapani Landslide, Jammu Himalaya

*R. P. Singh1, Dericks P. Shukla1, Chandra S. Dubey1, B. K. Mishra1 and T. Bhatnagar1

1Department of Geology, Centre for Advanced Studies, University of Delhi, Delhi-110007, India(*Email: [email protected])

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Fig. 1: Google Earth image for 2003-04 of Fagla landslide (Landslide 2) and Korapani landslide area.

Fig. 2: Roads on Korapani Landslide along which GPR, Total station survey was carried out.

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Fig. 3: (a) Cross section of the Korapani landslide area, created using Aster GDEM (dashed red lines) and Total station survey (blue line). (b) Cross section of the Korapani landslide, created using Aster GDEM (dashed red lines) and Total station survey (blue line) showing road sections and overburden-bedrock interface (dashed yellow lines).

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The Budhi Gandaki Hydropower Project has a capacity of 600 MW, is the storage type scheme, and includes 275 m long headrace tunnel, 225 m high earth fi ll dam at 2km upstream from the confl uence of Budhi Gandaki and Trishuli river, and 100m long by 30m wide and 46m m high underground powerhouse with its crown elevation at 348 m. The project site lies between Gorkha and Dhading districts.

The feasibility study of the project was completed in 1984 and is estimated to cost $1.50 billion. According to the feasibility study, the project is one of the most favored hydropower projects due to its high potential benefi ts and close proximity to the Capital. The reservoir of the Budhi Gandaki will have an area of 50 square km.

The main objectives of the present studies are to carry out fi eld investigations to collect basic geological information and to study the characteristics of foundations in order to identify stability and stress conditions for the tunnel and underground power house as well as other structure. Second objective is to suggest the required tunnel support.

In general, the rocks of project area are fair (RMR) and are slightly to moderately weathered in nature. Phyllite and dolomite the predominant rock type of the dam site area. The predominant rock types in the headrace tunnel alignment are quartzite and phyllite. Powerhouse site consists of phyllite, and band of siliceous dolomite. The rocks around

the project area dip predominantly to the North West. The surfacial deposits in the project area are mainly alluviums and colluviums. The nearest regional thrust of seismic value is the Main Boundary Thrust (MBT), which is located at a distance of about 15 km south of the project area. The another major regional thrust is the Main Central Thrust (MCT), which is located at a distance of about 40 km to the north of the project area.

Joint analysis clearly shows there is a probability of toppling failure at dam site, lateral wedge failure at power house as well as for tunnel. Joint analysis for Surge Tank, Intake Shaft, Intake Portal and Diversion outlet shows, very lateral wedge failure.

Wedge stability analysis for headrace tunnel shows that fi ve types of wedge are formed under the headrace tunnel in which wedge 2 is found to be critical one. The wedge weight 27 tonnes and have a safety factor equal to 0.40, which increase to 9.98 after the installation of shotcrete and rock bolts.

Wedge stability analysis for powerhouse cavern shows that fi ve types of wedge are formed under the underground cavern in which wedges 3 are found to be critical. The wedges weight 717,4825 and 4856 tonnes and have a safety factor equal to 0.00,0.95 and 0.27 respectively, which increase to 2.68,3.91 and 1.69 respectively after the installation of shotcrete and rock bolts.

Engineering geological and geotechnical studies of Budhi Gandaki Hydroelectric Project, central Nepal

*Rabindra Prasad Dhakal1, Prakash Chandra Adhikary2, Jayandra Man Tamrakar3 and Matrika Prasad Koirala4

1Himal Hydro and General Constructions Ltd, Post Box No. 12268, Kathmandu, Nepal, 2Central Department of Geology, Tribhuvan University, Kathmandu, Nepal

3Engineering Services, Nepal Electricity Authority, Kathmandu, Nepal4Department of Electricity Development, Ministry of Energy, Government of Nepal, 576 BhaktiThapa Sadak (4),

Kathmandu, Nepal(*Email: [email protected])

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The Lithostratigraphic classifi cation scheme developed for metasedimentary succession of Nepal Lesser Himalaya differs from researcher to researchers. There exist several homonyms and synonyms in the stratigraphic classifi cation and nomenclature of the succession. Most of the lithological units are developed in course of geological mapping and so detailed description of individual units, their correlation with pre-existing units are lacking. So, a revision of stratigraphic classifi cation and nomenclature of the metasedimentary succession of Nepal Lesser Himalaya is become essential. An attempt has been made to correlate the difference Lithostratigraphical units developed by various researchers in different sections of Nepal Lesser Himalaya and recommend an integrated workable stratigraphic scheme for the Midland metasedimentary succession. Considering the accepted principle and guidelines for stratigraphic classifi cation and nomenclature the following conclusions can be made:(1) It is more appropriate to name the considering

metasedimentary succession as Midland Group and recommend it as valid name for the considering rock succession.

(2) With some local variations, most of the rock unity identifi ed by Stocklin (1980) are recognizable in the central and western Nepal. The lower and middle Parts of the succession represented by Kunchha Formation, Fagfog Quartzite, Dandagan Phyllite, Nourpul Formation, Dhadhing Dolomite and Benighat Slate can be considered as workable units for the metasedimentary succession of entire Nepal Lesser Himalaya.

(3) The uppermost part of metasedimentary succession of Central Nepal, representing Malekhu and Robang formations seems to be much modifi ed in the western and Farwestern Nepal. It is represented by Sorek formation and Dhanpure Limestone in Western Nepal (Dhital et al 2002) and Dehimandu, Gadhi and Julaghat formations in Far Western Nepal (Mahara and Sah 2007).

(4) The upper part of the metasedimentary succession seems to be more complete in Far Western Nepal and it also contains the youngest lithostratigraphic unit named as Julaghat formation.

(5) Detailed stratigraphic works for the metasedimentary rock succession is still lacking from the eastern lesser Himalaya of Nepal.

(6) The entire metasedimentary succession is seems to be late Precambrian in age although for its upper part Lower to Middle Paleozoic age has been considered by some researches,but there is no suffi cient evidences in support to this.

(7) The proposed workable stratigraphic units for metasedimentary succession of Nepal lesser Himalaya with their equivalents are presented in Table-1.

Table 1: Proposed workable rock units of Metasedimentary succession of Lesser Himalaya with their equivalents.

Proposed Units Equivalent UnitsJulaghat Formation -Dhanpure Limestone Gadhi Formation (Mahara and

Sah 2007)Sorek Formation Kerabari Formation (Sakai

1983;1985)Malekhu and Robang Formations (Stocklin 1980)Dehimandu Formation (Mahara and Sah 2007)

Benighat Slate Galayang Slate (Hirayama et al. 1988)Black Slate (Arita et. al., 1984)Ramdighat formation (Sakai 1985; Hirayama et al. 1988)

Dhading Dolomite Darsing Dolomite (Hirayama et al. 1988)Surtibang Dolomite (Sharma et al. 1984)Chappani, Khoraidi and Saidi Formations (Sakai 1985)

Nourpur Formation Khamari Formation (Dhital and Kizaki 1987)Syangja Formation (Hirayama et al. 1988)Virkot Formation (Sakai 1985)Variegated Formation (Sharma et al. 1984; Arita et. al. 1984)

Lithostratigraphy of metasedimentary succession of Nepal Lesser Himalaya: A revision of standardization

Ram Bahadur SahCentral Department of Geology, Tribhuvan Unviersity, Kirtipur, Kathmandu, Nepal

145


Dandagaon Phyllite Uniyachaur Slate (Hirayama et al. 1988)Naya gaon Formation (Dhital et al. 1999)Heklang formation (Sakai 1985)Balewa Formation (Paudel and Dhital 1996)

Fagfog Quartzite Naudanda Quartzite (Paudel and Dhital 1996; Sakai 1983; 1985; Hirayama et al. 1988)Balle Quartzite (Dhital and Kizaki 1987)

Kuncha Formation Dangri Formation (Dhital and Kizaki 1987)Andhi Formation (Sakai 1984; 1985)Seti Formation (Paudel and Dhital 1996)

REFERENCES

Arita, K., Sharma, T., Fujii, Y., 1984. Geology and structure of the Jajarkot-Piuthan area, central Nepal. Journal of Nepal Geological Society Special Issue 4, pp. 5-27.

Dhital M. R., Thapa, P. B. and Ando H., 2002, Geology of inner Lesser Himalaya between Kushma and Syangja in western Nepal. Bull Dept. Geol. T.U, v. 9, pp. 1-60.

Dhital, M. R. and Kizaki, K., 1987, Structural aspects of northern Dang Lesser Himalaya. Bulletin of the College of Science, University of the Ryukus, v. 45, pp. 159-182.

Hirayama, J., Nakajima, T., Shrestha, S. B., Adhikari, T. P., Tuladhar, R. M., Tamrakar, J. M., Chitrakar, G. R., 1988, Geology of southern part of the Lesser Himalaya, west Nepal. Bulletin of the Geological Survey of Japan, v. 39, pp. 205-249.

Mahara A. S and Sah R. B, 2007, Lithostratigraphic classifi cation of Metasedimentary succession of Baitadi Area, Far western Nepal. Jour. SAN, v.6, pp. 1-10.

Paudel, L. P., Dhital, M. R., 1996, Geology and structure of the area between Pokhara and Kusma, western Nepal Lesser Himalaya. Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, v. 5, pp. 47-60.

Sakai, H., 1983, Geology of the Tansen Group of the Lesser Himalaya in Nepal. Memoirs of the Faculty of Science, Kyushu Univversity (Japan), Series D, Geology, v. 25, pp. 27-74.

Sakai, H., 1985, Geology of the Kali Gandaki supergroup of the Lesser Himalaya in Nepal. Memoirs of the Faculty of Science, Kyushu Univversity (Japan), Series D, Geology, v. 25, pp. 337-397.

Sharma, T., Kansakar, D. R., Kizaki, K., 1984, Geology and tectonics of the region between Kali Gandaki and Bheri Rivers in central west Nepal. Bulletin of the College of Science, University of Ryukyus, v. 38, pp. 57-102.

Stocklin, J., 1980, Geology of Nepal and its regional Frame-Jour Geol. Soc. London, v. 137, pp. 1-34

Stöcklin, J., 1980, Geology of Nepal and its regional frame. Journal of Geological Society of London v. 137, pp. 1-34.

146


Rapid rise of bed level near Lothar Khola Highway Bridge was noticed in the recent past. According to the local people nearly 7 m of river bed level was raised between 2003 and 2006, rendering the area into a hazardous zone - high risk of fl oods and land aggradations. Substantial arable terraces in the foothills are converted into non-arable terraces where marginalized people including Chepangs are largely residing. The situation is further exacerbated by ever increasing impacts of climate change -- erratic change in weather conditions such as early or late monsoon which is already evident as late plantation of paddy crops across the country was reported during South Asia Climate Change Conference, October 2009, Kathmandu.

In consideration to an appeal by the people of Chepang Community, one of the most underdeveloped and underprivileged people of Nepal, a tangible concept are being developed named as: the Community ‘Gegran’ Benefi ciary Group (CGBG) which is an income generation platform for all the people belonging to the target group. To establish the CGBG it would however take at least a year and further two more years will be required for a cycle of operation to complete. A social survey was also conducted by DWIDP (2008) under the leadership of the author focused to soil erosion in parts of Lothar Khola watershed, identifi ed number of problems linked to bed level rise and environmental degradation. Following the survey, a rigorous interaction with local community including then local member of dissolved Constituent Assembly Mr. Govind Chepang was also held. Present research is largely based on past fi eld works by the author in the Lothar Khola watershed and a comprehensive desk research.

The research intends to address critical hazards of Lothar Khola watershed as a whole and also sufferings faced by the

local community due to: i) rapid rise of bed level in Lothar Khola near Highway Bridge ii) lack of alternative income generation opportunity for the target group iii) increasing threats of natural disasters to the inhabitants of Lothar Khola watershed particularly residing along the banks of river and iv) ever deteriorating environment of Lothar Khola watershed.

A cost benefi t analysis is being carried out which clearly depicts a Net Profi t to CGBG at NRs. 299611125.00 with Net Income per Household NRs. 105127.00 per annum. Further an operational model comprising seven steps is being designed carefully. Anticipated outcomes of the proposed concept are: 1) Target Group people would generate suffi cient income through establishment of ‘Gegran’ business exclusively managed by the target community; 2) Bed level of Lother Khola posing risk to the Highway Bridge would bring back to normal level through collection of excess ‘Gegran’; 3) Imposed risks of natural disasters to poor migrant inhabitants residing in the banks of river around the Highway Bridge would be signifi cantly reduced; 4) Slash and burn subsistence agriculture would be substantially reduced and 5) On top of everything environment of the Lothar Khola watershed as a whole would be signifi cantly improved.

This concept under research would fi nally help establish CGBG that provides tangible benefi ts to the Chepang Community as an alternative to slash-burn cultivation for their sustenance livelihood and also provide benefi ts to other migrated people residing around the Lothar Khola Bridge since long. This could be one way out towards introducing and sustaining green-economy in Nepal that would contribute mitigate impacts of climate change.

Towards green economy through community ‘Gegran’ benefi ciary goup: A case of Lothar Khola watershed, Chitwan, central Nepal

Ramesh M. Tuladhar(Email: [email protected])

147


The 21 high gain short period velocimetric stations monitored by DMG/NSC allow detecting and locating every earthquake with magnitude greater than ML=2.2 within Nepal, insuring the trigger of the seismic alert for every event above ML=4.0. However, their dynamic is not suffi cient to determine also the peak ground acceleration (PGA), velocity (PGV) and displacement (PGD) at very short distances from the largest earthquakes, informations which are needed as critical inputs to seismic hazard assessment models. The acquisition at NSC of a complementary strong motion database by a dedicated accelerometric network appeared therefore to be a priority.

The project began with the installation of permanent accelerometric stations in 2009 in Pokhara (PKR at sediment), Kakani (KKN at rock) and Kathmandu (DMG at sediment) complemented 2 years later by new permanent installations at Dhunche (DHU at Rock) and Surkhet (SKT at sediment). After the Taplejung-Sikkim earthquake of ML=6.8 on 18th September 2011, additional temporary

accelerometric stations were deployed in Tumlingtar (TUM at rock), Taplejung (TAP at rock) and Illam (ILM at rock) to capture the largest aftershocks of the crisis. An additional permanent station fi rst installed in Dadeldhura, then moved to Ghanteshwar expand the network toward Far Western Nepal since mid 2012. During these 4 years of acquisition more than 400 accelerometric records of local earthquakes, covering events of magnitude 6.8≥ML≥2 at distances between 675 km and 20km from these sources have been acquired.

After describing the sites instrumented, we present some of the most typical or exceptional records including the ones from the September 18th 2011 Taplejung-Sikkim earthquake (ML=6.8) and November 12th 2011, Gorkha event (ML=5.0), We further describe some seismic aggressiveness parameters derived from these records. We then show how the new accelerometric records help complementing the existing weak motion database derived from the velocimetric records. We fi nally discuss its future capacity at evaluating seismic ground motion variability in Nepal.

Ground motion records from the accelerometer network of National seismological centre, Nepal

*R. Pandey1, M. Bhattarai 1, C. Timsina1, S. N. Sapkota1, U. Gautam1, L. B. Adhikari1, M. Jha1, T. Kandel1, P. Shrestha1, B. P. Koirala1, C. Gourraud1, V. Boutin2 and L. Bollinger2

1DMG, Lainchaur, Kathmandu, Nepal2DASE, Bruyères le Châtel 91297 Arpajon, France


148


The study area encompasses the eastern most tip of the Indian territory of Ladakh; here the strike–slip Karakoram Fault (KF) bifurcates in two strands viz. the SW Tangtse Strand and NE Pangong Strand (Rutter et al. 2007). The River Tangtse, a tributary of the River Shyok (Shyok-tributary of the River Indus) occupies a 94.18 km long course in the KF zone and covers an almost 2170 sq km basin area. Active nature of KF in the area is evidenced by the presence of various features like strath terraces (28 m), offset of streams (200-400 m), wide valleys fi lled with debris fl ow and fl uvio-lacustrine sediments at a height of ~50-60 m above the present day river level. Clean indications of fl ood drainage are evident from the geomorphology of the area. The whole area shows an interplay of fl uvial, lacustrine, colluvial and also aeolian deposits. The colluvial material that fi lls the incised valley is indicative of a tectonic uplift. The valley occupying the Tangtse strand is quite wide and completely fi lled with alluvial fan, and debris fl ow deposits. A west heading fault scarp is visible within the fan, and abandoned channel are clearly seen in the LISS-III satellite data. Unpaired terrace deposits are seen in the left bank of the river, with the oldest (T2) deposited ~50 ka and T1 between 30-20 ka BP. T0 is the present day river terrace. The River Tangtse fl ows through a very narrow gorge (nearly 300-400 m), cutting across the KF 18-20 km before joining the River Shyok. Patches of fl uvio-lacustrine sediments are also seen preserved at places. One of the fl uvio-lacustrine events dates to ~ mid Holocene time. In other places the lacustrine facies is distributed all along the river valley at ~50-60 m above the present day river level, on both fl anks of the river. The type section is ~40 m thick, composed of laminated mud and sand successions. These features indicate that the

River Tangtse was once blocked and the whole valley was occupied by a lake.

Within the lake sediments soft sediment deformational structures (seismites) that are related to earthquakes are well preserved. Apart from seismites, the clay bed show folding and faulting. Small scale reverse faulting is also observed within the clay units. The ~40 m thick fl uvio-lacustrine type section at Tangtse village has minimum of fi ve alternating fl uvial and lacustrine cycles (fi ning–up cycles), with the clay beds the scale of a few cm to ~5 m. Changes in magnetic susceptibility (the bulk representation of ferrimagnetic content) and Loss on Ignition data of the type section divides it into two broad phases.Phase 1 (0- 20 m level) is the older phase with higher susceptibility values that show a cyclic variation ,Phase 1 can be divided into several sub phases. However, Phase 2 (20-40 m) has low values throughout and only shows peaks of susceptibility at places where there is a clay lens or drop stone in the bed. The Loss on Ignition percentages ranges from ~1-15%. Three levels, 0.5-3.5 m, 16-22 m, and 30.2 m-top of the section, show comparatively higher values than rest of the section. The work on the chronology, textural analysis, and other magnetic parameters is in progress. Results will shed light on the variations in the climate during the deposition of this lake system and its relation to the fl uvio-lacustrine phases ~50, 30-20 and 5-6 ka BP.

REFERENCE

Rutter, E. H., Faulkner, D. R., Brodie, K. H., Phillips, R.J. and Serale, M. P, 2007, Journal of Structural Geology, v. 29, pp. 1315-1326.

Quaternary architecture of the Tangtse valley, Ladakh, NW Transhimalaya: Implications to tectonics, landform evolution and

climate

*Randheer Singh1, Binita Phartiyal1, Girish Ch. Kothyari2 and Anupam Sharma3

1Birbal Sahni Institute of Palaeobotany, 53-University Road, Lucknow-226 007, UP., India2Institute of Seismological Research, Raisan, Gandhinagar- 382382009, Gujarat, India

3School of Earth & Environmental Sciences, Central University of Himachal Pradesh, PO Box 21, Dhramshal, District Kangra, Himachal Pradesh 176215, India

(*Email: binita phartiyal @gmail.com)

149


In geoscience, a wide variety of terms has been used to describe any detached mass of soil, rock, or debris that moves down a slope mainly by gravitational forces. Working Party on World Landslide Inventory has suggested the informal defi nition of landslide as “The movement of a mass of rock, earth or debris down a slope”. This is the most adopted informal defi nition of landslide and was widely used in the International Decade for Natural Disaster Reduction (1990-2000). Landslides in the Nepal Himalaya are mainly of two types: 1) small-scale landslides, including debris fl ows, debris slides, rock falls, rock slides and so on and 2) large-scale landslides. It is well known fact that landslides in the Nepal Himalaya are scale-dependent, from the massive extent of a whole mountain range to very minor slope failures.

Interpreting of landslide processes in the Nepal Himalaya needs broad knowledge of both small-scale landslides and large-scale landslides. Both type of landslides are generally facilitated by the combined effect of intrinsic and extrinsic parameters. A trigger is an extrinsic event and for the Nepal Himalaya, an intense rainfall event or an earthquake or rapid stream erosion that causes a near-immediate response in the form of a landslide by rapidly increasing the stresses or strains and reducing the strength of the slope-forming materials. Study shows that for the small-scale landslides, rainfall is the major triggering agent and for large-scale landslide, most probably, mega earthquakes of geological past were major triggering agents. Comparison of small-scale scale landslides with triggering factor is quite easy but understanding of triggering factor of large-scale landslide is quite complicated. For small-scale landslide, intrinsic parameters also play major role in the landslide occurrence and they include bedrock geology, geomorphology, soil depth, soil type, slope gradient, slope aspect, slope curvature, land use, elevation, engineering properties of the slope material, land use pattern, drainage pattern, drainage

density and so on. Size and extent of rainfall induced small-scale landslides largely depends upon intensity and duration of the rainfall events.

Detail studies of small-scale landslides and large-scale landslides were conducted in central Nepal and both landslides were evaluated in terms of geological and geotechnical characteristics and distribution probability. Based on the general landslide classifi cations, in Nepal, the small-scale landslides landslide triggered by rainfall can be classifi ed as translational landslides, rotational landslides, followed in many cases by a fl ow-like landslide or debris fl ow. The failure surface of translational landslides is generally at a depth of 2–4 m and appears to affect the whole hill slope. Rotational slides were generally seen on residual soil where water on slope was not properly managed. These fl ows were generally initiated in small area at top of hill or head of gully and fl ow with extremely high velocity and erode its path which fi nally rich with high debris load and damaged every thing on its path. These fl ows generally had shallow depth (<2 m) at upper part of failed slope and lower part of fl ow had depth more than 3 m in many landslides. In many cases, the materials involved in all the fl ows were very similar and mainly consists of the gravel silt of colluvium origin. Landslides distribution map suggests that the orographic rainfall effects of monsoon cloud and frequent extreme rainfall events results higher concentration of landslides in central Nepal, in comparison to other parts.

Inventory map of large-scale landslides were also prepared for central Nepal and their distribution probability and typical characteristics were evaluated. An easy method of identifying large-scale landslide were also developed with a 3-D schematic diagram, which is expected to help in further research of the large-scale landslides in the Nepal Himalaya.

An overview of landslide science in the Nepal Himalaya

Ranjan Kumar DahalDepartment of Geology, Tribhuvan University, Tri-Chandra Campus, Ghantagar, Kathmandu, Nepal

Ehime University Center for Disaster Management Informatics Research, Ehime University, 3 Bunkyo-cho Matsuyama 790-8577, Japan


150


The rise and support of the 5000 m topographic scarp at the front of Indian-Eurasian collision in the Himalaya involves long-term uplift above a mid-crustal ramp within the Main Himalayan Thrust (MHT) system. Locking of the shallower portion of the fl at-ramp-fl at during the interseismic period also produces transient uplift above the transition zone. However, spatial and temporal relationships between permanent and transient vertical deformation in the Himalaya are poorly constrained, leading to an unresolved causal relationship between the two. Here, we use interferometric synthetic aperture radar (InSAR) to measure interseismic uplift on a transect crossing the whole Himalaya in central Nepal. The uplift velocity of 7 mm/yr at the front

of the Annapurna mountain range is explained by an 18–21 mm/yr slip rate on the deep shallow-dipping portion of the MHT, with full locking of the mid-crustal ramp underlying the High Himalaya. The transient uplift peak observed by InSAR matches spatially with the long-term uplift peak deduced from the study of trans-Himalayan river incision, although models of the seismic cycle involving thrusting over a ramp of fi xed geometry predict an ~20 km separation between the two peaks. We argue that this coincidence indicates that today's mid-crustal ramp in central Nepal is located southward with respect to its average long-term location, suggesting that mountain growth proceeds by frontward migration of the ramp driven by underplating of material from the Indian plate under the Himalaya.

Long-term growth of the Himalaya inferred from interseismic InSAR measurement

*Raphae Grandin1, Marie-Pierre Doin2, Laurent Bollinger3, Bé atrice Pinel-Puyssé gur3, Gabriel Ducret2, Romain Jolivet4 and Soma Nath Sapkota5

1Institut de Physique du Globe de Paris, UMR 7154, F-75005 Paris, France 2Ecole Normale Supé rieure, UMR 8538, F-75231 Paris, France

3CEA, DAM, DIF, F-91297 Arpajon, France4California Institute of Technology, Pasadena, 91125, CA, USA

5Department of Mines and Geology, National Seismological Centre, Lainchaur, Kathmandu, Nepal(*Email: [email protected])

151


Basaltic volcanic conglomerates near Wulgai in Balochistan occur in the sedimentary rock unit of the Bagh (melange zone) complex beneath the Muslim Bagh ophiolite (Fig. 1). The presence of Middle Triassic grey radiolarian chert in the upper, middle and lower horizons of the conglomerates suggests that the volcanic source rocks of these were erupted, eroded and re-deposited in the Middle Triassic (Siddiqui et al. 1996). The conglomerates are essentially made up of basaltic clasts that are amygdaloidal in nature and exhibit porphyritic, cumulophyric, intersertal and vitrophyric textures and show variation in the contents of the principal mineral components. The least altered samples comprise augite, olivine, plagioclase (An35-78) leucite and nosean. Wide range of anorthite contents in the plagioclase is due to albitization. These minerals occur as phenocrysts as well as tinny grains and microlites in a cryptocrystalline and glassy groundmass. Apatite ilmenite, magnetite and hematite occur as accessory minerals, and chlorite, calcite, zeolites, chalcedony and antigorite as secondary minerals.

