Intraplate magmatic processes associated with crustal accretion at the West Philippine Basin, Western Pacific

Abstract

The West Philippine Basin (WPB), located in the west half of the Philippine Sea Plate (PSP), experienced the superposition effects of back-arc spreading and intraplate processes. However, the magmatic processes for the intraplate geodynamics are unclear. In this study, we analyzed the major and trace element compositions of the plagioclase and clinopyroxene, and the Sr isotopic composition of the plagioclase in basalts collected from the Benham Rise (Site 292) during DSDP (Deep Sea Drilling Program) Expedition 31 and the off-spreading axis Vinogradov seamount (Site 100DS). The results show that clinopyroxene and plagioclase from the Benham Rise exhibit various disequilibrium characteristics, and their zoned textures were produced by multiple phases of magma replenishment in the magma chamber. The calculated parental magmas for clinopyroxenes in lavas from the Benham Rise and Vinogradov seamount show that they are produced by 10–20 % and 1–5 % partial melting of garnet pyroxenite, respectively. The Sr isotopic composition of plagioclase phenocrysts from the Benham Rise lavas showed that their parental magma could have originated from the same mantle source. The geochemical study of plagioclase and clinopyroxene implies the Benham Rise and Vinogradov seamount could be formed by the head and tail of the Benham mantle plume, respectively.