| The material circulation and deformation of the subduction zones,and the formation and evolution of the rifts are the important research contents of the major projects at home and abroad in the last decade.Thus,researches of the extensional and subduction structures are one of the international research hotspots at present.The Philippine Sea Plate possesses the typical trench-arc-basin systems in the world and preserves multi-stage extensional and subduction structures.Thus,the Philippine Sea Plate is an ideal laboratory for the study of global extension and subduction dynamics.Based on the latest high-resolution multichannel seismic and multibeam data collected by Institute of Oceanology,Chinese Academy of Sciences in 2015-2017,combined with the gravity and magnetic data,we use multichannel seismic interpretation,gravity-magnetic-seismic joint modelling and inversion,sedimentary basin analysis and numerical simulation methods to systematically study the geophysical characteristics of the typical extensional and subduction structures in the western Pacific.We try to explore the evolutionary model for the interaction area between the Philippine Sea Plate and the Caroline Plate,and further improve the researches for the evolutionary history of the Philippine Sea Plate since late Eocene.Our results show that obvious differences in the sedimentary and crustal structures appeared between the eastern and western Central Basin Fault in the West Philippine Basin.Before the early Oligocene,sedimentary sags were developed,and there was no disordered reflection within the crust of western Central Basin Fault,indicating the fast-spreading characteristics induced by the sufficient magma supply.Since the early Oligocene,less sedimentary basins were developed and disordered reflection occurred within the crust of eastern Central Basin Fault,proving that minor magmatic activities and strike slip tension control the late extension events of the West Philippine Basin.In the late Oligocene,hotspot volcanism remolded the Caroline Plate.Large-scale lava flow erupted at the surface forming the Caroline Ridge.Based on the seismic profiles,lava flow formed the layered instracrustal reflections and smooth basement.Intensive volcanism resulted in the destruction of preexisting sediments in the Caroline Basins.The collision between the oceanic plateau and the southeast boundary of the Philippine Sea Plate hindered the subduction process at the Yap Trench.This collision process induced the gradual separation of the Yap and Mariana subduction zones.During the late Oligocene-Miocene,sediments gradually developed on the smooth basement of the Caroline Ridge with the hotspot volcanism weakening.During the early-middle Miocene,the Caroline Ridge rifting was induced by the far-field stress and other comprehensive factors,forming the Sorol Trough.The rifting led to the widespread unconformity appearing within the overlying sediments.In the Miocene,numerous normal faults produced by the rifting of the Sorol Trough that weakened the crustal strength of the Caroline Ridge.The subduction process was active and thus led to the formation of horst and graben structures near the Yap Trench.Due to the subducting of oceanic plateau,seamounts and fault zones,the Yap subduction zone has experienced the subduction erosion with a extremely slow convergence rate.Above all,the migration of Proto-Yap-Mariana subduction zone has an important influence on the tectonic evolution of the Philippine Sea Plate since Oligocene.Because of the Pacific Plate retreat,the spreading of the Parece Vela Basin induced the late extension of the Central Basin Fault,which further led to the extension of the West Philippine Basin.The formation of the oceanic plateau in the Caroline Plate limited the retreat process of the Proto-Yap subduction zone.Subsequently,the subducting Caroline Ridge causes the erosional process of the Philippine Sea Plate.Thus,the evolution of subduction zone controls the tectonic style of the Philippine Sea Plate since Oligocene. |
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