The petrography and chemistry suggest that these rocks belong to mildly to strongly alkaline intra-plate volcanic rock series. Their low Mg# and low Cr, Ni and Co contents suggest that the parent magma of these volcaniclastics was not directly derived from partial melting of a mantle source, but resulted from fractionation in an upper level magma chamber, en-route to eruption. Their LILE and HFSE contents and enriched primordial mantle-normalized patterns with marked positive Nb anomalies are consistent with an enriched mantle source and provide further support to their within-plate geochemical signatures. The Zr versus Zr/Y relations suggest that the parent magma of the volcaniclastics was derived from about 10-15% melting of an enriched mantle source. It is suggested that the Wulgai volcanism may be related to the opening of a juvenile ocean basin that developed as Ceno-Tethys after the Early Triassic rifting of Alpide (Sengor et al. 1988) collage of micro-continental blocks (Afghan, Iran, Karakoram and Lhasa) from the northern margin of the Gondwana (Brookfi eld 1993; Metacalfe 1995).

Petrology of the Middle Triassic volcaniclstic rocks from Balochistan, Pakistan and its relationship with the break-up of Gondwana

*Rehanul Haq Siddiqui1, M. Qasim Jan2, Asif Hanif Chaudhry1 and Sikandar Ali Baig1

1Geoscience Advance Research Laboratories, Geological Survey of Pakistan, Shahzad Town, Islamabad, Pakistan.2 National Centre of Excellence in Geology, University of Peshawar, Pakistan


Fig. 1: Geological map of the Muslim Bagh area showing the location of the Wulgai volcaniclastics, Balochistan, Pakistan (modifi ed and reproduced after Siddiqui et al., 2011).

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REFERENCES

Brookfi eld, M. E., 1993. The Himalayan passive margin from Precambrian to Cretaceous times. Sed. Geol., v. 84, pp. 1-35.

Metcalfe, I., 1995, Gondwana dispersion and Asian accretion. Journal of Geology Series B., pp. 223-266.

Sengor, A. M. C., Altinar, D., Cin, A., Ustamer, T. and Hsu, K. J., 1988, Origin and assembly of Tethyside orogenic collage at the expence of Gondwanaland, In Charles, M. G. A. and

Hallan, A., (eds.), Gondwana and Tethys. Geological Society Special Publication. Oxford Univ. Press, v. 37, pp. 119-181.

Siddiqui, R. H. and Aziz, A. M., 1996, Geology, Petrochemistry and tectonic evolution of Muslim Bagh Ophiolite Complex Proc. Geoscience Coll., v. 16, pp. 11-44.

Siddiqui, R. H., Mengal, J. M., Hoshino, K., Sawada, Y. and Brohi, I. A., 2011, Back-Arc Basin Signatures from the Sheeted Dykes of Muslim Bagh Ophiolite Complex, Balochistan, Pakistan. Sindh University Research Journal, v. 43, pp. 51-62.

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Recent advances in our understanding of the Himalaya and adjacent regions have changed our perception and knowledge of how large mountain belts form. This understanding is being refl ected in increasingly sophisticated orogenic models, the key input data of which has largely been extracted from the exhumed mid-crustal core of the orogen, the Greater Himalayan sequence, and its bounding structures. Targeted mapping and sample collection in the upper Likhu Khola was carried out across the majority of the Greater Himalayan sequence in east-central Nepal to evaluate the tectonometamorphic evolution of the study area. The exhumed mid-crustal core exposed in the study area comprises upper greenschist to upper amphibolite grade metamorphic rocks that have been pervasively, ductily deformed. Mantled porphyroclasts and c, c’ and s fabrics consistently record top-to-the-south sense directed shear. The Likhu Khola rocks record an inverted metamorphic fi eld gradient as outlined by pressure and temperature estimates using THERMOCALC v.3.26 from nine specimens at different structural positions. Temperatures increase slightly up structural section but become constant within error for the upper portion of the study area. Pressure estimates initially increase up structural section followed by an abrupt pressure decrease coinciding with the initial occurrence of migmatitic rocks. This reversal in the apparent pressure gradient may indicate a discontinuity separating two distinct domains with different structural, thermal and metamorphic histories (e.g. Larson et al 2010; Yakymchuk and Godin 2012). In situ U-Th-Pb monazite geochronology was employed on six of the specimens used for pressure-

temperature analyses to provide temporal constraints on the timing of metamorphism. Multiple age domains, ranging from 27.2 Ma to 15.1 Ma, were noted for several monazite grains and are interpreted to represent distinct thermal events. Trace element data collected concomitant with each U-Th-Pb analysis using split stream LA-MC-ICP-MS exhibits a distinct trend of increasing heavy rare earth elements associated with decreasing monazite age. This is consistent with monazite crystallization from a melt partially sourced from garnet breakdown. Smaller monazite grains generally record a single age domain and may represent monazite growth following complete resorption of older material. The relationships between metamorphism, crustal melting, pressure-temperature conditions and monazite/garnet growth and resorption recorded in the Likhu Khola are crucial to elucidating the tectonometamorphic evolution of the Greater Himalayan sequence and providing constrains for new tectonic models.

REFERENCES

Holland, T. J. B. and Powell, R., 1998, An internally-consistent thermodynamic dataset for phases of petrological interest, Journal of Metamorphic Geology, v. 16, pp. 309–344.

Larson, K. P., Godin, L., and Price, R. A. 2010, Relationships between displacement and distortion in orogens: Linking the Himalayan foreland and hinterland in central Nepal, GSA Bulletin, v. 122, pp. 1116-1134.

Yakymchuk and Godin, 2012, Coupled role of deformation and metamorphism in the construction of inverted metamorphic sequences: an example from far-northwest Nepal, Journal of Metamorphic Geology, Manuscript ID: JMG-11-0050.R1

Tectonometamorphic evolution of the upper Likhu Khola region, east-central Nepal

*Richard From1, Kyle Larson1,2 and John Cottle3

1Department of Geological Sciences, 114 Science Place, University of Saskatchewan, SK, S7N 5E2, Canada 2Earth & Environmental Sciences and Physical Geography, 3333 University Way, University of British Columbia

Okanogan, Kelowna, BC V1V 1V7, Canada3Department of Earth Science, University of California, Santa Barbara, CA 93106, USA


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In order to reconstruct a continuous terrestrial record of the Indian monsoon during the last 700 kyr, pollen and charcoal analyses of a drill-core of lake sediments in the Kathmandu Basin was performed by the Paleo-Kathmandu Lake Project (Sakai et al. 2001). In this project, Fujii and Maki carried out pollen analysis of a 218-m-long core taken from the basin-fi ll sediments. As the results, an outline of the paleoclimatic changes in the valley during the last ca. 700 kyr was revealed, and millennial-scale climatic changes from 130 kyr to 15 kyr were clarifi ed. Furthermore, previous studies on the late Pleistocene glacial history in the Higher Himalaya were examined based on the reconstructed paleoclimatic record. We here present the results, and compare the paleoclimate record with that from the charcoal analysis by Sugimoto on the same samples. Then, we try to reconstruct the paleoclimate changes in the valley from a view point of fi re history.

The pollen diagram is divided into fi fteen fossil pollen zones from K-1 to K-15 in descending order, and they correspond to periods from MIS 2 to MIS 15. In the interglacial periods (MIS 5a, 5c, 5e, 7, 9, 11, 13 and 15), it was generally characterized by increase of warm climate index like as Castanopsis and Mallotus, and by increase of wet climate index like as Alnus, Betula and Carpinus. It means that the climate was hot and wet and it is inferred that the Indian monsoon was active. In addition, it is noteworthy that frequency of Alnus, Betula and Carpinus in MIS 11 was similar to those in early MIS 3 and late MIS 2.

The MIS 3 (K-3c, K-3b, 3a) can be divided into three stages: wet stage of K-3c (64-48ka), dry stage of K-3b (48-39ka), and wet stage of K-3a (39-26.5ka) on the basis of changes in ratio of dry and wet index pollen. During the whole period of MIS 3, it is inferred that mild climate was prevailed based on appearances of Castanopsis and Mallotus.

In the glacial periods (MIS 14, 12, 10, 8, 6, 4 and 2), Pinus, Gramineae, Artemisia and Chenopodiaceae were dominant, and Abies and Picea appeared though their percentages were low. It suggests that the climate in the glacial periods was cold and dry and it is inferred that the

Indian monsoon was weakened. Moreover, in 26-24 ka and 20-19 ka during MIS 2, it was estimated that cold and very dry climate was prevailed, because ratio of Pinus, Gramineae, Artemisia, Chenopdiaceae increase. On the other hand, it was cool and slightly wet in 24-20 ka, and mild and wet in 19-15 ka, because ratio of Alnus, Carpinus, Betula increase, and Castanopsis and Mallotus appear.

As the results of charcoal analysis, it was revealed that number of charcoal grains increased in the glacial periods, especially in MIS 2, 4, 6 and 12. Those high peaks considerably correspond to peaks of the total amount of dry climate index (Gramineae, Artemisia and Chenopodiaceae) and high values of δ13C (Mampuku et al. 2008). Therefore, it is inferred that in glacial periods, precipitation decreased due to weakening of Indian summer monsoon, and caused frequent wild fi re. This tendency is similar to that in core from the South China Sea.

Finally, in the southern slope of Mt. Everest, it was commonly recognized that mountain glaciers actively advanced and expanded during the Tangboche stage of MIS 3, and not so much advanced during the Periche stage of MIS 2, although continental glacier most expanded during the LGM in MIS 2. The paleoclimatic record from the Kathmandu Valley explains this difference as follows: it was so dry during the LGM that snow fall decreased due to weakening of Indian summer monsoon, on the other hand during the MIS 3, Indian summer monsoon was active and wet air invaded into the Everest area along the valley, and snow fall made grow mountain glaciers.

REFERENCES

Mampuku, M., Yamanaka, T., Uchida, M., Fujii, R., Maki, T. and Sakai H., 2008, Changes in C3/C4 vegetation in the continental interior of the Central Himalayas associated with monsoonal paleoclimatic changes during the last 600 kyr. Climate of the Past, v. 4, pp. 1-9.

Sakai, H., Fujii, R., Kuwahara, Y., Upreti, N. B., and Shrestha, D. S., 2001, Core drilling of the basin-fi ll sediments in the Kathmandu Valley for paleoclimatic study: preliminary results. Journal of Nepal Geological Society, v. 25 (Special Issue), pp. 9-18.

Reconstruction of paleomonsoon record in the Kathmandu Valley during the last 700 kyr: Approach from pollen and charcoal analyses

*Rie Fujii1, Misa Sugimoto1, Takeshi Maki2 and Harutaka Sakai1

1Department of Geology and Mineralogy, Kyoto University, Kyoto, 606-8502, Japan2Japan Agency for Marine-Earth Science and Technology, Yokosuka, 237-0061, Japan


155


Recent fi eldwork in eastern Nepal has shown that the M~8.2, 1934 earthquake ruptured the surface, rebutting the consensus that it was blind. Preliminary observations suggest that the primary 1934 rupture extended at least ≈150 km, from Bardibas to Dharan, within the region of strongest shaking. We present here new results of our ongoing search for the extension of this rupture and more ancient ones along that stretch of the MFT, between the Charnath and Devdhar Khola. Systematic mapping and sampling of uplifted terrace surfaces and abandoned paleo-channel meanders truncated by the megathrust was based on the interpretation of stereoscopic air photos, high-resolution satellite images, and 1/25,000 topographic maps. Several Total Station (TS) and Terrestrial Lidar Scanner (TLS) surveys provided high-resolution DEMs to quantify the 3D evolution of the geomorphic landscape and unravel sequential mechanisms of uplift and incision.

Where the Charnath Khola crosses the thrust, a hanging-wall paleo-channel now perched 15±1 m above river was abandoned around AD 870±30, which is consistent with a millennial uplift rate greater than 10 mm/yr. Since abandonment, the channel appears to have been uplifted by at least 2 earthquakes, likely the 1255 and 1934 events. The interpretation of a mega-trench, where the 1934 surface rupture appears to be also recorded, is in progress. Both walls of the trench show thin strath layers of cobbles and oxydized pebbles that either cap, or are truncated by, several 50°N-dipping thrust splays. Large collapse wedges, some of them deformed, and folded units imply surface rupture by at least 5 seismic events since about 8000 years ago.

Farther east near Dhangadhi (26.81ºN, 86.42ºE), in the Khutti Khola valley, our new high-resolution TS and TLS DEMs help identify 6 main hanging-wall terrace levels, uplifted from 4.4±0.3 m to 37.3±1 m above river. Samples from the lowest terraces yield 14C ages of ≈100 years BP, suggesting very recent uplift, probably by the 1934 earthquake. A second terrace level, dated by optical luminescence to be ≈ 1100 years old, stands 8.7±0.5 m above river. As at Charnath, this suggests that this second surface was uplifted by the 1934 and 1255 earthquakes, each with a characteristic slip of ≈ 4.4±0.3 m. Preliminary luminescence and 14C dating of samples collected from the highest terrace level indicate ages of 4250±250 years, which implies a late Holocene uplift rate also on order of 10 mm/yr. Moreover, assuming negligible hanging-wall terrace degradation and footwall fl uvial incision, the uplift of this highest terrace might have been the result of 8 events comparable to the most recent ones, with an average return time on order of ≈ 600 years.

East of Lahan, the MFT tends to show multiple splays offsetting strath terraces and folding gravel layers exposed in river-cuts. At the outlet of the Devdhar Nadi valley (26.65ºN, 86.55ºE), our TLS DEM helps map the relative elevations of uplifted terraces and of two abandoned meander channels in the hanging-wall. These paleo-channels stand 4.3 m and 8.3 m above the riverbed, with modern and 135 yrs BP 14C ages, respectively. This is also consistent with very recent tectonic uplift. Paleo-seismological interpretations and Quaternary dating, still in progress, should confi rm if traces of the great 1255AD and 1934 earthquakes are found here, as in the Sir and Charnath Khola, ~120 km farther west.

Geomorphology, paleoseismology and slip rate of the Main Frontal Thrust between the Charnath and Devdhar Khola, Eastern Nepal

*Rizza Magali1, Soma Nath Sapkota2, Paul Tapponnier1, Laurent Bollinger3, Marie Etchebes1, Yann Klinger4, Ramesh Pandey2 and Elise Kali1,5

1Earth Observatory of Singapore, Nanyang Technological University, Singapore 2Department of Mines and Geology, Kathmandu, Nepal

3CEA/DASE, Bruyeres le Chatel, France4Institut de Physique du Globe, Paris, France

5Institut de Physique du Globe, Strasbourg, France(*Email: [email protected])

156


Geological mapping is very important technique to predict geological condition for underground structures. It helps to construct geological model for site selection and designing of any underground structures. Geological uncertainty is directly proportional to the accuracy of geological mapping. More accurate geological mapping resulted fewer uncertainties. Precise delineation of faults and shear/weak zones is important part of the geological mapping to predict uncertainties. Generally geological condition is predicted based on surface rock outcrop and

structures by projecting down to the level of underground structures. Hence, geological mapping to predict geological condition for underground structures is a challenge in the tectonically active Nepal Himalaya due to thrusting, faulted, jointed and folded nature of rocks forming steep topography. The mapping is mostly focus on rock mass properties, discontinuities, faults, weak/shear zones, fractured zone, weathering, folds, and ground water conditions which are responsible for stability of underground structures. This paper highlights importance of geological mapping and challenges for underground structures.

Geological mapping in Nepal Himalaya: Importance and challenges for underground structures

S. C. SunuwarSN Power Holding Singapore Pte. Ltd., Lalitpur

(Email:[email protected])

157


An attempt has been made to assess seismic hazard in the Kathmandu Valley. Probabilistic Seismic Hazard Analysis (PSHA) method of Cornell (1979) has been used in the analysis. A FORTRAN77 code written by the principal author has been used in this study.

Based on seismicity pattern, geometry of seismicity belt and geological structures, ten potential aerial sources have been identifi ed and used in this study. Seismic Hazard Analysis is carried out at 27.42N and 85.18E). Probability of mean annual exceedances of target Peak Ground Acceleration (PGA), ranging from 0.01g to 2.0g, with an increment of 0.01g are calculated using Young’s (1997) predictive relation. The Peak Ground Acceleration at bedrock, corresponding to 10% chance of exceedance in 50 years is estimated to be 0.48 g (1 g = 9.8 m/s2).

During the 1934 Bihar-Nepal Earthquake, the Kathmandu Valley experienced intensities from IX to X (Pandey et. al. 1988). The PGAs calculated in this study

were converted into Modifi ed Mercalli Intensity (MMI) values using relation between seismic intensity (MMI) and PGA established by Trifunac and Brady (1975). Comparison of the converted intensities and the observed intensities (IX to X) during the 1934 Bihar-Nepal Earthquake correlate very well.

REFERENCES

Cornell, C. A., 1968, Engineering seismic risk analysis, Bulletin of the Seismological Society of America, v. 58, pp. 1583-1606.

Pandey, M. R. and Molnar, P., 1988, The distribution of intensity of the Bihar-Nepal Earthquake of 15 January 1934 and bounds on the extent of the rupture zone. Journal of Nepal Geological Society, v. 5, No. 1, pp. 22-44.

Trifunac, M. D. and Brady, A. G., 1975, A study on the duration of strong earthquake ground motion. Bulletin of the Seismological Society of America, v. 65, pp. 581-626.

Youngs, R. R., Chiyou, S., Silva, W. J., Humphrey, J. R., 1997, Strong ground motion attenuation relationships for subduction zone earthquakes, Seismological Res. Letters, v. 68, pp. 59-73.

Probabilistic seismic hazard analysis of Kathmandu Valley

*S. Rajaure1 and G. K. Bhattarai2

1Department of Mines and Geology, Lainchaur, Kathmandu, Nepal 2Khwopa Engineering College, Bhaktapur, Nepal


158


The Himalayan mountain belt is the premier example of continental collision tectonics and is seen as a proxy for understanding the evolution of ancient orogenic belts as Caledonides (e.g. Streule et al. 2010) and Variscan orogeny (e.g., Franěk et al. 2011). This mountain chain is also the source for inspiration and development of hypotheses that currently are among the focus topics of geosciences like syn-tectonic extension (e.g. Searle 2010), feedback relations between climate and tectonics (e.g. Clift 2010), rheology implications and exhumation consequences in response of crustal melting (e.g. channel fl ow model, Beaumount et al. 2001). In particular, the channel fl ow model is regarded as the best model to explain the Himalayan geology. In this model the metamorphic core of Himalaya, i.e. Greater Himalayan Sequences (GHS), is seen as a ductile partially molten channel extruding southward during the synchronous (23-17 Ma) shearing along a basal thrust (Main Central Thrust, MCT) and extensional detachment at the top (South Tibetan Detachment System, STDS) driven by focused erosion of Monsoon. This model explains a lot of features of the belt as the P-T-t path of metamorphic rocks, the quite homogeneous cooling ages of GHS and the occurrence of Northern Himalayan Gneiss Dome. By the way the Himalayan geology is far from being well known and understood. For these reasons is really important to test the applicability of such hypotheses in a spatial and temporal context (e.g. continuity, synchrony and applicability all along the belt).

Recently geologists working on GHS describe high-grade compressional shear zones (Carosi et al. 2010; Imayama et al. 2012) active before the beginning of the synchronous shearing along MCT and STDS, testifying that exhumation of GHS starts in same places before the activation of channel fl ow.

In this contribution we present structural, geothermobarometric and gechronological data of a new reported ductile shear zone (Mangri Shear Zone; MSZ) in the Mugu Karnaly Valley (Western Nepal) within the core of GHS. MSZ is a thick (4-5 km) ductile high-temperature

shear zone affecting metapelite and orthogneiss of GHS. This shear zone places high-grade sillimanite to cordierite bearing migmatitic rocks on kyanite bearing, locally migmatitic, rocks. Clear kinematic indicator such as S-C fabric, mica fi sh, rotated porphyroclasts and drag folds, observable both meso- to micro scale, reveal a top-to-the South sense of shear. Quartz in the granoblastic layers presents clear indication of GBM recrystallisation such as lobate grain boundaries and pinning microstructures and present chessboard extinction suggesting an high T (>650°C) of deformation, coherently with the fi ndings of sillimanite along the mylonitic foliation.

Application of internally consistent thermodynamic set of geothermobarometers on metapelites, indicates that the rocks of MSZ experienced prograde metamorphism, with “metamorphic peak” at a temperature of 690-725°C (±25°C) and a pressure of 0.75–0.8 GPa (± 0.1 GPa), close to kyanite-sillimanite boundary followed by isothermal decompression in the sillimanite fi eld,. This P–T path was compared with two selected samples of the footwall: 1) a Grt-St-Ky mylonitic micaschist from underlying Main Central Thrust Zone and 2) a Grt-Ky micaschist from the Ky zone. The fi rst sample shows a prograde path with a “metamorphic peak” at a temperature of 600-660°C (±25°C) and pressure of 1.05–1.10 GPa (± 0.1 GPa), while the second sample show a “metamorphic peak” at a temperature 680-700°C (± 25°C) and a pressure of 0.95–1.00 GPa (± 0.1 GPa), both in the kyanite stability fi eld. In summary, P-T estimates point out a gap of at least 2 kbars between footwall and hanging wall rocks juxtaposed by MSZ.

EMPA analyses and LA-ICPMS in situ U-(Th)-Pb geochronology reveal two generations of monazite in MSZ samples. The fi rst type (Mnz1), with low Y and high LREE, is the oldest one (~25 Ma); it was interpreted as an allanite-out reaction product, since no monazite but only allanite was found inside garnet. The second type (Mnz2), with high Y, forms mottled zones or discontinuous rims on the previous one. Mnz2 (18-17 Ma) is interpreted as formed from garnet breakdown during decompression and in equilibrium with

Structural, metamorphic and geochronologic constrains of a ductile shear zone within the core of Higher Himalayan Crystallines in western

Nepal: The Mangri Shear Zone

*Salvatore Iaccarino1, Carosi Rodolfo2, Chiara Montomoli1, Antonio Langone3 and Dario Visonà4

1Dipartimento di Scienze della Terra, University of Pisa, Pisa, Italy, 2Dipartimento di Scienze della Terra, University of Torino, Torino, Italy

3C.N.R.-Istituto di Geoscienze e Georisorse, UOS Pavia, via Ferrata 1 27100 Pavia, Italy 4Dipartimento di Geoscienze, University of Padova, Padova, Italy


159


xenotime found along foliation. Monazite–Xenotime thermometer reveals that the Mnz2 growth is between 450° and 680° C (±50°C), during cooling. In this way MSZ activity is confi ned between 25–17 Ma. The proposed P–T–t–D path is similar to Toijem Shear Zone described by Carosi et al. (2010), 40 km SE of Mugu Karnali Valley and also share strong similarities and the same P-T break with the Metamorphic Discontinuity (MD) recently described by Yakymchuk and Godin (2012), ~ 25 km to the NW of the study are.

The common history of these three shear zones suggests that GHS, in the Western Nepal, is not an uniform tectonic unit extruded southward in a crustal channel, as proposed in channel fl ow model, but the exhumation could be supported by in sequence shear zones, in a context of deformation propagation toward the foreland.

REFERENCES

Beaumount, C., Jamieson, R. A., Nguyen, M. H., and Lee. B., 2001, Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled of focuded surface denudation, Nature, v. 414, pp. 738-742.

Carosi, R., Montomoli, C., Rubatto, D., and Visonà, D., 2010, Late Oligocene high-temperature shear zones in the core of the Higher Himalayan Crystallines (Lower Dolpo, Western Nepal), Tectonics, v. 29, TC4029, doi: 10.1029/2008TC002400.

Clift, P., 2010, Enhanced global continental erosion and exhumation driven by Oligo-Miocene climate change, Geophysical Research Letters, v. 37, L09402, doi: 10.1029/2010GL043067.

Franěk J., Shulmann, K., Lexa, O., Tomek, Č, Edel J.-B. 2011 Model of syn-convergent extrusion of orogenic lower crust in the core of the Variscan belt: implications for exhumation of high-pressure rocks in large hot orogens, Journal of Metamorphic Geology, v. 29, pp. 53-78, doi: 10.111/j.1525-1314.2010.00903.x

Imayama, T., Takeshita, T., Yi, K., Cho, D.-L., Kitajima, K., Tsutsumi, Y., Kayama, M., Nishido, H., Okumura, T., Yagi, K., Itaya, T., and Sano, Y., 2012, Two-stage partial melting and contrasting cooling history within the Higher Himalayan Crystalline Sequence in the far-eastern Nepal Himalaya, Lithos, v. 134, pp. 1-22.

Searle, M. P., 2010, Low-angle normal faults in the compressional Himalayan orogen; evidance from the Annapurna-Dhaulagiri, Nepal, Geosphere, v. 6, pp. 296-315.

Streule, M. J., Strachan, R. A., Searle, M. P., and Law R. D., 2010, Comparing Tibet-Himalaya and Caledonian crustal architecture, evolution and mountain building processes, Geological Scoiety of London Special Publication, v. 335, pp. 207-232.

Yakymchuk, C. and Godin L., 2012, Coupled role of deformation and metamorphism in the construction of inverted metamorphic sequences: an example from far-northwest Nepal, Journal of Metamorphic Geology, v. 30, pp. 513-535.

160


A catastrophic fl ash fl ood in the Seti River in the morning of May 5, 2012 killed 72 people and caused huge damage to the lives and livelihood in Sadikhola and Machhapuchhre Village Development Committees of Kaski district, Western Nepal. The fl ood occurred in a clear day and no glacial lake of signifi cant size was spotted in the satellite images captured immediately before the disaster. An attempt has been made to fi nd out the cause of the fl ood which originated form very remote inaccessible area lying in the western slope of the Annapurna IV peak. Comparative analysis of the Landsat ETM satellite images of April 2012 and 6th May 2012 which were available online in NASA website revealed that the area of about 32000 square meter of the southern ridge 1.5 kilometer away from the Annapurna IV peak failed in the north western direction. The impact of descending mass of the failed mountain from 6850 m to 4500 m almost vertically pulverized the ice, sediment and rock. The pulverized mass formed dark brown cloud which was also captured by the ultralight aircraft of the Nepal Avia Club. The main direction of the failure was towards the North-West. The impact even triggered seismicity (at 9:09.56 a.m. local time) which was recorded all over the 21 stations of National Seismological Centre (Sapkota and Duvadi 2012). The seismicity was equivalent to 3.8-4.0 Richter Scale in magnitude. The closest seismic station at Dansing which is 32 km southwest from the area recorded the high signals for 70 minutes which corresponds to the duration of the debris fl ow. The huge vibration and the heat generated by the impact caused the glaciers located on the slope to fail towards the origin of the Seti River. This whole mass descended further down slope to 3300 m southwestern direction from where the Seti River starts. The huge mass of debris along with ice chunks rushed down the river as a debris fl ow for 20 kilometres downstream at Kharapani in just 28 minutes (almost 12 meters/second).

