湘南江永地区多期褶皱的变形特征及叠加关系

Structural Style and Superposed Relationship of Multi-period Folds in Jiangyong Area,Southern Hunan Province

湘南江永地区处于华夏陆块西北缘,自早古生代以来经历了多期构造变形,关于这些变形的研究对探索湘南地区及其邻区的构造演化过程具有重要意义。通过对江永地区古生界褶皱的构造要素测量和褶皱叠加关系的解析,识别出了3期4个方向的褶皱构造,按发育早晚顺序分别为第一期(D1)NE向褶皱,第二期(D2)NNE-近SN向褶皱、NW向褶皱,第三期(D3)近EW向褶皱。其中D1期NE向褶皱为下古生界独有的构造样式,本区及邻区上古生界仅记录了后2期(D2和D3)3个方向的褶皱作用。结合地层接触关系、岩浆活动及区域构造演化的综合分析,3期褶皱作用分别对应早古生代后期加里东陆内造山运动NW向挤压、中三叠世后期印支运动NWW向挤压以及晚三叠世-早侏罗世近SN向挤压等构造事件。

Jinagyong area is located in the northwest margin of the Cathaysian Block and has undergone multi-stage structural deformations since the Early Paleozoic.Research on these deformations is crucial for a better understanding of the tectonic evolution along and adjacent to southern Hunan.Based on statistical analysis of structural factors and superposed relationship of folds in Paleozoic in Jiangyong area,three phases and four directions of folds are identified in this research,namely the first stage(D1)NE trending folds,the second stage(D2)NNE-SN trending and NW trending folds,and the third stage(D3)EW trending folds.The first stage NE trending folds are of unique structural style of the Lower Paleozoic,while only the last two stages of folding in three directions are recorded in the Upper Paleozoic in Jiangyong area and its adjacent areas.Combining with the stratigraphic contact relationship,magmatic activity and regional tectonic evolution,this paper suggests that the three phases of folding correspond to the NW trending compression of the Caledonian intracontinental orogenic movement in the late Early Paleozoic,the NWW trending compression of the Indosinian movement in the late Middle Triassic and SN trending compression events during the Late Triassic to Early Jurassic,respectively.