Magmatism in the Nansha Trough on the southern continental margin of the South China Sea: Recent evidence from seismic profiles

Abstract

Nansha Trough, located in the southern part of Nansha Block, is an important boundary of the southern continental margin of the South China Sea, which has undergone complex tectonic superposition process, and is an important area for studying the subduction extinction of the Proto-South China Sea and the current expansion of the South China Sea. In this study, we make use of a new multi-channel seismic profile, which is almost parallel to the distribution of Nansha Trough, to systematically identify and analyze the magmatic activity in Nansha Trough for the first time, and combine the geophysical data such as gravity and magnetism to determine the attributes of seamounts in the trough. We found that all the seamounts in the trough were formed by magmatism, and underwent multiple episodes of magmatism, some of the seamounts were deposited with huge thick carbonate layers on the top. The magmatic rock mass in the trough shows different gravity and magnetic anomaly characteristics on the east and west sides, which may be related to magmatic stage, magmatic source and magmatic differentiation. Unlike the widely developed post-rift magmatism in the northern passive margin of the South China Sea, most magmatic activities in the Nansha Trough seem to ceased around 16Ma, which may be related to the dehydration and melting caused by the subduction plate rotation in the Proto-South China Sea.