The fl ood water sample collected 100 meter downstream of the Irrigation Dam located North of Pokhara city was analyzed. Lab analysis of the fl ood water sample revealed the density of the fl ow as 1.88 gm/cc. The result of sieve analysis of the dried suspended sediment sample showed that it mostly contains fi ne sand and silt (Fig. 1). Visual

examination of the coarse grains showed that it comprised of rock fragments of dolomite along with grains of quartz and micas. The rock fragments are angular to sub angular with medium sphericity. The sample also contains 27% of fi ne soil with grain size <0.075mm i.e. silt and clay sized material. In order to distinguish them further dry strength test and shaking test were performed. The oven dried sample got easily powdered by rubbing it with fi ngers. During shaking water easily drained at the surface of the soil which confi rmed that, the fi ner material in the fi nes is silt. Acid test done in the dried sediments indicated calcareous contents in the fl ood water. Dark grains showed effervescence when powdered.

Analysis of the satellite based hourly rainfall GSMaP NRT from the period form 20th April -6th May 2012 revealed that there were just 4 occurrences of rainfall which amounted less than 1 mm/hour in the source area of the avalanche. The rainfall >6 mm/hour which occurred in the Kharapani area on 4 May was localized rainfall which did not extend to the avalanche area.

The fl ooding in Seti River has caused great damage to the life and properties. According to the Ministry of Home Affairs forty people lost their lives and thirty two are still missing (all presumed dead) and fi ve are injured. Estimated economic loss is about 82 eighty two million rupees including 33 million private properties and remaining 49 nine million public properties (89 Nrs= 1US$). Devastating fl ood damaged seven house and seven shops. One km black-topped road two km gravel road, twenty fi ve electric poles, four suspension bridges at different places were damaged by the fl ood which affected daily operation. Flooding also swept away 12 vehicles including 7 tractors, 1 van, 2 motorbikes and 2 trucks. About 9.5 hectares paddy fi eld has been covered by sand. Flood also damaged two water mills and 45 meter drinking water supply lines resulting problem on water supply in Pokhara.

After the analysis of the satellite images, photographs taken by the Ultra Light Aircraft and the eye-witness accounts, we conclude that the fl ood of 5th May 2012 in

Cause, mechanism and impact of the Seti Flood of 5th May 2012, western Nepal

*Shreekamal Dwivedi and Yojana NeupaneDepartment of Water Induced Disaster Prevention, Pulchowk, Lalitpur, Nepal


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Fig. 1: The result of comparative analysis of the dried suspended sediment sample of 5th May and normal high fl ood of 19th May 2012.

the Seti river was caused by the massive avalanche which occurred due to the failure of the glaciated area located at 4500 a.m.s.l. on the South-Western slope of the Annapurna IV peak. The avalanche was triggered by the failure of the ridge at an altitude of 6850 meters and was located 1.5 km south of the peak which even generated surface waves detectable by Seismic Stations. Avalanche triggered high intensity fl ood, having density of 1.88 gm/cc, had similar characteristics to Glacier Lake Outburst Flood (GLOF).

REFERENCES

NASA website: http://visibleearth.nasa.gov/view.php?id=78070 accessed on 30 May 2012 (ETM Landsat GeoTiff images)

Sapkota, S. and Duvadi, A., 2012, Report submitted by the committee formed to fi nd out the cause of the Seti Flood of 5th May 2012 to the Chief Secretary, Government of Nepal (Unpublished report).

162


Mass movement of slope materials is a major process in the development of slopes in mountain regions. Geologically young and tectonically active Himalayan Range is characterized by highly dynamic physical processes such as large earthquakes, high intensity rainfall during monsoon periods and landslides and other mass movement processes. Mass movement in the Nepal is scale- dependent, from the massive extension of whole mountain ranges (gravity tectonics), through the failure of single peaks, to the smallest slope failures. Among them mega-landslides are not easy to recognize if these landslides are completely dissected. These mega- landslides are basically found as huge landslide dams and isolated hills.

The Midlands in Nepal Himalaya belongs to the Lesser Himalayan Zone and situated at north of the Mahabharat Range. Both Mahabharat Range and Midlands have many numbers of deep-seated landslides. Most of them are almost stable and provide gentle slopes for cultivation and settlement, although some of them are still active and slow moving creep. The slip surface of such landslide has remarkable amount of clay mineral accumulation which suggests hydrothermal alteration caused from the Miocene leucogranites (Hasegawa et al. 2008).

The Midlands have gentle topography compared to the Mahabharat ranges. The slopes are also comparatively less steep than in other zones of Himalaya. Thick soil formations found in slopes of the Midlands are originated from deeply

weathering of rocks. These thick weathering crusts are distributed in the surroundings of wide valleys such as Kathmandu Valley. This indicates that wide valley (basin) formation is the important factor of erosion control.

Sakai et al. (2006) suggested that muddy debris fl ow deposits dammed up the Proto-Bagimati River to form the Paleo- Kathmandu Lake at 1 Ma in the southern margin of the Kathmandu Basin and the Pleistocene rapid uplift of the Mahabharat Range since 1 Ma. We propose another hypothesis of origin of the Paleo- Kathmandu Lake from the viewpoint of large-scale landslides. Our hypothesis is that the Kathmandu valley had been a upstream of a branch river of the Indrawati River and a huge landslide dammed up the branch river at the north of Nagarkot. An isolated hill to the north of Nagarkot is estimated as dissected mega-landslide which had occurred before 1 Ma. Overfl ow from the Paleo- Kathmandu Lake have started at the southern margin of the Kathmandu Basin which is known as the Bagmati River.

REFERENCES

Hasegawa S., Dahal R. K., Yamanaka M., Bhandary N. P., Yatabe R., Inagaki H., 2009, Causes of large-scale landslides in the Lesser Himalaya of central Nepal, Environmental Geology, v. 57, pp. 1423-1434, dOI: 10.1007/s00254-008-1420-z.

Sakai H., Sakai H., Yahagi W., Fujii R., Hayashi T., Upreti B. N. , 2006, Pleistocene rapid uplift of the Himalayan frontal ranges recorded in the Kathmandu and Siwalik basins, Palaeogeography, Palaeoclimatology, Palaeoecology, v. 241 (1), pp. 16-27.

Role of mega-landslides in valley development in the Nepal Himalaya

*Shuichi Hasegawa1 and Ranjan Kumar Dahal 2, 3

1Department of Safety Systems Construction Engineering, Kagawa University, Takamatsu, Japan 2Department of Geology, Tri-Chandra Campus, Tribhuvan University, Ghantaghar, Kathmandu, Nepal

3Disaster Management Informatics Research Center, Ehime University, Matsuyama, Japan.(*Email: [email protected])

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A wide spread felsic magmatism as integral part of Saltoro range occurs at triple point junction of Ladakh, Saltoro and Karakoram blocks in the Nubra valley, between Khalsar Thrust (KT) and Karakoram Fault (KF) referred herein as Tirit granitoids (68±1 Ma, Wienberg et. al. 2000) which are considered equivalent to calc-alkaline granitoids of Ladakh batholith. Enclaves hosted in Tirit granitoids (TG) have been investigated in order to understand emplacement mechanism and magma chamber processes. Country-rock xenoliths (porphyritic andesite and dacite) and microgranular enclaves containing small mafi c xenoliths can be observed hosted in TG. Xenoliths of blackish porphyritic andesite (up to few tens of cm across) as stopped lithic fragments having sharp contact with TG are less frequent, whereas green coloured, millimetres to centimetres sized xenoliths of dacitic composition are more frequent in the matrix of TG. Partially digested small dacitic lithic fragments exhibit corroded to diffused margins which point to wide spread assimilation of dacitic volcanic materials by the intruding TG melt enroute while passing through stratifi ed deep volcanic sequences. On the other hand, undigested lithic xenoliths of porphyritic andesite strongly suggest stopping of andesite volcanic materials as roof pendants into TG melt at their emplacement level. Careful examination of physical features and mineral assemblage of xenoliths hosted in TG suggest their close resemblance with Khardung volcanics (porphyritic andesite and dacite), which evidently explain the intrusive relation of TG with Khardung volcanics in a sub-volcanic environment. It is worthwhile to mention

that less frequent microgranular enclave (10 cm across) contains several small mafi c xenoliths (less than 1 cm) of dacitic composition similar to as commonly observed in TG. These features are clearly indicative of coeval nature of ME magma globules and host TG magma, which together passed through the dacitic volcanic sequence prior to their fi nal emplacement below the porphyritic andesite volcanic layers. Ladakh granitoids however contain frequent mafi c to hybrid microgranular enclaves (Kumar 2010) but lack xenoliths of volcanic materials except found in the eastern margin of Ladakh granitoids which contain xenoliths of volcanics compositionally dissimilar to the Khardung volcanics. TG are cross-cut by a number of post-plutonic mafi c dykes and aplitic veins. Based on fi eld and microtextural evidences it is suggested that multiple coeval pulses of magmatism occurred extensively all along the Ladakh and Saltoro ranges which were emplaced at differential levels (mid-crustal to sub-volcanic) prior to their displacement along Khalsar Thrust.

REFERENCES

Weinberg, R. F., Dunlap, W. J. and Whitehouse, M., 2000, New fi eld, structural and geochronological data from Shyok and Nubra Valley, Northern Ladakh: linking Kohistan to Tibet. Geological Society of Landon, Special Publications, v. 170, pp. 235-275.

Kumar, S., 2010, Mafi c to hybrid microgranular enclaves in the Ladakh Batholith, Northwest Himalaya: Implications on calc-alkaline magma chamber processes, Journal of Geological society of India, v. 76, pp. 5-25.

Enclaves in Tirit granitoids, Nubra Valley, Northern Ladakh: Evidence of sub-volcanic emplacement and partial assimilation

*Sita Bora1, Santosh Kumar1, Brajesh Singh2 and Umesh K. Sharma3

1Department of Geology, Centre of Advanced Study, Kumaun University, Nainital, India, 2Mineral Sales Private Limited (RMML), Baldota Enclave, Hospet-583203, India

3Department of Science and Technology, New Delhi, India (*Email: [email protected])

164


Between the Mahra Khola and the Arun River, the structure of the frontal part of the Himalayas is somewhat different from that observed in regions to the west or east. To the west, for >100 km, the range front is relatively linear and simple, as described for instance by Lave and Avouac (2000), among others. Here, the Main Frontal Thrust (MFT) is separated from the Main Boundary Thrust (MBT) and related splay-thrusts (e.g., Main Dune Thrust) by a rather broad piggy-back syncline (Hetauda Dun) fi lled with upper-Siwalik and younger Quaternary deposits. At about near Mahra Khola this regular structure ends, as most of the thrusts divide and start stepping southwards along a roughly NNE-trending zone marked by alternating anticline and syncline terminations. The broad Dune also divides, and then dramatically narrows eastwards. To the east, near the Arun, such foreland thrust migration terminates abruptly along a lateral ramp, as all the principal thrusts step back and nearly merge to continue eastwards for 100 km along the edge of the Lesser Himalayas.

This presentation is the output of an exceptional effort to collect data from a variety of techniques combining traditional well proven (e.g., analysis of aerial photographs and topographic maps, analysis of sections observed in trenches, 14C dates), and more advanced methods like LIDAR topographic measurements, subsurface seismic imaging, radar and electrical resistivity tomography). Our work was mainly concentrated in central Eastern Nepal along he Ratu and Charnath rivers to search for past earthquakes that ruptured the MFT.

We were fi rst engaged in a systematic search for remnants of seismic scarps as well as for datable strath terraces or any datable evidence for past discrete uplift events. For this purpose we scouted in detail a 150 km-long stretch of the Main Frontal Thrust. We discovered in the epicentral track of the 1934 earthquake low level terraces in the hangingwall of the thrust system (often mapped as T2) typically standing 3 to 6 meters above adjacent river beds,

and very often bounded by fresh looking free-faced scarps. These T2 terraces, clearly associated to the last earthquake rupturing the surface, are one generation among up to 7 levels of strath terraces standing in the hangingwall of the thrust with a potential at some places to unravel a pluri-millennial history of the thrust activity.

This presentation will synthesize fi rst the regional morphotectonic and structural observations collected along the Main Frontal thrust from Mahara to Karmala rivers. The regional mapping is complemented by local high resolution geomorphic maps prepared on high resolution topography estimated by total station toposurveys and Lidar topographic imaging on sites with local interest (Sir Khola, Bardibas, Charnath) and often constrained by 14C ages.

Constraints on the main frontal thrust subsurface geometry, necessary to translate the local uplift rates in slip rates on the fault, were then acquired through dedicated geophysical surveys. Among them, three shallow seismic profi les reveal hanging wall and footwall structures down to 300-400 m as well as the positions and attitudes of the shallow acting thrust planes.

All these observations throw some light on several aspects of the regional active tectonics, including the extension of the great 1934 earthquake surface rupture along this stretch of the Himalaya.

Analysing the fl ight of terraces everywhere we looked north of the MFT trace, of signs of a young seismic event in the form of low-level terraces freshly uplifted by only a few meters in the last couple of centuries. The correlative, almost inescapable inference is that this event ought to be the 1934 Bihar Nepal earthquake. If confi rmed by sub-surface investigations, this proposition would be much more surprising since fi nding the surface rupture of this great early 19th century earthquake has thus far eluded seismologists, geodesists and paleoseismologists alike.

Hunting of past earthquake along the Main Frontal Thrust using recent geomorphic feature in the area between the Mahara Khola to Dharan in

central and eastern Nepal*Soma Nath Sapkota1, Paul Tapponnier2, Laurent Bollinger3, Yann Klinger4, Indira Siwakoti1 and

D. R. Tiwari1

1Department of Mines and Geology, National Seismological Centre2Earth Observatory Singapore

3DASE, France4IPGP, France

(*Email:[email protected])

165


Ice streams and glaciers are responsible for transporting most of the ice on continents. Direct observations of glacier motion and laboratory studies of ice rheology have identifi ed three main mechanisms by which ice masses move. These are by internal deformation of the ice itself, and through two processes which take place at the base of the glacier: basal sliding and deformation of water-saturated weak sediments. Flow by internal ice deformation takes place in all ice masses, and generally accounts for motion of a few meters per year. However, basal motion occurs only where the bed is at the pressure melting point such that water is present. Where basal motion takes place, glaciers may move at tens to hundreds, and sometimes a few thousand, meters per year. The seismic method is very useful to investigate ice dynamics. In this work we present some results obtained from seismic data acquired on Thwaites Glacier (West Antarctica- Fig. 1). However, this methodology can be applied elsewhere in the world, as for example in the Himalayan-Karakoram region, where many large glaciers are present and should be monitored to study the effects of global warming.

THE STUDY AREA

Thwaites Glacier, located in an overdeepened basin that extends far inland, is one of the fastest and largest glaciers draining the West Antarctic Ice Sheet. Together with Pine Island Glacier, it is one of the main candidates for a potential catastrophic collapse of the marine ice sheet along the Amundsen Coast. Recent studies indicate that the glaciers along the Amundsen Coast are thinning rapidly. In particular, the most dramatic changes have occurred on Pine Island Glacier and Thwaites Glacier, where the speed near the grounding line increased more than 25% between 1974 and 2008. These studies evidence, however, some differences between the two glaciers, suggesting that Thwaites Glacier is more stable than Pine Island glacier. Joughin and others (2009) used models constrained by remotely sensed data to infer basal properties. The results indicate strong basal melting in areas upstream of the grounding lines of both glaciers, where the ice fl ow is fast and the basal shear stress is large.

Farther inland, they found mixed bed conditions for both glaciers, alternating from regions of low drag (i.e. deforming

sediments), to regions providing greater basal resistance (i.e. non-deforming sediments or even crystalline bedrock). In particular, for Thwaites Glacier they reported that the areas characterized by strong bed are more extensive than the weak regions, explaining the higher degree of stability with respect to Pine Island Glacier.

The main purpose of this work is to verify these hypothesis using the seismic method and, more generally, to show that active single-component seismic data can be effectively used to image the internal and subglacial structures of the ice sheets and to determine the bed properties of the subglacial environments.

Fig. 1: West Antarctica map showing the location of Thwaites Glacier (THW, red triangle). Black triangles

indicate the distribution of main subglacial lakes in Antarctica.

SEISMIC DATA ANALYSIS AND RESULTS

During the 2008-2009 Antarctic fi eld season, 60 km of refl ection seismic data were collected ~200 km inland of the current grounding line of Thwaites Glacier, consisting of one 40-km profi le along fl ow and two 10 km transverse profi les. The applied processing adopted the 'true-amplitude' approach, which preserves the real amplitudes of the refl ected signals (Yilmaz 2001), and included:

Glacier basal conditions inferred from seismic data

*Stefano Picotti1, Flavio Accaino1 and Franco Pettenati1

1National Institute of Oceanography and Experimental Geophysics - OGS, Trieste, 34010, Italy (*Email: [email protected])

166


(1) reconstruction of the fi rn vertical velocity profi le and refraction statics using diving waves;

(2) surface-consistent predictive deconvolution for the ghost elimination and wavelet compression; and

(3) surface-consistent residual statics using the cross-correlation method.

The imaging technique adopted in this work consists in an iterative updating procedure for refi ning and improving an initial model in depth, involving pre-stack depth migration, residual move-out analysis and seismic refl ection tomography (Yilmaz 2001). At each iteraction, both velocity and refl ector geometries are updated, until the two set of parameters reach a good degree of stability. This procedure goes on until the quality of pre-stack depth migration is not suffi cient. The fi nal migrated section (Fig. 2) evidence the presence of a sedimentary basin in the upstream (left) part of the survey, where low basal shear stress was estimated (Joughin and others 2009). The depositional structures of the basin, including its bottom, are clearly identifi able. In the downstream (right) part of the migrated section the tectonic features are also very clear and the presence of faults is evident. The imaged complex bed tomography seems to be in according with the estimated high basal shear stress (Joughin and others 2009).

We also carried out a full Amplitude Versus Offset (AVO) inversion, which converts the seismic processed and balanced pre-stack data to refl ectivities, which have clear physical meanings, i.e. relative change in the material parameters. The results of AVO highlight moderate variability in the spatial coverage of basal sediments. We evidence alternation of low deformable sediments (type A sediments) and moderate deformable sediments (type B sediments), and some variability between these two types of sediments. The inversion also indicates, accordingly to Joughin et al. (2009), a prevalence of type B sediments in the upstream (left) part of the survey, and a prevalence of type A sediments in the downstream (right) part of the survey. The transition between the two subglacial regimes coincides with a change in bed topography.

REFERENCES

Joughin, I. and 6 others 2009, Basal conditions for Pine Island and Thwaites Glaciers, West Antarctica, determined using satellite and airborne data. J. Glaciol., v. 55(190), pp. 245–257.

Yilmaz, O., 2001, Seismic Data Analysis: Processing, Inversion and Interpretation of Seismic Data. SEG Series: Investigation in Geophysics, Tulsa.

Fig. 2: Final pre-stack Kirchhoff depth migration, where the vertical axis indicates the depth below sea level (bls). The average glacier surface elevation is about 1300m and the CMP interval is 10 m.

167


How and when the Tibetan plateau developed has long been a puzzling question with implications for the current understanding of the behaviour of the continental lithosphere in convergent zones. We present and discuss recent data acquired in geology and geophysics and through igneous and metamorphic petrology and palaeo-altitude estimates. It appears from this research that Tibet initially resulted from the accretion of the Gondwana continental blocks to the southern Asian margin during the Palaeozoic and Mesozoic eras. These successive accretions have potentially favoured the creation of local landforms, particularly in southern Tibet, but no evidence exists in favour of the existence of a proto-Tibetan plateau prior to the Cenozoic. Moreover, before the India-Asia collision, the Tibetan crust had to be suffi ciently cold and rigid to transfer the horizontal forces from India to northern Tibet and localize the deformation along the major strike-slip faults. However, these successive accretions associated with subductions have contaminated the Tibetan lithospheric mantle and largely explain the potassium- and sodium-rich Cenozoic magmatism. Another consequence of this contamination by fl uids is the softening of the Tibetan lithosphere, which favoured intra-continental subductions (Figure 1). The timing and the geochemical signatures of the magmatism and the palaeo-altitudes suggest the early growth of the Tibetan plateau. By the Eocene, the southern plateau and the northern portion of Himalaya would be at an altitude of approximately 4000 metres, while the central and northern Tibetan plateau was at altitudes of approximately 2000 to 3000 meters at the Eocene-Oligocene transition. From all of these data, we

propose a model of the formation of the Tibetan plateau coupled with the formation of Himalaya, which accounts for more than 2000 km of convergence accommodated by the deformation of the continental lithospheres. During the earlyEocene (55-45 Ma), the continental subduction of the high-strength Indian continental lithosphere dominates, ending with the detachment of the Indian slab. Between 45 and 35 Ma, the continental collision is established, resulting in the thickening of the internal Himalayan region and southern Tibet and the initiation of intra-tibetan subductions. By 35 Ma, the southward subduction of the intra-tibetan Songpan-Ganze terrane ends in slab break-off and is relayed by the oblique subduction of the Tarim the Athyn Tagh propafated northeastward beneath the Qilina Shan. Southward, the dextral Red River Fault accommodated the southeastward extrusion of the Indochina block. During the Miocene, specifi cally, between 25 and 15 Ma, the Indian slab undergoes a second break-off, while the central part of Tibet is extruded eastward. Northward, the continental subduction beneath the Qilian Shan continues. Discontinuous periods of magmatic activity associated with slab detachments play a fundamental role in the convergence process. These periods lead locally to a softening of the mid-crust by magma heat transfer and to the granulitisation of the lower crust, which becomes more resistant. We propose that due to these alternating periods of softening and hardening of the Tibetan crust, the rheological behaviour of the convergence system evolves in space and time, promoting homogeneous thickening periods alternating with periods of localised crustal or lithospheric deformations.

Importance of continental subductions for the growth of the Tibetan plateau

*Stéphane Guillot and Anne ReplumazISTerre, University of Grenoble, 1381 rue de la Piscine, 38041 Grenoble cedex 9, France


168


Fig. 1: Interpretative cross-section of the Himalaya-Tibet orogenic system at the mantle scale, including the tomographic anomalies. MFT: Main Frontal Thrust, MBT: Main Boundary Thrust, MCT: Main Central Thrust, STD: South Tibetan Detachment, XF: Xianshuine Fault, KF: Kunlun Fault, NKT: North Kunlun Fault, HF: Haixan Fault, NST: Nan Shan Thrust. MFT: Main Frontal Thrust, MBT: Main Boundary Thrust, MCT: Main Central Thrust, MHT: Main Himalayan Thrust.

169


Topography develops in response to the interplay of constructive tectonic forces and destructive erosional forces. Many of the erosional forces at play in an orogenic system – fl uvial, hillslope, and glacial processes – are infl uenced by regional climate. In suffi ciently large orogens, regional climate is in turn affected by topography (e.g. orographic precipitation). The resulting interdependent relationship between climate and topography is widely studied, but still poorly understood. Particularly, the role of glaciers – perhaps the most effective erosive agent and highly susceptible to climatic infl uence – is not well documented. In the Arun valley of the eastern Nepalese Himalaya, glaciers compete with fl uvial erosion fueled by a strong India Summer Monsoon (ISM). The Arun valley is located near the beginning of the ISM moisture conveyor and receives up to ~80% of its annual precipitation during the monsoon period between June and September. ISM-sourced rain falls on a steep, two-tiered precipitation gradient caused by the orographic barriers of the Lesser Himalaya near the southern Himalaya front and the Higher Himalaya in the north, with a rain shadow over Tibet (Bookhagen & Burbank 2010). Additionally, there are several glaciers in the northern and upper reaches of the Arun river system. We reconstruct the recent (102-103 yr) pattern of erosion in the valley to tease out the infl uences of ISM precipitation and of glaciation on regional erosion and hydrologic discharge patterns. We have collected 5 river sand samples from the main stem Arun river and 19 river sand samples from its tributaries for detrital cosmogenic radionuclide (CRN) analysis. These samples, which span from the confl uence of the Arun, Tamor, and Sun

Kosi rivers to the town of Num and across the fi rst high-low-high precipitation gradient, provide averaged basin-wide erosion rates for the Arun and each contributing watershed (Bierman and Steig 1996; Granger et al. 1996). The CRN-derived erosion rates are compared to modern sediment fl ux data to quantify the difference between instantaneous erosion (sediment-fl ux) and time-averaged long-term erosion (CRN rates). Climate-based sediment transport is modeled using the Soil & Water Assessment Tool (SWAT) hydrological model to reproduce modern sediment fl ux rates and CRN-derived longer-term erosion rates. The hydrological model is calibrated for this region using 265 stream discharge stations in the Arun valley. Modeling sediment transport allows for testing of what climate scenarios are necessary to produce the long timescale erosion rates, such as increased snow/glacial cover or an increased incidence of extreme monsoon events.

REFERENCES

Bierman, P. and Steig, E. J., 1996, Estimating rates of denudation using cosmogenic isotope abundances in sediment, Earth Surface Processes and Landforms, v. 21, pp. 125-139.

