湘中盆地龙山穹窿构造样式及其成因机制

The structural style and genetics mechanism of the Longshan dome in Xiangzhong basin, Xuefengshan orogenic belt

本文选取湘中盆地龙山穹窿体为研究对象,主要沿二条近正交剖面开展了详细的野外地质调查、构造解析工作。系统地对龙山穹窿体进行了地层产状、轴面劈理产状、逆冲断层及其擦痕线理进行了测量和统计。根据褶皱样式与轴面劈理的配套关系,并结合卷入叠加变形的地层,以及轴面劈理的错切关系综合分析,确定NE-SW向褶皱叠加在近WNW-ESE向(近EW向)褶皱之上,确定叠加干涉样式属于Ramsay分类中典型的穹盆叠加样式。在区域地质关系与演化对比基础上,确定龙山穹窿是加里东期和燕山期褶皱复合叠加变形的结果;依据剖面构造分析及前人研究成果,确定泥盆系与前泥盆系间的区域性角度不整合和南华系与基底间拆离断层为两套区域性潜在滑脱层,并认为滑脱层在龙山穹隆体形成和发育过程中具有控制作用。通过对二期古构造应力场的恢复,重建了区域构造演化,建立了龙山穹窿体由拆离断层及软弱层控制的褶皱叠加构造模型。龙山穹窿体的褶皱叠加过程在华南大陆,特别是雪峰山造山带构造演化中具有代表性,表明加里东运动和燕山运动的叠加和复合是雪峰山造山带的重要构造表现形式,这为深入研究雪峰山造山带结构与演化提供了依据。

This study selected the Longshan dome in Xiangzhong basin, Xuefengshan orogenic belt as an objective to perform detailed field geological survey and structural analysis for two near crosscutting sections. Measurement and statistics were carred out on stratigraphic attitude, axial plane cleavage, thrust fault and its related striation, and paleo-structural stress of the Longshan dome. Based on the relationship between fold style and axial plane cleavage, along with the stratum analysis, the study determined that NE-SW-tending fold superimposes on near EW-trending fold, forming the dome-shaped superimposed style defined by Ramsay classification. Relation of the regional geology and evolution determined in this study that the Longshan dome was the product of superimposed Caledonian and Yanshanian fold combination. According to section structure analysis and previous results, it can be determined that the regional angular conformity beween Devonian and pre-Devonian basins and detachment fault between Nanhua System and basement are two sets of regional potential detachment layer, which has controlling effect on the formation and development of the Longshan dome. Restoration of the two ancient tectonic stress fields reconstructed the evolution of regional structure and the superimposed fold tectonic model controlled by detachment fault and strata in the Longshan dome was also established. Fold superimposed precess of the Longshan dome is of typical representative in South China block, especially in the tectonic evolution of Xuefengshan orogenic belt, indicating that superimposition and recombination of Caledonian movement and Yanshanian movement is an important pattern of the Xuefengshan orogenic belt. This study provides solid ground for understanding structure and evolution of the Xuefengshan orogenic belt.