Punctuated growth of an accretionary prism and the onset of a seismogenic megathrust in the Nankai Trough

Ocean drilling in the Nankai Trough forearc suggests a new scenario for the evolution of the Nankai subduction zone. Continuous subduction since the Late Cretaceous has been a common tectonic scenario, although the plate subduction was transferred from the Pacific Plate to the Philippine Sea Plate during the Miocene. Seismic reflection studies coupled with drilling have demonstrated that two episodes have controlled the recent evolution of the Nankai forearc: a resurgence of subduction at similar to 6 Ma after cessation since similar to 12 Ma and rapid growth of the accretionary prism since similar to 2 Ma because of the influx of large amounts of terrigenous sediments from the Japan Alps in central Japan. Both episodes were synchronous with large-scale plate reorganizations. The westward subduction of the Philippine Sea Plate initiated both in the Ryukyu and the Philippine trenches at similar to 6 Ma. Rifting in the Okinawa and Mariana troughs started at similar to 6 Ma. Compressive tectonics in northeast Japan started at similar to 3-2 Ma, and resultant mountain building with active surface erosion commenced in central Japan at similar to 2 Ma. This recent compressive tectonic phase might be due to the initiation of convergence of the Amurian Plate with the Okhotsk or North American Plate along the eastern margin of the Japan Sea. In addition to this event, the strong collision and indentation of the Izu-Bonin Arc since similar to 2.5 Ma was also enhanced in central Japan.