The lithosphere-asthenosphere boundary in the Tien Shan-Karakoram region from S receiver functions: Evidence for continental subduction

Significant S-to-P converted wave energy from the crust-mantle and lithosphere-asthenosphere boundaries (the Moho and the LAB, respectively) has been observed in the Tien Shan and Karakoram orogenic belts and used for the determination of the thickness of the crust and the mantle lithosphere. The Moho lies at depths of 45-65 km in the Tien Shan and adjacent regions and deepens to similar to 70 km depth in Pamir and Karakoram. The thickness of the lithosphere varies between 90 and 120 km underneath the Tien Shan and increases to a value of 160 km beneath the Tarim Basin. To the south of the Tarim Basin the lower boundary of the Asian lithosphere can be clearly followed to a depth of 270 km beneath central Pamir and Karakoram, while the Indian lithosphere is observed beneath the Karakoram dipping from 130 km to 170 km towards the north. The observations indicate a scenario of continental collision and subduction, consistent with seismicity and the surface wave tomography results.