Opposite thrust systems under the Subei-South Yellow Sea Basin: A synthesis on the closure of the eastern Tethyan Ocean

Abstract

Early Mesozoic geodynamic and tectonic relations between different blocks in East China remain controversial. The Subei-South Yellow Sea Basin (SB-SYSB) is located at the junction of different blocks and tectonic zones, including the North China Block (NCB), South China Block (SCB), Sulu Orogen and Tan-Lu Fault Zone (TLFZ). Therefore, the basin is a key location for understanding the regional geologic evolution of East China. Here, we present the geometry and kinematics of opposite thrust systems (OTSs) under the SB-SYSB based on seismic profiles, well data, magnetic reversion data and field observations. The OTSs are composed of two sets of thrust systems with opposite senses of motion: the northern top-to-the-southeast thrust system (N-TS) and southern top-to-the-northwest thrust system (S-TS). According to the structural styles, the N-TS and S-TS can be divided into the root, middle and frontal belts. The strikes of thrusts show a shift from NNE to NE- ENE and then to nearly E-W from west to east. The OTSs were suggested to have formed during the end of the middle Triassic to the middle Jurassic, and its deformation intensity decreased from west to east and from the root belt to the frontal belt. Combining these lines of evidence with published geochronological data for the Dabie-Sulu Orogen and other structural elements in East China, we provide a comprehensive synthesis and propose a new tectonic model to explain the early Mesozoic geodynamic and tectonic relations in East China. We emphasize the following points: (1) The Sulu Orogen might extend to the Northern Depression in the offshore SYSB and be bounded by the North Fault of the Central Massif to the south, indicating that the Sulu Orogen is significantly wider than stated in previous studies. (2) The N-TS was driven by the subduction of the YZB and the exhumation of the Sulu HP–UHP metamorphic rocks. In contrast, the S-TS was probably controlled by the orogenic uplift of the Jiangnan Orogen. (3) The dragging of the thrusts in the SB-SYSB and adjacent areas indicates that the sinistral motion of the TLFZ was coeval with the formation of the OTSs and was likely caused by the clockwise rotation of the SCB. (4) Finally, this clockwise rotation probably triggered intense corner compression between the Sulu Orogen, TLFZ and East Marginal Fault of the Yellow Sea, resulting in a genetic relation among the Sulu Orogen, the SCB, the Korean Peninsula and the Xu-Huai Belt.