Print Xia Shaohong research team of Guangzhou Marine Laboratory carried out the research on P-wave velocity structure by using the active source OBS wide-angle seismic data, which provided important information for in-depth understanding of magmatism and crustal extension in the continental margin of the northern South China Sea. Relevant research results were recently published in Tectonophysics.
The northeastern continental margin of the South China Sea is a unique continental margin, which is characterized by weak magmatism in the early stage of rifting and strong magmatism in the late stage of rifting. At the same time, there is also a complex relationship between crustal extension and magmatism in this region. Understanding the development scale, material properties and structural model of magmatism in the northeast of the South China Sea is of great significance for the study of regional tectonic evolution. The wave velocity ratio (VP / VS) obtained from seabed seismic data can be used to reveal rock physical properties, and the comprehensive study of shear wave (S wave) and wave velocity ratio (VP / VS) can effectively understand the crustal material composition in this area. Therefore, the deep crustal structure and related rock physical properties can be comprehensively studied to explore regional tectonics and magmatism.
In this study, OBS Data (NS5 survey line) collected in Dongsha sea area are collected, and the structural models of P-wave, S-wave and VP / vs data are obtained by inversion method. The results show that the VP of the high-speed body in the lower crust is 7.0-7.5 km / s ± 0.05-0.25 km / s, and the VP / VS is 1.70-1.82 ± 0.05, indicating that its composition is mainly basic, which is a magnesium rich gabbro formed by later magmatic intrusion.
The results show that the crustal tension and thinning degree of the ocean land transition zone in the northeast of the South China Sea is intense, forming a large number of extensional faults. In the later stage, the magma is easy to migrate to the shallow along the fault, which increases the intrusion degree of deep mafic magma to the Sea (VP / vs tends to increase to the sea), which leads to the thinner thickness of the high-speed body of the lower crust on the ocean side.