Evolution of Meso-Cenozoic subduction zones in the ocean-continent connection zone of the eastern South China Block: Insights from gravity and magnetic anomalies

Abstract The evolution of unified East Asian continental margin was accompanied by large-scale magmatic and tectonic events. Here we investigate the tectonic evolution history of the ocean-continent connection zone in the eastern South China Block (SCB) during the Mesozoic-Cenozoic subduction of the (Paleo-) Pacific plates based on gravity and magnetic methods that provide a window to the deep crustal structure. The decomposed multi-scale gravity wavelets reveal subduction-related intra-crustal structures and the deep structure of the Mesozoic Greater South China Block (GSCB). The depth of Moho discontinuity was inverted by gravity data, constrained by the latest global crustal model of CRUST 1.0, and the inverted depth is closely consistent with and slightly larger than the depth on seismic profiles. The undulation of the Moho discontinuity beneath the South China Block and the deep supra-crustal faults along the continental margin are considered to be associated with the subduction of the (Paleo-) Pacific plates. In general, the Moho depth in the eastern SCB gets shallower from west to east. The oblique subduction-related strike-slip faults can be traced on the 7.4 km-upward continued field of the magnetic anomaly. The geologically-indistinct Jurassic magmatic arc along the SCB continental margin is verified by residual crustal field of the Bouguer gravity anomaly. The southern Ryukyu-Taroko line is speculated as the inland segment of the Early Jurassic paleo-subduction zone, and represents the southeastern paleo-plate boundary of the GSCB in the Jurassic. As the backarc-arc-forearc paleo-system migrated eastwards since the Early Cretaceous, the subduction zone retreated to the current Taiwan-Okinawa Trough, and the Jurassic magmatic arc-forearc was transformed to a backarc, indicating an eastward migration or jumping of the Yanshanian subduction along the continental margin of the SCB. The tectonic boundary of the Mesozoic GSCB was also identified through the magnetic anomaly field and the high-order gravity field.