Geochemistry and Mantle Potential Temperature of Late Cenozoic Basaltic Rocks from the Northern and Western Continental Margins of the South China Sea

Abstract

Deep dynamic processes of the evolution of the South China Sea (SCS) are recorded by the large-scale magmatism in the SCS and its surrounding regions. The geochemical analysis of whole-rock and olivine phenocryst was conducted on the Late Cenozoic basaltic rocks, which are exposed in the continental margins of the northern (the Leiqiong Area) and western (the Kontum Area) SCS. Consistent geochemical characteristics were shown on the basaltic rocks based on the results, which are similar to OIB from intra-plate environment. Mantle potential temperature (T<i>_p </i>) was measured by MgO of parental magma compositions and by olivine-liquid equilibria thermometry, with an average of 1489°C beneath the Leizhou Peninsula, 1555°C beneath the Northern Hainan and 1458°C beneath the Kontum Area. Compared with T<i>_p </i> of SCS MORB, the mantle excess temperature is about 78–175°C in the studied areas. The highest excess temperature within typical plume-affected regions. Our results provide the evidence based on temperature for the existence of the Hainan Plume. The data of highest T<i>_p </i> under the North Hainan may indicate the upper reaches of mantle plume. The mantle source of post-spreading magmatism in SCS and its surrounding region is likely to be correlated to that of pre-spreading volcanic activities in the northern continental margins.