巧家拉分盆地结构特征及其形成演化过程分析

为了探明巧家盆地的性质、成因以及其演化过程，通过详细野外调查，结合区域构造特征对巧家盆地展开了初步的研究. 首先基于详细的野外调查工作，掌握了研究区基本地质背景条件以及盆地表面的沉积特征；进而，对盆地中心区域进行了钻孔勘测，得到了盆地内部结构特征，结合区域地质背景和盆地结构特征，对其形成演化过程进行了分析. 研究结果表明:巧家盆地为典型的拉分断陷盆地，主要受小江走滑断裂带的控制；盆地内部结构主要包括了5个地层层序，从下到上分别为古河流冲积层、昔格达组地层、静水沉积层、泥石流洪积层以及河流阶地，并解释了各层成因；首次发现在距盆地下游边界3 km处曾发生过大规模堰塞堵江事件；堰塞事件发生于距今3万年左右；初步推测该拉分盆地形成于第三纪晚期，后期又经历了断陷湖沉积、堰塞沉积、泥石流洪积以及河流冲积等作用；区域断块阶段、局部拉分断陷阶段、断陷湖相沉积阶段、堰塞沉积阶段、堰塞消亡阶段以及不均匀升降阶段为盆地形成的6个阶段，与盆地内部土层层序有较好的对应性. 

Structural Features and Evolutionary History of Qiaojia Pull-Apart Basin

In order to explore the features, formation and evolution process of the Qiaojia Basin, detailed field investigation was carried out. Firstly, based on the investigation, the basic geological background conditions of the study area and the sedimentary characteristics of the basin surface were mastered. Further, the borehole survey was carried out on the central area of the basin, and the internal structural characteristics of the basin were obtained. Combing with the regional geological background and the structural characteristics, the formation and evolution process of the basin was analyzed. The results show that the Qiaojia Basin is a typical pull-apart basin, which is mainly controlled by the Xiaojiang Fault. The internal structure of the basin mainly includes five stratigraphic sequences: the alluvial layer of the ancient river, the hydrostatic sedimentary layers, the debris flow alluvium, and the river terraces. It is first discovered that a large-scale damming event occurred 3 km from the downstream boundary of the basin about 30 000 years ago. It is presumed that the basin formed during the late Tertiary period, and later experienced the effects of pull-apart process, damming process, debris flow events, and alluvial events. Through rigorous analysis and research, the evolution process of the basin was divided into 6 stages: regional dislocation, local pull-apart rifting, rift lake deposition, barrier lake deposition, barrier lake breaking, and uneven lifting.