3-D density structure under South China constrained by seismic velocity and gravity data

Until now the crustal structure of South China has been studied through 2-D seismic surveys. While informative, the results generated from these surveys cannot be easily interpreted from a regional outlook due to the sparse sampling of the area. In this paper, we have investigated the 3-D density structure of South China based on an integrated dataset, namely: P-wave velocities previously determined from seismic profiles and Bouguer gravity anomalies. The density structure is solved through a robust inversion of Bouguer anomalies with the help of Grav3D software, so that the results can be extended to zones lacking constraints or sufficient deep seismic coverage. The key issues arising from this density analysis shed new lights on South China, as: (1) The Moho depth extracted from the density model is consistent with the information supplied by deep seismic soundings. (2) The linearly increasing density below the eastern part of the Dabie orogenic belt, in a frame of low density at the bottom of the middle crust, is consistent with the speculated dome of relatively high P-wave velocity suggested by previous deep seismic soundings, and understood as a geophysical fossil of the continental collision/extrusion. (3) The Chenzhou–Linwu fault seems to be the southern transection of the boundary between the Yangtze and Cathaysia blocks constrained by our crustal density model. (4) Different laws formulated as linear relationships between seismic velocity and density allow distinguishing the tectonic units forming South China. These laws are the consequence of the crustal composition and temperature distribution. •We investigate the 3-D density structure of South China based on an integrated dataset.•The predicted Bouguer gravity anomaly agrees well with the observed anomaly.•CLF is the south segment of the boundary between the Yangtze and Cathaysia blocks.