Objectives Located at the intersection of the Eurasian Plate, the Pacific Plate and the Indian Plate, the South China Sea has experienced complex tectonic activities such as continental rupture and seafloor spreading. It is very important to determine the three-dimensional density structure of the lithosphere in the South China Sea and its adjacent areas for understanding the deep tectonic characteristics, plate evolution and dynamic mechanism of the region. At present, the study of density structure in this area mostly uses seismic wave profile data, and there are few regional studies. Therefore, it is very important to obtain the regional 3D density structure by using the characteristics of large scale and high resolution of gravity data.

Methods Based on high-precision gravitational field model data, potential field separation of Bouguer gravity anomalies is carried out, and the remaining Bouguer gravity anomalies are retrieved by wave-number domain 3D density imaging method.

Results We have obtained large-scale high-resolution three-dimensional density structures of the lithosphere in the South China Sea and adjacent areas, showing density distribution characteristics at depths of 5-90 km.

Conclusions The results show that the density distribution of the lithosphere presents density fluctuations and abnormal distribution at different depths. Beneath the central basin, there is relatively low-density mantle compared to the adjacent areas, which is associated with the high heat flow background of the ocean basin. In the areas of the Zhongsha Islands, Nansha Trough, high-density anomalies are observed. These high-density perturbations are speculated to result from mantle material upwelling, causing high-density mantle material to intrude into the relatively low-density lower crust. In the Manila Trench, a pronounced low-density anomaly is observed within the mantle, attributed to subduction processes where the low-density oceanic crust is subducted into the high-density mantle.