Mantle sources and magma genesis of Late Cenozoic basalts in Weizhou Island, Guangxi, China

As the youngest Quaternary volcanic island in China, the volcanic activities of Weizhou Island are characterized by multi-stage, multi-cycle and multi-eruption centers, however, whether the volcanic rocks in this island have mantle source and what is the genesis of the magma remain controversial. Here, we present a comprehensive study of mineral chemistry, whole-rock major and trace elements, and Sr-Nd-Pb isotopes of basalts from Weizhou Island, aiming to reveal their mantle sources and magma genesis. The basalts from Weizhou Island are mainly alkali basalts, which were barely contaminated by crustal material and experienced fractional crystallization of olivine and clinopyroxene, showing oceanic island basalt (OIB)-like trace elements and Sr-Nd-Pb isotopic signatures as follows: with a light rare earth elements (LREEs) enrichment and a heavy rare earth elements (HREEs) depletion, and highly fractionation of LREEs and HREEs ((La/Yb)N=14.42 similar to 28.64), significant positive abnormalities in Nb and Ta. Furthermore, they have relatively homogeneous Sr-Nd-Pb isotope ratios that show a trend of binary mixing between depleted mantle (DM) and enriched mantle ? (EM2). Moreover, the EM2 component may be originated from the Hainan mantle plume. The positive Sr/Sr* (1.21 similar to 2.36) and Eu/Eu* (1.01 similar to 1.11) anomalies indicate the existence of recycled gabbro oceanic crust in its source region. Combining the previous seismic tomography results and geochemical data, we suggest that the Late Cenozoic magmatism of the South China Sea and its surrounding areas may be controlled by the Hainan mantle plume. In the upwelling mantle plume, the recycled gabbro oceanic crust is partially melted and reacts with mantle peridotites to produce garnet pyroxenites (silica-deficient pyroxenite). Therefore, we suggest that basalts from Weizhou Island may be originated from a mixing source of garnet pyroxenites and unreacted peridotites