Magmatism and tectonic evolution of the Parece Vela Basin and the drilling proposal

Studying the geological evolution of the Philippine Sea Plate (PSP) is the key to understand the formation and evolution of the trench-arc-basin systems in the West Pacific region. The Parece Vela Basin (PVB) and the Shikuko Basin are formed during the second spreading epoch of the western Pacific back-arc system, during which important information about the growth of the Philippine Sea Plate and westward subduction process of the Pacific Plate beneath the PSP is recorded. In this study, the geological and geophysical characteristics of PVB and subdivided the basin into four sub-units are summarized. In the eastern sub-unit, the sediment is thin and the seafloor topography is complex, and the observed magnetic anomalies range from 10 to 5D. The submarine lavas from the sub-unit have similar trace element characteristics to those of back-arc basin basalts and so in isotope imprint to those of the Indian Ocean type MORB (mid-oceanic ridge basalt). In the western sub-unit, the sediment is thick (up to 3500 m), the seafloor topography is smooth, the magnetic anomalies are not recognizable, and the compositions of the submarine lavas of the sub-unit are similar to those of the eastern sub-unit. The southern sub-unit, composed by seamounts, rifts, and hills, exhibits a complex morphology. The magnetic anomalies are not recognizable. The lavas from the sub-unit have transitional trace element characteristics between N(normal)-MORB and IAB (island arc basalt), and isotopic features of the Indian Ocean type MORBs (similar to the eastern and western sub-units’). In the rift sub-unit, the sediment is thin, the seafloor topography is composed of detachment faults and oceanic core complexes, and the water depth of seafloor can reach up to 7500 m. There occurred some residual fertile peridotite, and refractory peridotite as well. Finally, we proposed 8 possible drilling sites in the PVB in attempt to solve some key scientific issues related to tectonic, magmatic, deep mantle, sedimentation, and subduction processes.