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Scientists have found that the deep mantle structure of the South China Sea is asymmetrical in the north and south


Recently, the interforest team of the Key Laboratory of Marginal Sea and Ocean Geology of the Institute of South China Sea Oceanology, Chinese Academy of Sciences has made an important breakthrough in the study of deep structure in the South China Sea, obtained for the first time geophysical evidence of the relatively water-rich mantle of the southern South China Sea, and found that the seismic wave velocity structure of the South China Sea is asymmetrical north-south. The results were published in Nature Communications. Lin Ma is the corresponding author of the paper, Tian Jinyu is the first author, and Xu Min, Zhang Fan and Zhang Xubo are collaborators.

South China Sea seabed seismic experiment. Photo courtesy of the research team

The South China Sea is one of the largest marginal seas in the world, and in the past 100 million years, a large number of earth plates have subducted below the South China Sea from the east, west and south directions, so the deep part of the South China Sea is called the “underground palace” of subduction plates. However, due to the limitations of seafloor observations, little has been known about the deep structure of this “underground palace”.

In June 2017, the Lin team carried out a high-resolution passive-source seabed seismic experiment in the southwest sub-basin of the South China Sea for the first time aboard the “Experiment 3” research vessel, and performed three-dimensional high-resolution “CT” imaging of the “underground palace” in the South China Sea.

Shear wave velocity structure of mantle in the southwest subsea basin of the South China Sea: plane change (top) and profile change (bottom). Photo courtesy of the research team

In the southwest subbasin of the South China Sea, the research team found that there is a significant anomaly of low seismic shear wave velocity at a depth of 40-80 km in the southern part of the basin, and the anomaly peaks at a depth of about 50 km. After deep thermodynamic and lithogeochemical analysis, the research team concluded that the upper mantle in the southern South China Sea is relatively rich in water, and speculated that these waters may be due to the dehydration of subducted plates.

Combined with the current structure of the South China Sea, the interforest team proposed a new mantle evolution model of the southwest subsea basin of the South China Sea. Lin believes that for more than 10 million years, the fractured ancient South China Sea subduction plate continued to release dehydration during the sinking process, resulting in a relatively water-rich southern mantle (~150-300 ppm).

Mantle evolution map of the southwest subsea basin in the South China Sea. Photo courtesy of the research team

This study is of great significance for revealing the “underground palace” structure of the subduction plate in the South China Sea, the origin of a large number of volcanoes and islands in the South China Sea, and the water cycle in the earth’s subduction zone.

The above research was jointly funded by the National Natural Science Foundation of China and the Chinese Academy of Sciences. (Source: China Science News, Zhu Hanbin, Li Shu)

Related paper information:https://doi.org/10.1038/s41467-023-38385-w



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