Crustal and upper mantle structure beneath SE China from joint analysis of receiver functions and Rayleigh-wave dispersion

Abstract

Summary Various geodynamic models, such as a mantle plume, lithospheric delamination, and the subduction of paleo-Pacific plate, have been proposed to account for the Mesozoic magmatic activity and related mineralization in SE China. However, previous seismic velocity models are insufficient in resolution to constrain the accompanying crust-mantle interactions, which limits our understanding of the deep geodynamic processes responsible for the Mesozoic magmatism in SE China. In this study, we construct a new 3-D shear-wave velocity model of the crust and upper mantle beneath SE China using joint inversion of receiver functions and Rayleigh-wave dispersion. We also determine the crustal thicknesses and Vp/Vs ratios by H-k stacking of receiver functions. Compared to the western Cathaysia Block, the coastal volcanic-intrusive belt (CVIB) southeast of the Zhenghe-Dapu Fault shows relatively high-velocity anomalies in the lower crust and high Vp/Vs ratios, indicating significant underplating of mafic material beneath the CVIB. Furthermore, it is noticeable that the asthenospheric low-velocity anomalies are stronger beneath the CVIB than beneath the interior of SE China, suggesting a southeastward increase in the intensity of asthenospheric upwelling and partial melting, which was likely responsible for the strong volcanism and the inferred mafic underplating beneath the CVIB. Our observations provide new evidence and more details for the northwestward subduction and subsequent rollback of the paleo-Pacific plate causing the Late Mesozoic magmatism in SE China.