Continent-ocean transition in the northern South China Sea by high-quality deep reflection seismic data

Continent-ocean transition (COT) , one of the important features of passive continental margins, is crucial for understanding the rupture of continental lithosphere, subsequent seafloor spreading, and formation and evolution of passive continental margins. Some authors have delineated the location of the COT in the northern South China Sea by analyzing gravity, magnetic and seismic data, but the results are quite different and dependent on the data used. In this paper, we investigate the distribution and characteristics of the COT in the northern South China Sea based on newly acquired high-quality deep reflection seismic profiles. The range of the COT is determined based on the criteria of the seaward rapid uplift of the Mohorovicic discontinuity (Moho) and the rapid thinning of the crust thickness. Our results suggest that the COT in the northern South China Sea is located between the thinned continental crust in the continental margin and the normal oceanic crust in the ocean basin. It is the crust transformed by magmatism and thinned rapidly. Magmatic intrusion occurs in the deep crust of the COT. The average depth of Moho is 21. 9 km and the mean crustal thickness is 20. 2 km in the thinned continental; The average depth of Moho is 12. 0 km and the mean crustal thickness is 8. 1 km in the normal oceanic crust. The Moho depth and crustal thickness of the COT change sharply. The width of the estimated COT is approximately 46 similar to 99 km. The location of the COT determined in this paper is reasonable, as tested by the distribution of magnetic anomaly strips and the negative free air gravity anomaly. It is suggested that the characteristics of the COT in the northern South China Sea fall between those of typical volcanic and non-volcanic continental margin.