Multi‐channel seismic reflection study of tectonic–sedimentary features and subduction initiation in the middle Kyushu–Palau Ridge and adjacent basins

AbstractThe Kyushu–Palau Ridge and adjacent basins are ideal locations for investigating the formation and evolution of marginal seas and initiation of plate subduction. In this study, the tectonic–sedimentary features and crustal structure of the Kyushu–Palau Ridge and adjacent basins were investigated using newly obtained deep seismic reflection and borehole data. The initial mechanism of subduction in the West Philippine Sea and its tectonic evolution are discussed. Two sets of sedimentary strata with different provenances occur in the eastern Philippine Basin. The thickness of the lower strata is variable, and most of the sediment was sourced from island arc volcanism on the Kyushu–Palau Ridge. These strata thicken towards the Kyushu–Palau Ridge, and volcaniclastic rock aprons are developed near the foot of the Kyushu–Palau Ridge. The upper strata have a relatively uniform thickness and comprise fine‐grained, deep‐water marine sediments. The crustal thickness of the West Philippine and Parece Vela Basins is 6–7 km, which is similar to the global average thickness of oceanic crust. The Moho beneath the West Philippine Basin has a broad and undulating form that mimics the thickness of the oceanic crust beneath the sediments. The depth to the Moho decreases towards the Central Basin Spreading Center. The Moho beneath the Parece Vela Basin is planar, which is in contrast to the undulating nature of the oceanic crust base in this area. The West Philippine Basin may have been located at the northern margin of Australia in the Southern Hemisphere during the Mesozoic. It developed gradually in a continental margin arc as a result of Palaeogene inter‐arc and oceanic extension and contains fragments of continental crust. Seismic profiles and drillhole data in the West Philippine Basin reveal that compression occurred during the Eocene. Subduction along the paleo‐Izu–Bonin–Mariana arc may have been caused by the far‐field effects of the India–Asia collision. Subduction was accompanied by lateral propagation and a compressive stress field until the break‐up of the island arc at ca. 30 Ma.