Bookhagen, B. and Burbank, D. W., 2010, Towards a complete Himalayan hydrological budget: Spatiotemporal distribution of snowmelt and rainfall and their impact on river discharge, Journal of Geophysical Research, v. 115, F03019, doi:10.1029/2009JF001426.

Granger, D. E., Kirchner, J. W., Finkel, R., 1996, Spatially averaged long-term erosion rates measured from in situ-produced cosmogenic nuclides in alluvial sediment, Journal of Geology, v. 104 (3), pp. 249-257.

Spatial and temporal erosion variability and its drivers in the Arun valley, eastern Nepalese Hiamalaya

*Stephanie Olen1, Bodo Bookhagen2 and Manfred Strecker1

1Institute of Earth and Environmental Science, Universität Potsdam, Potsdam 14476, Germany,2Department of Geography, University of California – Santa Barbara, Santa Barbara, CA 93106, USA


170


The mountainous Rivers receive signifi cant contributions from the snow and glacier melt. Thus, there is a pressing need for modeling ice and snow melt from the high Himalayas for sustainable water resource management, fl ood forecasting, as well as in the study of glaciers’ response to climate change. Koshi basin in Nepal covers the major Snowfed and Glacierfed Rivers from the Himalayas. In this perspective, this study deals with the runoff modeling of the glacierized watersheds of Koshi basin in Nepal. A conceptual TANK model is used for runoff modeling from the 22 glacierized watersheds (which are above 4000 metres above sea level). At fi rst, the glacierized watersheds are distributed into 16 altitude zones of 300m each and are differentiated into debris-covered and debris-free glacier area and rocky area. The hydro-meteorological data from the 2 stations-Dingboche in Khumbu and Kyanjing in Langtang are used

in the study. With regards to the proximity of the stations, 11 watersheds are associated with Khumbu while the rest 11 are associated with Langtang. Thermal resistance and meteorological data are used to calculate melt from debris-covered glaciers. Snow melt and glacier melt are calculated from surface energy balance model in these altitude bands of the studied basins for the year 2002. The calibration of the model for Langtang and Khumbu stations show the model effi ciency of 95.93% and 91.53% respectively with a good correlation between observed and simulated hydrographs. The calibrated parameters of the station are used to generate runoff from the watersheds associated with the stations. The simulated runoff from these 22 watersheds can be used as snow and glacier melt input to other semi distributed hydrological models in simulating the discharge of whole Koshi basin.

Runoff modeling of glacierized watersheds of Koshi basin in Nepal

*Subash Tuladhar1, Narendra Man Shakya2 and Maheswor Shrestha3

1Hydrologist Engineer, Department of Electricity Development, Ministry of Energy, Government of Nepal 2Professor, Institute of Engineering, Pulchowk Campus, Lalitpur, Nepal

3Hydropower Engineer, Department of Electricity Development, Ministry of Energy, Government of Nepal(*Email: [email protected])

171


A narrow but persistent belt of Gondwana (Permian) rocks are overridden by the meta-argillaceous Proterozoic Daling rocks along the Darjeeling frontal belt. However, the Gondwana rocks, subsequently, override the Neogene Siwalik rocks across the Main Boundary Thrust (Acharyya 1994). We describe here the well exposed MBT zone from Kalijhora-Tista area. The older diamictite bearing and upper structural Gondwana unit is truncated and not exposed

here. However, the footwall rocks of MBT developed discontinuously folded sequence of the Lower Siwalik (Chunabati Formation) which is well exposed between Kalijhora and Andherijhora (Fig. 1). A much less deformed northerly dipping homoclinal sequence of Mid Siwalik rocks is exposed further south up to the southern termination of the hill-front.

Nature of deformation of the frontal wedge of Darjeeling-Sikkim Himalayas, India

*Subhajit Ghosh1, Puspendu Saha1, Rwiti Basu1, Sujoy Dasgupta2, S.K.Acharyya2, Nibir Mandal2 and Santanu Bose1

1ETL, Dept. of Geology, University of Calcutta, Kolkata, 700 019, India 2Dept. of Geology, Jadavpur University, Kolkata, 700 032, India


Fig. 1: L ocation map of the study area.

172


Orogen parallel tight folded (Fig. 2) sequence of coal bearing Gondwana is well exposed along the Kalijhora section. Incompetent coal/carbonaceous beds are intensely folded with very low plunge. This zone is highly sheared forming mélangic paste of carbonaceous rocks. Associated thicker sandstones are less deformed, but are fractured, brecciated (Fig. 3) and locally boudinaged.

Narrow MBT zone is subvertical around Kalijhora and it locally dips south beneath the Chunabati rocks. Gondwana sandstones from this zone are also locally overturned. A carbonaceous mélange containing disrupted and boudinaged blocks of both Gondwana and Chunabati sandstone is exposed at the MBT in the Tista river section. Immediately

north of MBT, very coarse Gondwana arkose are exposed, which are fractured and brecciated. Whereas, south of MBT, without any gap, tightly folded Chunabati sandstone (Figs. 4 and 5) with minor dislocations zones. The folded Chunabati rocks are almost continuously exposed up to the confl uence of Andherijhora with the Tista river. The style and geometry of orogen parallel folds developed in the Gondwana and the Lower Siwalik Chunabati rocks are closely similar and distinct. The Chunabati rocks exposed along the Tista river cannot be divided into two zones separated by the South Kalijhora Thrust as proposed by Mukul, 2000. On the other hand, the homoclinal sequence of the Mid Siwalik rocks exposed further south of Andherijhora thrust are much less deformed and unaffected by any thrust imbrications.

Fig. 2: Tight folds in Gondwana coal-carbonaceous shale,viewing from NE.

173


Fig. 3: Gondwana sandstone showing evidence of brittle deformation: fragments of angular quartz grains in a fi ne graind matrix.

Fig. 4: Tight folds in Chunabati Lower Siwalik sandstone, viewing from E, little South of MBT, along the Tista river section.

174


Fig. 5: Biotite and muscovite grains show kinking and quartz grains are seen to be recrystallized in Chunabati sandstone.

REFERENCES

Acharyya, S. K., 1994. The Cenozoic foreland basin and tectonics of theEastern Sub-Himalaya: problems and prospects. Himalayan Geology, v. 15, pp. 3–21.

Mukul, M., 2000. The Geometry and Kinematics of the Main Boundary Thrust and related Neotectonics in the Darjiling Himalayan Fold-and-thrust belt, West Bengal: Journal of Structural Geology, v. 22 (9), pp. 1261-1283.

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Undergoing mountain building process, unstable steep slopes and fragile geological formations make Nepal one of the most hazardous countries in the world. The topographical variation as well as diversifi ed geological characteristics within very short width of the country along with heavy monsoon rainfall makes Nepal highly prone to climate induced disasters. Of all the disasters reported, fl oods and landslides are the most devastating in terms of the number of deaths that occur and the damages they cause. Of the total death by any type of natural disaster in 2010, 29.02% were by fl ood and 24.55% were by landslides and 71.35% of the total affected families were by fl oods (DWIDP 2011). If we look at longer time data, 7918 people died, 6,67,347 families affected and estimated Rs. 22248.35 million were lost by the fl ood, landslide and avalanches during last 28 years between 1983-2010 (DWIDP 2011).

Impact of climate change has intensifi ed the vulnerability of climate induced disasters including fl oods, landslides, glacial lake outburst fl oods (GLOFs) and debris fl ows and is likely to be exacerbated in the future. From 1906 to 2005 the global average surface temperature increased by 0.74°C and this rate can be increased as warming trend over the 50 years from 1956 to 2005 is nearly twice that for the 100 years from 1906 to 2005 (IPCC 2007). Recently, Nepal is ranked the 4th most climate vulnerable country in the world due to the global warming by one of the study and 11th with respect to fl ood risk (UNDP 2004). One of the studies by Practical Action (Practical Action 2009) reveals that the average temperature of Nepal is in increasing trend throughout the country, with maximum increasing trend of 0.08 °C per year in Dhankuta district of eastern Nepal. In an average, the maximum temperature is increasing at a rate of 0.05° C/year. As a result of such a temperature rise, there is high rate of glacier melting in the Himalaya and subsequently there is increase in the numbers of glacial lakes. Many of such lakes are in danger of breaching that has increased the vulnerability of the downstream communities for fl ood. IPCC, 2007 estimates that almost 20 per cent of the glaciated areas in Nepal (above 5,000 m) are expected to be snow- and glacier-free if the air temperature increases by 1°C and 2°C rise in air temperature will cause loss of almost 40 per cent of the total area under snow (IPCC 2007). The resultant

changes in regional hydrology and water resources will have negative impacts on hydropower generation, irrigation, and drinking water supply as well. in addition to the climate induced disasters. To further increase the vulnerability of the downstream communities in the Siwalik and Terai zones of Nepal for fl ood and landslides, there is increase in the annual mean precipitation and extreme precipitation events. Foothills of the Siwalik and Mahabharat range are receiving highest intensive rainfalls. Frequency analysis of the extreme rainfall event trends during 1976-2005 reveals that the foothill of the Churia, which is the main source of many rivers in the Tarai, received the highest intensive rainfalls for 10, 20, 50 and 100 years of return periods (Practical Action, 2009). The monsoon precipitation pattern is also changing with fewer days of rain and more high-intensity rainfall events. Both trends have resulted in an increase in the magnitude and frequency of water-induced disasters like fl oods, landslides and debris fl ow. Such intensive and unpredictable rainfalls together with the weak rocks and high rate of deforestation in the Siwaliks cause the increased and unpredictable fl ood events in the downstream Terai. This problem is particularly prominent in the river basins which are originated from the Mahabharat range and Siwaliks of Nepal. The rate of sedimentation in the Terai is so high that the river beds in many river basins of eastern Nepal are well above the existing settlements. All these facts refl ect the necessity of detail study of glaciers, lowering the water level in the glacial lakes that are potential for GLOF and concrete actions for fl ood risk reduction especially in the Terai of Nepal with the approach of upstream downstream linkages.

REFERENCES

DWIDP, 2011, Disaster Review 2010, Annual Report, Government of Nepal, Ministry of Water Resources, Department of Water Induced Disaster Prevention (DWIDP), Kathmandu.

IPCC, 2007, Climate change 2007: Impacts, adaptation and vulnerability - Summary for policymakers. A report of the Working Group II of the Intergovernmental Panel on Climate Change, Fourth Assessment Report.

Practican Action, 2009, Temporal and Spatial Variability of Climate Change over Nepal (1976-2005), Practical Action Nepal Offi ce, 76p.

UNDP, 2004, A Global Report: Reducing Disaster Risk, United Nations Development Program.

Natural disaster in Nepal and its projection in the context of climate change

Subodh DhakalDepartment of Geology, Tribhuvan University, Tri-Chandra Campus, Nepal


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The Himalayan fold-thrust belt is commonly described as slices of the Indian upper crust and adjacent terranes imbricating one on top of another to form a deformed pile of upper crustal material and is a result of the ongoing Indo-Asia collision. The Main Central thrust is traditionally viewed as a fi rst thrust fault activated during Early-Miocene time (Hodges et al. 1996; Johnson et al. 2001) to accommodate the strain built up during the collision in central Nepal, and placed Greater Himalayan rocks over Lesser Himalayan rocks. U-Pb analysis of zircons from a Greater Himalayan orthogneiss in the Galchhi shear zone (west-northwest of the Kathmandu valley) in central Nepal yield a Late Cambrian-Early Ordovician crystallization age. Metamorphic overgrowths on the zircon rims have a Late Oligocene age. Extending the Galchhi shear zone towards the northeast, the trend corresponds to the previously identifi ed Main Central thrust/Mahabharat thrust zone, the fault under the Kathmandu klippe. An undeformed pegmatite vein cross-cuts kyanite bearing dark schist in the shear zone near Okharpauwa (northwest of the Kathmandu valley) yields a Late Oligocene U-Pb crystallization age of zircons. Similarly, another undeformed pegmatite vein cross-cuts the foliation of dark gray schist from Jitpur Phedi (East of Okharpauwa, northwest of the Kathmandu valley) yields a zircon crystallization age of Late Oligocene-Early Miocene time. These ages suggest an older tectonic event was active between Late Oligocene and Early Miocene, which predates the activity on the Main Central thrust in the Kathmandu klippe in central Nepal.

An older south vergent thrust fault, the Langtang thrust, is present within Greater Himalayan rocks in central Nepal north of the Kathmandu klippe, and was active at ~22 Ma (Kohn et al. 2004; Kohn 2008), prior to motion on the Main Central thrust. Detrital zircon age populations from two rock samples in the hanging wall of the Langtang thrust sheet

suggests a depositional age of Late Neoproterozoic, and an augen orthogneiss sample yields a zircon crystallization age of Early Ordovician. Two quartzite samples from the hanging wall of the Galchhi shear zone also yield Late Neoproterozoic depositional ages. These ages establish the rock as Greater Himalayan rock and not Lesser Himalayan rock. The crystallization age of the granitic gneiss and zircon age populations of the klippe rock in the Galchhi and Langtang areas suggest the Langtang thrust roots into a higher stratigraphic level within Greater Himalayan rocks with a shallow dip towards the north, carries stratigraphically upper level Greater Himalayan rock in the leading edge of the thrust sheet, and transposes older age rock against the hanging wall of the Main Central thrust sheet. These data also suggest that the klippe rock is Greater Himalayan rock and that the Galchhi shear zone is the southern continuation of the Langtang thrust that emplaces the Kathmandu klippe. The Main Central thrust must merge with the Langtang thrust under the Kathmandu klippe and emerge as a single fault south of the klippe.

REFERENCES

Hodges, K. V., Parrish, R. R., Searle, M. P., 1996, Tectonic evolution of the central Annapurna Range, Nepalese Himalayas, Tectonics, v. 15(6), pp. 1264-1291.

Johnson, M. R. W, Oliver, G. H. H., Parrish, R. R., Johnson, S. P., 2001, Synthrusting metamorphism, cooling, and erosion of the Himalayan Kathmandu Complex, Nepal, Tectonics, v. 20, pp. 394-415.

Kohn, M. J., Wieland, M. S., Parkinson, K. D., Upreti, B. N., 2004, Miocene faulting at plate tectonic velocity in the Himalaya of central Nepal, Earth and Planetary Science Letters, v. 228, pp. 299-310.

Kohn, M. J, 2008, P-T-t data from central Nepal support critical taper and repudiate large scale channel fl ow of the Greater Himalayan Sequence, Geologial Society of America Bulletin, v. 120, pp. 259-273.

Is the fault that carries the Kathmandu klippe the Main Central Thrust or an intra-Greater Himalayan thrust?

*Subodha Khanal and Delores M. Robinson1Department of Geological Sciences, University of Alabama, Tuscaloosa, AL 35487, USA


177


In the recent years, the existing water consumption in Kathmandu Valley has been increasing but there has no signifi cant increase in the quantity of water supply. The present water supply system in the Kathmandu Valley also consists of groundwater exploited through the deep wells drilled at various locations. However, it has been reported that the groundwater level of the valley has been declining. In order to carry out necessary steps to control further lowering of groundwater table and also to raise the water table as far as possible, it is urgently necessary to carry out effi cient steps. One of this may be the identifi cation of recharge zone and carry out artifi cial groundwater recharge. The previous studies have already shown that the northern part of the valley is having high potential of groundwater recharge. The average annual precipitation in the valley is around 1600 mm of rain. The rainwater is drained through a number of rivers, streams and rivulets that discharges to the Bagmati River. The study area has covered all the major sub-basins of Bagmati River Basin, namely Bishnumati, Manohara Khola, Dhobi Khola and Nakkhu Khola Sub-basins. The Kathmandu Valley is an intermountain valley having the centripetal drainage pattern. Hence all the rivers fl ow towards valley center to conjoin with Bagmati River that eventually drains out from the valley. The Bagmati River Basin occupies an approximate catchment area of 625

km2 before it debouches out of the valley through the Chovar gorge.

The study is focused to accurately delineate the recharge zone and evaluate the potentiality for the artifi cial groundwater recharge. For this the use of GIS and remote sensing has been carried out which is followed by fi eld observations. The available aerial photographs and satellite images are used for identifi cation of the recharge zone and to identify the potential locations for carrying out artifi cial groundwater recharge. It has been realized that it is necessary to work towards recovering the depleted groundwater table in order to mitigate the possible disasters due to groundwater depletion in the Kathmandu Valley. For this, one of the approaches could be the artifi cial recharge through surface spreading, which is still possible at the upper reaches of the rivers. However, in the built up area, the only way for groundwater recharge is through the well injection. The potential areas for artifi cial groundwater recharge have been identifi ed. These areas lie at the upper reaches of the Bagmati and Manohara Rivers. Likewise, the wells existing in the northern groundwater districts can be used for the groundwater recharge through water injection. The study delineates the potential areas of artifi cial groundwater recharge and it should be protected so that it could be utilized for the purpose in future. Similarly, additional wells should be drilled for water injection at the appropriate locations.

Study of recharge zone and potential area of groundwater recharge in the Kathmandu valley

Swostik Kumar Adhikari¹, *Dinesh Pathak¹ and Nir Shakya²¹Department of Geology, Tri-Chandra Multiple Campus, Tribhuvan University, Ghantaghar, Kathmandu, Nepal

²Ground Water Resource Development Board, Babarmahal, Kathmandu, Nepal(*Email: [email protected])

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The Kathmandu Valley is one of several intermontane basins in the Lesser Himalayan Belt, and is fi lled with fl uvio-lacustrine sediments more than 600 m in thickness. Lineaments trending NE-SW have been identifi ed within the basin. Although some of these lineaments are inferred to be active faults, no concrete evidence of fault activity has yet been found, apart from the Thankot Fault, which runs along the foot of the Mt. Chandragiri in the southern part of the basin. We have discovered evidence of fault activity in the uppermost Pleistocene in the Gothatar area in central Kathmandu Valley.

Pleistocene sediments in the northern and eastern Kathmandu Valley are found in three lacustrine terraces (Gokarna, Thimi and Patan). Evidence of fault activity was found in the sediments of the Gokarna Terrace. The Gokarna Formation, deposited between 50 and 39 ka, forms the lower part of the Gokarna Terrace, whereas the upper part consists of the Tokha Formation (19-14 ka). The Gokarna and Tokha strata are almost horizontal except for delta front deposits. Consequently, local inclination of sediment layers, including fl uvial channel deposits, can be recognized as deformation structures formed in association with fault activity immediately beneath the sites where such inclination occurs. We discovered a gently inclined set of strata in the middle part of the Gokarna Formation around Gothatar, at a site located on one of the lineaments. The inclined strata consist of a fl uvial channel fi ll and an overlying landslide deposit. The landslide deposit contains deformed and brecciated marsh deposits, and extends well to the east of

Gothatar, where the strata become almost horizontal. An approximately 4 m decrease in level of the fl uvial channel and landslide deposits over a distance of about 300 m to the west suggests this inclined interval forms a fl exure buried in the terrace sediments. The rapid disappearance of the overlying lacustrine mud beds around the fl exure indicates that this structure controlled the distribution of mud beds, and that fl exure activity ceased before mud deposition started. The lower part of the landslide deposit in the fl exure zone contains many open cracks, indicating tension stress exerted in the early phase of landslide; the landslide itself is interpreted to have been triggered by the formation of the fl exure. Many small normal faults occur in the sediments at this site, possibly also suggesting presence of a major fault (or a set of faults) beneath this area, probably trending NE-SW as represented by the lineament. Although the age of the fl exure has not yet been obtained, it is estimated to have formed around 37 ka, based on previous 14C data.

There is no distinct evidence of formation of other fl exures after ca. 37 ka in this area. However, the ~20 m difference in level of the top of the Gokarna Terrace between the east and west of the Murupani area, adjacent to Gothatar, may be an indication of post-37 ka fault activity. The recurrence time of the fault activity is unknown, but presence of three landslide deposits (proxies of fault activity below the fl uvial plain) within fl uvio-lacustrine sediments aged between 39-34 ka imply a recurrence time of about 2 k.y. Additional topographic and stratigraphic studies are required for the assessment of the future risk of fault activity.

Evidence of fault activity recorded in the Pleistocene fl uvio-lacustrine succession in Kathmandu Valley, Nepal

*T. Sakai1, A. P. Gajurel 2, H. Tabata3, N. Ooi 4 and B. N. Upreti 2

1Department of Geoscience, Shimane University, Matsue 690-8504, Japan, 2Department of Geology, Trichandra Collage, Tribhuvan University, Ghantaghar, Kathmandu, Nepal

3Applied Satoyama Study Laboratory, Mino 501-3721, Japan4ONP Laboratory, Neyagawa 572-0021, Japan


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Ward No. 5 and 6 of Gangapur Village Development Committee (VDC), Banke District, western Nepal were inundated in 2000 due to the blockade of the Singhya River by the fl ood-driven sediments brought by the Dhondra River while shifting its original channel. Consequently, about 305 families were completely displaced due to the inundation in and around their home and farmlands. Then onward of 2000, the Dhondra River started depositing sandy sediments in and around the confl uence point during each monsoon fl oods. As a result, cultivated lands on either side of the Singhya River were further inundated. This paper briefl y summarizes the causes of the disaster and its consequences to the displaced people, and surrounding geo-environment.

The investigated site covers mainly Siwalik (also known as the Churiya hill range) and also a part of the Terai plain, situated to the south of the Siwalik. The Siwalik range in the area is composed of sedimentary rocks namely, shale, sandstone and conglomerate. These rocks are highly jointed, comparatively soft and easy to weather. A thrust fault, known as the Himalayan Frontal Thrust (HFT), forms the boundary between the Siwalik and the Terai plane, which consists of about 1500 m thick alluvium sediments underlain by Siwalik rocks. The Terai is subdivided into Bhaber Zone, Middle Terai and Southern Terai based on the nature of the sediments laid down in the area. Generally, coarser materials (mainly boulders and gravels) are found in the Bhabar Zone, at the foothill of the Siwalik. Just to the south of Bhaber zone is the Middle Terai where sediments like gravels and sands are predominant. The Southern Terai is located to the south of the Middle Terai and the sediments are consisted of mainly silt and clay. The study area covers a part of the Bhaber Zone and a part of the Middle Terai.

The Siwalik hill range, in the study area, is covered with thick forest whereas the Terai is a cultivated land with scattered villages. The area receives monsoon precipitation during June to September and also a less amount of winter precipitation during the months of January and February.

Summer season is very hot and maximum temperature exceeds 40 degrees Celsius occasionally. The winter season is also comparatively warmer as the mean maximum temperature does not drop down below 15 degrees Celsius. The majority of the inhabitants of the area are native people, known as Yadab, and the migrated people, of different casts and ethnic groups, are insignifi cant. The area is accessible with a graveled road connected with a few earthwork roads. But during rainy seasons, the area becomes inaccessible due to the lack of bridge over rivers crossing the roads. Agriculture and livestock are the main source of livelihood.

The Dhondra River is a seasonal stream originated in the northern most part of the Siwalik range. The river takes its course almost north-south within the hilly areas and then takes south-westward turn once it emerges into the Terai plain (Bhaber zone) until it converses with the East Rapti River (the main drainage of the area) in the Middle Terai. In fact, the Dhondra River channel was limited only upto the eastern part of the Dhondra village until around1950 indicating that the river discharge was not huge and the river water was infi ltrating down completely through the porous river channel at that time. Its channel was extended upto the East Rapti River just around 1960 due to the extreme fl ood event that caused sudden increase in river discharges signifi cantly. Then onward, the river was gradually shifting westward in each Monsoon fl oods. The Dhondra River and the Shinghya River were about 3 km apart at their confl uence with the East Rapti River prior to the fl ooding event of 1995. In 2000, the Dhondra River suddenly shifted remarkably westward and blockaded the fl ow of Shinghya River, a tributary of the East Rapti River.

The fi eld investigation revealed a fact that the Dhondra River bed is not a smooth surface as there are rock exposures across the river bed. The bedding of these rock exposures dips due south with an angle that varies between 25 and 45 degrees. Generally three prominent set of joints are well developed. These rock exposures have formed low-lying

Flood in Gangapur Village, Banke District: An example of climate-induced disaster in Nepal

*Tara Nidhi Bhattarai1 and Rabindra Osti2

1Department of Geology, Tri-Chandra Campus, Tribhuvan University, Ghantaghar, Kathmandu, 2International Centre for Water Hazard and Risk Management, Public Works Research Institute,

Minamihara 1-6, Tsukuba 305-8516, Japan(*Email: [email protected])

180


(less than a meter in height in average) dams or barriers at several locations across the river. These barriers have behaved like natural check dams, which catch sediments and reduce river velocity. The width of the Dhondra River is a narrow one within the Siwalik range but it is deep enough to transport all the water even during fl ooding events. But in the Terai region, it is shallow and high discharge is often spilled out as fl ood water.

It was also observed that almost all the displaced families illegally encroached the nearby forest land to build residential huts for them. Besides, they started illegally cutting trees in the forest to sale in the nearby markets as a means of livelihood. In addition, they also initiated excavation of rocks in the river bed (rock exposures forming natural check dams across the river bed) and river banks, especially along the Dondra River, as a means of producing construction materials to be sold in nearby cities. Further, their cattle such as goats, buffaloes, cows and oxen were also taken to the forest for grazing. These activities have resulted deforestation, soil erosion in forest and graze lands, bed and bank erosion along the Dhondra River, sheet erosion on the deforested land, fl ash fl oods in seasonal streams causing sedimentation on cultivated land, increase sediment load in river waters, and drying out of springs and water sources.

