Present-Day Crustal Movement and Focal Mechanism Solutions, and Plate Interaction Since Late-Miocene in the Eastern South China Sea

The plate convergent belt in the eastern South China Sea (SCS) is an important window for studying the tectonic evolution of the SCS and the Philippine Sea (PhS) since late-Miocene. We studied the plate interactions of this area since the late-Miocene based on block kinematics, morphology of the subducted SCS slab and focal mechanism solutions (FMS). At the late stage of the late-Miocene, the westward motion of the PhS plate was first impeded by its collision with the Palawan micro continental plate in the south, and then by the collision of the Luzon arc with the South China continental margin in the north. Consequently, the middle part between the two collision zones became a passage where westward movement of the PhS plate continued relatively smoothly. Because of these two impediments, the rate of westward motion increased northwards to its maximum in the northern Luzon and then decreased northwards, leading to the westward migration of the Manila trench. The subducted SCS slab, however, did not roll back accordingly due to the SE-directed mantle flow. As a result, the subducted slab suffered strong push and slightly reverse bending of the subducted slab occurred in the contact face between PhS and SCS lithosphere. According to this model, morphology of the Manila trench was shaped by the differential westward motion rates from south to north of the northern Luzon, and the width of the subducted slab played little role. Furthermore, the double arc in the north Luzon arc was also induced by a differential westward moving velocity along the arc. A shear zone whose location coincides with the east arc might have facilitated its formation.