Mantle structure and dynamics beneath SE Tibet revealed by new seismic images

Abstract

The structure and dynamics in SE Tibet are the key to understand the tectonic evolution of the Tibetan Plateau. In this study we determined high-resolution P-wave seismic images in the upper mantle and transition zone in SE Tibet by jointly inverting the travel-time residuals of local events and the relative travel-time residuals of teleseismic events recorded by very dense seismic stations. We revealed a high-velocity body in the upper mantle beneath South China that represents the root of the Yangtze Craton. The high-velocity body extends in the entire Yangtze Craton at 300–450 km depths, but it is constrained just beneath the Sichuan Basin and surrounded by extensive low-velocity zones to the southwest at 65–250 km depths. We propose that the Yangtze Craton is destructed laterally by the mantle flow extruded from the Tibetan Plateau. We obtain a low-velocity column in the upper mantle under the Tengchong volcano as well as the visible high-velocity bodies in the upper mantle and transition zone below the low-velocity column. The images suggest that the Tengchong volcano is closely related to the subduction of the Burma plate and caused by the dehydration of the subducted slab. The present study reveals unprecedented details of the mantle structures beneath SE Tibet and provides new insights into the geodynamics of the Tibetan Plateau and its interaction with the stable Yangtze Craton.