Download Tectonics, Dynamics and Geomorphology of the Eastern Tibetan

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.