S n velocity tomography beneath the Himalayan collision zone and surrounding regions

Abstract

We present a tomographic S n velocity model of the uppermost mantle beneath the Himalayan collision zone and surrounding regions. A total of 43,905 S n phases are used in the investigation. The average S n velocity in the study area is approximately 4.6 km/s, and the velocity perturbations reach 0.2 km/s. The S n velocity distribution is consistent with P n tomography results obtained previously. High velocities are found under the Indian plate, the Tarim Basin, and the Sichuan Basin, whereas low S n velocities are found beneath the Myanmar region, the Hindu-Kush region, and the Lhasa block and western Qiangtang block. These results support the idea that the lithosphere of the Indian plate is subducted into the mantle and causes the upwelling of hot material. The eastwest variability of the S n velocity beneath the Indian plate and southern Tibet indicates that the underthrusting of the Indian continental lithosphere may be in a piecewise manner. The differences between the thermal structure of the crust and upper mantle in southern Tibet suggest that this region may be represented by a tectonic model of hot crust and cold mantle, supporting the idea that crustal material flow may occur in this region.