Mantle Sources And Magma Genesis Of Late Cenozoic Basalts From 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 center,but the mantle source and magma genesis still 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,as well as compares it with the late Cenozoic basalts from the South China Sea and its surrounding areas,aiming to reveal their mantle sources and magma genesis,and attempt to provide important information and constraint for the petrogenesis of late Cenozoic basalts from the South China Sea and its surrounding areas.The volcanic rocks from Weizhou Island are mainly alkali basalts in composition,and experienced crystallization differentiation of olivine and clinopyroxene.The chondrite-normalized rare earth elements curves show enrichment of light rare earth elements?LREEs?and depletion of heavy rare earth elements?HREEs?,and strong fractionation of light and heavy rare earth elements??LREE/?HREE=7.92?12.22,?La/Yb?_N=14.42?28.64?.The primitive mantle-standardized trace element spider diagram shows obvious positive anomalies of Nb and Ta,as well as high Nb/U and low ratios of?La/Nb?_N and?Th/Nb?_N,which are obviously different from those of the continental crust,suggesting that there is almost no contamination of crustal materials during magmatic rising process.The Sr-Nd-Pb istope ratiosarerelativelyhomogeneous,⁸⁷Sr/⁸⁶Sr=0.703492?0.703741,¹⁴³Nd/¹⁴⁴Nd=0.512914?012977,²⁰⁸Pb/²⁰⁴Pb=38.5574?38.9179,²⁰⁷Pb/²⁰⁴Pb=15.55871?15.6525,²⁰⁶Pb/²⁰⁴Pb=18.4361?18.7327.Weizhou Island basalts show oceanic island basalt?OIB?-like trace elements and Sr-Nd-Pb isotopic characteristics,and the mantle end member show a trend of binary mixing between depleted mantle?DMM?and enriched mantle II?EM2?,which may both originate from Hainan mantle plume.The trace element simulation,whole rock Ca O content,Fe O^T/Mn O ratio and olivine Ni O content similar to Hawaiian basalts indicate that Weizhou Island basalt may originate from partial melting of mixed mantle peridotite and garnet pyroxene.Positive Sr?Sr/Sr*=1.21?2.36?and Eu?Eu/Eu*=1.01?1.11?anomalies signify the existence of recycled gabbro oceanic crust in the source region.Combining the previous seismic tomography results and geochemical data,we suggest that late Cenozoic magmatism of the South China Sea and surrounding areas may be controlled by the Hainan manlte 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 originate from a mixing source of garnet pyroxenites and unreacted peridotites.