A distinct contrast in the lithospheric structure and limited crustal flow across the northeastern Tibetan Plateau: Evidence from Vs and Vp/Vs imaging

Abstract

The uplift mechanism and geodynamic model of the northeastern (NE) Tibetan Plateau remain controversial. Two competing models have been proposed for the uplift of the NE Tibetan Plateau, including crustal shortening through folding or thrust faulting and the middle-lower crustal flow model. Here, we applied the joint inversion of surface wave dispersions and receiver functions with P-wave velocity constraints on a dense linear broadband seismic array to obtain the Vs and Vp/Vs profiles of the crust and uppermost mantle across northeastern Tibet. The inversion yields robust structural images that show stark Vs and Vp/Vs jumps across the West Qinling fault from the Songpan-Ganzi and Kunlun-West Qinling terranes (south) to the Qilian and North China terranes (north). The results reveal that regional low-Vs/high-Vp/Vs anomalies present in the middle-to-lower crust, which may be the signature of viscous flow, are distinctly limited south of the West Qinling fault. In contrast, the imaged physical properties of the crust and mantle lithosphere north of this fault manifest a rigid pattern, which is inferred to be originated from the North China craton underthrust below the northern margin of the Tibetan plateau. Our seismic imaging indicates that the NE corner of the Tibetan Plateau does not currently serve as the flow channel of the ductile material from the central and northern Tibet.