As the Siwalik hills are the fi rst monsoon barrier, intense precipitation occurs to the southern slope of the hills and also in the Terai region. This results high discharge in the rivers and streams originated in the Siwalik hills. The Dhondra River is one of the seasonal streams of this kind. The intense precipitation events in the monsoon season give rise high discharge which fl ows with high velocity owing to the steep river bed gradient. As soon as the river water

emerges in the Terai plain, the velocity reduces signifi cantly due to low river bed gradient. Consequently, coarser sediments start depositing causing river bed rise. This situation has promoted fl ooding as the river depth becomes shallow and discharge spills over the banks in the Terai region. This process seems to be responsible for the shifting of the Dondra River channel westward since 1995. After 1995, intense and localized precipitation started occurring in its catchment almost each year resulting huge discharge in the river. It promoted even bigger fl ooding events than before, and shifting of the river channel westward was also accompanied faster accordingly. In the fl ooding event of 2000, owing to the huge sediment-loaded discharge, the river channel shifted further westward blockading the Shinghya River, whose discharge was comparatively less due to almost no rainfall in its upper catchment. It means the area suffered with localized precipitations. As already mentioned above, as the natural check dams created by rock exposures are being excavated along with removing the big boulders scattered along the river bed by local people, river is transporting all the sediments directly to the lower reaches of the river. This process is responsible for depositing huge amount of sands each year around the confl uence point with the Singhya River.

The above mentioned impacts may be minimized by aforestation and forest conservation in sediment production zone, managing graze land properly, prohibiting rock excavation along river beds and banks strictly, introducing alternative source of livelihood to the effected families, constructing check dams across the river channel (in sediment transportation zone), and building embankments (in sediment deposition zone) on either side of the river in Terai plain.

181


The geometry of the crust beneath any collisional mountain range is a key information to understand the forces and dynamics that characterize the orogen. Compared to topography, crustal geometry determines the isostatic state of the orogen. The geometry of the underthrusted plate is also relevant to assess its rheology and its effective elastic thickness. Furthermore, the overall crustal geometry exerts a control on the shape of the main plate interface or thrust fault system on which the largest earthquakes nucleate. Finally, the geometry of sub-surface structures is one of the most important input and control parameter of numerical models that aim to simulate the short- and long-term behavior of the orogen.

In the Himalayas, studies on the above topics have all been undertaken. However, most studies focused on individual cross-sections across the Himalayas (mostly in Central Nepal), and proposed scenarios and models along 2D profi les. Whether the imaged structures and drawn conclusions also hold along the entire (ca. 2500 km long) Himalayan arc is seldom discussed due to diffi cult fi eld conditions, and therefore also to the sparseness of available geophysical data. In the meantime, both topographical and geological maps suggest that signifi cant variations exist along the arc, at least on surface. Investigating lateral variations at depth is therefore a prime target as the main geophysical characteristics (crustal thickness, fl exural rigidity, maximum magnitude of potential earthquakes, etc.)

may also very well vary along the entire Himalayan arc.

In the past three years, we have focused our efforts on acquiring new geophysical data that can provide constraints on crustal geometry. In fi ve fi eld campaigns, we have carried out gravity measurements along several profi les perpendicular to the orogen from Far-West-Nepal to Eastern Bhutan, acquiring 366 new data points. This new dataset, complemented by existing data in Nepal and Sikkim, as well as further to the North and South, is now covering more than 1200 km of the Himalayan arc (Fig. 1). This enables us to provide a fi rst assessment of the lateral variability of crustal geometry by comparing numerous arc-perpendicular gravity anomaly profi les.

Bouguer anomaly profi les crossing the orogen show a clear East-West variation in the shape of the underthrusted India plate. Compared to the relatively low angle deepening of the crust in Central Nepal, it plunges at a steeper angle in Far-West-Nepal and in Bhutan. Thermo-mechanical numerical models that aim to explain this lateral variability invoke variations in both rheology and in the crustal structure of India entering the collision system. The lateral variability of structures, also seen on an interpolated map of existing Moho depth estimates, may well cause different seismogenic behavior in different parts of the arc. A fi rst test to estimate regional earthquake hazard, following the method of Song and Simons (2003), also will be presented.

Lateral variability of crustal geometry in the Himalayas from west Nepal to Bhutan

Théo Berthet1,*György Hetényi2, Rodolphe Cattin1, Cédric Champollion1, Jamyang Chophel3, Erik Doerfl inger1, Dowchu Drukpa3, Paul Hammer4, Sarah Lechmann4, Nicolas Lemoigne1, Som Sapkota5

1Géosciences Montpellier, UMR5243–CC60, Université Montpellier 2, Place E.Bataillon, 34095 Montpellier cedex 5, France

2Swiss Seismological Service, ETH Zürich, Sonneggstrasse 5, 8092 Zürich, Switzerland3Seismology and Geophysics Division, Department of Geology and Mines, Post Box 173, Thimphu, Bhutan

4Department of Earth Sciences, ETH Zürich, Sonneggstrasse 5, 8092 Zürich, Switzerland5National Seismological Centre, Department of Mines and Geology, Lainchur, Kathmandu, Nepa


182


Fig. 1: Gravity data coverage in the Nepal, Sikkim and Bhutan Himalayas. Existing data is shown by colors according to Bouguer anomaly (in mGal). New data coverage is shown by red circles.

REFERENCE

Song, T.-R. A. and Simons, M., 2003, Large Trench-Parallel Gravity Variations Predict Seismogenic Behavior of Subduction Zones, Science, v. 301, pp. 630-633.

183


We document geodetic strain across the Nepal Himalaya using GPS times series from 30 stations in Nepal and southern Tibet, in addition to previously published campaign GPS points and leveling data, to determine the pattern of interseismic coupling on the Main Himalayan Thrust fault (MHT). The noise on the daily GPS positions is modeled as a combination of white and colored noise, in order to infer secular velocities at the stations with consistent uncertainties. We then locate the pole of rotation of the Indian plate in the ITRF 2005 reference frame at longitude = -1.34°±3:31°, latitude=51.4°±0.3° with an angular velocity of Ω = 0.5029 ± 0.0072°/Myr. The pattern of coupling on the MHT is computed on a fault dipping 10° to the north and whose strike roughly follows the arcuate shape of the Himalaya. The model indicates that the MHT is locked from the surface to a distance of approximately 100 km down dip, corresponding to a depth of 15 to 20 km. In map view, the transition zone between the locked portion of the MHT and the portion which is creeping at the long term slip rate seems to be at the most a few tens of kilometers wide and to coincide

with the belt of midcrustal microseismicity underneath the Himalaya. According to a previous study based on thermo-kinematic modeling of thermo-chronological and thermo-barometric data, this transition seems to happen in a zone where the temperature reaches 350°C. The convergence between India and South Tibet proceeds at a rate of 17.8 ± 0.5 mm/yr in central and eastern Nepal and 20.5 ± 1 mm/yr in western Nepal. The moment defi cit due to locking of the MHT in the inter-seismic period accrues at a rate of 6.6 ± 0.4 1019 Nm/yr on the MHT underneath Nepal. For comparison, the moment released by the seismicity over the past 500 years, including 14 MW ≥ 7 earthquakes with moment magnitudes up to 8.5, amounts to only 0.9 1019 Nm/yr, indicating a large defi cit of seismic slip over that period or very infrequent large slow slip events. No large slow slip event has been observed, however, over the 20 years covered by geodetic measurements in the Nepal Himalaya. We discuss the magnitude and return period of M>8 earthquakes required to balance the long term slip budget on the MHT.

Convergence rate across the Nepal Himalaya and interseismic coupling on the Main Hi-malayan Thrust: Implications for seismic hazard

Thomas Ader1, 2, Jean-Philippe Avouac1, Jing Liu-Zeng3, Helene Lyon-Caen2, Laurent Bollinger4, John Galetzka1, JeGenrich1,Marion Thomas1, Kristel Chanard1, Soma Nath Sapkota5, Sudhir Rajaure5,

Prithvi Shrestha5, Lin Ding3 and Mireille Flouzat4

1Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.2Ecole Normale Supérieure, 24 rue Lhomond, 75004 Paris, France

3Key Laboratory of Continental Collision and Tibetan Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, People Republic of China

4Commissariat à l'énergie Atomique, DAM, DIF 91297 Arpajon Cedex, France5National Seismological Centre, Department of Mines and Geology, Lainchaur, Kathmandu, Nepal.

184


INTRODUCTION AND OBJECTIVES

The Himalaya and the Tibetan Plateau are the result of the India’s indentation with the southern margin of Asian plate. Some key-features of this collisional process are: mountain building, crustal shortening or thickening, widespread deformation 1000-3000 km from the collision zone, presence of a high plateau, low seismic velocity anomalies in the upper mantle, and high-rate tectonic convergence. The average convergence rate is 50–60 mm/yr since 45 Ma, which is accommodated not only in the Himalayan-Tibet belt but also farther north, with nearly 20 mm/yr across the western Tien Shan alone.

The Tibet region is a zone of particular interest. It shows a mixture of normal and strike-slip faulting which reveals east-west extension and crustal thinning, while to the north and northeast of the plateau, additional high terrains refl ect crustal thickening and continued mountain building. The suture between the India and the southern margin of Eurasia now lies within the Tibetan Plateau.

A large diversity of geophysical methods has been used to study the lithosphere of the Himalaya and Tibet regions, such as deep seismics, seismic tomography, magnetotellurics, potential fi elds, and geothermics. In the last 20 years, a number of international broadband seismic experiments have been carried out across the Tibetan Plateau to investigate the crustal and upper mantle structures. Studying the area at a lithospheric scale is an essential starting point for improving the understanding of the collision of these two continental plates and their resulting deformation. Shortening and thickening by pure shear, delamination, convective removal of the lithospheric mantle, extrusion of blocks by faulting and thrusting of the Indian lithospheric mantle beneath Asia are some of the hypotheses proposed to explain the lithospheric structure of this mountain belt. It is widely accepted that a hot and thin lithosphere beneath the North-East of the Tibetan Plateaus is necessary to explain the huge topography, gravity, geoid and hot crustal temperature of this region (Jiménez-Munt et al., 2008).

In this work we present a 2-D lithospheric model that traverses ~2300 km along a SSW–NNE trending transect

crossing, from India to Asia, the eastern region of the Himalaya, Tibetan Plateau, Qaidam Basin, Qilian Mountains and Beishan (Fig. 1). This region has experienced a long history of accretion, arc and microcontinental collisions, and associated tectonism during the Phanerozoic, resulting in a wide variety of geological composition and structure. We want to investigate the lithosphere and upper mantle downward to 400 km, in order to defi ne the LAB geometry and to quantify the thickness variations along the profi le. We aim to revise critically the mantle characteristics, the mineralogical composition, and its effect on density. Recent works in petrology have shown the dependence of the density of the mantle on temperature, pressure, composition, and tectonic evolution. If we characterize the upper mantle properties, we can better understand the evolution of these areas, and estimate the geodynamic processes responsible for the lithospheric structure we observe. We apply a combination of numerical techniques which integrate potential fi eld equations (gravity and geoid) with isostatic (elevation), thermal (heat fl ow and temperature distribution), and petrophysical models (Afonso et al. 2008).

DATA AND FIRST RESULTS

Geophysical data were collected from different global datasets: elevation data is taken from GINA Global

TopoData (http://www.gina.alaska.edu), with values in a 30 s grid spacing; geoid height data derive from the Earth Geopotential Model EGM2008, fi ltered to eliminate the contribution of density anomalies deeper than 400 km depth; the Bouguer gravity anomaly was computed applying the complete Bouguer correction to free-air satellite data, using a reduction density of 2670 kg/m3. The mantle composition we used is NCFMAS system, based on Holland and Powell (reviewed by Afonso, 2010) thermodynamic database.

The results show that the Tibetan Plateau is supported by a thick lithosphere (down to ~255 km depth) in the south and thin and hot lithosphere (120 km of lithospheric thickness and ~1050 ºC at Moho depth) in the north. In the Himalayan foreland and the Beishan Basin the lithospheric thickness is 140 and 160 km depth, respectively.

2D lithospheric structure of Himalaya collision zone from geophysical and petrological data

*Tunini Lavinia, Jiménez-Munt Ivone and Fernàndez Manel 1Institute of Earth Sciences Jaume Almera, c. Solè i Sabaris, s/n, 28028 Barcelona, Spain


185


Afonso, J. C., Ranalli, G., Fernàndez, M., Griffi n, W. L., O’Reilly, S. Y. and Faul, U., 2010. On the Vp/Vs - Mg# correlation in mantle peridotites: implications for the identifi cation of thermal and compositional anomalies in the upper mantle. Earth Planet. Sci. Lett., v. 289, pp. 606-618.

Griffi n, W. L., O'Reilly, S. Y., Afonso, J. C. and Begg, G., 2008, The composition and evolution of lithospheric mantle: a re-evaluation and its tectonic implications. J. Petrol. doi:10.1093/petrology/egn033

Jiménez-Munt, I., Fernàndez M., Vergés J., and J. P. Platt, 2008, Lithosphere structure underneath the Tibetan Plateau inferred from elevation, gravity and geoid anomalies. Earth Planet. Sci. Lett., v. 267, pp. 276–289.

Figure 1. Localisation of the studied profi le.

We considered petrological-geochemical studies on xenoliths for the lithospheric composition beneath the Tibetan Plateau, while for India and Asia lithospheric mantle, a standard Proterozoic composition from Griffi n et al. (2008) has been used to fi t the model.

REFERENCES

Afonso, C., Fernández, M., Ranalli, G., Griffi n, W. L. and Connolly, J. A. D., 2008, Integrated geophysical-petrological modeling of the lithosphere and sublithospheric upper mantle: methodology and applications. Geochem. Geophys. Geosyst.,v. 9, Q05008.

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The age of the India-Asia collision and the extent of the pre-collisional margins of India (‘Greater India’) and southern Eurasia are key factors to understand collision processes and the evolution of the Tibetan Plateau. Recent revival of the discussion on the timing of collision triggered large amounts of new work. The southern margin of the Lhasa Block is now much better constrained by palaeomagnetic data. On the Indian northern plate margin sparse but signifi cant data exists for the more eastern Tethyan Himalaya around a longitude of ~88.5°E (Patzelt et al. 1996; Yi et al. 2011), while for the western edge of the Indian plate no any meaningful palaeomagnetic results, suitable for an estimate of the extent of Greater India, were available to date. Such data must come from rocks which on the one hand predate the collision age but on the other hand are not too old (as between Triassic and Creataceous India rotated almost 60° counterclockwise which due to the Earth’s magnetic fi eld geometry prevents from determining the Greater India extent accurately). Additionally, sampled units should be as close to the plate margin as possible, and they must be located north of the major thrust systems, in particular north of the MCT,.

In our report we provide fi rst palaeomagnetic insight on the extent of Greater India at its western edge. The Paleocene Dibling limestone in northwestern Zanskar (~ 34°N, 76.5°E) seems to be the only possible target in the NW Himalaya which (i) fulfi lls the above criteria of location and age, and (ii) at least in few areas is not affected by the regional low-grade metamorphism that reaches even Paleocene strata of the Tethyan sediments in this region. Intensities of the natural remanent magnetization (NRM) in the Dibling limestone turned out to be very weak. Alternating fi eld demagnetization (AfD) separated a low-coercivity (LCC) and high-coercivity component (HCC), and a residual very hard remanence being resistant to AfD. Magnetite is dominating the NRM in most samples, carrying both the LCC (removed at ca. 30 mT) and HCC (isolated at >30 mT) likely due to different domain states of particle fractions, while the stable component contributing ~5100% to the NRM can be related to hematite. Selection criteria based on thresholds based on the NRM intensity, the ratio of NRM/ (: magnetic susceptibility), and the %contribution of hematite to the NRM: (1) too small NRM intensities prevent from a

suffi ciently accurate determination of remanence directions; (2) distinctly low NRM/ ratios indicate weak fi eld-parallel alignment of magnetic moments; (3) conspicuously high NRM/ ratios possibly arise from remagnetization; (4) a high %contribution of hematite can be related to a higher degree of weathering. Analysis of accepted HCC remanence directions was done on a specimen level using common Fisher statistics but also inclination-only statistics. The data scatter of the HCC is unfortunately relatively high. Nevertheless antiparallel normal reverse directions and a fold test indicate that we have detected a reasonably well-defi ned primary remanence from which we can derive a fi rst palaeomagnetic constraint on the extent of Greater India at its western edge.

From the resulting data of the HCC we can conclude that the plate margin region of northwestern Zanskar was near an equatorial position at the time of remanence acquisition (62-55 Ma). Together with the expected palaeolatitude determined from the apparent polar wander path of India this results in a much smaller amount of Greater India extent at the longitude of ~76.5°E (NW Zanskar) compared to the northern Indian plate margin in the eastern Himalayan region at ~88.5°E (Patzelt et al. 1996; Yi et al. 2011). The difference can be explained by rotational underthrusting (Klootwijk et al. 1985; Appel et al. 1991).

REFERENCES

Appel, E., Müller, R., and Widder, R., 1991, Palaeomagnetic results from the Tibetan Sedimentary Series of the Manang area (north central Nepal), Geophys. J. Int., v. 104, pp. 255-266.

Klootwijk, C. T., Conaghan, P. J., and Powell, P. J. McA., 1985, The Himalayan arc: large-scale continental subduction, oroclinal bending and back-arc spreading. Earth Planet. Sci. Lett., v. 75, pp. 167-183.

Patzelt, A., Li, H. M., Wang, J. D., and Appel, E., 1996, Palaeomagnetism of Cretaceous to Tertiary sediments from southern Tibet: evidence for the extent of the northern margin of India prior to the collision with Eurasia, Tectonophysics, v. 259, pp. 259-284.

Yi, Z., Huang, B., Chen, L., and Wang, H., 2011, Paleomagnetism of early Paleogene marine sediments in southern Tibet, China: Implications to onset of the India-Asia collision and size of Greater India, Earth Planet. Sci. Lett., v. 309, pp. 153-165.

Greater India extent at its western edge: First palaeomagnetic constraints

Ursina Liebke1, *Erwin Appel1 and Alberto Resentini2

1Department of Geosciences, Tübingen Univ., Hölderlinstr. 12, 72074 Tübingen, Germany2Department of Earth Sciences, University of Milano, Via Santa Sofi a 9/1, 20122 Milano, Italy


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Marine carbonates are found in the Manipur Ophiolitic Melange of the Indo-Myanmar Orogenic Belt (MOB), NE India. The carbonate facies included Maastrichian (?) planktonic foraminiferal limestone, cherty limestone, and calcarenite. The microfacies recognized in the limestone is mainly biomicrite deposited in the shallow marine (tidal fl at) or shallow carbonate ramp environment.

Stable Carbon and Oxygen isotopic ratios of the limestones has been studied for the fi rst time from the Manipur Ophiolitic Melange zone. The isotopic ratios also suggest shallow marine depositional environment for the limestones. The δ13C ratio of the CH2, KANGA-CA, MOVA-EA, SOK-1, UKL-B2, HUN -6A and PHUN-1 varies from +0.89 %0 PDB to +2.74 % PDB. The, δ18O ratio varies from -8.5 %0 PDB to -11.4 %0 PDB. In H section samples (H1, H1A, H2, H3, H3A, H4, H4A, H6, HG, HGA) the C isotope ratio δ13C% PDB varies from +1.33 to +2.10 and δ18O % PDB from -6.29 to -7.31 in limestone. The C and O isotopic ratios from other samples recorded are as follows: UK andUK1 (δ13C, 1.26-1.36 %0 PDB ; δ18O-7.21 to -7.31), P7 and P7A (δ13C %0 , +1.93- to +1.98 ; %0 , δ18O -6.55 to -6.73 ) and E1 and E1A samples the ratios vary from +1.07 to +1.30 for δ13C %0 PDB and –8.89 to –11.35 δ18O % PDB. Ca /Mg and Mg / Ca ratios confi rm the rock as limestone and dolomitic limestone. High content of silica and alumina in the carbonate rocks indicate their siliceous and argillaceous nature. Enrichment in Ca/Mg ratio of the carbonates suggest their non- hypersaline/evaporitic conditions or supratidal depositional environment. The presence of foraminifera, high Ca/ Mg ratio and phosphorous is indicative of subtidal to intertidal conditions. However the absence of benthic forms of foraminifera and sedimentary structures does not support a deeper condition. Low Sr content indicate shallow marine environment.

The present stable isotopic ratios from the Manipur Ophiolitic Melange have indicated the humid and warm paleoclimatic conditions in shallow marine environment. A global correlation of the present C and O isotope data from the Manipur Ophiolite belt has been attempted for the fi rst

time. Recent study from the post Cretaceous-Palaeogene (K/Pg) boundary Santa Elena borehole from the Chicxulub impact crater (Urrutia and Cruz 2008 ) has shown that δ13C values vary from 1.2 to 3.5 %o (PDB) and δ18O values from -1.4 to -4. 8% (PDB). The Paleocene marine carbonate cores from the North Pacifi c Ocean also show similar carbon and oxygen isotope ratios. (Urrutia et al. 2008; Corfi eld and Norris 1998; Corfi eld and Cartlidge 1992).Palaeocene stable carbon and oxygen isotope variation from Lakadong Limestone, South Shillong Plateau, Meghalaya shows similar environment and isotope chemostratigraphy (Tewari 2004; Tewari et al. 2007; 2010). The Palaeocene Beds of the Liburnia Formation, NW Adriatic-Dinaric platform, Slovenia are open shelf subtidal marine limestone (Ogorelec et al. 2001) and the δ13C values range from 2.3 to 0.1% (PDB). The oxygen isotope ratios of the Lakadong Limestone from Meghalaya are more negative when compared with the Chicxulub crater and may be related to local paleogeographic conditions. The δ18O values from Santa Elena core is more or less similar to the DSDP hole in the North Pacifi c Ocean (Urrutia and Cruz 2008). Tewari et al. (2007) and Ogorelec et al. (2001) have shown that the Cretaceous-Paleogene (K/Pg) boundary marine carbonates from the Padriciano section in the North Adriatic platform are highly depleted in δ13C values (-3.62 to -10.01 %o PDB) and δ18O values range from -3.85 to -5.47 %o (V-PDB).

REFERENCES

Corfi eld, R. M. and Norris, R. D., 1998. The oxygen and carbon isotopic context of the Paleocene/Eocene Epoch boundary. In Late Paleocene Early Eocene Climatic and Biotic Events in the Marine and Terrestrial Records (eds Aubry, M. P. and Berggern, W.), Columbia University Press, New York, pp. 124–137.

Corefi eld, R. M., and Cartlidge, J. E., 1992, Terra Nova, v. 4, pp. 443-455.

Tewari, V. C., 2004, Extraterrestrial impact on Earth and extinction of life in the Himalaya. In: Life in the Universe, Kluwer Academic Publishers, Netherlands, pp. 245-248.

Tewari, V. C., Stenni , B., Pugliese , N., Drobne, K., Riccamboni , R., and Dolneck , T., 2007, Peritidal sedimentary depositional facies and carbon isotope variation across K/ T boundary

Carbon and oxygen isotopic ratios of the Manipur Ophiolitic Melange zone carbonate facies of Indo-Myanmar orogenic belt, NE India

*Vinod C. Tewari1, A. K. Singh1, A. N. Sial2 and N. Ibotombi Singh3

1Wadia Institute of Himalayan Geology, Dehradun-248001, Uttarakhand2NEG- LABISE, University of Pernambacu, Recife, Brazil

3Department of Geology, D.M. College of Science, Manipur, Imphal -795138(*Email: [email protected])

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carbonates from NW Adriatic platform, Palaeogeog., Paleoclimt., Paleoecol., v. 255, pp. 77-88.

Tewari,V. C., Lokho, K., Kumar, K. and Siddaiah, N.S., 2010. Late Cretaceous - Paleocene basin architecture and evolution of the Shillong shelf Sedimentation , Meghalaya , Northeast India. Jour. Indian Geol. Cong. , v. 2(2), pp. 61-73.

Urrutia, F. J., Perez-Cruz, J., Morales-Pucnte, P. and EscobarSanchez, E., 2008, Stratigraphy of the basal Paleocene

carbonate sequence and the impact breccia carbonate contact in the Chicxulub crater: stable isotope study of the Santa Elene borehole rocks. Int. Geol. Rev., v. 50, pp. 75–83.

Ogorelec, B., Drobne, K., Jurkovsek, B., Dolenec, T. and Toman, M., 2001, Paleocene beds of the Liburnia Formatin in Cebulovica (Slovenia, NWAdriatic–Dinaric platform). Geologica, v. 44, pp.15-65.

189


Signifi cant dependence of water use on groundwater resources has triggered its extraction beyond natural recharge in the Kathmandu Valley. Yet, groundwater development is continuing without adequate focus on its protection and management. An understanding of groundwater storage potential and challenges to realize the potential may provide a scientifi c basis for developing groundwater protection and management plans. This paper discusses delineation of groundwater aquifers, their spatial distribution, and estimation of groundwater storage potentials of the aquifers in the area. The ‘potential’ in this paper refers to the volume of groundwater that can theoretically be extracted if the aquifer were completely drained. Three hydrogeologic layers were delineated above the bed rock; deep aquifer, clay aquitard, and shallow aquifer. The storage potential was calculated as a multiple of aquifer volume and storage coeffi cient (or specifi c yield). Storage coeffi cient (or specifi c

yield) data were taken from secondary sources. Results showed that the total storage potential of the shallow aquifer is high (1.5 Billion-Cubic-Meters, BCM) compared to the deep (i.e., 0.6 BCM). Storage potential per unit area in the shallow aquifer ranges from less than 100 to 6,800 m3/400 m2 where as that in most parts of the deep aquifer is less than 1,000 m3/400 m2. Based on available information of current level of groundwater, the groundwater storage potentials of the aquifers above the current groundwater level were also estimated. It showed that the shallow aquifer has the potential to store as much as 226.5 Million m3 of groundwater. If the space could be fi lled by artifi cial and/or managed aquifer recharge for future use, it could play a signifi cant role in augmenting water supply in the valley, and therefore, in reducing the water crisis. However, there exist challenges. This paper also discusses strategies and associated challenges to realize the potentials.

