The Upper Mantle Structure Beneath the Pamir, Tianshan and Adjacent Regions

Abstract In the northwestern India‐Asia collision zone, intensive tectonic deformation (e.g., orogenic uplift and crustal exhumation) is observed, but its relationships with deep mantle dynamics remain controversial. Here, we construct a 3D P‐wave velocity model of the upper mantle beneath the Pamir, Tianshan, and adjacent regions using teleseismic tomography with seismic data from 353 stations and 3,321 teleseismic events. Our tomographic model reveals a striking subvertical boundary between the low‐velocity central Tianshan and the high‐velocity Tarim lithosphere beneath the southern Tianshan fault system, indicating that the Tarim lithosphere has been sub‐horizontally compressing the central Tianshan lithosphere. Furthermore, a high‐velocity anomaly is observed in the upper mantle beneath the central Tianshan, which is interpreted as the delaminated Tianshan lithosphere due to the compression of the Tarim. In the Pamir‐Hindu Kush region, a slab‐like high‐velocity anomaly extends into the mantle transition zone (MTZ) beneath the Hindu Kush. This, along with our imaged flat high‐velocity anomaly beneath the Pamir, suggests that the Indian lithosphere is steeply subducting beneath the Hindu Kush and sub‐horizontally underthrusting beneath the Pamir. Additionally, the underthrusting Indian lithosphere may force the Tajik lithosphere to delaminate beneath the western Pamir, as suggested by a steeply dipping high‐velocity anomaly. A large‐scale high‐velocity anomaly is imaged near the base of the MTZ beneath the Pamir and Karakoram, which likely represents the detached Indian lithosphere due to the breakoff of the Indian slab ∼20 Ma.