Geodynamic and kinematic model of the South China Sea and regional plates since the end of seafloor spreading

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 whole northern SCS continent-ocean boundary (COB) that consists of a northeastern SCS COB segment (called ‘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.We demonstrated that the two-plate kinematic model is the best framework to explain the existing data. The boundary between Eurasia and Philippine Sea plate is a ~NS oriented left-lateral lithospheric shear fault called the Manila transcurrent fault (MTF). The MTF initiated ~18 Ma at the onset of the tear and progressively moved eastward, creating the intra-oceanic Luzon arc. The MTF ancestor was a N337° oriented left-lateral shear fault, while the HB-PSP/EU motion was changing to N307°, allowing the HB-PSP plate to subduct between the two lips of a westward propagating tear fault until ~7 Ma. Since ~7 Ma, the MTF-PFZ constantly moved westward and 23° clockwise rotated from N337° to ~NS, which began collision ~7 Ma ago along the EU margin. 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. This work is supported by Key projects of the Chinese National Natural Science Foundation (contracts 91958212, 42106078).