Groundwater storage in the Kathmandu Valley: Potentials and challenges

*Vishnu Prasad Pandey and Futaba KazamaInternational Research Center for River Basin Environment (ICRE), University of Yamanashi, 4-3-11 Takeda,

Kofu, Yamanashi 400-8511, Japan(*Email: [email protected])

190


Knowledge of the exhumation of the Lesser Himalayan (LH) tectono-stratigraphic unit is important to the development of models of crustal deformation and to testing proposals that the erosion of this unit has contributed to changes in ocean geochemistry (e.g. Chesley et al. 2000; Pierson-Wickmann et al. 2000). Since most of the LH is unmetamorphosed, using bedrock to determine the timing of exhumation has been confi ned to fi ssion track studies, and the majority of work has concentrated on using the earliest isotopic/petrographic detection of LH detritus in the dated foreland basin sedimentary record to constrain the timing of exhumation (DeCelles et al. 1998; Huyghe et al. 2001; Najman et al. 2009; 2010; Robinson et al. 2001; Szulc et al. 2006). Bulk Sm-Nd analyses of foreland basin mudstones, and U-Pb analyses of detrital zircons have been used, since the LH and the Higher Himalaya (HH), which was exhuming previously, have been considered to differ in their Sm-Nd characteristics and zircon age spectra. However, the HH, exhumed earlier and of high topography, continues to dominate the detrital load shed to the basin, thus hindering detection of the subordinate LH due to dilution of the signal when bulk isotopic analyses are used. Additionally, emerging work shows that there is some overlap in the U-Pb age spectra of zircons and bulk Nd from the HH and LH (McKenzie et al. 2011). Thus there is ambiguity in the detection of the earliest LH detritus in the foreland basin; erosion of the LH was occurring by 11 Ma, but may have begun by 16 Ma (Bernet et al. 2006).

In addition to Ar-Ar analyses on detrital micas and Sm-Nd analyses on conglomerate clasts, we employed new techniques to the foreland basin succession in order to detect LH input:

(1) Re-Os analyses on mudstones. Material of high 187Os/188Os is found in the LH (e.g. Pierson-Wickmann et

al., 2000) but has not so far been recorded in the HH.

(2) U-Pb analyses on detrital rutiles. HH and LH rutiles are distinguishable by their different cooling ages (Bracciali et al, see poster at this conference, and this study).

(3) Sm-Nd on detrital apatite. Sm-Nd analyses on single grains will not be subject to the dilution issues of bulk analyses and recent work has employed this technique to distinguish HH from trans-Himalayan detritus (Henderson et al. 2010).

We will discuss the effectiveness of these techniques in distinguishing HH from LH detritus in the foreland succession and thus further constraining the exhumation of the LH.

REFERENCES

Bernet, M., Van der Beek, P., Pik, R., Huyghe, P., Mugnier, J. L., Labrin, E., and Szulc, A., 2006, Miocene to Recent exhumation of the central Himalaya determined from combined detrital zircon fi ssion-track and U/Pb analysis of Siwalik sediments, western Nepal: Basin Research, v. 18, pp. 393-412.

Chesley, J. T., Quade, J., and Ruiz, J., 2000, The Os and Sr isotopic record of Himalayan paleorivers: Himalayan tectonics and infl uence on ocean chemistry: Earth and Planetary Science Letters, v. 179, pp. 115-124.

DeCelles, P. G., Gehrels, G. E., Quade, J., and Ojha, T. P., 1998, Eocene early Miocene foreland basin development and the history of Himalayan thrusting, western and central Nepal: Tectonics, v. 17, pp. 741-765.

Henderson, A., Foster, G. L., and Najman, Y., 2010, Testing the application of in situ Sm–Nd isotopic analysis on detrital apatites: A provenance tool for constraining the timing of India–Eurasia collision: Earth and Planetary Science Letters, v. 297, pp. 42-49.

Huyghe, P., Galy, A., Mugnier, J.L., and France-Lanord, C., 2001, Propagation of the thrust system and erosion in the Lesser

The timing of exhumation of the Lesser Himalaya

*Y. Najman1, G. Foster2, I. Millar3, R. Parrish3, M. Bickle4, D. Mark5, L. Reisberg6, R. Mckenzie7 and R. Rhiede8

1LEC, Lancaster University, Lancaster, LA1 4YQ, UK2NOC, Southampton University, UK.

3NIGL, BGS Keyworth, Nottingham, UK.4Dept Earth Sciences, Cambridge University, UK

5SUERC, East KIlbride, UK6CRPG, CNRS-Nancy, France

7Dept Earth Sciences, University of Califormia Riverside, USA8Inst. of Earth and Environmental Science, University of Potsdam, Germany


191


Himalaya: Geochemical and sedimentological evidence: Geology, v. 29, pp. 1007-1010.

McKenzie, N. R., Hughes, N. C., Myrow, P. M., Xiao, S. H., and Sharma, M., 2011, Correlation of Precambrian-Cambrian sedimentary successions across northern India and the utility of isotopic signatures of Himalayan lithotectonic zones: Earth and Planetary Science Letters, v. 312, pp. 471-483.

Najman, Y., Bickle, M., Garzanti, E., Pringle, M., Barfod, D., Brozovic, N., Burbank, D., and Ando, S., 2009, Reconstructing the exhumation history of the Lesser Himalaya, NW India, from a multitechnique provenance study of the foreland basin Siwalik Group: Tectonics, v. 28. TC5018, doi:10.1029/2009TC002506

Pierson-Wickmann, A.-C., Reisberg, L., and France-Lanord, C., 2000, The Os isotopic composition of Himalayan river bedloads and bedrocks: importance of black shales.: Earth and Planetary Science Letters, v. 176, pp. 203-218.

Robinson, D. M., DeCelles, P. G., Patchett, P. J., and Garzione, C. N., 2001, The kinematic evolution of the Nepalese Himalaya interpreted from Nd isotopes: Earth and Planetary Science Letters, v. 192, pp. 507-521.

Szulc, A. G., Najman, Y., Sinclair, H. D., Pringle, M., Bickle, M., Chapman, H., Garzanti, E., Ando, S., Huyghe, P., Mugnier, J. L., Ojha, T., and DeCelles, P., 2006, Tectonic evolution of the Himalaya constrained by detrital Ar-40-Ar-39, Sm-Nd and petrographic data from the Siwalik foreland basin succession, SW Nepal: Basin Research, v. 18, pp. 375-391.

192


The Tibetan Plateau is often called the water tower of the big rivers in Asia, and as high as 40% of the runoff of some of the upper reaches of these rivers is from glaciers.

Under global warming, some major changes are taking place in the Tibetan Plateau, including glacial fl uctuations, lake variations, changes of wet land and grassland degradation. Glacier process is among the major changes. The glacial retreat on the TP has caused direct consequences, particularly the immediate and strong impact on the hydrological processes in this region. Their retreat also relates directly to environment, water resources, ecology, and disasters such as glacial lake outburst fl oods and other foods in the region (1-2). The impact can be tremendous in the region because it houses the world’s largest population (more than one billion).

The glacial mass centered by the Tibetan Platea is the largest in China and whole Asia. According to the latest glacial inventory, there are 36,918 glaciers in the Tibetan Plateau with a glacial area of 49,903 km2, acconting for 80% of all the glaciers in China, 84% of total glacial area in China and 82% of total glacial volume in China. Some of these glaciers extend north into the arid and desert region, and become the main water resource for arid central Asia, especially for the Tarim Basin. Some extend south into the warmer, wetter forests and concentrate around the Brahmaputra and Yarlung Tsangpo Rivers, which benefi t the local residents as their water resource. They, however, cause serious social problems in the region at the same time.

Glaciers in the Tibetan Plateau are sensitively responsing to climate change in the past 100 years, particularly in the recent decades. Under global warming, glaciers in the Tibetan Plateau are extensively retreating. Retreating glaciers reaches 80-95% of the total glaciers. Glacial area retreated by 4.5% in the past 20a and by 7% in the past 40a. Some glaciers which were advancing are now retreating with larger and larger retreating amplitude. The magnitude of glacial retreat from 1997-2006 is larger than that from 1987-1996, which means that glacial retreat is accelerating in the past decade!

Infl uenced by the differential geographical patterns of climatic change in the Tibetan Plateau, the glaicial retreat in

the southern and southeastern Tibetan Plateau are obviously larger than than in the central Tibetan Platea. Observed single glacier also shows largest retreat in Mt Karakorum and southeastern Tibet, and smallest retreat in central plateau.

In the most intensively retreating southestern Tibetan Plateau, we observed in detail the Glacier No. 12, in the Palongzangbu River and found that 55% of the area of the Glacier No.12 had melted away from 1980 to 2005. We have also observed the Ata Glacier which is a neighboring glacier of the Glacier No. 12. The annual retreat of Ata Glacier was 30-40 m before 1980, and increased to 50m afterwards.

Glacial fl uctuation is the consequence of the balance (often called glacial mass balance) between glacial accumulation and glacial ablation. Glacial mass balance is mainly controlled by temperature, temperature, therefore, dominates glacial fl uctuation in the long run.

Glacial retreat in the Tibetan Plateau is impacting different aspects of hydrological processes in the Tibetan Plateau, including dischsrge increase in some rivers, lake level rising, more frequent glcial-terminus lake outburst fl ood, glacial debris fl ow. Our study focused on two issues, glacial-water-supplied lake expansion fl ood (GLEF) and glacial-terminus lake outburst fl ood (GLOF) induced by glacial retreat is a serious problem on the Tibetan Plateau and its surrounding regions.

In the Tibetan Plateau, there are more than 1000 glacial-water-supplied lakes and more than 3000 glacial-terminus lakes. Most of the lakes are now more or less related to GLEF and GLOF because of more glacial melting water supply. The Nam Co Lake, the largest lake over the Tibetan Plateau, is an example infl uenced by GLEF. In the Nam Co Lake basin, the glacial area has decreased 22 km2 (11%) from 1970 to 2000. At the same time, lake area has increased 38 km2 (2%) from 1970 to 2000. GLEF is devastating pasture nearby the large lakes in the Tibetan Plateau. Under the impact of glacial retreating, glacial terminus lake appears or enlarges and causes GLOF. The Laigu Glacial-Terminus Lake in southeast Tibetan Plateau is rapidly expanding. The lake area of the Laigu Glacier terminus lake was only 0.42 km2 in 1980, increased to 0.71 km2 in 1988, and to 2.22 km2 in 2001. In 2005, it increased to 2.55 km2. GLOF will damage the roads, villages in the lower reaches.

Glacial retreat and its impact in Tibetan Plateau under global warming

Yao TandongInstitute of Tibetan Plateu Research, Chinese Academy of Sciences


193


It is time to take measures to deal with the glacial retreating and related consequences. We propose some here for consideration:

(1) A complete category of hazard distribution caused by glacial retreat, GLEF and GLOF

(2) Early warning systems at the most dangerous sites of GLEF and GLOF

(3) Engineering measures including water pipes to drainage water from the most dangerous GLOF and GLEF

194


The mapping and classifi cation of the two main laterally extensive thrust sheets of the Himalaya, the Greater Himalayan Sequence (GHS) and the Lesser Himalayan Sequence (LHS), in eastern Nepal and adjacent Tibet are approximate and disputed. This is partially because most geochronological studies have focused on a rather limited area, thought to include the LHS-GHS contact zone either in eastern Nepal or in Tibet. A wider perspective is gained here by a ~200 km long continuous Trans-Himalayan geochronological transect along the Arun river valley, from the Main Boundary Thrust in the south to the South Tibetan Detachment in the north. Sampled rocks include mostly orthogneisses (7 samples) and two paragneisses collected at the northernmost part of the transect, near and ~20km north of Kharta (southern Tibet).

Regardless of sample location, all the orthogneisses have concordant ~1.8 Ga ages and mostly simple CL oscillatory-zoned zircons. The lower intercepts of the discordia lines are Cenozoic (<55 Ma), consistent with partial lead loss during the Himalayan orogeny. Imprints of older metamorphic events are absent. The uniformity in zircon age and morphology is interrupted only upon entering

an overlying, paragneiss-dominated, litho-stratigraphic unit near Kharta in southern Tibet. Zircons in this unit span a wide range of ages, from ~1.8 Ga to ~430 Ma. Relatively rare CL-dark, low Th/U rims indicate recrystallization of zircon at ~16 Ma.

The new U-Pb zircon ages suggest that there is no stratigraphic or structural discontinuity along the Arun valley from the Num orthogneiss in Nepal to the Ama Drime orthogneiss in Tibet. The Num and Ama-Drime orthogneisses have identical Palaeoproterzoic protoliths and belong to the same thrust sheet. Moreover, our fi eld observations suggest that the transition to the overlying high-grade metasedimentary unit (unanimously accepted as GHS) has a similar stratigraphy and metamorphic grade above the Num and Ama Drime orthogneisses. This suggests that mechanisms of juxtaposition of the Num/Ama Drime orthogneiss and the overlying GHS unit are similar at both settings.

Surprisingly, even orthogneiss horizons within the phyllitic sequence of the ‘Arun Window’ that underlie the Num orthogneiss near Tumlingtar have 1.8 Ga U-Pb zircon ages.

U-Pb zircon geochronology along the Arun River, eastern Nepal: Consistency of ~1.8 Ga ages from the Main Boundary Thrust to the Ama

Drime Antiform in southern Tibet

*Yaron Katzir1, Itai Haviv1,2, Jean-Philippe Avouac2, Matthew A. Coble3 and Tzahi Golan1 1Department of Geological and Environmental Sciences, Ben Gurion University of the Negev, Beer Sheva 84105, Israel

2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena CA 91125, USA3Stanford-USGS Micro Analytical Center, Stanford CA 94305, USA


195


ASTER sensor was launched in December 1999, onboard the fi rst NASA’s EOS series of satellite, Terra. ASTER covers a wide spectral region with 14 bands from visible to thermal infrared. Three visible and near infrared (VNIR) bands, six shortwave infrared (SWIR) bands, and fi ve thermal infrared (TIR) bands have a spatial resolution of 15, 30 and 90 m, respectively. In addition, ASTER has an along track stereo observation capability with the bands 3N and 3B in near infrared region, which provide us ASTER digital elevation model (DEM) data and the highly performed geometrical corrections (Yamaguchi et al. 1998). ASTER-TIR is the fi rst and still now the only satellite-borne multispectral TIR remote sensing system with spectral, spatial and radiometric resolutions adequate for geological applications.

Based on the analysis of TIR spectral properties of typical rocks on the Earth, several mineralogical indices

including the Quartz Index (QI), Carbonate Index (CI) and Mafi c Index (MI) for detecting the lithology and mineralogy using ASTER-TIR are successfully developed (Ninomiya et al. 2005).

In this paper, we have accomplished mosaic mapping of the VNIR false color image and the indices in the central segment of the Yarlung Zangbo suture zone covering the rectangle region N30E86 – N28E90, rather wide region compared to the coverage of a single ASTER scene, that is about the square of 60 km. The ASTER data selection, calculation of the indices and the generation of the mosaic image are executed effi ciently using our original software, combined use of some commercial software including ER-Mapper. Fig. 1 shows the ASTER-VNIR mosaic false color image covering the study area, assigned band 1 for blue, band 2 for green and band 3N for red. Some geometrical information is superimposed into the image.

Lithological mapping in the central segment of the Yarlung Zangbo suture zone using ASTER data

*Yoshiki Ninomiya1 and Bihong Fu2

1Geological Survey of Japan, AIST, Tsukuba, 3058567, Japan,2Center for Earth Observation and Digital Earth, Chinese Academy of Sciences, Beijing, 100094, China


Fig. 1: ASTER-VNIR mosaic false color image covering the study area with some geographical information superimposed.

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As one example of the mapping results derived in this study, we present in this abstract Fig. 2 showing the color composite image of the indices, assigned blue for MI, green for CI and red for QI. With the regional mosaic images covering wide area presented here, we can observe the major geological structures along the Yarlung Zangbo suture zone, for example, the ultramafi c rocks in the ophiolite zone along the suture zone, and the zonal carbonate and quartz rich sedimentary rock units which supposed to be the accretionary wedges according to the subduction along the suture zone. Also, feldspar rich granitic rocks and the gypsum or gypsiferous argillites can be detected with the indices.

At the presentation, we show the theoretical basis defi ning the indices and the result images of the mosaic

mapping of the indices. Then, we discuss the expected contributions to geology by utilizing the mosaic images of the indices covering full segments of the Yarlun Zangbo suture zone or the entire Tibetan region to be generated by extending this study.

REFERENCES

Ninomiya, Y., Fu, B. H. and Cudahy, T. J., 2005, Detecting lithology with Advanced Spaceborne Thermal Emission and Refection Radiometer (ASTER) multispectral thermal infrared “radiance-at-senseor” data. Remote Sensing of Environment, 99, 127-135.

Yamaguchi, Y., Kahle, A. B., Tsu, H., Kawakami, T. and Pniel, M., 1998, Overview of Advanced Spaceborne Thermal Emission and Refl ection Radiometer (ASTER), IEEE Transactions on Geoscience and Remote Sensing, 36, 1062-1071.

Fig. 2: The color composite image of the indices, assigned blue for MI, green for CI and red for QI, for the fi xed data range to each index, that is, 0.79 to 0.95 for MI, 1.005 to 1.055 for CI and 0.97 to 1.055 for QI. Image color and the expected rock types for the typical bodies (denoted as white dots) are written over for the assistance of interpretation with the black and white printed material, as well as some geographical information are superimposed.

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The India/Asia collision resulted in the Tibet plateau, the Himalayan orogen and the E- or SE-ward lateral escape of a large number of materials from the plateau. The SE Tibet plateau (e.g. the Indochina block) is characterized by a wedge and southward spread and a clockwise escape of material around the NE corner of the India plate.

The tectonic framework of the west Yunnan block (located at the northern part of the Indochina block) includes the Simao, Baoshan, and Tenchong laterally extruded microblocks, and is bounded by the Ailaoshan-Red River shear zone (ALRRSZ), the Lancnagjiang right/left strike-slip shear zone (LCJSZ Jiali-Gaoligong right strike-slip shear zone (JL-GLGSZ) and the Sagaing-Nabang right strike-slip shear zone (SG-NBSZ), from east to west.

The activation timing of these strike-slip shear zones has been determined by previous studies through 40Ar/39Ar analysis. The ALS-RR started at ~36-34 Ma and reaction timing began at about 28-10 Ma; the generated shear heating of the ZS-LCJSZ from 32 to 22 Ma, and its 40Ar/39Ar data range from 19 to 14 Ma; the existed JL-GLGSZ was active at about 21-12 Ma and the SGSZ occurred at 36-16 Ma.

Our new SHRIMP and LA-ICP-MS U-Pb dating on zircon show the initiation of the Nabang shear zone with high temperature fabrics (>650°C) at the northern segment of the SGSZ yields ~53-54Ma. The Nabang Shear zone experienced 44-41 Ma, 33-28 Ma, 22-20 Ma and 15 Ma poly-metamorphism and deformation events, which reveal probably the oldest age of these strike-slip shear zones in

the west Yunnan, and the initiation of the Indo-Asia oblique collision.

However, horizontal shear zones (or detachment) in a few areas, such as Mogok, Doi Inthanon, Doi Suthep, Ruili and Dicangshan areas exposed in the SE Tibet plateau have been recognized. But the constructed timing and relationship of the vertical shear zones and these horizontal shear zones, as well as the escape mechanism of the material from Tibet are still not clear.

New fi eld observations and kinematic analysis for horizontal shear zones in the south Tengchong (STC), Zongshan (ZS) and Diancangshan-Ailaoshan (DCS-ALS) areas indicate that the widespread horizontal shear zones (or detachments) are associated with vertical JL-GLGSZ, LCJSZ and ALRRSZ in the west Yunnan, refl ecting decoupling between the overlying Paleozoic sedimentary sequence and the Pre-cambrian metamorphic basement. 40Ar/39Ar dating for horizontal mylonites indicates the STC detachment occurred at 23 Ma (Bi), the ZS detachment yields the 19 Ma (Bi), and the DCS detachment is of 15 Ma (Bi). This reveals that the coeval activation timing of horizontal and vertical shear zones existed in Miocene.

Shear sense on these horizontal shear zones shows that the Baoshan and Simao microblocks were moving southward as lateral escape relative to both sides blocks of Yangze and Tengcong. A new tectonic escape model is proposed: lateral escape fl ow of materials in the SE Tibet probably occurred in drawer-type space bounded by horizontal and vertical strike-slip shear zones in Miocene.

Tectonic escape model during Indo-Asia collision: new insights from the relationship between vertical and horizontal shear zones in SE Tibet

*Zhiqin Xu, Zhihui Cai,Huaqi Li, Guanwei Li and Hui CaoState Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of

Geological Sciences, 26 Baiwanzhuang Road, Beijing 100037, P. R. China. (*Email: [email protected])

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Predominant stretching structures in the Greater Himalayan Crystalline Complex (GHC) are trending perpendicular to the belt and linked to the southward exhumation of the GHC between the South Tibet Detachment and the Main Central Thrust. However, our fi eld investigations in southern Tibet reveal the widespread presence of gently dipping mylonites with a penetrative orogen-parallel stretching lineation, which defi ne the detachments between the Tethyan Himalayan sedimentary sequence and the underlying GHC. Both fi eld criteria and fabrics of quartz and sillimanite indicate top-to-the-east shearing in the Yadong detachment (eastern GHC), coexistence of top-to-the-east and top-to-the-west shearing in the Nyalam detachment (central GHC), but top-to-the-west shearing in the Pulan detachment (western GHC). The characteristic slip systems of quartz and sillimanite

suggest that the lateral fl ow underwent sillimanite-grade to greenschist-grade conditions. SHRIMP U-Pb ages of zircon from mylonites indicates that the orogen-parallel extension occurred at 28-26 Ma in the Yadong detachment and at 22-15 Ma in the Pulan detachment. While 40Ar/39Ar ages of biotite and muscovite yield 13-11 Ma for the Yadong detachment, coeval with the activation of the South Tibet Detachment. Combined with previous studies, we propose that due to the lateral crustal thickness gradients in a thickened crust, orogen-parallel gravitational collapse occurred within the convergent Himalayan orogen in the late Oligocene-Miocene. This tectonic denudation triggered and enhanced the partial melting and channel fl ow of the GHC in the Miocene.

Orogen-parallel extension and exhumation of the Greater Himalaya in the late Oligocene and Miocene

*Zhiqin Xu1, Qin Wang2, Arnaud Pêcher3, Fenghua Liang1, Xuexiang Qi1, Lingsen Zeng1, Huaqi LI1 Zhihui Cai and Hui Cao1

1 State Key Laboratory of Continental Tectonic and Dynamics, Institute of Geology, Chinese Academy of 2Geological Sciences, Beijing 100037, China

2 State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, China

3 ISTerre, University of Grenoble and CNRS, Maison des Géosciences, 1381, rue de la Piscine, 38400 Grenoble, France(*Email:[email protected])

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Flat and steep subductions are end-member modes of oceanic subduction zones with fl at subduction occurring at about 10% of the modern convergent margins and mainly around the Pacifi c. Continental (margin) subduction normally follows oceanic subduction with the remarkable event of formation and exhumation of high- to ultrahigh-pressure (HP-UHP) metamorphic rocks in the continental subduction/collision zones. We used thermo-mechanical numerical models to study the contrasting subduction/collision styles as well as the formation and exhumation of HP-UHP rocks in both fl at and steep subduction modes. In the reference fl at subduction model, the two plates are highly coupled and only HP metamorphic rocks are formed and exhumed. In contrast, the two plates are less coupled and UHP rocks are formed and exhumed in the reference steep subduction model. In addition, faster convergence

of the reference fl at subduction model produces extrusion of UHP rocks. Slower convergence of the reference fl at subduction model results in two-sided subduction/collision. The higher/lower convergence velocities of the reference steep subduction model can both produce exhumation of UHP rocks. A comparison of our numerical results with the Himalayan collisional belt suggests two possible scenarios: (1) A spatially differential subduction/collision model, which indicates that steep subduction dominates in the western Himalaya, while fl at subduction dominates in the extensional central Himalaya; and (2) A temporally differential subduction/collision model, which favours earlier continental plate (fl at) subduction with high convergence velocity in the western Himalaya, and later (fl at) subduction with relatively low convergence velocity in the central Himalaya.

Flat versus steep subduction: Contrasting modes for the formation and exhumation of high- to ultrahigh-pressure rocks in continental collision

zones

*Zhonghai Li 1, Zhiqin Xu 1 and Taras Gerya 2

1 State Key Lab of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, China

2 Institute of Geophysics, ETH-Zurich, Switzerland

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The Qinghai-Tibetan Plateau, of eastern Tethys domain, is mainly composed of fi ve terranes, such as Altun-Qilian-Kunlun, Baryan Har-Songpan Ganzi, Qiangtang, Lhasa and Himalaya terranes. Among the terranes, from north to south, there are A’neymaqen, Jinsha, Bangong-Nujiang and Yarlung-Tsangpo suture zones (Yin and Harrison 2000�Xu et al. 2006). A’neymaqen and Jinsha sutures are thought to represent the relic of Paleo-Tethyan ocean basins, accompanied by early Mesozoic orogenesis. But, Bangong-Nujiang and Yarlung-Tsangpo zones are thought to be Neo-Tethyan sutures. So, the Lhasa terrane, one component of

Qinghai-Tibetan Plateau, controlled by Yarlung-Tsangpo and Bangong-Nujiang sutures, is usually regarded as a late Mesozoic to Cenozoic Tectonic zone (2500 km long and 150-300 km wide). Its earlier evolution is not clear. A common idea is that the basement and Paleozoic cover of the Lhasa terrane is similar to the Himalayan terrane. The two terranes are both thought to originate from Gondwana land (Xu et al. 2006). The Lhasa terrane was fi nally separated from Gondwana land because of the formation of Yarlung Tsangpo Neo-Tethyan ocean.

