The geological nature and geodynamics of the Okinawa Trough, Western Pacific

There is a continuing hot debate on whether the geodynamics in the West Pacific indicate either a marginal basin or back‐arc basin, since the nature, evolution and formation mechanism are not well known. Research on the Okinawa Trough (OT), which is an active back‐arc basin, has important scientific significance for discussing the opening and development of a marginal basin or back‐arc basin. This paper synthesizes data on the crustal thickness, heat flow, hydrothermal activity and fault patterns to determine the geological nature of the OT. By comparing the thicknesses of initial oceanic crusts of global passive continental margins and marginal basins in the West Pacific, the central and southern OT are interpreted to be at the early stage of seafloor spreading, generating new oceanic crust at the spreading centre, while the northern OT is at the mature stage of continental rifting, having the character of transitional crust. The NE‐ and NNE‐trending faults are dominant in the OT. The NE‐trending strike‐slip faults control the stratigraphic succession and structural framework of the OT. The NNE‐trending strike‐slip faults triggered the back‐arc rifting or extension and evolved into transform faults with the emergence of oceanic crust. The Cenozoic tectonic jumping in the East Asia Continental Margin, including the OT, indicates that the eastward movement of the mantle flow under the Eurasian Plate should be the main dynamic source. Because the Philippine Sea Plate is obliquely and passively subducted, the evolution of the OT can be divided into three stages. The first stage is the initial rifting, triggered by the back‐arc normal faulting. The second stage is the passive spreading, triggered by the strike‐slip pull‐apart process or transtensional faulting of NNE‐trending faults. The third stage is the initial divergence of the relic and Ryukyu island arcs, triggered by new‐born oceanic crustal spreading. Copyright © 2016 John Wiley & Sons, Ltd.