Mapping the Moho depth and ocean-continent transition in the South China Sea using gravity inversion

Abstract

• The lithosphere thermal gravity anomaly in the South China Sea is calculated. • The depth of the Moho surface in the South China Sea is obtained by inversion in spherical coordinates with the thermal gravity anomaly correction. • We delineate the ocean-continent transition (OCT) of the northern South China Sea. In this paper, the depth of the Moho surface in the South China Sea is investigated by the gravity inversion method under the spatial-domain spherical coordinate system based on the global gravity field model WGM2012. The gravity data are corrected for the lithospheric thermal gravity anomaly due to the large negative residual thermal anomaly caused by lithospheric extension in the ocean and continental margins. The calculation results show that the thermal anomaly is mainly concentrated near the residual oceanic ridges in the South China Sea and that the density anomalies caused by the anomaly show a “fusiform” variation with depth; i.e., the anomaly is larger in the middle of the lithosphere and smaller at the top and bottom. The Moho inversion results indicate that the depth of the Moho surface in the South China Sea ranges from 7 to 32 km with an overall northeastward wedge-shaped distribution and is characterized by a shallow basin and a deep perimeter. In addition, a depression of the Moho surface remains under the remnant oceanic ridges, with the depth increasing by 2–5 km, and the depth of the Moho surface on both sides of the basin changes rapidly. Further, we determined the location of the OCT in the South China Sea based on the Moho depth mapped by gravity inversion and combined it with the results of seismic reflection profiles and other relevant geophysical data; its width is approximately 200 km in the east and 70 km in the west.