Tectono-magmatic evolution of the Philippine Sea Plate: A review

Abstract

• Geological and geophysical characteristics of the PSP. • Tectonic evolution of the PSP as a key to the west Pacific trench-arc-basin system. • Subduction initiation, origin of basins and intraplate magmatism. • Relationship between subduction input and arc/back-arc output. The West Pacific Margin incorporates 75% of global marginal basins/back-arc basins. These basins and their adjacent trenches and island arcs constitute a huge trench-arc-basin system created by the interactions among three tectonic plates (the Pacific, Eurasian, and Indian plates) since about 50 Ma. Located among these three plates, the Philippine Sea Plate (PSP) is surrounded by a series of subduction zones, e.g., the Philippine Trench to the west, the Ryukyu Trench and the Nankai Trough to the north, the Izu-Bonin-Mariana (IBM) Trench to the east, and the Yap and Palau trenches to the south. Plate reconstruction shows that the PSP was originally located near the equator, and it has gradually moved northward since the Early Cenozoic. In addition, due to multiple subducted slab rollback events and the related multiple rifting of the proto-IBM Arc, several important tectonic units have been formed, including back-arc basins and relic/active arcs. The back-arc basins include the West Philippine Basin (WPB, spreading at 65-35 Ma), the Shikoku Basin (SKB, spreading at 27-15 Ma), the Parece Vela Basin (PVB, spreading at 29-15 Ma), and the Mariana Trough (MT, spreading from 5 Ma to present), and the main arcs include the Relic Kyushu-Palau Arc (ridge) (KPR, termination at 29 Ma), the Relic West Mariana Arc (ridge) (WMR, termination at 6Ma), the Active IBM Arc (since 11 Ma), and the Yap Arc (since 24 Ma). The geochemistry of these main tectonic units is as follows. The WPB has undergone back-arc spreading and intraplate magmatism, producing many rock types such as back-arc basin basalts (BABBs) similar to normal mid-oceanic ridge basalt (NMORB) and/or enriched mid-oceanic ridge basalt (EMORB) in the central basin, and oceanic island basalts (OIBs) in the Benham Rise and the Urdaneta. In addition, several Late Mesozoic arc terranes (e.g., the Amami Plateau, the Daito Ridge, and the Huatun Basin) developed in the WPB. The SKB mainly contains back-arc basin basalts (BABBs). After termination of the spreading in the SKB, two groups of seamounts with ages of 15-7 Ma formed. One group has undergone subduction. The other group (the Kinan Seamount Chain) is characterized by an OIB and mixed mantle source (Indian Ocean MORB and enriched mantle type one (EM1) geochemical signatures. The PVB basement rock is composed of back-arc basin basalts (BABBs). However, the southern PSP basin is very complex. The Mariana Trough mainly contains BABBs, with island arc basalts (IABs) occurring in the spreading center near the island arc. The IBM Arc mainly contains 52-51 Ma fore-arc basalts, 49-45 Ma boninites, and <45 Ma mature island-arc magmatic rocks. The two relic arcs (the KPR and the WMR) mainly contain IABs. The basement rocks in these back-arc/arc tectonic units are isotopically similar to Indian Ocean MORB. Thus, the West Pacific Ocean, e.g., the PSP, is an ideal place for studying several important geological processes, including interactions between large-scale tectonic plates, subduction initiation, back-arc spreading, intra-oceanic subduction, intraplate magmatism in a back-arc basin, and the geochemical cycle of a subduction zone.