Integrated Geophysical Research on the Tectonic Attribute of Conjugate Continental Margins of South China Sea

Abstract

Abstract In this paper the density and magnetic structures along 6 typical profiles in the South China Sea were determined by inversion of the latest gravity and magnetic data based on the results of rock property analysis and whole‐sea magnetic basement distribution, then the deep structures were further compared and analyzed. The inversion was constrained as much as possible by the sea bottom seismometer (OBS) and multi‐channel seismic (MCS) data, such as for profile FF0 the newest MCS data collected in 2009 by the 973 Project “Continental Margin Dynamics and Oil/Gas Resource Potential of South China Sea” were used in interval velocity analysis, and the OBS2009 data of Nansha section were combined with gravity data in structure modeling. Based on the deep structures and the density/magnetic characteristics of the 6 profiles, it is inferred that the tectonic attributes of both the northern and southern margins of South China Sea are basically of non‐volcanic type. To the east of profile CC0 in the north margin there is a high‐density layer in the lower crust accompanied with active magma activity, however, the evidence of typical seaward dipping reflectors is lacking; therefore it is inferred that the high‐density layer, as well as the shallow magmatic rocks, are the products of continental margin rifting after seafloor spreading. The magnetic basement and the deep structures of Zhongsha Uplift and Liyue Basin are very similar; they are deduced to belong to the same block before the pull‐apart of the sea basin, being a pair of conjugate points of the northern and southern margins of the South China Sea. The integrated geophysical interpretation of the south margin of SW Sub‐basin indicated that the Mesozoic group exists near the foot of continental slope, but it may not be continuous on the entire profile.