湘东南印支运动变形特征研究

Study on the Deformation of Indosinian Movement in Southeastern Hunan

关于华南中三叠世晚期印支运动变形特征,一种观点强调其重要性或认为其形成了NNE向为主的上古生界盖层褶皱;另一种观点则认为印支运动强度不大,上古生界NNE向主体褶皱形成于燕山运动甚至更晚。鉴于此,本文重点对湘东南印支运动的构造线走向展开了研究,厘定其为NNE向,反映区域NWW向挤压作用。对资兴三都、宜章瑶岗仙、桂东沙田等晚三叠世—侏罗纪残留盆地进行的研究表明,早燕山构造层下伏不整合面切割了上古生界中NNE向褶皱;以NNE走向为轴将不整合面旋转至水平,恢复上古生界岩层走向及构造线方向为NNE向。不整合面之下的地层层位普遍存在沿东西方向的快速变化。以上表明湘东南印支运动构造线为NNE向而非EW向,区域挤压应力方向为NWW向而非SN向。其动力机制可能与扬子和华夏板块之间产生陆内汇聚有关。结合区域资料,认为印支运动中华南不同地区的构造背景及构造体制存在显著差异。

There exist different view points about the deformation characteristics of the Indosinian Movement during late Middle Triassic in south China. Someones emphasize on the importance of the Indosinian Movement or consider that the NNE-trending folds in Late Paleozoic cover were formed in the movement, while others hold that the movement was weak and the NNE-trending folds were formed in Yanshanian Movement, or later. Therefore the writers studied emphatically on the lineament trend of Indosinian Movement in southeastern Hunan, and ensured NNE-trending of the lineament which indicated regional NWW compression. The studies on the Late Triassic—Jurassic rudimental basins in Sandou of Zixin, Yaogangxian of Yizhang and Shatian of Guidong show that the unconformity surface under early Yanshanian tectonic layer incised the NNE-trending folds in Upper Paleozoic. Rotating the unconformity surface to horizontal along the trending direction, writers recovered the NNE-trending of the Upper Paleozoic layers and structural lineament. There exist rapid variation of layers under the unconformity surface along E—W direction. The facts indicate that the lineament trend of Indosinian Movement in southeastern Hunan was NNE rather than E—W, and accordingly the regional compressional stess was NWW rather than S—N. The dynamic mechanism of the Indosinian Movement in southeastern Hunan can be related with the intracontinental subduction—convergence between the Yangtze and Cathaysia block. Combining regional data, writers consider that the tectonic settings and regimes of Indosinian Movement in different areas of South China were different.