Presentation on theme: "3-D Finite Element Modeling of the Rise and Fall of the Himalayan-Tibetan Plateau Mian Liu and Youqing Yang Dept. of Geological Sciences, University of."— Presentation transcript:
3-D Finite Element Modeling of the Rise and Fall of the Himalayan-Tibetan Plateau Mian Liu and Youqing Yang Dept. of Geological Sciences, University of Missouri-Columbia
Some of the fundamental questions of the Tibetan tectonics What causes the E-W extension in Tibet? When did the “collapse” start? When did the Tibetan plateau uplift? What are the temporal and spatial evolution of the mountain building in Tibet? How was the >2000 km crustal shortening accommodated? What controlled the strain partitioning between crustal thickening and lateral extrusion?
GPS velocity relative to stable Siberia Data from Larson et al., 1999; Chen et al., 2000; Wang et al., 2001 Earthquake focal mechanism showing E-W extension Data from Harvard Catalog
Active crustal deformation in Tibet: 3-D finite element model & rheology
Crustal Stress Indicated by Earthquake Data Predicted Stress State in the upper crust
Elevation reduced to 50% of present values No E-W extension predicted Basal shear = 30 MPa under Himalayas and south Tibet A narrow zone of nearly N-S Extension – South Tibetan Detachment Fault system?
Long-term history of the Himalayan-Tibetan orogen Viscous thin-sheet model (England & Houseman, 1986) Plasticine analog model (Tapponnier et al., 1986)
3-D finite strain model x10 vertical exaggeration Indian plate Tarim Sichuan Basin Asia
Conclusions The E-W extension in Tibet can be explained by gravitational collapse of the plateau. Major E-W extension started only when the plateau reached ~75% of its present values. Assuming a flat Asian continent before the Indo-Asian collision, the plateau would have grown from S to N, and from W to E; most part of the plateau probably reached >3 km 10-20 million years ago. The lower crust flow largely controls the topographic evolution; the motion of the upper crust may be significantly different from that in the lower crust. Partitioning of the shortened crustal mass between thickening and lateral extrusion/erosion changed with time. Mass accommodated by mountain building may have peaked ~10 Myr ago; extrusion and erosion become increasingly important.
If lithostatic stress condition was applied at the south China block, strike-slip would be promoted and the elevation in the eastern Tibetan plateau should be 1 km lower, velocity higher, slop steeper.