Tectonic characteristics and extensional-compressional rates of the North-east Sag of South Yellow Sea Basin

Typical seismic sections are selected for delicate structural interpretation upon the basis of structural features of the North-east Sag of the South Yellow Sea Basin. The balanced cross-section technique and the extensional - compressional rates calculation method are used to reconstruct the tectonic evolution cross-sections for different tectonic evolutionary stages. The characteristics of extensional - compressional rates are analyzed. The results suggest that the North-east Sag of the South Yellow Sea basin is characterized by extensional structures, strike slip structures (negative flower patterns), inversion structures etc. by the Yizheng movement in Late Jurassic and the Sanduo movement by the end of Oligocene. Accordingly, the sag was obviously in compressional status during the deposition of Late Jurassic and Oligocene when the Tk40 and T20 unconformity interfaces were formed. In order to quantify the characteristics of the regional stress field, the paper also reconstructed the tectonic evolution of the north-east sag. Taking the two tectonic movements as the boundaries, the sag is subdivided into three stages of tectonic evolution i.e. the initial faulting- depression stage from Late Triassic to Jurassic, the rifting inversion stage from Cretaceous to Oligocene, and the regional subsidence stage from Neogene to Quaternary. The temporal and spatial variations in the extensional - compressional rates and the tectonic evolution of north-east sag in South Yellow Sea basin represent the local response to the regional stress field, such as the change in convergence rate and motion azimuth between the Pacific plate and the Eurasian plate since Late Mesozoic.