Small 660-km seismic discontinuity beneath Tibet implies resting ground for detached lithosphere

Abstract

Using seismic profiles comprising of high-resolution, triplicate waveforms across apertures of over 1,000 km, we show that because of high P wave speed (VP) near the bottom of the mantle transition zone, the contrast in VP across the 660-km discontinuity beneath central Tibet is small: only about 70% of that beneath the northern Indian shield. This subhorizontal anomaly of high VP is most likely a remnant of detached mantle lithosphere that recently sank to depth, thus providing key evidence for a direct connection between continental collision near the surface and deep-seated dynamics in the mantle. Copyright 2007 by the American Geophysical Union.