川西安县构造的变形特征及演化

安县构造由于山地条件和地质结构复杂等原因,地震资料品质较差,构造存在多解性。前人多采用基底卷入的前展式逆冲叠瓦构造模型进行解释;结合露头与钻井资料分析认为逆冲三角带的构造模型更加科学、合理。安县构造自北西向南东可分为3个构造带:北川-映秀断层至安县-灌县断层之间的叠瓦构造带、安县-灌县断层下盘的山前隐伏带和坳陷内部弱变形带。山前隐伏带以发育逆冲三角带构造为特征,垂向上具有分层变形特征,自上而下可分为4个体系,即侏罗系、中-下三叠统外来推覆体、中-下三叠统滑脱层之上的须家河组1、2、3段和中-下三叠统滑脱层之下的古生界。安县构造在晚三叠世以安县-灌县断层活动为代表,逆冲推覆强烈并有较大的水平收缩变形量;晚侏罗世至新生代水平收缩变形量相对小而基底隆升明显,白垩纪末构造已基本形成,新生代构造继承发展。

Structural Deformation of Anxian Structure and Structural Evolution in Western Sichuan Area

The varied topography and complex structure of Anxian Structure caused the poor resolution of seismic data,where structure was multi-explained.Basement-involved insequence imbricate structural model were adopted by predecessors for interpretation.Based on the analysis of outcrops and drilling data,it was considered that the thrust triangle zone structure was more reasonable.Anxian Structure could be divided into three structural belts from the northwest to southeast,namely the imbricate structural belt was located between Beichuan-Yingxiu Fault to Anxian-Guanxian Fault,foreland concealed belt was located in the footwall burial belt of Anxian-Guanxian Fault and weak deformation depression belt.Foreland concealed belt had the feature of triangle zone.And four structural layers could be divided,namely Jurassic,lower-middle triassic thrust nappe,Member 1-2-3 of Xujiahe Formation and Mid-lower member of Palaeozoic System.Anxian Structure develops Anxian-Guanxian Fault and thrust nappe in late Triassic and horizontal contraction was large.From late Jurassic to Cenozoic,horizontal contraction is small,while uplift of basement is obvious.At the end of Cretaceous Anxian Structure is basically formed,and structure is successively developed in Cenozoic.