SURFACE DEFORMATION AND LOWER CRUSTAL FLOW IN EASTERN TIBET

Field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the ea stern Tibetan plateau since about 4 million years ago. Instead, centra l eastern Tibet has been nearly stationary relative to southeastern Ch ina, southeastern Tibet has rotated clockwise without major crustal sh ortening, and the crust along portions of the eastern plateau margin h as been extended. Modeling suggests that these phenomena are the resul t of continental convergence where the lower crust is so weak that upp er crustal deformation is decoupled from the motion of the underlying mantle. This model also predicts east-west extension on the high plate au without convective removal of Tibetan lithosphere and without eastw ard movement of the crust east of the plateau.