JOUR.GEOL.SOC.INDIA, VOL.79, MAY 2012

542 NEWS AND NOTES

mobilized by the post-crystallizationalteration processes. The Sm–Nd isotopesystem in the Hutti metabasalts has beenleast disturbed giving an isochron age of2662±81 Ma which is suggested as the ageof formation of their precursors. Combinedwith the published U–Pb SHRIMP ages onzircons from the felsic volcanic rocks it isinferred that the Hutti greenstone beltformed over a period of =86 Ma.

Based on U-Pb isotope study carried outon zircon and titanite from the Huttigranitoid rocks it is inferred that these rockswere intruded between 2569±17 Ma and2528±36 Ma ago. Different phases of

granitoid magmatism contributingsubstantially to the continental crust havetaken place around the Hutti areaapproximately between 2530 and 2580 Maago. These ages are comparable with thoseof the granitoid rocks surrounding the Kolarand Ramagiri greenstone belts. The 207Pb/206Pb titanite age of 2532±9 Ma for theYelagatti granitoid rocks is not recorded inthe granitoid rocks from any other part ofthe Hutti area. This age is indistinguishablefrom the zircon ages of 2532±3 Ma and2528±1 Ma for the Kambha Gneisses of theKolar area and the Gangam Complex of theRamagiri area, respectively. The major

greenstone belts of the eastern Dharwarcraton have evolved coevally at ca. 2700Ma ago and are older than the surroundinggranitoid rocks. In the eastern Dharwarcraton granitoid magmatism took place asdistinct pulses and the plutons werejuxtaposed during Neoarchaean byhorizontal tectonic forces with thesupracrustal rocks emplaced in an island-arc type setting forming the boundarybetween them.

Summary of the lecture delivered at themonthly meeting of the Geological

Society of India on 25 January 2012.

Response of the Rivers in Himalaya to Late Pleistocene-Holocene Climate and NeotectonicEvolution of the Orogeny – Pradeep Srivastava, Wadia Institute of Himalayan Geology, Dehra Dun

Himalaya in its S-N transect is traversedby several roughly E-W trending thrustsnamely the Himalayan Frontal Thrust (HFT,the youngest), the Main Boundary Thrust(MBT), the Main Central Thrust (MCT), theSouth Tibetan Detachment (STD), theCounter Thrust (CT) and apart from thisthere are several intra-formational thrustslocated between HFT and MBT and alsobetween CT and Indus Tsangpo Suture Zone(ITSZ). These thrusts are south vergingbetween HFT and STD and most are northverging between STD and ITSZ (Thakur,1981; Jamieson et al. 2004). There areseveral normal faults between STD and CT.The topography slopes southward from littlenorth of STD to HFT and northward fromnorth of STD to ITSZ. This suggests thatthe Himalayan prism may have evolved ina bivergent manner where both the halvesof the prism deform to counter balance thestresses generated due to the northwardmovement of the Indian Plate. Thisstructural pattern is not uniform and varieslaterally. These thrusts/fault when interactwith domes like Tso Morari behave asnormal fault. This however still requiresdetailed structural studies, especially in thearea north of STD.

Optically stimulated luminescencedating of strath terraces around Himalayan

Frontal Thrust (HFT) along rivers Gangaand towards the Indus Tsangpo Suture Zone(ITSZ) along the river Indus is carried out.In the frontal Himalaya, the terraceformation took place at ~11 ka where theSiwalik ranges are incised at the rate of~7 mm/a (Sinha et al. 2010; Ray andSrivastava, 2010). The chronology indicatedthat the aggradation and incision of GangaRiver followed the climate change duringthe Late Pleistocene-Holocene and that theHimalayan wedge is showing, both, in-sequence and out-of-sequence deformation.The geomorphic data and the chronologyfrom the Indus river also suggests activeuplift and formation of strath terraces duringthe Late Pleistocene and the river hasincised into the mollasse sediments at ~2mm/a. Thus if the incision rate are indicativeof uplift rates both the front and the hinter-land of the Himalaya are actively deforming.According to the critical taper wedge modelof the evolution of Himalaya, thedeformation should be focused at themountain front and should diminish towardsthe hinterland and that explains the upliftalong the HFT. It is proposed that the IndusRiver is responding to the activity along thecounter thrust and several intra-formationalthrusts, within the mollasse sequence, andforming the strath terraces. This probably

is indicating the bivergent nature ofdeformation in the Himalaya.

References

JAMIESON, S.S.R., SINCLAIR, H.D., KIRSTIEN,L.A. and PURVES, R.S. (2004) Tectonicforcing of longitudinal valleys in theHimalaya: morphological analysis of theLadakh Batholith, North India.Geomorphology, v.58, pp.49-65.

RAY, Y. and SRIVASTAVA, P. (2010) Wide-spread aggradation in the mountainouscatchment of the Alaknanda-GangaRiver System: Timescales and implica-tions to Hinterland-foreland relation-ships. Quaternary Sci. Rev., v.29,pp.2238-2260.

SINHA, S., SURESH, N., KUMAR, R., DUTTA,S. and Arora, B.R. (2010) Sedimento-logic and geomorphic studies on theQuaternary alluvial fan and terracedeposits along the Ganga exit. Quater-nary Internat., v.227, pp.87-103.

THAKUR, V.C. (1981) Regional frameworkand geodynamic evolution of the IndusTsangpo Suture Zone in LaddakhHimalaya. Trans Royal Soc. Edinburgh:Earth Sci., v.72, pp.89-97.

Summary of the lecture delivered at themonthly meeting of the GeologicalSociety of India in November 2011