TIMING AND GENESIS OF CENOZOIC MAGMATISMS IN THE SOUTH CHINA SEA AND SURROUNDING AREAS

The Cenozoic magmatic activities in the South China Sea (SCS) are similar with its surrounding areas. It may be divided into three stages following the spreading of the SCS: pre-spreading (32 Ma), syn-spreading (32~15.5 Ma), and post-spreading (< 15.5 Ma). The pre-spreading rocks are bimodal volcanic rock suite which is typically exposed in the Sanshui basin; the syn-spreading magmatic rocks in the SCS basin are typical MORB according to the data from IODP expedition 349, but the limited syn-spreading magmatic rocks in eastern Guangdong and western Taiwan are alkali basalts; the post-spreading magmatism can be subdivided into two periods: the early period dominated by tholeiites and the late predominated by alkali basalts. The geochemical characteristics of the Cenozoic magmatic rocks (expect the syn-spreading MORB) in the SCS and its surrounding areas are consistent and similar with OIB, indicating that the mantle source is heterogeneous, which is composed of a DMM and an EM end member, and show the Dupal isotope anomaly. However, there are controversies in the issues such as the nature and origin of the EM end member, cause of the Dupal isotope anomaly, and the existence of the Hainan plume. The plume may produce OIB-like magmas, but not all OIB-like magmas are produced from the plume, mantle metasomatism can also have important impact on the magmatism. In this paper, it's considered that carbonate fluids metasomatism in the mantle source may play an important role in the Cenozoic magmatism in the SCS and its surrounding areas. The research on the diagenetic process is not enough yet. These are the places where attention needs to be paid to in the future research work.