四川盆地北部前陆构造叠加区正断层成因机制

Genetic mechanisms of normal faults in the superimposed structural zone in the foreland area of the northern Sichuan Basin

苏楠 陈竹新 翟咏荷 潘颖 王丽宁 任荣 张宇轩 谢武仁 武赛军

Nan SU Zhuxin CHEN Yonghe ZHAI Ying PAN Lining WANG Rong REN Yuxuan ZHANG Wuren XIE Saijun WU

四川盆地北部侏罗系广泛发育正断层，但其在持续前陆盆地挤压背景下的成因机制尚不明确。通过不同构造位置三维地震断裂详细刻画和对比分析，研究了挤压背景下侏罗系正断层形成的主控因素、形成机制和多期叠加地质过程。研究表明：① 四川盆地北部侏罗系正断层是地层隆起过程中岩层弯曲拉张时张应变的结果，在平面上具有均匀分散的分布特征。形成了大量两条或多条对倾的小断距、短延伸正断层组成的地堑结构。② 其发育的方向和数量受到周缘冲断带挤压方向和构造期次的控制，在各期次均发育与挤压方向垂直的正断层。③ 盆地内正断层是龙门山-米仓山-大巴山陆内造山运动的响应。前缘隆起过程中地层褶皱控制了断层发育，构造叠加区多期次、多方向构造活动导致形成复杂正断层组合。④ 正断层不是挤压应力场的直接结果，而是挤压背景下隆起变形的伴生构造。

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.

10.11743/ogg20250210