Active Rift System in the Okinawa Trough and Its Northeastern Continuation

Abstract

Recent submarine, geological and geophysical investigations have revealed that the present central rift system of the Okinawa Trough which is an active extensional axis of the trough has been formed since about 2 Ma. Two stages of the formation processes of the Okinawa Trough can be distinguished. The crustal thinning and thus eastward drifting of the Ryukyu Arc may have occurred during late Miocene to middle Pliocene time (about 6-4 Ma) at the first stage. The extensive subsidence may have occurred at the second stage since late Pliocene time (about 2 Ma). The Okinawa Trough and its northeastern continuation might be identified as a plate boundary of a newly proposed Southwest Japan Micro-plate. Based on the relationship between backarc basin and subducting slab development, one model for the origin of the backarc basin is proposed. The model suggests that the heat related to opening processes of the Okinawa Trough might rise up from the independent portion of the subducting plate.