High-resolution crustal and upper mantle shear-wave velocity structure beneath the central-southern Tanlu fault: Implications for its initiation and evolution

Abstract

The Tanlu fault is a well-known lithosphere-cutting, strike-slip fault in eastern China and it has played an important role in regional plate tectonics since the middle Mesozoic. However, the initiation mechanisms and tectonic evolution of the Tanlu fault remain controversial, in part due to the absence of constraints from deep structures. In this study, we inverted 5–150 s surface-wave dispersion data collected from 253 permanent stations and 111 temporary stations in the vicinity of the central-southern Tanlu fault and obtained both isotropic and azimuthally anisotropic shear-wave velocity (Vs) models in the crust and upper mantle simultaneously. The new Vs models reveal unprecedented multiple patterns of anomalies. There is, for example, an arc-shaped pattern of fast directions found in the South China plate (SCP), providing direct evidence of the sudden termination of the Tanlu fault at its southern end; orogen-parallel fast directions and high-velocity anomalies were detected beneath the Dabie and Sulu orogens, which are believed to be the residue of the delaminated lithosphere. Based on the evidence collected, we propose a four-stage tectonic model for the Tanlu fault. The tectonic model suggests that the area has been subjected to multiple geologic processes since the Early Mesozoic, including oceanic-continental collision, continental-continental collision, break-off of oceanic slabs, lithospheric delamination, and convective erosion resulting from corner flow. As such, the proposed tectonic model reconciles the newly discovered Vs anomalies as well as various previous findings, providing profound insight into regional deformations and the evolution of the Tanlu fault and its adjacent areas.