Teleseismic P wave tomography and mantle dynamics beneath Eastern Tibet
We determined a new 3 D P wave velocity model of the upper mantle beneath eastern Tibet using 112,613 high quality arrival time data collected from teleseismic seismograms recorded by a new portable seismic array in Yunnan and permanent networks in southwestern China. Our results provide new insights into the mantle structure and dynamics of eastern Tibet. High velocity (high V) anomalies are revealed down to 200 km depth under the Sichuan basin and the Ordos and Alashan blocks. Low velocity (low V) anomalies are imaged in the upper mantle under the Kunlun Qilian and Qinling fold zones, and the Songpan Ganzi, Qiangtang, Lhasa and Chuan Dian diamond blocks, suggesting that eastward moving low V materials are extruded to eastern China after the obstruction by the Sichuan basin, and the Ordos and Alashan blocks. Furthermore, the extent and thickness of these low V anomalies are correlated with the surface topography, suggesting that the uplift of eastern Tibet could be partially related to these low V materials having a higher temperature and strong positive buoyancy. In the mantle transition zone (MTZ) broad high V anomalies are visible from the Burma arc northward to the Kunlun fault and eastward to the Xiaojiang fault, and they are connected upward with the Wadati Benioff seismic zone. These results suggest that the subducted Indian slab has traveled horizontally for a long distance after it descended into the MTZ, and return corner flow and deep slab dehydration have contributed to forming the low V anomalies in the big mantle wedge. Our results shed new light on the dynamics of the eastern Tibetan plateau.