Geodynamic and plate kinematic context of South China Sea subduction during Okinawa trough opening and Taiwan orogeny

Abstract

The geodynamics and plate tectonics of the South China Sea (SCS)-Taiwan region since Miocene times are uncertain because the former extent and tectonic configuration of the subducted easternmost SCS along the Manila trench is uncertain. Here we unravel the regional kinematic context from main offshore constraints including published unfolding of the Manila slab from seismic tomography, which provides insight on restoring the subducted part of the SCS. We reconstruct a bayonet-shaped, stepped northern SCS continent-ocean boundary (COB) that consists of a northeastern SCS COB segment we call ‘S3’, trending N070° that roughly parallels the present SCS shelf; a 350-km long ~N-S trending segment S2 that steps north to Hualien; and, a third segment S1 that extends from east of Hualien beneath the Ryukyu subduction zone trending N085° that ends near Miyako Island in the Ryukyus.The distance between present COB and S1 gives extension through time in the Okinawa trough, with a maximum of ~100 ± 20 km extension since late Miocene (10 Ma). We interpret S1 as a zone of weakness since ~18 Ma that ruptured from Miyako Island to east of Hualien as a tear fault, with the Huatung basin-Philippine Sea plate (HB-PSP) subducting northwestward between the two sides of the tear fault. The Manila transcurrent fault initiated ~18 Ma ago at the onset of the tear and progressively moved eastward, creating the intra-oceanic Luzon arc, which began collision ~7 Ma ago along the EU margin. From ~7 to 6.5 Ma Taiwan was uplifted west of the Longitudinal valley. The Luzon arc and forearc basins were shortened within the Coastal range. Plate kinematic reconstructions from ~18 Ma to Present are synthesized in terms of continental or oceanic nature of the main PSP-HB and EU entities before their subduction that provide new understanding on Taiwan, PSP-SCS kinematics, and regional histories.