Interaction of the Indian and Asian Plates Under the Pamir and Hindu‐Kush Regions: Insights From 3‐D Shear Wave Velocity and Anisotropic Structures

Abstract

The Pamir‐Hindu‐Kush region is widely cited as a best place to study opposing continental subduction on Earth. Yet, subducting slab morphology of the Indian and Asian plates under this region remains elusive. Here we report new shear wave velocity and radial anisotropy models from Rayleigh and Love wave tomography to constrain the geometry of these two slabs. Together with previous tomographic studies, we show that the Indian slab exhibits along‐strike variation with subhorizontally underthrusting into the Pamir and high‐angle subduction under the Hindu‐Kush. We speculate that the Indian slab was probably detached and sank into the mantle transition zone under the Pamir, while break‐off process is ongoing under the Hindu‐Kush. The Asian lithospheric mantle and lower crust are inferred to be subducting southward into the North Pamir. Two opposing subducting slabs could have interacted under the Pamir, resulting in thickening crust, horizontally stretched midcrustal flow, and horizontal mantle flow. These dynamic processes could explain surface geologic observations and potentially constrain the causes of intermediate‐depth seismicity.

Subduction of the Indian Plate and the Nature of the Crust Beneath Western Tibet: Insights From Seismic Imaging

“…We interpret this HVA body as the subducted ILM. If we conservatively define this HVA body with a Vs value of 4.6 km/s, similar to that in the Pamir region (Liang et al, 2020), then the lower boundary of the ILM locates at ~210‐km depth, slightly deeper than that from receiver function (Zhao et al, 2010) and shallower than that from joint inversion of receiver functions and Rayleigh wave dispersion (Matchette‐Downes et al, 2019). In this case, the northern extent of the subducted lithospheric mantle is interpreted to reach to ~100 km north of the BNS to the Qiangtang terrane, best viewed in cross sections (Figures 8a and S12 to S15).…”

Deep crustal contact between the Pamir and Tarim Basin deduced from receiver functions

“…A previous receiver function analysis shows a double Moho structure at 50-90 km depth in both the western and central Pamir, which hints at underthrusting of the Tajik and Alai lower crust beneath western Pamir (Schneider et al, 2013(Schneider et al, , 2019. Plate motion vectors, shear-wave velocity and radial anisotropy models, and seismotectonic analysis testify that crustal materials flow outward from the interior of the Pamir toward the western flanks and/or extrude upward along with a series of thrust faults (Liang et al, 2020;Metzger et al, 2020;Schurr et al, 2014). Conversely, the more rigid Tarim crust may hinder the eastward extrusion of the east Pamir (Metzger et al, 2020;Schurr et al, 2014).…”

Shear‐Wave Velocity Reveals Heterogeneous Geometry of the Main Himalayan Thrust System and Deep Structure Beneath the Nepal Himalayas

“…It can be obtained from discrepancy of Rayleigh-and Love-wave phase velocity maps. Radial anisotropy has been obtained in other regions of the Himalayan-Tibetan Orogen (e.g., Guo et al, 2012;Liang et al,2020;Liu et al, 2021;Xie et al, 2013), but a high-resolution radial anisotropy model is still lacking under the Nepal Himalayas.…”