Seaward jump of the subduction zone associated with ridge collision — an example from the Suruga Trough
Abstract The Suruga Trough has evolved from a trench to the slope basin environment of sedimentation since the collision between the Izu Peninsula and Honshu Island in the middle Pleistocene. In the future, about 0.5 Ma after present, this slope basin will be filled up by sediments, and it is expected that the Suruga Trough will eventually become a fore-arc basin. The same systematic change of sedimentary basins cyclically occurred at several times since the late Miocene. Five cycles including an anticipated one are recognized in the Suruga Trough region. Sedimentary basins adjacent to the collisional plate boundary show a change from trench to slope basin in one cycle, and develop to forearc basin in the next cycle. These cycles have gradationally advanced from the landward to the seaward side in that region with the westward motion of the Philippine Sea Plate up to the late stage of Izu cycle. During this plate motion, the dimensions of accreted mass in each cycle have been diminished in size associated with the shortening of time required in each cycle. The Philippine Sea Plate motion has changed to the northwest since 0.5 Ma B.P. and the following Zenisu cycle, the boundary of which strikes at a NE-SW trend, has been developed. In the same plate motion, the Shichito cycle has already begun at present. The Nankai Trough might have been a dextral slip transform fault between the subduction zone in the Suruga Trough region and in the Hyuga region before 2 Ma B.P. and has changed to an active plate subduction boundary with the northwestward motion of the Philippine Sea Plate during the Izu cycle.