Teleseismic P‐Wave Tomography Evidence for the Indian Lithospheric Mantle Subducting Northward Beneath the Qiangtang Terrane

Abstract

AbstractWe collected all the available arrival time data recorded by the temporary seismic stations from the projects of PASSCAL, INDEPTH‐II, INDEPTH‐III, HIMNT, WKL and TIBET 973, and phase reports from the International Seismological Center from January 1990 to February 2004 in Tibet and its surrounding areas. In the tomographic inversion, we used 139021 P‐wave arrival times from 9649 teleseismic events recorded by 305 seismic stations. Our study area covers the southern Ganges plain in India to the northern Tarim basin and Qaidam basin in China. Our tomographic images show that the subducting angles of Indian lithospheric mantle are different under different areas, but their front locations are all beneath the Qiangtang terrane. The tomographic image along 88°E shows that the Indian lithospheric mantle is underthrusting northward with a dip angle of about 22° beneath the center of Qiangtang terrane at about 34°N latitude, and its frontier has reached to the deep part of the upper mantle. The tomographic image along a northeasterly profile shows that the Indian mantle underthrust nearly horizontally under Tibet from the Ganges plain to 33°N. Then, the Indian mantle broke off down to the asthenosphere and caused the asthenophere upwelling. A consequence of the asthenophere upwelling was to form a big low‐velocity zone beneath the Qiangtang terrane.