Crustal and Uppermost Mantle Structure Across the Tibet-Qinling Transition Zone in NE Tibet: Implications for Material Extrusion Beneath the Tibetan Plateau

Based on a dense linear seismic array traversing the eastern margin of the Tibetan Plateau into the Qinling Belt, we conducted a joint inversion of receiver functions and surface wave dispersion curves under P wave velocity constraints and simultaneously derived a crustal and uppermost mantle Vs profile with a Vp/Vs profile. Our observations indicate that the Qinling Belt, of which the lower crust exhibits Vp/Vs values less than 1.8 that are indicative of an intermediate to felsic composition, is currently not serving as a channel accommodating the extrusion of middle to lower crustal materials of the Tibetan Plateau. Channelized ductile mantle flow from beneath the Tibetan Plateau through the Qinling Belt would be feasible only at sublithospheric depths (i.e., in the asthenosphere). Our results suggest that the extrusion of ductile middle to lower crustal materials accompanied by fault-related tectonics and isostatic buoyancy resulting from lithospheric detachment (triggered by asthenospheric flow) may have jointly engendered the plateau uplift and expansion in the Tibet-Qinling transition zone.