The geometry and kinematics of the intersection area of eastern Sichuan and the Dabashan fold-thrust belt

The intersection area of eastern Sichuan and the Dabashan fold-thrust belt is located in the northeastern Sichuan Basin and is composed of the Wenquanjing-Macaoba anticline belt, the Yunanchang anticline belt and the Fangdoushan anticline belt. The formation and evolution of the intersection area is controlled by the eastern Sichuan structural belt and the Dabashan structural belt. Therefore, this study is relevant for understanding the collision between the South China plate and the North China plate and its subsequent evolution. Based on field investigations, drilling data, logging curves and 2D seismic data, guided by fault related folding theory, this paper reveals the geometric features of the intersection area with four seismic profiles which were precisely interpreted to reconstruct the tectonic kinematics process of the study area by using 2D move software. This paper concludes that: (1) the intersection area shows a giant synclinorium structure in the south-north direction and can be divided into three vertical structural layers by three detachment layers; the gypsum-salt bed of Lower Triassic Jialingjiang formation, the mudstone and shale of the Silurian, and the mudstone and shale of the Lower Cambrian. The upper structural layer mainly occurs as decollement, whereas there are many faults in the middle and lower structural layers where duplex structures, pop-up structures and fault-bend folds developed. (2) In the study area, the deformation of the middle structural layer is the strongest, with a structural shortening rate of 10%; the shortening rates of about 6% in the upper and lower structural layers are relatively small. Also, the shortening rate of each structural layer gradually increases from west to east. (3) Since the Mesozoic, the evolution of the study area has been divided into three stages: stable sedimentary stage from the late Triassic to the late Jurassic, opposite thrusting stage from the early Cretaceous to the early Paleogene, and the shaping stage from the late Paleogene to the present. © 2020, Science Press. All right reserved.