The Okinawa Trough: Genesis of a back-arc basin developing along a continental margin

Abstract

The Okinawa Trough is the only example of a marginal back-arc basin type at a young stage of evolution that developed along a continental margin. The first phase of crustal stretching and subsidence occurred during late Miocene-early Pliocene times. A second major phase occurred after the latest Pliocene or early Pleistocene, with en échelon rift axes along the axes of the Okinawa Trough, oblique to the general trend of the arc and trench. Crustal separation and active spreading has occurred in the central and southern Okinawa Trough, but the north Okinawa Trough is only in a rifting stage. The development of the basin has several correlations with the general tectonism of the arc system: 1. (1) There was a synchronism between opening and subsidence of the Okinawa Trough and tilting and subsidence of the fore-arc terrace. 2. (2) Back-arc rifting was initiated in the volcanic arc and propagated along it during the Neogene. Remnants of a volcanic arc are found on the continental side of the basin. The beginning of the back-arc spreading observed in the central and southern Okinawa Trough correspond to a relative minimum in the activity of the volcanic arc. 3. (3) The timing and kinematic evolution of the Taiwan collision and the south Okinawa Trough opening suggest a connection between these two events. Such a collision-lateral back-arc opening model could explain the initiation of the opening of back-arc basins, but additional phenomena such as thermal convection, retreating trench model or anchored-slab model are indispensable to maintain extension in the back-arc basin.