Trench-parallel stretching and folding of forearc basins and lateral migration of the accretionary wedge in the southern Ryukyus: A case of strain partition caused by oblique convergence

Detailed seafloor mapping in the area east of Taiwan revealed trench-parall el stretching and folding of the Ryukyu forearc and lateral motion of the a ccretionary wedge under oblique convergence. East of 122 degrees 40'E, a st eep accretionary wedge is elongated in an E-W direction. A major transcurre nt right-lateral strike-slip fault accommodates the strain partitioning cau sed by an oblique convergence of 40 degrees. A spectacular out-of-sequence thrust may be related to the subduction of a structural high lying in the a xis of the N-S trending Gagua Ridge. This asperity is likely responsible fo r the uplift of the accretionary wedge and forearc basement and may have au gmented strain partitioning by increasing the coupling between the two plat es. West of 122 degrees 40'E, the low-taper accretionary wedge is sheared i n a direction subparallel to the convergence vector with respect to the Ryu kyu Are. The bayonet shape of the southern Ryukyu Are slope partly results from the recent (re)opening of the southern Okinawa Trough at a rate of abo ut 2 to 4 cm/yr. Right-lateral shearing of the sedimentary forearc with res pect to the nonlinear Ryukyu backstop generates trench-parallel extension i n the forearc sediment sequence at dilational jogs and trench-parallel fold ing at compressive jogs. The Hoping Basin lies above a diffuse trenck/trenc h/fault (TTF) or TFF unstable triple junction moving toward the south along a N-S transform zone which accommodates the southward drift of the Ryukyu Are with respect to Eurasia.