龙门山南段大邑地区断裂带活动多期性研究

Study on the multi-phased fault activity in Dayi area,Longmenshan region,Sichuan province

四川省大邑地区地处龙门山南段,是有名的地震多发地区。文章基于现代构造地质学理论,通过地震解释及构造几何分析、断层相关褶皱原理与几何分析方法、运动学正演模拟方法,开展了对大邑地区断裂带活动多期性研究,结果表明大邑地区断裂带活动具有多期性的特点。自印支期以来主要经历了两期三次构造活动:印支晚期的低角度逆冲推覆过程,须家河组四段(T3x4)中上部形成生长地层;喜马拉雅期Ⅰ幕,隐伏断层再次活动,造成侏罗系与下伏三叠系的变形差异;喜马拉雅期Ⅱ幕,龙门山构造带区域应力场向前传递,大邑地区形成高角度逆冲断层,断层沿深部滑脱层在大邑地区向上逆冲直至地表,早期隐伏断层被错断,伴随次级断层、反冲断层产生。

The south Longmenshan area of Dayi region in Sichuan province is well known for its multiple seimic activities.Based on the modern geotectonic theories,seismic interpretation and structural geometry analysis,principle of folding related to fault and the geometric analysis method and kinematic forward modeling method is studied the multi-phased activities of the fault belts in Dayi area.The result is that Dayi area since indo-chinese epoch has been exposed to three stages of tectonic movements:1)the late indosinian low angle thrust nappe process during which the growth strata in upper Xujiahe formation(T3x4)formed;2)episode HimalayanⅠduring which buried faults reactivated and differential deformation between Jurassic strata and the underlying Triassic strata occurred;3)episode Himalayan Ⅱ during which stress field of the Longmenshan tectonic belt was transmitted forward with high angle thrust fault occurring along deep detached layer and thrusting to surface in Dayi area where the early buried faults are displaced and sub-faults and recoil fault formed.