Evolution of structural characteristics with multistage stress fields in the Sikeshu Sag, Junggar Basin

Objective The Sikeshu Sag of the southern Junggar Basin is tectonically located in the western thrust belt of the North Tianshan Mountains. The basin has undergone multiple stages and multidirectional tectonic movements since the Palaeozoic. Clarifying the structural characteristics and evolutionary process of the structural system in the study area is critical for petroleum exploration and development in such petroliferous basins. Methods Utilizing the seismic data interpretation and the outcrop geological investigation of the Sikeshu Sag, spatial-temporal variations in the structural patterns and stress fields were revealed, and a tectonic evolution model was established. Results This study indicates that the compressional inversion and strike-slip structures were widely developed in the deep-buried layers of the Sikeshu Sag, but the thrust and decollement structures were more prevail in the shallow layers of the Sikeshu Sag. According to the structural style, the Sikeshu Sag can be divided into the southern compressional fault-fold belt, central strike-slip compressive-torsional belt, and northern uplift belt. The Sikeshu Sag experienced two periods of strong tectonic uplift, corresponding to the peak period of two stages of fault activity. The tectonic environment and stress field conditions underwent multiple changes: the NNW-SSE extension driven by the back-arc rifting during the late Carboniferous to early-middle Permian, the rift-depression transition triggered by the NNW-SSE extrusion of the Zaire orogenic movement during the late Permian to Triassic, the regional depression induced by the NNW-SSE extrusion of the peripheral orogenic belt and Chepaizi uplift during the late Jurassic to Palaeogene, and the reactivation of foreland caused by NS extrusion of North Tianshan Mountains during the Neogene. Conclusion This study explores the tectonic evolution of the Sikeshu Sag under multiphase stress fields, which favors the better understanding of the overall tectonic pattern changes in similar petroliferous basins and provides new insights for the next steps of petroleum exploration in the study area.