The resulting velocity models show a north-south contrast in crustal seismic velocities in the Pamir, with very low P velocities (5.7-5.9 km/s at 15-30 km depth), coupled with relatively low (<1.70), at mid-crustal levels in the southern part of the orogen. At sub-Moho depths, we image an arcuate high-velocity (8.2-8.6 km/s) slab dipping south in the eastern Pamir and east in the Pamir始s southwest, underlying the intermediate-depth earthquakes. On top of the high-velocity slab and just above the onset of deep seismicity, between a depth of 60 to 100 km, very low compressional wavespeeds (around 7.1 km/s) and high ratios (猢?.80) attest to subducted crustal rocks. Additionally, we carried out 2D numerical thermomechanical modeling of the continental collision in the Pamir, focusing on the fate of the crust and mantle lithosphere of the Asian and Indian plates. Seismic velocities were computed from the modeling results, and the resulting images were compared with the velocity distributions obtained from seismic traveltimes.
Combining tomography and modeling results, we infer that a substantial amount of crustal material is pulled down beneath the Pamir by cold mantle lithosphere to depths of at least 80-100 km. From there on, only lower crust and mantle lithosphere continue their subduction, and earthquakes occur inside the lower crustal layer probably due to metamorphic reactions. The buoyant Asian upper and middle crust does not penetrate deeper into the mantle, but pools at this depth level, from where it might eventually exhume or relaminate.