The new volcanics record in Sanshui Basin and its relationship with the spreading of the South China Sea

Sanshui Basin is the only basin that has Cenozoic volcanic records in the northern adjacent land area of the South China Sea, and the age of the last volcanic eruption in this basin is 38Ma. This age is also the last eruption age before the South China Sea spreading in its northern land. Based on the K-Ar isotope dating method, the basalts (29.27±1.52Ma) and rhyolite (28.25±1.14Ma) were first found in Sanshui Basin. This bimodal volcanic rock that represents intraplate rifting tectonic setting postponed the volcanic records from Palaeocene-Middle Eocene to Mid-Oligocene. As we all know, the initial age of the South China Sea spreading is about 32Ma. So, it has great significance to answer if there is the relationship between the South China Sea spreading and its surrounding land volcanic activity. Meanwhile, the findings have important significance for establishing early spreading evolution model of the South China Sea.