Geochemical evolution and origin of Late Cenozoic basalts from north Hainan Island (southern China)

Intraplate basalts usually have complex compositions and genetic processes. Since the Oligocene, voluminous intraplate basalts have developed in the north Hainan Island. These basalts show a wide spectrum of compositions from quartz tholeiites, through olivine tholeiites, to alkaline olivine basalts and basanites. Extensive studies have been carried out on those basalts; however, the problem of geochemical evolution pattern of the basalts to their eruptive history still needs to be paid more attention. In this study, we report newly analysed whole-rock major, trace and Sr-Nd-Pb isotopic data for the olivine basalts of the Daotang Formation. These data, along with the existing geochemical data of the basalts of other ages (formations) in north Hainan Island, reveal a sequential evolution pattern, which begins with eruptions of alkaline basalt followed by tholeiitic basalt during the Middle Pliocene to the Pleistocene, and immediately followed by outpourings of more alkaline series in Holocene. The initial alkaline basalt and the following tholeiitic basalt during the Middle Pliocene to the Pleistocene might have been formed by the low to higher degree of partial melting of garnet lherzolite, while the Holocene alkaline rocks were more likely to have been formed by the partial melting of garnet pyroxenite. The Sr, Nd and Pb isotopic compositions of the basalt in north Hainan Island document a PREMA (prevalent-mantle) reservoir in their mantle source, and it has been modified by sediments derived from ancient continental crust (EMU). The possible occurrence of Hainan mantle plume could explain the complex compositions and origins of the Late Cenozoic basalts in north Hainan Island well. © 2022 Geological Society of China. All rights reserved.