Multiscale structures of crust-mantle beneath the South China block and their geodynamic implication

Abstract

The South China block is an ideal location in which to study the impact of paleo-Pacific plate subduction on the upper mantle and crustal structures of the overriding plate, as well as the mechanism of lithospheric thinning. By integrating data from permanent seismic stations of the China Seismic Network and a dense seismic array at Xuefeng Mountain, this study employed P- and S-wave receiver functions (RFs) to image multiscale structures of crust-mantle across the South China block, thereby providing constraints for a comprehensive understanding of its tectonic evolution. The main findings are as follows: (1) The thickness of lithosphere and crust gradually decreases from northwest (NW) to southeast (SE). (2) Beneath the Xuefeng Mountain uplift zone, the P-to-S conversion from the 660 km discontinuity arrives earlier than that predicted from a one-dimensional model, other weak discontinuities can be traced in the upper mantle, including the lithosphere-asthenosphere boundary, the crust becomes thinner, and the Conrad discontinuity becomes deeper. Referring to previous results from tomography and geological reconstructions, we deduce that lithospheric delamination might have occurred beneath the Xuefeng Mountain uplift zone, and the delaminated lithosphere penetrated the upper mantle and reached the mantle transition zone.