Since the Early Cenozoic, the Philippine Sea Plate (PSP) has undergone a complex tectonic evolution. During this period the Parece Vela Basin (PVB) was formed by seafloor spreading in the back-arc region of the proto-Izu-Bonin-Mariana (IBM) arc. However, until now, studies of the geological, geophysical, and tectonic evolution of the PVB have been rare. In this study, we obtained in situ trace element and major element compositions of minerals in basalts collected from two sites in the southern part of the PVB. The results reveal that the basalts from site CJ09-63 were likely formed via ~10% partial melting of spinel-garnet lherzolite, while the basalts from site CJ09-64 were likely formed via 15%–25% partial melting of garnet lherzolite. The order of mineral crystallization for the basalts from site CJ09-64 was olivine, spinel, clinopyroxene, and plagioclase, while the plagioclase in the basalts from site CJ09-63 crystallized earlier than the clinopyroxene. Using a plagioclase-liquid hygrometer and an olivine-liquid oxybarometer, we determined that the basalts in this study have high H2O contents and oxygen fugacities, suggesting that the magma source of the Parece Vela basalts was affected by subduction components, which is consistent with the trace element composition of whole rock.