GEOGRAPHY

Research on the continental transition zone of the northern continental margin of the South China Sea


Recently, the South China Sea Institute of Oceanology, Chinese Academy of Sciences and the Institute of Deep Sea Science and Engineering of the Chinese Academy of Sciences have made new progress in the research of the continental transition zone (COT) in the northern South China Sea by comprehensively using the wide-angle seismic data of the three-dimensional seabed seismometer (OBS), multi-channel reflected seismic data, and international ocean drilling results. The results were published in Structural Physics. Yuan Ye is the first author of the paper, He Enyuan and Zhao Minghui are the corresponding authors, and Zhang Cuimei, Gao Jinwei, Zhang Jiazheng and Sun Zhen are co-authors.

COT three-dimensional deep seismic detection experiment and research line map of the northern continental margin of the South China Sea. Photo courtesy of the research team

The COT of the northern continental margin of the South China Sea is the transition region between the thinned crust and the new oceanic crust of the tensile fracture continental margin, and its deep structural characteristics reflect the interaction pattern of magmatic activity and tectonic movement of the tensile fracture continental margin during the rupture evolution period, and provide a geological basis for the formation mechanism of deepwater-ultra-deepwater oil-gas basins in China. From May to July 2018, the research team carried out OBS detection experiments in the IODP367/368/368X drilling area of the northern continental margin of the South China Sea with the National Natural Science Foundation of China (NSFC) on board the National Natural Science Foundation of China National Geophysical Shared Voyage (NORC2018-08).

The researchers focused on the L2 line crossing the COT region, and used the RayInvr forward and Tomo2d inversion methods to obtain the forward / inverse longitudinal wave velocity structure and velocity spread characteristics below the measurement line. Based on the velocity model, they proposed a fracture-fracture geological evolution model of the northern continental margin of the South China Sea by using multiple data and IODP drilling results as shallow constraints, and comparing with the L5 line and 3D tomography results.

Studies have shown that the transition process from land to ocean in the northern continental margin of the South China Sea is very rapid, forming narrow COT. The magma bottom intrusion in the same tensile fracture period forms a high-speed layer of the lower crust. The crust under the continental crust is extremely thinned due to ductile deformation in the late tensile fracture, and magma appears rapidly under reduced pressure melting, which eventually leads to the rupture of the crust and the rapid expansion of the seabed.

This study provides important deep seismic detection data for the land margin of the South China Sea. From the perspective of two-dimensional velocity structure, the range of COT and the structural characteristics of the earth’s crust in the northern continental margin of the South China Sea were analyzed, and the differences of COT in different tensile fracture sections of the northern continental margin of the South China Sea were proposed, which revealed the complex tension-fracture mechanism, which is of great significance for in-depth understanding of the tectonic-magma interaction in the process of continental margin fracture evolution. (Source: China Science News, Zhu Hanbin, Li Shu)

Related paper information:https://doi.org/10.1016/j.tecto.2023.229984



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