Early Mesozoic orogenesis newly discovered in the Lhasa terrane, south Tibet

*Li Hua-Qi and Xu Zhi-QinInstitute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China


Fig. 1. The spatial distribution of early Mesozoic orogenic belt in the Lhasa terrane and the related igneous rocks of Neopaleozoic- early Mesozoic. SG-YZ: Songpan-Gaze-Yangtze composite terrane; NQT-SM: Northern Qiangtang-Simao terrane; SQT-BS: Southern Qiangtang-Baoshan terrane; HM: Himalaya terrane; IND: India block; MBT: Main boundary fault; JS-ALS: Jinsha-Ailao suture zone; SL-CMS: Shuanghu-Lancang-Cangmeng suture zone; BNS: Bangong-Nujiang suture zone; YLZBS- Yarlung Tsangpo suture zone.

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However, the discovery of eclogite belt northeast of Lhasa city (Fig. 1) shed new light in contrast to the above-mentioned general understanding of the Lhasa terrane. The petrography, chronology and geochemistry studies indicate that the eclogite′s protolith should be of Paleo-Tethyan oceanic crust (C-P era), with eclogite facies metamorphic age of 262±5 Ma. This means that there might be a new Paleo-Tethyan boundary in the Lhasa terrane (Yang et al. 2009).

Regional structure analysis and muscovite 40Ar/39Ar dating of muscovite-quartz schist, eclogite and retrograde eclogite indicates that the closure of the Paleo-Tethyan ocean basin and the following collision of northern and southern parts of the Lhasa terrane occurred at 220-240 Ma. It was an early Mesozoic collsional orogenesis. This event is further confi rmed by coeval magmati te along the Lhasa-Bomi - Tengchong area. These evidences suggest that the early Mesozoic orogenesis in the Lhasa terrane is widely distributed from Coqen area in the west, and then extends eastward through the Lhasa and Sumdo area, fi nally

turns around the eastern Himalayan syntaxis into Bomi -Tengchong region. The newly discovered orogenisis should be very important for understanding the Lhasa terrane evolution and distribution scale of eastern Paleo-Tethyan ocean (Fig. 1).

REFERENCES

Xu, Z. Q., Li, H. B. and Yang, J.S., 2006, An orogenic plateau, the collage and orogenic types of the Qinghai-Tibet plateau. Earth Science Frontiers, v. 13, pp. 1-17.

Yang, J. S., Xu, Z. Q., Li, Z. L., Xu, X. Z., Li, T. F., and Robinson, P. T., 2009, Discovery of an eclogite belt in the Lhasa block, Tibet. A new border for Paleo-Tethys? Journal of Asian Earth Sciences, v. 34, pp. 76-89, doi:10.1016/j.jseaes.2008.04.001.

Yin, A. and Harrison, T. M., 2000, Geologic evolution of the Himalayan-Tibetan orogen, Annual Review of Earth and Planetary Sciences, v. 28, pp. 211-280, doi:10.1146/annurev.earth.28.1.211.

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Deformed and metamorphosed Proterozoic sedimentary successions constitute the Lesser Himalayan thrust slices (LHS) along the entire strike of the Himalayan orogen. In Eastern Himalaya, the LHS is generally bound by the Main Central thrust (MCT) in the north and Main Boundary thrust in the south. However, the Proterozoic metasedimentary succession around Lumla (Lumla Formation) in the Higher Himalaya of western Arunachal Pradesh is known to form an isolated outcrop surrounded by the Higher Himalyan Crystallines (HHC). The Lumla Formation, with an exposed aggregate thickness of c. 800m, consists of three stacks of quartzite-phyllite (mica schist) with intercalations of impure limestone (marble) in the middle stack, and local development of thin carbonaceous shales (coal) both in the lower and upper stacks. Rarely preserved small scale ripples, low-angle stratifi cation in quartzites, wavy to fl aser bedded heterolithic quartzite-pelite, and algal laminite in the limestone (marble) indicate a shallow marine environment of deposition with intermittent restriction in circulation attested by carbonaceous shale (coal).

Recent mapping confi rm the Lumla Formation to be overthrust by migmatitic HHC gneisses, representing a structural window. The thrust at the base of HHC gneisses around Lumla has a shallow dome form. Thrust transport of the HHC rocks is consistently toward the south (SW) on either fl ank of the domal structure along a traverse between Zemithang in the north and Fuma in the south. Inverted metamorphism in a narrow zone close to the upper bounding thrust of the Lumla succession is similar to that reported from the MCT zone north of Dirang. Close to the thrust zone, both the HHC rocks and the Lumla Formation rocks in the footwall are marked by common development of L-S fabric in sheared migmatitic gneisses or garnet-kyanite (sillimanite) bearing pelitic schists, consistently south vergent mesoscopic folds on foliation, shear bands, and symmetric to asymmetric boudins on leucogranite bands. In addition, two internal thrusts (detachments) separate limestone bearing the middle part of the Lumla Formation from the quartzite-metapelite dominant upper and lower parts. N-S and E-W open folds and crenulation cleavages overprint earlier tight to isoclinal folds and associated axial plane foliation in quartzite-metapelite rocks around Lumla.

Based on detrital zircon geochronology, the Lumla Formation has been correlated with the (Meso-) Proterozoic Dirang Formation (Yin et al. 2006). Presence of c. 1.8-1.6 Ga old intrusive granite gneisses, like Bomdila gneiss/Ziro gneiss in the Lesser Himalaya of Arunachal Pradesh could have acted as a possible source for the detrital zircons in the Dirang Formation, and explain similar Precambrian antiquity of the zircons in the Lumla quartzite. The Lumla window of Proterozoic rocks in conjunction with the LHS in Sikkim and Arunachal Pradesh suggest signifi cant northward extention of the Proterozoic basin(s) in this region, and an extensive E-W sea lane bordering northern margin of India during the Proterozoic. More recently, c. 822 Ma zircons are reported from the Zemithang gneiss (Yin et al. 2010). Thus, more than one episode of Proterozoic deformation and magmatism could have affected the LHS and its northward extension that now occurs in a structural window around Lumla. Recent recognition of the arc source for LHS volcaniclastics along with granitoids from northwestern Himalaya (Kohn et al. 2010), Bhutan (Long et al. 2011) and Arunachal Pradesh (Bikramaditya Singh 2010), reinforces the idea of a subduction related convergence along the Proterozoic northern margin of India with implications for Columbia and Rodinia reconstructions (e.g. Saha 2011). Reactivation of older structures during crustal shortening related to the India-Asia collision is a distinct possibility, and whether the inverted metamorphism close to upper bounding thrust of the Lumla window is a fall out of the Cenozoic Himalayan orogeny needs further investigation.

REFERENCES

Bikramaditya Singh, R. K., 2010, Geochemistry and petrogenesis of granitoids of Lesser Himalyan Crystallines,western Arunachal Himalaya, Journal of the Geological Society of India 75, 618-631.

Kohn, M., Paul, S.K. and Corrie, S.L., 2010, The lower Lesser Himalayan sequence: A Paleoproterozoic arc on the northern margin of the Indian plate, Bulletin Geological Society of America 122, 323-335.

Long, S., McQuarrie, N., Tobgay, T., Rose, C., Gehrels, G. and Grujic, D., 2012, Tectonostratigraphy of the Lesser Himalaya of Bhutan: Implications for the along-strike

Lumla window, Eastern Himalaya – stratigraphy, structure, and implications for extra-peninsular Proterozoic basins in India

*Dilip Saha1, Saheli Sanyal1 and Tapos Goswami2

1Geological Studies Unit, Indian Statistical Institute, Kolkata 700108, India. 2Department of Applied Geology, Dibrugarh University, Dibrugarh 786004, India

*(E-mail: [email protected])

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stratigraphic continuity of the northern Indian margin, Geological Society America Bulletin 123, 1406-1423.

Saha, D., 2011, Proterozoic sequences in Eastern Himalaya, their deformation and implication for supercontinent reconstructions in the Proterozoic involving northern margin of greater India, IAGR Conference Series 12, 9-10.

Yin, A., Dubey, C.S., Kelty, T.K.,. Gehrels, G.E., Chou, C.Y., Grove, M. and Lovera, O., 2006, Structural evolution of

the Arunachal Himalaya and implication for asymmetric development of the Himalayan orogen, Current Science 90, 195-206.

Yin A., Dubey, C.S., Webb, A.A.G., Kelty, T.K., Grove, M., Gehrels, G.E. and Burgess, W.P. 2010, Geologic correlation of the Himalayan orogen and Indian craton: Part 2. Structural geology, geochronology, and tectonic evolution of the Eastern Himalaya, Geological Society of America Bulletin 122, 360-395

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The Himalaya, on the southern slopes of the Tibetan plateau contains one of the largest concentrations of the glaciers and permanent snowfi eld. There are 9575 glaciers with different shape and size in the Indian part of the Himalaya (Raina and Srivastava 2008). It is very unfeasible to study the entire glaciers by ground instrumental data because of their inaccessibility, remoteness, rugged terrain and harsh weather conditions. Therefore, to understand the climatic variability over the Himalaya, two glaciers have been selected in central Himalaya viz. Chorabari (30°41’-30°48’N and 79°1’-79°6’E) and Dokriani (30°49'-30°52'N and 78°47'-78°51'E). The aim of this study is to understand the relationship between meteorological (climate) parameters and mass balance fl uctuation. Six Automatic Weather stations (AWS) have been installed in both of the glaciers, three in Chorabari Glacier, Mandakini basin and three in Dokriani Glacier, Bhagirathi basin to measure the meteorological parameters. The meteorological parameters viz. air temperature, wind speed and direction, relative humidity, vapour pressure, sun duration, net radiation,

albedo, precipitation, snow surface temperature are being continuously recorded for both the glaciers since June 2011. Mass balance and glacier dynamic studies have also been conducted on both of the glaciers by glaciological method since 1992 on Dokriani Glacier and 2003 on Chorabari Glacier. The result shows that both of the glaciers have negative mass balance during the study period and the average climatic conditions of the glaciers are almost same. The annual average specifi c balance during the year 2007-2011 was calculated -0.78 m w.e. a.-1 and -0.40 m w.e.a.-1 and the average frontal recession was observed 8.6 and 20 m a.-1 for Chorabari and Dokriani glaciers respectively. It has been found that the average wind speed (3-5 m/s) in the winter is more than in the summer (2-3 m/s) and the average rainfall were measured between 1200 to 1350 mm for both of the glaciers.

REFERENCES

Raina, V. K. and Srivastava, D., 2008, Glacier Atlas of India. Geological Survey of India, Bangalore.

Temporal and Spatial Changes in Himalayan Glaciers - Impact of Climate Variability

*K. Kesarwani, B. Pratap, M. Mehta, R. Bhambri, R. and D. P. DobhalCentre for Glaciology, Wadia Institute of Himalayan Geology, 33 G.M.S. Road, Dehradun, Uttarakhand, India


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Dhauladhar range (D-range), trending NW-SE, lies south of the Pir Panjal range between the Beas and Ravi rivers. It lies in the outer Lesser Himalaya with steep gradient and abrupt physiographic and tectonic break to the south against the Siwalik foreland basin of the Kangra reentrant The southern margin of the D-range is demarcated at the base by the closely spaced Main Central Thrust (MCT) and the Main Boundary Thrust (MBT) which are responsible for the uplift and exhumation of the mountain range. The altitude at the water divide of the D-range decreases from 5000 m in southeast to 2800 m in northwest along the regional orogenic trend. Although the structural and stratigraphic framework is continuous and same along the D-range; we divide the range along regional strike, based on altitude and climate-tectonic features into two segments, the eastern segment with altitude between 5000 m and 4000 m and the western segment with altitude between <4000 m and 2800 m. An intermontane, post-Siwalik, Kangra basin is developed south of the eastern segment of the D-range front in the Kangra area, and the valley-fi ll terraces occur along the Ravi river north and rear side of the western segment of the D-range in the Chamba region. The main body of the D-range is made of granite massif, and the granite has been used as a marker lithology in tracing the provenance for the Kangra basin and the Ravi river terraces. The D-range was affected by glaciations-deglaciation during the last glacial cycle and the LGM, and the eroded fl uxes are preserved in the Kangra basin to the south and the Chamba basin to the north of the D-range. The Kangra basin is fi lled by the post-Siwalik late Quaternary fan sediments. The fans debris is largely made of granites derived from the lower Paleozoic Dhauladhar granite with subordinate provenance from the lower Tretiary and Lesser Himalayan formations. The proximal to middle part of the fans is dominated by debris fl ows with out-size large granite boulders suggesting catastrophic fl ood events.

The fl uvial deposits are associated in the middle to distal part of the fans. The fan sediments have yielded OSL ages ranging 78-30 ka, 40-32 ka and 16-7.5 ka. There are glacial lakes and small glaciers on the crestal parts of the western segment of the D-range at altitude ranging 4000-5000 m. The occurrence of glacier erratics and moraine lobes on the southern fl ank of the D-range at altitude as low as 2600 m in some locations suggest that the extent of glaciation was similar to that described in Garhwal, and Rohtang in Lahaul area. There are pedogenised loess horizons occurring within the fan sediments indicating cold-arid followed by warm-wet climatic episodes. The warm-wet climate as indicated by pedogenisation prevailed during an interval between the glacial periods. The Kangra basin fans represent para-glacial fans deposited south of the ice margins of the Dhauladhar glaciers. The Kangra basin was formed as a piggy-back basin over the hanging wall of the Jawalamukhi Thrust. A renewed uplift phase of the D-range took place during Late Quaternary corresponding to timing of unconformity between the Upper Siwalik Boulder conglomerate and the post-Siwalik Kangra basin sediments. The renewed uplift phase of the range is constrained between 0.5 Ma age of the top part of the Upper Siwalik Boulder conglomerate and the oldest OSL age of 78 Ka in the Kangra fan sediments. The D-range has a characteristic tectonic-geomorphic setting. The D-range altitude varies along its regional, NW-SE, orogenic trend ranging between 4000m and 5000 m above mean sea level (amsl) in the eastern segment and between <4000 m and 2800 m in the western segment. The lateral, east-west, extent of the Kangra basin is restricted to its provenance of the D-range having elevation between 4000m and 5000 m, and the basin does not extend further west south of the D-range on the westrrn segment. The Jawalamukhi Thrust, over which the piggy- back Kangra basin developed, extends south of both the eastern as well

Late Quaternary uplit-erosion of the Dhauladhar range and formation of Kangra intermontane basin and Ravi river terraces pull-apart basin,

northwest Himalaya-Climate-tectonic linkage

V. C. Thakur and M. JoshiWadia Institute of Himalayan Geology, Dehradun – 248001, India

206


as western segments, suggesting that the higher elevation of the D-range in the eastern segment has implication in the formation of the Kangra basin. The Chamba region lies on the northern side of the Dhauladhar range water-divide. The Ravi river fl ows largely northwest on the rear fl ank of the D-range. In the upstream as well as in the downstream direction, the river fl ows in a narrow confi ned channel characterized with absence of river terraces. Whereas there are well preserved valley-fi ll terraces and debris fl ow fans occur in abnormally wide width river valley basin, designated as the Chamba basin, extending ~20 km both to the east and west of Chamba town. Four levels of terraces are recognized in the basin. The terraces T4, T3, T2 are the valley- fi ll, whereas T1 is the strath terrace. The heights of these terraces from the river beds are 188 m, 89 m, 54 m, and 10, respectively. The terraces contain outsize boulders and cobble- pebble sized clasts of largely Dhauladhar granite, with subordinate quartzite, sandstone and phyllite.The OSL dating of the terraces assign abandonement ages 50 ka for T4, 30 ka for T3 , 17 ka for T2 aqnd 8 ka for T1. These

terraces were developed in the Chamba pull-apart basin. The Kangra basin is developed to the south on the mountain front of the eastern segment of the D-range where elevation is higher between 5000 m and 4000 m, The eastern segment of the D-range receives maximum, average 3000 mm/yr, and focused precipitation due to its higher elevation. The high erosion resulting due to glaciations-deglaciation event inducing stress changes generated a renewed uplift of the D-range during late Quaternary. The late Quaternary uplift was synchronous with development of the piggy – back Kangra basin to the south due to reactivation of the Jawalamukhi Thrust. This is indicated by the occurrence of the strath terraces on the hangtingwall of the JT giving abondonement ages between 32 ka and 17 ka. The Chamba basin is developed to the north of the D-range on the rear side of the D-range western segment where the elevation is lower between 3500 m and 2800 m. The valley fi ll terraces in the Chamba area, representing a major aggradational climatic episode, were deposited in a pull-apart basin developed due to non liner strike-slip movement.

207


In the eastern Nepal Himalaya a peculiar, laterally continuous, sheet of orthogneiss occurs at the base of the Main Central Thrust Zone. This granitic augen gneiss is locally known as Num or Paphlu orthogneiss (in the Arun valley and lower Khumbu, respectively) and represents the easternmost equivalent of the Ulleri orthogneiss of central Nepal (see Goscombe et al. 2006 for a review). This 200-600 m thick orthogneiss body is structurally sandwiched between the lowermost phyllitic schists of the Lesser Himalayan Sequence and the uppermost medium-grade metapelites of the Main Central Thrust Zone. Although few relics of the granitic protolith are locally preserved (e.g. Kfs porphyroclasts, strongly deformed magmatic enclaves), the Num/Paphlu orthogneiss is pervasively deformed and a well developed mylonitic foliation, defi ned by biotite and muscovite, is generally observed (e.g. Carosi et al. 2008).

Decimetre- to metre-thick shear zones are widespread in the Num/Paphlu orthogneiss (e.g. Carosi et al. 2008) and come with a signifi cant increase in their mica content. Micro-structurally, the transition from the hosting augen gneiss to the micaceous levels is marked by: (i) the abrupt increase in phyllosilicates, which defi ne a pervasive schistosity; (ii) the abrupt decrease of quartzo-feldspatic levels, which may be locally absent and (iii) a marked grain size reduction (see also Carosi et al. 2008).

The most interesting aspect of these micaceous levels, however, is their very peculiar assemblage which is signifi cantly different from that of the hosting orthogneiss. In particular, (i) pale brown phlogopite and colourless or pale green Mg-chlorite (XMg=0.7-0.8) occur instead of biotite (Mosca et al. 2012); (ii) kyanite is locally very abundant, especially in the inner portion of the shear zones (locally transformed in kyanite-phlogopite schist); (iii) Mg-rich colourless tourmaline rims occur around dark-green Fe-rich relict cores very similar to tourmaline observed in the hosting orthogneiss and (iv) large post-kinematic albite porhyroblasts locally overgrow the foliation defi ned by phlogopite.

Overall, these structural and mineralogical evidences suggest that the micaceous levels occurring within the Num/Paphlu orthogneiss may represent the product of a metasomatic transformation of the granitic protolith along shear zones, and that the circulating fl uids were enriched in Mg and Al.

This is the fi rst report of a widespread Mg-Al metasomatic process in the Himalayan chain. Very similar Mg-rich metasomatic rocks have been reported from the Alps (e.g. “whiteschists” and “leucophyllites”, e.g. Ferrando et al. 2009), although their genesis is still highly debated (e.g. Ferrando 2012 for a review). The broad distribution of these Mg-rich micaceous levels in eastern Nepal attests the regional character of the metasomatic process, in analogy with that observed in the Alpine chain.

REFERENCES

Carosi, R., Frassi, C., Montomoli, C., Pertusati, P. C., Groppo, C., Rolfo, F. and Visonà, D., 2008, Non-coaxial heterogeneous deformation in the Num orthogneiss (Arun valley, Mt. Makalu area, eastern Nepal), Himalayan Journal of Sciences, v. 5, p. 34.

Ferrando, S., Frezzotti, M. L., Petrelli, M. and Compagnoni, R., 2009, Metasomatism of continental crust during subduction: the UHP whiteschists from the Southern Dora-Maira Massif (ItalianWestern Alps), Journal of Metamorphic Geology, v. 27, pp. 739-756.

Ferrando, S., 2012, Mg-metasomatism of metagranitoids from the Alps: genesis and possible tectonic scenarios, Terra Nova, in press.



Regional-extensive Mg-Al metasomatism in the Main Central Thrust Zone of eastern Nepal

Elena Dalla Fontana1, *Chiara Groppo1, Simona Ferrando1, Franco Rolfo1,2

1Department of Earth Sciences, University of Torino, Torino, I-10125, Italy 2IGG-CNR, Torino, I-10125, Italy(*Email: [email protected])

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Soil liquefaction is a devastating geotechnical phenomenon associated with earthquakes that causes failure of foundations, soil embankments and dams, especially in cities built on young alluvial deposits. Therefore, the ability to predict liquefaction potential is important and valuable for seismic hazard assessment. The conventional approach to evaluating liquefaction potential at any given point is through the use of borehole data. The liquefaction potentials within sedimentary basins vary over short distances with local soil properties. Visiting and studying geotechnical data in borehole at every location within a study area to measure liquefaction potential is usually diffi cult or expensive. Therefore the purpose of this study is to evaluate liquefaction potentials at unsampled locations where borehole data are not available based on the measured liquefaction potentials at selected borehole locations. The application and the importance of the geostatistical

analytical technique (kriging method) for the estimation of liquefaction potential at unsampled locations are shown. The data set consists of liquefaction potential values measured at randomly distributed boreholes in sedimentary basins. With the use of calculated liquefaction potentials at sampled locations, the experimental semivariograms were constructed. The experimental variogram characterizes the spatial variability of the calculated liquefaction potential. To interpolate the liquefaction potential over the entire area, the ordinary kriging spherical model was applied. In applying the kriging method, both isotropic and anisotropic models were used; however, the anisotropic model exhibited a better fi t for interpolating sedimentary deposits. The interpolated liquefaction potentials are validated with the measured liquefaction potentials of an independently collected second set of boreholes. The interpolated liquefaction potentials show strong concurrence with the measured values.

Hazard zoning of liquefaction potential at sedimentary deposits

Rama Mohan PokhrelCentral Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal


209


Active mountains supply the largest sediment fl uxes experienced on earth. At mountain range scale, total erosion is often estimated by using power low stream analysis or remote sensing approaches, or by analyzing sediments provenance, which provide rough long-term estimates. Erosion is indeed controlled by rock uplift and climate, hence by a wide range of processes (detachment, transport and deposition), all operating within drainage basin units, with time and spatial patterns that are quite complex at local scale. In the Himalayas, the sediment cascade is particularly effi cient, as favoured by high, glaciated peaks, together with narrow valleys and steep hillslopes, in a monsoon-contrasted, climatic context.

We focus on the Kali Gandaki valley, along the gorge section across the Higher Himalaya (e.g. from Jomosom down to Tatopani). Along this reach, we identify sediment sources, stores and sinks, and specifi cally consider hillslope interactions with valley fl oor, in particular valley damming at short and longer time scales, and their impact on sediment budgets and fluxes. A detailed sediment budget is presented, constrained by available dates and/or relative chronology, ranging from several 10 kyr to a few decades. Studied sites include from north to south rock/debris-avalanches (Jomosom, Dhumpu), Pairothapla-Talbagar and Tatopani debris landslides, Ghatte khola debris fan, and terraces

systems preserved at confl uence sites along the lower slopes of the valley. On the basis of repeated geomorphic surveys and mapping, and thanks to DEM facilities, the volume of each sedimentary unit is estimated, including lacustrine sediments trapped upstream of landslide and/or glacial dams. Debris volume eroded and/or deposited during the last decades is also calculated.

Obtained results span over two orders of magnitude that can best be explained by the type and magnitude of erosional processes involved. In fact, within a given reach, most erosion is accomplished as pulses triggered by landslide collapses and/or outburst events, all the more rapid that debris involved is loose and erodible. Alternation of alluviation events and incision stages can then be reconstructed, and their relation with sismo-tectonic and/or climatic triggering events suggested, according to the time scale considered. From our results it appears that if large landslides contribute signifi cantly to the denudation history of active mountain range, more frequent, medium to small scales landslides are in fact of primary concern for Himalayan population. This suggests that in a very dynamic environment like the Himalayas, a sediment budget and fl uxes approach is a useful tool for assessing and managing potential threats to human settlements and infrastructures that are increasingly developing along these Himalayan valley corridors.

Erosion assessment in the Middle Kali Gandaki (Nepal): a sediment budget approach

*Monique Fort 1, Etienne Cossart2

1University Paris Diderot (USPC) and CNRS UMR 8586 PRODIG, GHSS, Case 7001, 5 rue Thomas Mann F-75 205 Paris Cedex 13, France

2University Paris 1-Panthéon Sorbonne and ) and CNRS UMR 8586 PRODIG, 2 rue Valette, F-75005Paris France


210


Multi-annual to decadal scale high resolution stable isotope (δ18O and δ13C) data from ~ 17cm long, U/Th dated stalagmite from the Eastern Kumaun Himalaya provides a record of minor and major climatic fl uctuations in the last ~1800 years. Although, the stalagmite was not grown in the isotopic equilibrium, yet the δ18O signal is evident for palaeoclimatic reconstruction around the study area and surroundings which fall within similar precipitation regimes. The sample is largely made up of aragonite.

The δ18O and δ13C values vary between 4.31‰ to -7.61‰ and -3.44‰ to -9.1‰ respectively. The stalagmite grew with comparatively higher rate from 830-910 AD and 1600-1640

AD, the former corresponds to the lower part of Medieval Warm Period (MWP) and later represents the middle part of Little Ice Age (LIA). A distinct dry phase with a major shift in δ18O values by ~ 3‰ is recorded after the termination of MWP from 1210 to 1440 AD. Spanning from ~1440 to 1880 AD, the LIA is represented by sub-tropical climate as of today, whereas, the post-LIA was comparatively drier. It seems that during wetter/warmer conditions, the ITCZ was located over the cave location and when it shifted southward of the cave location, precipitation over the study area was decreased. A prominent drop in δ18O and δ13C values during the post-LIA period may also have been additionally infl uenced by anthropogenic activity in the area.

