STRUCTURAL CHARACTERISTICS AND EVOLUTION PROCESSES OF INTRACRATONIC STRIKE-SLIP FAULTS: A CASE FROM THE GAOSHITI-MOXI AREA, CENTRAL SICHUAN BASIN, SW CHINA

Geologists have realized that the development of intracratonic strike-slip faults plays important control on the hydrocarbon migration and accumulation. In this research, a case from the Gaoshiti-Moxi area in the central Sichuan basin was analyzed to understand the structural evolution of intracratonic strike-slip faults. Firstly, the faults’ geometry was characterized based on 3D seismic sections and coherent attribute slices of key horizons. The displacements of the primary faults at different depths were also quantified to understand the spatial variation of fault throws. The shearing direction of strike-slip faults was then decided according to both the faults’ alignment and horizontal offsets’ distribution in plan view. Subsequently, multi-phased structural evolution models were proposed. In section view, subvertical faults and negative flower structures were interpreted beneath the Triassic strata, whereas reverse faults and positive flower structures were interpreted within the Triassic strata. In plan view, the faults developed in the Lower Cambrian and Upper Permian are characterized with nearly W-E trending faults comprised of a series of soft-linked faults with small offsets. In contrast, the faults developed in the Upper Triassic present en-echelon patterns trending NWW. Three stages of faulting deformation in the Gaoshiti-Moxi area were identified by considering both the statistics of fault offsets and pre-existing regional structural belts in basements. (1) The initial stage from Late Sinian to Early Cambrian was dominated by the NEE trending tensional stress, resulting in the development of dextral transtensional faults. (2) The later stage of Late Permian was dominated by the NNW trending tensional stress, with sinistral transtensional faults developed in the Permian strata. However, the faulting intensity in Late Permian is obviously was decreased compared to the initial faulting stage. (3) In the Late Triassic stage, being controlled by the NW trending contraction due to the uplift of the Longmenshan Mountain, en-echelon transpressional faults with small offsets were developed in the Triassic strata. The structural models proposed in this study may improve understanding in the multi-staged structural evolution of the intracratonic strike-slip fault systems.