斜向逆冲断层相关褶皱的正演模型与实例分析  

Forward Modeling of Oblique-thrust Fault-Related-Folds and Instances Analysis

作　　者：张猛[1] 贾东[1] 王毛毛[1] 李志刚[1] 李一泉[1] 

机构地区：[1]南京大学地球科学与工程学院,南京210046

出　　处：《地质论评》2013年第6期1207-1217,共11页Geological Review

基　　金：国家科技重大专项(编号2011ZX05003-002;2011ZX05009-001);国家自然科学基金资助项目(编号41202145)的成果

摘　　要：斜向逆冲作用在自然界普遍存在,研究斜向逆冲断层相关褶皱的构造几何学特征,识别断层相关褶皱是否存在斜向逆冲有重要意义。文章采用Trishear 4.5、Gocad以及Trishear3D软件构建一系列不同滑移量的断层转折褶皱和断层传播褶皱的二维正演剖面,通过连接一系列不同排列方式的二维剖面建立了三种不同逆冲滑移方向的断层转折褶皱和断层传播褶皱的假三维模型,通过不同假三维模型的比较分析来探讨斜向逆冲断层相关褶皱的构造几何学特征。研究发现,斜向逆冲断层相关褶皱区别于正向逆冲断层相关褶皱的特征主要有两点:①正向逆冲断层相关褶皱层面等高线图上的最高点与后翼等高线中点的连线以及水平切面上的核心点与后翼中点的连线方向均与断层走向垂直,而斜向逆冲断层相关褶皱的最高点以及核心点与后翼中点的连线方向均与断层走向斜交,并且最高点与后翼等高线中点的连线方向或者核心点与后翼中点的连线方向均与逆冲滑移方向一致;②在褶皱平行断层走向纵剖面上,正向逆冲断层相关褶皱各个层面最高点的连线是直立的,而斜向逆冲断层相关褶皱各个层面最高点的连线发生倾斜。通过这两个特征可以判别褶皱是否存在斜向逆冲以及逆冲的方向。将模型分析结果运用到四川盆地西南部三维地震勘探资料所覆盖的邛西背斜和大兴西背斜的实例中。研究结果表明,两个背斜均存在右旋斜向逆冲,逆冲方向与各自断层走向的夹角均为70°左右,邛西背斜和大兴西背斜的逆冲方向分别是NE79°和NE77°左右,这与龙门山南段晚上新世以来的主应力方向以及反演的汶川地震最大主应力方向一致。Oblique thrusting is widespread in nature and it is important to analyze the structural geometry of oblique-thrust fault-related-fold and identify whether oblique thrusting exists or not. The pseudo-3D models of fault- bend-fold and fault-propagation-fold with different slip directions are constructed by linking a series of 2D forward cross-sections which are built by Trishear4.5, Gocad and Trishear3D programs to discuss the structural geometry of oblique-thrust fault-related-folds. The results indicate that there are two main distinctions between oblique-thrust fault-related-folds and dip-thrust fauh-related-folds. One distinction is that the line linking peak point and midpoint of back limb in the contour map or the line linking core point and midpoint of back limb in the horizontal slice of dip-thrust fault-related-folds is perpendicular to fault strike while the similar line is not perpendicular to fault strike in oblique-thrust fault-related-folds and the line is parallel to slip vector. The other distinction is that the line connecting every peak point of all bedding planes on the cross-sections parallel to fault strike is vertical in dip-thrust fault-related-folds while the line would be oblique to horizontal plane if oblique thrusting exists. The two distinctions can be used to identify whether oblique thrusting exists or not and estimate the slip directions of fault-related-folds. Qiongxi and Daxingxi anticline covered by 3D seismic data in the southwest of Sichuan basin are chosen as two examples for the research. This research indicates that oblique thrusting exists in two anticlines and the intersection angles between slip direction and fault strike are both about 70°. The slip vectors of Qiongxi anticline and Daxingxi anticline are about NE79°and NE77°respectively, which is consistent with the stress field of Longmen Shan since the late Pliocene and the most compressive stress direction inferred from coseismic slip of the Wenchuan earthquake.

关 键 词：斜向逆冲断层相关褶皱 假三维模型 构造几何学 邛西背斜 大兴西背斜 

分 类 号：P542.2[天文地球—构造地质学]