~1,800 years record of climatic variation from the Indian Himalaya: Speleothem study

*Jaishri Sanwal1, B. S. Kotlia2, S. M. Ahmad3, C. P. Rajendran1 and Kusala Rajendran1

1 Centre for Earth Sciences, Indian Institute of Science, Bangalore, 560 12, India2 Centre of Advanced Study in Geology, Kumaun University, Nainital, 263 002, India

3 National Geophysical Research Institute, CSIR, Uppal Road, Hyderabad, 500 007, India(*Email: [email protected])

211


Himalayan accretionary orogen is formed by collision of Asian and Indian continental plates during Late Cretaceous – Tertiary following the subduction and closure of Neotethyan oceanic crust along intra-oceanic arcs and arc-continental accretion. Ladakh batholith is formed by multiple pulses of calc-alkaline metaluminous tonalite-granodiorite to peraluminous granite magmatism mostly occurred between 67 Ma and 45 Ma with some early discrete magmatic pulses formed at ca 100 Ma. Coeval mafi c to hybrid microgranular enclaves (ME) are ubiquitous in granitoids of Ladakh batholith whereas xenoliths are meager or absent. Ladakh batholith is considered product of multistage magma mixing of multiple pulses of mantle- and crustal-derived magmas concomitant fractional differentiation and mingling processes (Kumar, 2010). In a series of published literature a wide range of ages on the timing of India-Asia collision has been suggested using variety of geological methods, which led to the development of two school of thought, one favouring 50-55 Ma age of collision whereas another opposed that India and Asia did not collide prior to 35 Ma. We report here direct evidence on the timing of India-Asia collision based on U-Pb and Lu-Hf isotopes of zircons from a xenolith, ME and granitoids of Ladakh batholith. Most Hf isotopic data of LG and ME have shown positive εHf(t) values and young Hf model ages (200-980 Ma) comparable well to those observed in east Karakoram-Ladakh (Ravikant et al., 2009) and Gangadese batholith (Ji et al. 2009), which strongly suggest involvement of juvenile magma source

in their genesis and/or mixing between felsic and mafi c magmas. Zircons from a magmatic xenolith hosted in a calc-alkaline granitoid (51.2 Ma) of eastern Ladakh have yielded an average age of ca 518 Ma with negative εHf(t) values and old Hf model ages (1685-1740 Ma) typical of Proterozoic continental crust. Zircons from a granitoid (50 Ma) of Ladakh batholith also exhibits heterogeneous Hf isotopic ratios and negative εHf(t) values suggesting contribution of older Indian continental crust in their evolution. It is therefore concluded that ca 50-51 Ma mark a concrete timing of India-Asia collision.

REFERENCE

Ji, Wei-Qiang, Wu, Fu-Yuan, Chung, Sun-Lin, Li, Jin-Xiang and Liu, Chuan-Zhou, 2009, Zircon U-Pb geochronology and Hf isotopic constraints on petrogenesis of the gangadese batholith, southern Tibet, Chemical Geology, 262, 229-245.

Ravikant, V., Wu, F. Y., Ji, W. Q., 2009, Zircon U-Pb and Hf isotopic constrainsts on petrogenesis of the Cretaceous-Tertiary granites in eastern Karakoram and Ladakh, India. Lithos, 110, 153-166

Kumar, S., 2010. Mafi c to Hybrid Microgranular Enclaves in the Ladakh Batholith, Northwest Himalaya: Implications on Calc-alkaline Magma Chamber Processes, Journal of Geological society of India.76, 5-25.

Timing of Asia-India collision evident from Zircon U-Pb Chronology and Lu-Hf Isotopes of granitoids and xenolith of Ladakh Batholith,

Northwestern Indian Himalaya

*Santosh Kumar1, Brajesh Singh2, Fu-Yuan Wu3, Wei-Qiang Ji3

1Department of Geology, Centre of Advanced Study, Kumaun University, Nainital 263 002, India2Mineral Sales Private Limited, Baldota Enclave, Hospet 583 203, India

3Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China3Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China


212


The Greater Himalayan Sequence (GHS), one of the main tectonic units of the Himalayan range, shows an impressive continuity running from east to west for more than 2000 kilometers. Large volumes of granites were intruded in its upper portion, below the South Tibetan Detachment System (STDS; Burchfi eld et al. 1992; Searle 1999; Beaumont et al. 2001; Carosi et al. 2002; Grujic 2006; Godin et al. 2006 with references; Visonà et al. 2012). The deformation within the crystalline rocks is referable to pervasive non-coaxial deformation mainly related to a top-to-the south sense of shear developed in the time span of activity of the STDS and MCT.

Several shear zones and/or faults have been recognized within the GHS, usually regarded as out of sequence thrusts with respect to the MCT (Mukherjee et al. 2011 with references therein). However, geological investigations in the GHS of Western Nepal allow the authors to identify different generations of shear zones with different kinematics and, moreover, different ages.

A high-temperature top-to-the SW shear zone (Toijem shear zone) has been documented in the core of the GHS in lower Dolpo (western Nepal), whose activity has been constrained at ~26 Ma by U-Pb on monazite (Carosi et al. 2010) before the onset of shearing of the MCT. Going to the NW, in the Mugu-Karnali valley an even thicker (up to 4 km) shear zone (Mangri shear zone) has been recently detected in the middle part of the GHS, again pointing to a top-to-the SW sense of shear. It separates the upper part of the GHS (with the occurrence of sillimanite along the main foliation) from a lower part mainly made by kyanite-bearing gneiss and micaschist. The age has been constrained by U-Pb on monazite at ~25-17 Ma. The difference in Pressure experienced by the hanging-wall and footwall rock is at least ~2 Kbar.

The two shear zones are responsible for the exhumation of the hanging wall rocks before the well-known period of exhumation by extrusion or channel fl ow of the GHS by the contemporaneous activity of the Main Central Thrust and South Tibetan Detachment System.

The Mangri and Toijem shear zones can be correlated to the Metamorphic Discontinuity described by Yakymchuck and Godin (2012) in the Karnali valley few dozen kilometres to the NW of Mugu-Karnali river.

Considering the metamorphic discontinuitity recently reported in the nearby Karnali area to the NW (Yakymchuck and Godin 2012) and the Mangri and Tojiem shear zones it is evident that the core of the GHS in Western Nepal is characterized by a major tectonic and metamorphic discontinuity allowing shearing and exhumation of GHS rocks in a time span from 26 to 17 Ma.

In addition, by connecting the tectonic-metamorphic discontinuities in central and eastern Himalaya it is evident the occurrence of a regional-scale feature, at the same level in the GHS, separating the sillimanite-bearing gneiss and schist in upper part of the GHS from the kyanite bearing gneiss and schist in the lower part. This regional tectonic-metamorphic discontinuity triggered the earlier exhumation of the GHS, before the classical onset of MCT (Carosi et al. 2010). Tectonic discontinuities within the GHS have been always regarded as out of sequence thrusts with respect to MCT. Our study demonstrates the limiting occurrence of out of sequence thrusts in central Himalayas and the occurrence of in-sequence ductile shear zones active before MCT.

Recent fi eld and satellite-image investigations documented a large granitic body (nearly 110 km2) intruding both the uppermost portion of the GHS and the lower portion of the Tibetan Sedimentary Sequence (Bertoldi et al. 2011). U-Pb-Th ages from zircons and monazites extracted from the main granitic body and dykes intruded in the TSS point to an emplacement age at ~23-24 Ma. This age constraint represents a pin point for the upper limit of the movement of the ductile portion of the STDS in Western Nepal with important consequences for the exhumation history and mechanisms of the GHS. If MCT was active starting from 25 Ma in western Nepal the undeformed granite intruding the STDS at ~23-24 Ma strongly limits the timing of contemporaneous activity of MCT and STDS at only 1-2 My.

Was the exhumation of the Greater Himalayan Sequence in central Himalayas totally driven by STD and MCT?

*R. Carosi1, C. Montomoli C2, S. Iaccarino2, D. Rubatto D3 and Visonà4

1Dipartimento di Scienze della Terra, via Valperga Caluso, 35 10125, Torino, Italy, 2Dipartimento di Scienze della Terra, via S. Maria, 53, 56126, Pisa, Italy

3Research School of Earth Sciences, The Australian National University Canberra, 0200 Australia4Dipartimento di Geoscienze, Università di Padova Via Gradenigo, 6 35131, Padova, Italy


213


A number of observations and new data, pointing to a more complex deformation history of the GHS, place a limit to contemporaneous activity of STDS and MCT and consequently to channel fl ow mechanism of exhumation and even to the extrusion of the crystalline unit in western Nepal: (1) the limited thickness of the GHS (largely below the 20-30 km required for an active channel fl ow; Godin et al. 2006); (2) the exhumation of the upper portion of the GHS happened before the MCT-STDS activity by activation of shear zones (Tojiem and Mangri shear zones); and (3) the contemporaneous activity of MCT and STD as well as the extensional decoupling of TSS and GHS happened for a very short time span (1-2 Ma only).

REFERENCES Beaumont, C., Jamieson, R. A., Nguyen, M. H., and Lee,

B. , 2001, Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled to focused surface denudation, Nature, v. 414, pp. 738–742.

Bertoldi, L., Massironi, M., Visona’, D., Carosi, R., Montomoli, C., Gubert, F., Naletto, G., Pelizzo, M. G., 2011, Mapping the Buraburi granite in the Himalaya of Western Nepal: remote sensing analysis in a collisional belt with vegetation cover and extreme variation of topography, Remote Sensing of Environment, v. 115, pp. 1129-1144.

Burchfi el, B. C., Z. Chen, K. V. Hodges, Y. Liu, L. H. Royden, D. Changrong, and Xu, L., 1992, The South Tibetan Detachment System, Himalayan Orogen: Extension contemporaneous with and parallel to shortening in a collisional mountain belt, Geol. Soc. Am. Spec. Publ., v. 269, p. 41.

Carosi, R., Montomoli, C. and Visonà, D., 2002, Is there any detachment in the Lower Dolpo (western Nepal)?, C.R. Geoscience, v. 334, pp. 933-940.

Carosi, R., C. Montomoli, and Visonà, D. 2006, Normal-sense shear zones in the core of Higher Himalayan Crystallines (Bhutan Himalaya): Evidence for extrusion?, Geol. Soc.London, Spec. Publ., v. 268, pp. 425-444.

Carosi, R., Montomoli, C. and Visonà, D., 2007, A structural transect in the Lower Dolpo: Insights on the tectonic evolution of Western Nepal, J. Asian Earth Sci., v. 29, pp. 407–423.

Carosi, R., Montomoli, C., Rubatto, D., and Visonà D., 2010, Late Oligocene high-temperature shear zones in the core of the Higher Himalayan Crystallines (Lower Dolpo, Western Nepal). Tectonics, v. 29, p. TC4029, doi:10.1029/2008TC002400.

Godin, L., D. Grujic, R. D. Law, and M.P. Searle (2006), Channel fl ow, ductile extrusion and exhumation in continental collision zones: an introduction, Geol. Soc. Spec. Publ., 268, 1-23.

Grujic, D. (2006), Channel fl ow and continental collision tectonics: an overviw. Geol. Soc. Spec. Publ., 268, 25-37.

Larson, K.P. and Godin, L., 2009, Kinematics of the Greater Himalayan sequence, Dhaulagiri Himal: implications for the structural framework of central Nepal, Journal of the Geological Society, London, 166, 25-43.

Leech, M.L., 2008, Does the Karakoram fault interruptmid-crustal channel fl ow in the western Himalaya?, Earth Planet. Sci, Letters, v. 276, pp. 314-322.

Mukherjee, S., Koyi, H. A., and Talbot C. , 2011, Implications of channel fl ow analogue models for extrusion of the Higher Himalayan Shear Zone with special reference to the out-of-sequence thrusting, Int. J. Earth. Sci. (Geol Rundsch), DOI 10.1007/s00531-011-0650-6.

Searle, M. P. 1999, Extensional and compressional faults in the Everest-Lhotse Massif, Khumbu Himalaya, Nepal, J. Geol. Soc. (Lond.), v. 156, pp. 227-240.

Visonà D., Carosi R., Montomoli C., Tiepolo M. and Peruzzo L., 2012, Miocene andalusite lucogranite in central-east Himalaya (Everest-Masang Kang area): Low-pressure melting during heating. Lithos, v. 144-145, pp. 194-208.

Yakymchuk, C. and Godin L., 2012, Coupled role of deformation and metamorphism in the construction of inverted metamorphic sequences: an example from far-northwest Nepal, Journal of Metamorphic Geology, v. 30, pp. 513-535.

214


The Kashmir earthquake 2005 (Mw 7.6) generated widespread mass movements in NW Himalaya, Pakistan. These are mainly catastrophic rock avalanches, rockslides, rock falls and debris falls, ranging in volume from a few hundred cubic meters to hundred of million cubic meters. More than 100 mass movement events have been identifi ed during fi eld survey to analyse the infl uence of volume on travel distance. The mass movements and their travel distances have been analyzed, using empirical models, widely adopted in the existing literature. The empirical approaches were used to analyze the relationship among various geometrical parameters like volume, Fahrböschung angle, height of fall, surface area, and mass movement travel distance. The mobility of mass movements is expressed as the

ratio between the height of fall (H) and travel distance (L) as function of volume. The volume (V) is generally estimated by multiplying the deposit area (A) by average thickness (D). The results indicated that Fahrböschung angle showed clear tendency to decrease with increasing mass movement volume. Moreover, mass movements with small volumes have variable values of Fahrböschung angle. A linear trend with strong correlation exists between the height of fall and travel distance for all types of the mass movements. The empirical results of Kashmir earthquake data is consistent with previously published data of other parts of the world. The relationships established by empirical analysis can be signifi cantly used to assess and mitigate the geological risks posed to the potential affected area.

Effects of volume on travel distance of mass movements triggered by the Kashmir earthquake 2005, NW Himalaya, Pakistan.

*Muhammad Basharat1, 2 and Joachim Rohn1

1GeoZentrum Nordbayern, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen 91054, Germany, 2Institute of Geology, University of Azad Jammu and Kashmir, Azad Kashmir 13100, Pakistan


215


AAccaino, F., 165Acharya, K. K., 81, 124, 135Acharyya, S. K., 171Ader, T., 64, 183Adhikari, B. R., 11Adhikari, D. P., 31Adhikari, L. B., 19, 91Adhikari, S. K., 177Adhikary, P. C., 143Agheem, M. H., 93Ahmad, S. M., 12, 210Ahmad, T., 122Ahsan, A., 47Alexeiev, D. V., 29Amidon, W., 77Ansari, M. A., 134Appel, E., 34, 186Argles, T. W., 20, 88Arnaud, N., 128Avouac, J. P., 63, 64, 68, 77, 183, 194,

BBaig, S. A., 151Balzer, D., 30Banerjee, P., 47Banerjee, S., 101Barbot, S., 77Baruah, S., 47Basharat, M., 214Basu, R., 171Baudry, C., 13Bäumler, R., 75Berthet, T., 181Bhambri, R., 204Bhandari, S., 76, 127Bhandary, N. P., 69, 116Bhatnagar, T., 22, 140Bhattacharya, A., 43Bhattarai, G. K., 157Bhattarai, M., 19, 91Bhattarai, T. N., 179Bi, R., 66Bickle, M., 190Bilham, R., 43Blard, P. H., 92Bollinger, L., 13, 19, 47, 80, 91, 129, 150, 155, 164, 183, Bookhagen, B., 169Bora, S. 163

Author Index

Bose, S., 171Boutin, V., 147Boutonnet, E., 128Bracciali, L., 85Bräuning, A., 70Brook, B., 12

CCai, Z., 197, 198Calligaris, C., 23Calsteren, P., 122Cao, H., 197, 198Carosi, R., 16, 27, 158, 212Cattin, R., 181Champollion, C., 181Chanard, K., 64, 77, 183Chaudhry, A. H., 151Chitrakar, G. R., 57Chophel, J., 181Choudhury, S., 47Chowdhury, F., 64Chung, S. L., 125Coble, M. A., 194Collerson, K. D., 12Condon, D. J., 85Cook, K. L., 78Cossart, E., 209Costa, E., 53Cottle, J., 109, 153

DDahal, R. K., 116, 149, 162Danhara, T., 58, 60 Dasgupta, S., 171Davis, W. J., 128Devkota, S., 82Dhakal, R., 135, 143,Dhakal, S., 175Dhital, M. R., 81, 106, 124Ding, L., 34, 183Dobhal, D. P., 204Doerfl inger, E., 181Doin, M. R., 150Dorbath, C., 47Dorji, K. D., 75Draxler, I., 11Drukpa, D., 43, 181Dubey, C. S., 22, 36, 140Ducret, G., 150

216


Dumperth, C., 66Dwivedi, S., 160

EEckert, S., 34Ehret, D., 66Etchebes, M., 90, 155

FFarley, K. A., 63Ferrando, S., 53, 56, 207Flouzat, M., 64, 183Fontana, E. D., 207Fort, M., 209Foster, G., 190France-Lanord, C., 9, 50, 92From, R., 153Fu, B., 195Fuchs, M., 30Fujii, R., 154

GGajurel, A. P., 9, 50, 178Galetzka, J., 64, 183Gallo, F., 50Gao, L. E., 86Gaudemer, Y., 80Gautam, P., 127Gautam, U., 19, 91, 147Genrich, J., 64Gervais, F., 79Gerya, T, 199Ghaffar, A., 6Ghimire, N., 115Ghosh, S., 171Golan, T., 194Golonka, J., 107Goswami, T., 202Gourraud, C., 19, 91, 147Grandin, R., 150Greenwood, L. V., 88Griessinger, J., 70Groppo, C., 25, 53, 54, 56, 207Gruber, F. E., 98Guillot, S., 29, 130, 167, Gyawali, B. R., 127

HHacker, B., 32, 119Hammer, P., 181Hang, T. L., 90Hanisch, J., 69

Harris, N. B. W., 20, 88, 122Harrison, M. T., 63Hasegawa, S., 116, 162Hattori, K. H., 128, 130Haviv, I., 63, 194Hayashi, D., 105He, D., 1, 38Heimsath, A., 78Heizler, M., 63Hetényi, G., 181Hideki Iwano, 60Hirabayashi, Y., 95Hirata, T., 60, 58Horstwood, M. S. A., 85Hu, G., 86Hua-Qi, L., 200

IIaccarino, S., 158, 212Islam, M. B., 3Ivone, J. M., 7, 184Iwano, H., 58, 60

JJain, A. K., 1, 2Jan, M. Q., 93, 111, 151JeGenrich, 183Jessup, M., 109Jha, M., 19, 91, 147Ji, W. Q., 211Jolivet, R., 150Joshi, L. M., 12Joshi, M., 205Joshi, P. R., 42, 135Joshi, S. P., 131

KKafl e, N., 124Kali, E., 47, 155Kandel, T., 19, 91, 147Kaphle, K. P., 53Kargel, J., 38Katzir, Y., 194Kazama, F., 189Kellett, D. A., 79Kesarwani, K., 204Khadka, D., 42Khan, M. A., 93Khan, P. K., 134Khan, R. A., 14

217


Khanal, S., 176Khorshed Alam, A. K. M., 3, 47Klinger, Y., 80, 90, 129, 155, 164Koike, T., 95Koirala, A., 69Koirala, B. P., 19, 91, 147Koirala, M. P., 105, 143Koirala, R., 82, 74Korh, A. E., 101Kornfeld, D., 34Kothari, G. C., 15Kothyari, G. C., 148Kotlia, B. S., 12, 210Krobicki, M., 107Kuhn, D., 30Kumar, S., 163, 211

LLaghari, A., 93Lal, N., 136Lalchawimawii, 72Lalrinchhana, C., 72Lanari, P., 130Langone, A., 158Larson, K., 40, 79, 153Lavé, J., 9, 50, 65, 92Lavinia, T., 184Law, R., 109Lazar, I., 107Lechmann, S., 181Lee, S., 115Lee, Y. H., 78, 125Leloup, P. H., 128Lemoigne, N., 181Leonard, G., 38Li, G., 197Li, H., 197, 200Li, Z., 199Liang, F., 198Liang, R., 12Liebke, U., 186Limbu, D. K., 82Liu, D. 34Liu, J., 86Liu-Zeng, J., 183Lizong, W., 131Lombardo, B., 54Loury, C., 29Lupker, M., 92Luthra, T., 36Lyon-Caen, H., 183

MMahara, A. S., 5Maharjan, N., 82Maki, T., 154Malsawma, J., 72Malz, N., 119Manandhar, S. P., 57Mandal, N., 171Manel, F., 7, 184Manglik, A., 4Mark, D., 190Martin, A. J., 35Mattey, D., 122Mckenzie, R., 190Mehta, M., 204Mergili, M., 98Mikolaichuk, A. V., 29Millar, I., 190Mischke, S., 85Mishra, B. K., 22, 36, 140Momohara, A., 76Monalisa, 111Montomoli, C., 16, 27, 158, 212Mool, P. K., 131Morin, G., 50Mosca, P., 25, 53, 54, Mottram, C. M., 20Mueller, J. P., 98

NNajman, Y., 83, 190Nepal, K. R., 101, 103Nepali, D., 57Nesterov, E. M., 45, 48Neupane, P., 63Neupane, Y., 160Ningreichon, A. S., 22Ninomiya, Y., 195

OOlen, S., 169Ooi, N., 178Osti, R., 179

PPalin, R. M., 96, 121, 125Pandey, P., 82Pandey, R., 155Pandey, R., 19Pandey, R., 91, 147Pandey, V. P., 189Paquette, J. L., 128

218


Parrish, R. R., 20Parrish, R. R., 85, 88Parrish, R., 192Patel, R. C., 136Pathak, D., 177Paudayal, K. N., 11, 76, 121Paudel, L. P., 38, 74, 82, 115Paudel, M. R., 112Paudel, P. N., 133Paudyal, K. R., 74, 82Pavankumar, G., 4Pêcher, A., 130, 198 Pelgay, P., 43Pettenati, F., 51, 165Pfänder, J. P., 119Phartiyal, B., 15, 148Picotti, S., 51, 165Pinel-Puyssé gur, B., 13, 150Piya, B., 57Plessen, B., 85Pokhrel, R. M., 208Pokhrel, T., 82Poretti, G., 23Poudel, K. R., 38Pratap, B., 204

QQi, X., 198

RRai, J., 72Rai, L. K., 81Rai, S. M., 60Railsback, L. B., 12Rajaure, S., 157, 183Rajendran, C. P., 18, 210Rajendran, K., 18, 210Ralte, V. Z., 72Rapa, G., 56Ratschbacher, L., 32, 119Rayner, N., 96, 121, 125, Raza, W., 12Regmi, D., 38Reisberg, L., 190Replumaz, A., 167Resentini, A., 186Rhiede, R., 190Riedel, F., 85Riel, N., 130Rizza, M., 90, 155Robert, A., 7Roberts, N. M. W., 88

Robinson, D. M., 35, 176Robyr, M., 101Rohn, J., 66, 214Rolfo, F., 25, 53, 54, 56, 207Rolland, Y., 29Rubatto, D., 212Rutte, D., 32

SSaha, D., 202Sah, R. B., 144Saha, P., 171Sakai, H., 58, 60, 154Sakai, T., 178Sanwal, J., 12, 210Sanyal, S., 202Sapkota, S., 19, 64, 65, 80, 91, 129, 147, 150, 155, 164, 181,

183 Schleier, M., 66Schmitt, A. K., 40Schneider, J. F., 67, 98Schwartz, S., 130Searle, M. P., 96, 109, 121, 125Seth, P., 2Shakya, N. M., 170Shakya, N., 177Sharma, Anup., 15, 148Sharma, Anus., 38Sharma, U. K., 163Shrestha, A., 131Shrestha, M., 2, 95, 170Shrestha, P. L., 19Shrestha, P., 91, 132, 183Shrestha, R. B., 131Shukla, C. P., 22Shukla, D. P., 36, 140Sial, A. N., 187Siddiqui, R. H., 151Singh, A. A K., 187Singh, B., 14, 163, 211Singh, N. I., 187Singh, N., 22Singh, P., 136Singh, R. P., 22, 36, 140Singh, R., 148Singh, S., 2Sinha, A. K., 10Sirovich, L., 51Siwakoti, I., 164Stearns, M., 32St-Onge, M. R., 96, 121, 125Strecker, M., 169Streule, M., 109

219


Sugimoto, M., 154Sunuwar, S. C., 156Sushmita, 2Szeliga, 43

TTabata, H., 178Taft, L., 85Tajbakhsh, M., 22Takigami, Y., 58, 60Talukdar, R. C., 139Tamrakar, J. M., 143Tamrakar, N. K., 42, 132, 133Tandong, Y., 192Tapponnier, P., 47, 80, 129, 164, Tariq, S., 23Tewari, V. c., 187Thakur, V. C., 205Thapa, B., 38Thiagarajan, S., 4Thoithoi, L., 22Thomas, L., 122Thomas, M., 183Timilsina, M., 116Timsina, C., 19, 91, 147Tiwari, D. R., 19, 80, 91, 164, Torizin, J., 30Tuladhar, R. M., 146Tuladhar, S., 170

UUlak, P. D., 127Upreti, B. N., 60, 101, 103, 178Usham, A. L., 22

VVan der Woerd, J., 47, 90Vergés, J., 7Vernant, P., 43

Vidal, O., 130Visonà, C., 16Visonà, D., 27, 158, 212

WWagreich, M., 11Wang, L., 95Wang, Q., 198Warren, C. J., 20, 88Waters, D. J., 96, 109, 121, 125Webb, A. A. G., 1, 40, 61Weller, O., 125Weynell, M., 85Wiechert, U., 85Winkler, A., 85Wu, F. Y., 211

XXiang, W., 66Xibin, T., 90Xie, K., 86Xinzhe, S., 90Xiwei, X., 90Xu, X. W., 125Xu, Z., 197, 198, 199Xue, Y., 95

YYatabe, R., 116Yoshida, M., 101, 103Yu, H., 61Yule, D., 65

ZZeng, L., 86, 198Zhang, H., 85Zhao, J. X., 12Zhi-Qin, X., 200

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