gruppo nazionale di geofisica della terra solida 27° convegno nazionale
DESCRIPTION
NEW INSIGHTS INTO THE BASEMENT STRUCTURE OF THE WEST SIBERIAN BASIN FROM FORWARD AND INVERSE MODELLING OF GRACE SATELLITE GRAVITY DATA. Gruppo Nazionale di Geofisica della Terra Solida 27° Convegno Nazionale 6 - 8 Ottobre 2008, Trieste Carla Braitenberg - PowerPoint PPT PresentationTRANSCRIPT
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LithoFLEX
NEW INSIGHTS INTO THE BASEMENT STRUCTURE OF THE WEST SIBERIAN
BASIN FROM FORWARD AND INVERSE MODELLING OF GRACE SATELLITE
GRAVITY DATA
Gruppo Nazionale di Geofisica della Terra Solida27° Convegno Nazionale
6 - 8 Ottobre 2008, Trieste
Carla BraitenbergDepartment of Earth Sciences, Trieste University
Jörg EbbingGeological Survey of Norway, NGU, Trondheim
Department for Petroleum Technology and Applied Geophysics, NTNU Trondheim
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LithoFLEX
Overview
• Goals
• Starting point and data
• Gravity field modelling and inversion
• Results and conclusions
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LithoFLEX
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LithoFLEX
Goals
• Identification of terranes of WSB
• Identify rift structure and relation to underlying crust WSB
• Thickness of basalt layer
• Interpretation of the gravity field in WSB
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LithoFLEX
Starting point
• Gravity anomaly and Geoid undulations
• Regional seismic profiles
• Sediment thickness (pre- and post volcanic)
• Moho model
• Uncertain basalt layer extent
• Hypothesized rifts in basin•Vyssotski et al., 2006
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LithoFLEX
Topo
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LithoFLEX
Global gravity fields
• Grace satellite– given in spherical harmonic development. – GFZ-Potsdam (Förste et al., 2008): EIGEN-
GL04C– Up to degree and order 120: satellite only.– Up to degree and order 360: integration with
terrestrial data.
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LithoFLEX
Gravity anomaly
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LithoFLEX
Bouguer field
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LithoFLEX
Gravity Modeling
• Gravity effect of known masses:– Crustal thickness variation
• Fixed density contrast
– Sediments• Compaction: density increase with depth• Use velocity increase with depth
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LithoFLEX
Moho
(Kovylin, 1985)
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LithoFLEX
Moho gravity
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LithoFLEX
Base pre-volcanic sediments
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LithoFLEX
Converting TWT to velocity-depth
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LithoFLEX
Gravity of sediments
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LithoFLEX
Residual gravity
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LithoFLEX
Gravity Inversion
• Residual Gravity– after correction of known masses
• Gravity inversion of residual– Superficial mass
• 5 km reference depth, fixed density contrast
– Lower crust • Density variation in layer 20 km above Moho
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LithoFLEX
Residual gravity- low pass filtered (150km)
mgal
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LithoFLEX
Residual gravity high-pass filtered
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LithoFLEX
Lower crustal density variation
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LithoFLEX
Surface layer inversion
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LithoFLEX
Crustal model gravity
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LithoFLEX
Isostatic anomaly
Loads: topography and sediments
mgal
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LithoFLEX
Interpretation
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LithoFLEX
Results 1/4
• Rifts: positive gravity anomaly– Basalt fill necessary: up to 3 km thick.
• Rift-graben structures identified– Koltogor- Urengoy – Khudottey -> 100 km west– Khudosey– North and South Khatanga– Yenisey– Ob
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LithoFLEX
Results 2/4• Deviation from classical relation
Topography- Bouguer anomaly
• Density increase needed in lower crust to explain gravity field– Arch-like structure along eastern border to
Siberian craton– NE-SW trending mid-basin high density
anomaly• Extending from Pur Taz South-westwards
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LithoFLEX
Conclusions 1/2• Rift structures:
– Yenisei rift (1500 km length) underlain by high density arch
– rifts in mid basin: underlain by moderately increased density
• Compares well to results from QUARTZ (Morozova et al., 1999) deep seismic profile
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LithoFLEX
Conclusions 2/2• Crustal blocks:
– South-, Mid-, North- and Northwest- segments of basin
– Smooth transition to Kara Sea and Yenisey-Khatanga trough
• Eastern Arch
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LithoFLEX
Thank you for your attention!
Reference: the work is summarized in the paper: Braitenberg C. and Ebbing J. (2009) New insights into the basement structure of the West Siberian basin from forward and inverse modelling of GRACE satellite gravity data, in editorial process Journal of Geophysical Research.