安徽宿松地区河塌乡构造窗的厘定及成因探讨

Determination and Genesis of the Tectonic Window at Heta, Susong, Anhui

河塌乡拗陷区域上呈拉长"卵形",走向北东。拗陷内中二叠统孤峰组与外围志留系-泥盆系岩石呈断层接触关系,其构造属性一直存在较大争议。野外调查发现,拗陷南、北两条边界断层的几何学、运动学特征基本一致,为同一条低角度逆冲断层,走向北东,倾向北西,是研究区内逆冲推覆构造的主滑脱面。滑脱面上盘发育一系列相互平行的线状褶皱和叠瓦状逆冲断裂带,呈北东向展布;滑脱面下盘构造变形特征表现为北东向褶皱构造被北西西向褶皱构造叠加、改造。上、下两盘岩石构造变形特征迥异,形成机理不同,具有自己独立的构造演化历史。此外,在拗陷西南侧周家屋一带还发现有飞来峰构造。据此厘定河塌乡拗陷为推覆型构造窗,拗陷内孤峰组为原地系统,外围志留系-泥盆系为外来推覆岩片,构造演化开始于印支期初,定位于燕山期末,推覆岩片的根带位于河塌乡北侧吴正湾一带,长岭村北是推覆构造的前峰带。

The Heta depression is located in the Zhimaling-Hengshan area,southwest of Heta Country,Susong,Anhui.It exhibits a NE-trending elongated oval.The Middle Permian Gufeng Formation with the Silurian-Devonian is fault contact in the depression.There has been controversy on its tectonic property.The study indicates that the geometrical and kinematic characteristics of the boundary<javascript:showjdsw('showlj_1','lj_1')>faults(F3 and F4)are basically the same.They are the same one low angle thrust,showing the NE-trending veins with NW-dip and being the major detachment surface of the thrust nappe structure.The Silurian and Devonian in the hanging wall of the detachment surface is mainly affected by NW-SE direction tectonic stress field(σ1:150°-160°∠5°-10°).A series of parallel folds and stacking thrust faults are developed.Structure traces to the NE;The Gufeng Formation in the footwall of the detachment surface was influenced by the NW-SE(σ1:331°∠2°)and NNE-SSW(σ1:12°∠11°)tectonic stress field.The tectonic deformation is characterized by NE fold structure and superimposed and modified by the NWW fold structure.The rocks in the hanging wall and footwall have the different tectonic deformation characteristics and forming mechanism as well as independent structural evolution history,does not belong to the same tectonic system.In addition,a klippe structure is exposed in Zhoujiawu on the southwest side of the depression.Accordingly,the Heta depression is a nappe type tectonic window.The Gufeng Formation within the depression is autochthonous system,the peripheral Silurian-Devonian is an externally nappe silver exotics system).It is considered that the nappe structure<http://dict.youdao.com/w/nappe structure/>began at early Indo-Chinese epoch,located at the end of Yanshanian,rand the root zone of nappe silver was located in the Wuzhengwan area,north Heta.The north of Changling Village is the pre-tectonic belt.