雪峰山中段古生代变形的特征及意义——以绥宁-靖州-天柱-新晃剖面为例

对雪峰山中段绥宁-靖州(会同)-天柱-新晃剖面的研究表明,雪峰山中段的变形自东向西减弱,由东部的向西倒转紧闭褶皱过渡到西部的开阔褶皱。东部(绥宁-靖州段)卷入褶皱的为南华系和震旦系—下古生界,褶皱样式表明东部在南华系与板溪群之间存在一区域性的滑脱面,本段缩短11km。剖面西段(靖州(会同)-天柱-新晃段)卷入变形的为板溪群、南华系和震旦系—下古生界,主要滑脱面位于板溪群下部或冷家溪群与板溪群之间,该段缩短46km。东西2段之间的界线是早期控制板溪群和南华系沉积的正断层。研究得出的缩短量为最小值,与前人的研究结果一致,表明古生代雪峰山逆冲推覆距离不大。雪峰山中段石炭系与南华系之间的超覆不整合、靖州盆地的构造属性和雪峰山剖面的变形特征显示,雪峰山中段的变形发生在早古生代。雪峰山早古生代变形是早期裂谷的反转,属薄皮构造。

Paleozoic deformational characteristics of the central Xuefeng Mt.and impli-cation-A case study on the Suining-Jingzhou-Tianzhu-Xinhuang section,China

The Suining-Jingzhou (Huitong)-Tianzhu-Xinhuang section of the central Mt.Xuefeng shows that the deformation of the central Mt.Xuefeng gets weaker from the east to the west, i.e. from the west-vergencing tight folds in the east to the open folds in the west. The deformation has affected the Nanhuan System and Sinian System-Lower Paleozoic strata in the eastern section (Suining-Jingzhou), and the style of folds indicates that there is a regional decollement between the Nanhuan System and the Banxi Group in the east. The shortening of the eastern section is about 11km. The deformation has affected the Banxi Group, Nanhua System and Lower Paleozoic strata in the western section (Jingzhou-Tianzhu-Xinhuang), the regional decollement mainly occurred in the lower part of the Banxi Group or between the Banxi Group and Lengjiaxi Group. The shortening of the western section is about 46km. The boundary between the western and the eastern sections is the normal fault controlling the early depositing of the Banxi Group and the Nanhuan System. This study has obtained the minimum shortening distance across the central Mt.Xuefeng, which is similar to previous data. This means that no large scale thrusting had ever occurred in the Mt.Xuefeng during the Paleozoic.The facts of the overlap unconformity between the Carboniferous and penetratively deformed Nanhuan Systems in the central Mt.Xuefeng, the tectonic attribute of the Jingzhou basin, and deformational style along the section indicated that the deformation of the Proterozoic and Lower Paleozoic strata in the central Mt.Xuefeng took place in Early Paleozoic. The Paleozoic deformation in the Mt.Xuefeng was the result of the inversion of the early rift, which belongs to thin-skinned structure.