南大巴山冲断褶皱带区域构造大剖面的构建和结构分析

大巴山冲断带的结构复杂,在平面上城口-房县断裂将其分为北、南大巴山冲断褶皱带,北大巴山被认为是南秦岭造山带和扬子地块之间的拼合带,南大巴山代表了典型的前陆冲断褶皱带的特点。本文主要针对南大巴山冲断带进行构造解析。研究指出,南大巴山冲断带剖面上具有多层次和多期次滑脱变形的特点:浅层次的滑脱面为下三叠统嘉陵江组灰岩中的石膏层,卷入的层序为其后的中生界;深层次滑脱体系为沿着震旦系页岩和嘉陵江组膏盐层两个滑动面之间活动形成的冲断变形。完成了切过南大巴山不同构造部位的3条多资料约束的综合地质剖面,以此详细解析了冲断带深浅层次的冲断结构及分布规律,在平衡恢复的基础上,分析了该冲断带的几何结构和运动过程,确定了大巴山和川东两个不同构造单元的空间对接关系,提出南大巴山冲断带为一多层次、空间上强烈收缩的复杂薄皮冲断体系。

Construction and structural analysis of regional geological sections of the southern Daba Shan thrust-fold belts.

The Daba Shan thrust belt has very complex structures, and could be divided into two parts by the Chengkou-Fangxian fault. The north part (North Daba Shan) is regarded as the conjunction between the South Qinling Orogen and the Upper Yangtze block, while the south part (the South Daba Shan) is a typical thrust-fold belt. In this paper, we focus on the structures of the South Daba Shan thrust-fold belt. The result indicates that it has multi-level and multi-stages deformation. The upper system is controlled by detachment along the gypsum layers in the limestone of the lower Triassic Jialingjiang Formation, and nearly all the Mesozoic strata are involved into the deformation. While the lower system is confined between two detachment surfaces: The gypsum layers in the lower Triassic Jialingjiang Formation and the shale in the Sinian. We accomplish three comprehensive regional geological sections, as well as their balance restoration sections, across the South Daba Shan based on geophysical data and field investigation. According to them, we study in detail the structure and distribution of the upper and the lower thrust systems, their geometric and kinematic characteristics, and the spatial relationship between the Daba Shan and the Chuandong thrust-fold belts. We conclude that the South Daba Shan thrust belt is a complex multi-level thin-skinned thrust system with strong deformation and shortening.