湖南桑植—石门复向斜走廊剖面构造特征分析

STRUCTURAL CHARACTERISTICS OF THE CORRIDOR SECTION IN SANGZHI-SHIMEN SYNCLINORE

为了查明桑植—石门复向斜的地表、地下构造特征及其相互间的关系,采取了详细的地表走廊剖面的测量,以及结合地震勘探资料和大地电磁测深(MT)资料的综合解释。桑植—石门复向斜可进一步划分为四个次一级的构造带,从北向南依此是:堰塘湾构造带、四望山构造带、江垭构造带及教子垭构造带。江垭构造带和教子垭构造带的地面构造特征与地下构造特征具有一致性,基本上为构造简单的北倾斜坡;而四望山构造带的地面构造特征与地下构造特征存在着明显的不协调性。这种变形特征可解释为沿盖层间滑脱面的逆冲,以及断弯背斜的形成,上覆构造层中的褶皱向下消失在滑脱面上,形成所谓的“无根褶皱”。

A ground geological survey and an interpretation on synthesis of seismic data and MT data for the corridor section of the Sangzhi-Shimen synclinore are used to study the properties of both the ground structure and the underground structure of the Sangzhi-Shimen synclinore as well as the relationship between them. The Sangzhi-Shimen synclinore can be divided into four para-tectonic belts. From north to south, they are Yantangwan tectonic belt, Siwangshan tectonic belt, Jiangya tectonic belt and Jiaoziya tectonic belt. Based on the comprehensive analysis of MT profile data and seismic data for the Jiaoziya structure belt and Jiangya structure belt, it is found that the ground tectonic shape is essentially according to that of the underground structure. However, in the Siwangshan structure belt, the ground structure is not according to the underground structure. Through analysis of the slip surface and tectonic pattern, the discordances of the ground structure and the underground one can be accountered for by the thrust of the decollement and the formation of fault-curve anticline. This kind of fold resulted from the covering tectonic layers disappears in the decollement surface, which leads to the formation of the non-rooted folds.