[S-IT19] Coupling of deep Earth and surface processes

[SIT19-03] An evolution model of the Okinawa trough: Slab rollback and coupling between the Philippine Sea plate and the Eurasian plate

*Ban-Yuan Kuo¹, Shu-Chuan Lin (1.Institute of Earth Sciences, Academia Sinica)

Keywords:backarc basin, slab rollback, interface coupling, Okinawa trough

Continental backarc basins (BAB) associated with subduction zones often originate from extension on the overriding plate induced by slab rollback. A preeminent example of continental BAB is the Ryukyu arc–backarc system, where the Ryukyu arc, an arc-shaped lithospheric sliver, is currently splitting from the Eurasian margin with the Okinawa Trough (OT) accommodating the lithospheric stretching. This process is driven by the rollback of the subducting Philippine Sea Plate. We present a dynamic model that describes how the OT has evolved to its present form. Unlike previous global backarc extension models, our model considers along-axis variations in subduction interface coupling as reported in literature: the interface coupling is strong at the edge of the Taiwan orogen, abruptly decreasing in short distance to the east, and increasing progressively toward the Japan end. Opening is therefore most active on the western segment of the BAB system, making the northern segment passively dragged along. This model is consistent with our recent ambient-noise tomography in northern OT where seismic anisotropy exhibits a fast direction sub-parallel to the strike of the arc, a signature of a backarc extension dominated by shearing.