New insights into the structure of the Yinggehai Basin and its tectonic implications, South China Sea: Evidence from scaled physical models

The Yinggehai Basin is situated at the junction of Indochina and the northern South China Sea (SCS). The origin of the Yinggehai Basin is generally believed to be controlled by the rotation of the Indochina block along the Red River shear zone (RRSZ), which was formed by the collision of India with Asia during the Oligocene. However, the Eocene structural mechanisms of this basin remain debatable. Some studies suggest that the Eocene reactivation of the palaeo-suture zone (which serves as a precursor to the RRSZ) has influenced the region. In contrast, others propose that the NNW–SSE extension of the northern SCS caused by the subduction of the palaeo-SCS towards Borneo in the Eocene has played a significant role. To address these controversies, our study takes into account these two crucial factors using physical analogue modelling. The experimental results, including slow sinistral strike-slip along the palaeo-suture zone and the adjacent NNW–SSE extension, successfully explain the observed fault pattern during the Eocene period. It is noteworthy that the former primarily controlled the Eocene structure in the northern region of the Yinggehai Basin, whereas the latter played a pivotal role in shaping the ENE–WSW Eocene structures on the eastern slope of the basin. The westward propagating faults of the Qiongdongnan basin are cut off by the Yinggehai Basin structures at later large-scale rotation stage. The experiment indicates that the basin evolution exhibits diachronous characteristics, with subsidence in the south occurring later than in the north. Our modelling results provide valuable insights into the key controlling factors that shaped the evolution of the basin during each stage. Furthermore, our findings offer evidence of the interaction between two significant tectonic processes: Indochina extrusion and the opening of the SCS.