Geophysical Field Characteristics And Reconstruction Of Seafloor Spreading Processes Of The Philippine Sea Plate

Philippine Sea Plate has a special geotectonic position where is located in the junction of Eurasian Plate,Pacific Plate and Indian-Australian Plate.Owing to the three plates' multi-period subduction and collision since the late Mesozoic,the Philippine Sea Plate developed the world's most significant trench-arc-basin system,since the late Mesozoic,and its genesis and tectonic evolution can constrain the complex kinetic process of the ocean-continent transitional zone in the Western Pacific effectively.Based on gathering the latest geological and geophysical survey and research achievement in the research field and its vicinity,combining the the data of bathymetric,gravity,geomagnetic,Ocean Drilling Project and oceanic crust age,the manuscript discusses the geological and geophysical features of the Philippine Sea Plate.Furthermore,the periodic expansion characteristics of the research area is expounded in detail and a scenario of evolution from 61 Ma to present was proposed on the basis of geological and geophysical data.The main conclusions are listed as follows:(1)The genesis and tectonic evolution of the Philippine Sea Plate is mainly controlled by the tectonic movement of the Eurasian Plate,Pacific Plate and Indian-Australian Plate.According to the difference of geophysical field,the Philippine Sea Plate can be divided into three tectonic units that include the West Philippine Basin,Shikoku-Parece Vela Basin and Mariana Trough.The different formation age constitutes the time sequence of the multi-period back-arc spreading of the Philippine Sea Plate,for the reason that all kinds of geological and geophysical data indicate the Philippine Sea Plate experienced multi-phase back-arc spreading and many times tectonic rotation,and the ages of these three structural units are becoming younger from west to east.(2)The staged expansion of the West Philippine Basin,Shikoku-Parece Vela Basin and Mariana Trough is the mainly characteristics of the Philippine Sea Plate.The difference of the evolution degree and expansion characteristics indicate that the evolution process of the Philippine Sea Plate consists of eight stages.The West Philippine Basin is the combined effects of the plate subduction and the upwelling of hot asthenosphere beneath the basin.It's worth mentioning that the northward retreat of the trench located along the Izu-Bonin Arc and the southward retreat of the trench bounding the Philippine Arc provided the driving forces during the opening of the West Philippine Basin.Shikoku Basin,Parece Vela Basin and Mariana Trough are products of the island arc's periodic rifting caused by the seaward migration of trench,as well as the back-arc spreading.(3)Philippine Sea Plate consists of four back-arc or inter-arc basins.Summarizing the spreading characteristics of these basins,we concluded that the general opening processes starts from rifting,and is followed by fast spreading,slow spreading,and deformation after spreading.Rifting is the first stage of formation of back-arc basin,and the major characteristics of the stage are lithospheric extension and thinning,leading to the crustal rupture and the propagating of spreading ridge.Oceanic crust forming in back-arc area with high speed is the second stage and it has a relatively higher velocity.Compared to the second stage,the third phase has a relatively low speed.Tectonic activities always happened after the spreading,and post-spreading magmatism is the common phase at the end of spreading or after the opening of the basin based on the petrological and geochemical characteristics,as well as the dating data at the spreading axis.