湖南常德-安仁NW向断裂左旋走滑与安仁“y”字型构造

五峰仙-铁丝塘断裂属NW向常德-安仁断裂的南东段,为基底隐伏断裂。在安仁县城以西,于断裂北侧发育NNW向印支期褶皱;安仁县城以东,于断裂南、北两侧均发育NNE向褶皱,从而组成“y”字型不协调构造。研究认为,“y”字型构造形成机制为:五峰仙-铁丝塘断裂在印支运动中具基底左旋走滑性质,走滑所派生的近东西向挤压应力场,及走滑所产生的牵引作用,使安仁以西NNE向构造线产生逆时针旋转,从而形成NNW向褶皱。安仁以东由于紧邻NNE向茶陵-郴州主俯冲汇聚断裂,NW向断裂走滑量相对较小,派生应力与牵引效应小,而区域NWW向挤压应力大,从而于断裂两侧均形成与区域构造线一致的NNE向褶皱。NW向断裂的左旋走滑使断裂北东面成为隆起区,而断裂南东面则成为拗陷区。对区域构造发展背景分析后认为,印支期可能为湘东NW向断裂中生代活动最强烈的时期,多条NW向断裂的左旋走滑,可能与雪峰山弧形构造和祁阳“山”字型构造的形成有关。

"Y" -TYPE STRUCTURE IN ANREN COUNTY, HUNAN, AND THE SINISTRAL STRIKE- SLIP OF CHANGDE- ANREN NW - TRENDING FAULT

Wufengxian-Tiesitang fault is the southeastern range of Changde-Anren NW-trending fault, and a basement hidden fault. On the west of Anren county seat, the NNW-trending folds occur on the north part of the fault; On the east part of the Anren county seat, the NNW-trending folds occur on both the north and south parts of the fault, thus the "y"-type structure was resulted. In the study, the authors considered the formation mechanism of the "y"-type structure as follows: the EW-trending compression stress field was derived from the sinistral strike-slip of Wufengxian-Tiesitang fault in Indosinian orogeny and the traction of the sinistral strike-slip made the NNE-trending structural lineament produce sinistral torsion in the west part of the Anren county seat, thus the NNW-trending folds were resulted. Because the area on the east part of the Anren county seat is near the regional primary subduction-fault, namely the NNE-trending Chaling-Chenzhou fault, the Wufengxian-Tiesitang NW-trending fault had little strike-slip measure, so the derivative stress and traction were smaller, and at the same time the regional NWW-trending principal stress was stronger, which produced NNW-trending folds. The sinistral strike-slip of Changde-Anren NW-trending fault resulted in the upwarping region on the northeast part of the fault, and the downwarping region on the southwest part. On the basis of analysis of the regional tectonic setting, the authors proposed that the Indosinian was in all probability the period of strongest movement of NW-trending faults in east Hunan in Mesozoic, and the sinistral strike-slip of NW-trending faults in Indosinian is probably one of the formation mechanisms of the Xuefengshan arc structure and the Qiyang arc structure.