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Tectonics, Dynamics and Geomorphology of the Eastern Tibetan Plateau Leigh Royden (MIT 54-826, Cambridge, MA 02139, phone 617- 2531292, fax 617-258-7401, email [email protected]), Marin Clark and Clark Burchfiel Eastern Tibet is a major source of the sediments deposited along the East and South China Sea margins. Thus its uplift history is closely linked to the spatial and temporal patterns of Cenozoic sedimentation along the adjacent continental margins, both because uplift drives surface erosion and because the increasing elevation of the plateau is thought to have triggered the onset of the Indian monsoon in Miocene time. The eastern Tibetan plateau stands approximately 5 km above sea level with a crustal thickness approaching 70 km, nearly double the thickness of normal continental crust. Large-scale crustal shortening features are absent at the surface and the crust appears to have thickened by eastward flow of weak material within a deep crustal channel, without significant disruption of the surface rocks and sediments. This has producing wide (~2000 km) gently sloping topographic margins where the adjacent crust is weak, and narrow (~50 km) steep topographic margins where the adjacent crust is strong. This deep crustal flow has resulted in non-lithostatic pressure gradients in the deep crust and is expressed at the surface by excess topography and high-standing mountains where flow impinges on areas of strong crust that indent the plateau margin. The eastern plateau is mantled by an erosion surface that appears to predate uplift of the plateau. Surface uplift created by crustal flow has resulted in the rapid incision of major rivers into this erosion surface, as well as river capture events and major geographical reorganization of the rivers that drain the plateau. Because of the lack of geological surface structures associated with plateau uplift, understanding and dating the geomorphic evolution of eastern Tibet, and the associated sedimentation in the East and South China Seas, remains one of the best avenues for constraining its lithospheric dynamics.