Indian mantle corner flow at southern Tibet revealed by shear wave splitting measurements

We constrain anistropic seismic structure in the southernmost Tibet and the Tethyan Himalays using SKS and SKKS phases recorded from a temporary seismic network, operated from July 2004 to August 2005 in conjunction with the Hi-Climb project. Shear wave splitting is not detected at 16 stations, most of which are located near and to the north of the Indus-Yalong suture (IYS). For the first time anisotropy with an N-S fast direction and 0.4 similar to 1 s delay times is observed to the region about 50 km south of the IYS. This weak anisotropy correlates with the flat part of the subducting Indian lithosphere and could be caused by northward asthenospheric flow and shear at the base of the Indian lithosphere. The null measurements in the vicinity of the IYS are most likely the result of a vertical asthenos pheric flow, the corner flow induced by the subvertical subduction of the Indian lithosphere just south of the Bangong-Nujiang suture (BNS). Observations of the systematic changes in mantle anisotropy from southern Tibet to the central Tibet provide evidence for different mantle flow fields between the Indian and the Eurasian asthenospheric mantle, which are separated by a subvertical Indian lithosphere at the BNS.