Study On Thermal Isostasy Of South China Sea

Located on the southeastern of the Pacific,the South China Sea is the biggest marginal sea,and surrounded by three plates of Pacific,Eurasian,and Indo-Australia.Influenced by the Tethys tectonic domain,The geologic process of the South China Sea is very complicated.In order to understand the formation and evolution of the crust better,the study on the thermal balance of South China Sea crust has helped us understand the changes in crust tectonics,deep thermal mechanisms,and large-scale dynamics.In order to facilitate the study,according to the structural characteristics of South China,8 tectonic units can be extracted from the South China crust: Beibuwan basin,Zhujiangkou basin,Qiongdongnan basin,Taixinan basin,Xisha plot,Southwest sub-basin,Liyue basin,Nanshahaicao-wenlaishaba basin.Summarize the P-wave velocity structure of major tectonic units in South China Sea.according to the wave velocity(Vp)-density(?)conversion method proposed by Hasterok and Chapman,the P-wave velocity structure of South China Sea tectonic unit will be converted into a density structure.Summarize the seismic section passing through each structural unit,and deal with the observation elevation data,the adjusted elevation data and heat flow data of each structural unit,the density of the tectonic unit crust can be calculated by the wave velocity(Vp)-density(?)conversion method.Calculate the height of the elevation after correction and the heat flow average value of the structural unit,map it to the “standard” thermal isostasy curve: We found that Beibuwan basin,zhujiangkou basin,Qiongdongnan basin,Taixinan basin,Liyue basin,Nanshahaicao-wenlaishaba basin are in thermal isostasy state.The Xisha plot,Southwest sub-basin are not in thermal isostasy state.According to the data,The average crustal density of Beibuwan basin is 2753±9kg/m3;The average crustal density of Zhujiangkou basin is 2780±10kg/m3;The average crustal density of Qiongdongnan basin is 2740±10 kg/m3;The average crustal density of Taixinan basin is 2618±10 kg/m3;The average crustal density of Xisha plot is 2651±9 kg/m3;The average crustal density of Southwest sub-basin is 2883±12kg/m3;The average crustal density of Liyue basin is 2655±12 kg/m3;The averagecrustal density of Nanshahaicao-wenlaishaba basin is 2660±10 kg/m3.In general,the average crustal density of the structural unit of South China Sea is lower than that of global average.