DEEP SEISMIC-REFLECTION EVIDENCE FOR CONTINENTAL UNDERTHRUSTING BENEATH SOUTHERN TIBET

THE Himalaya and adjacent Tibetan plateau, constituting Earth's larges t region of elevated topography and anomalously thick crust, formed as a consequence of Cenozoic collision between India and Asia-itself con sidered the archetypal continent-continent collision1-3. Here we repor t the first results from an attempt to image the structure of the crus t beneath this region using deep seismic reflection profiling. Our app roximately 100-km-long profile, acquired in the Tethyan Himalaya, show s a mid-crustal reflection that probably marks the active thrust fault along which the Indian plate is underthrusting southern Tibet; upper- crustal reflections with geometries suggestive of large-scale structur al imbrication of the upper crust; and Moho reflections from the base of the double-normal-thickness crust underlying the region. These resu lts lend substantial support to the view that crustal thickening benea th southernmost Tibet was accomplished by wholesale underthrusting of Indian continental crust beneath the structurally imbricated upper cru st comprising the Tethyan Himalaya.