A refined Moho depth model from a joint analysis of gravity and seismic data of the South China Sea basin and its tectonic implications

Abstract

As a typical marginal sea in the western Pacific, the South China Sea (SCS) has experienced a complex evolutionary process, and mapping its Moho depth can help us understand the accretion process of the oceanic crust. In this study, we present a refined Moho depth model in the SCS based on gravity inversion constrained by seismic data. For a more reliable gravity-derived Moho depth, an improved sediment thickness grid is constructed from a large volume of seismic reflection/refraction data. The gravity-derived Moho depths are in good agreement with the seismically determined ones, with the majority of differences falling within ±2.5 km. Our results reveal a significant crustal thickness asymmetry across the mid-ocean ridge of the East Sub-basin of the SCS basin since the ridge jump at 23.6 Ma. We attribute this asymmetry to higher residual mantle temperature and more magma supply north of the spreading center. The higher mantle temperature to the north is evidenced by the shallower Curie depth estimated from magnetic anomalies than to the south of the spreading ridge.