Abstract:

Normal faults are widely distributed throughout the Jurassic strata in the northern Sichuan Basin. However， their genetic mechanisms are yet to be clarified under the continuous compression from foreland basins. A detailed characterization and comparative analysis of faults at various structural locations is conducted using 3D seismic data， and the major controlling factors， genetic mechanisms， and multi-phase structural superimposition process of the Jurassic normal faults are investigated under a compressional tectonic setting. The results indicate that the Jurassic normal faults in the northern Sichuan Basin are a product of tensile strain caused by the folding and bending of strata during uplift. These faults exhibit a uniform and scattered planar distribution， forming numerous graben structures consisting of two or more normal faults with small throws and short displacements that dip in opposite directions. The strikes and numbers of these faults are controlled by the compressional directions and structural phases of surrounding thrust belts， with normal faults perpendicular to the compressional directions formed in each structural phase. The Jurassic normal faults within the northern Sichuan Basin are formed in response to the intracontinental orogeny of the Longmenshan， Micangshan， and Dabashan mountains. Stratum folding and bending formed during the formation of front uplift lead to the development of these faults， with multi-phase， multi-directional tectonic activities in the superimposed structural zone resulting in the formation of complex normal fault assemblages. The Jurassic normal faults in the northern Sichuan Basin are associated structures formed during uplift and deformation in a compressional tectonic setting rather than resulting directly from compressional stress fields.

Key words: tensile strain, genetic mechanism, normal fault, superimposed structure, foreland basin, Sichuan Basin