桂西右江裂谷的伸展作用和伸展不整合

Extension and extensional unconformity ofthe Youjiang rift in western Guangxi

桂西地区普遍发育的下—中三叠统浊积岩系与古生界碳酸盐岩系之间的所谓“不整合接触关系”是一个重要的又有争议的地质问题。通过对这类接触关系的深入细致调查和分析,笔者发现它是由中二叠世末开始持续大规模拉张的右江裂谷因拉张伸展运动使局部层位缺失所致,为伸展不整合。右江裂谷的伸展作用始于泥盆纪初,在中二叠世末至中三叠世最为强烈,于三叠纪晚期裂谷抬升成陆时才结束,其特点为发生的空间规模大、持续时间长,由此形成的古潜山构造在后期构造发展及成矿作用中具有重要意义。

The so-called 'unconformable contact relationship' developed generally between Mid-Lower Triassic turbidite sequences and Paleozoic carbonate sequences in western Guangxi is an important and controversial geological problem. Based on deep-going and careful investigations and analysis, the authors find that such a contact relationship resulted from the absence of some strata due to large-scale sustained extension of the Youjiang rift belt that began at the end of the Middle Permian, which is called extensional unconformity. The extension of the Youjiang rift began at the beginning of the Devonian, got strongest between the end of the Middle Permian and Middle Triassic and did not end until the rift was uplifted and became land in the Late Triassic. Its main characteristics are large spaces and a long duration. The paleo-buried hill structures that formed in the extension have great significance in later tectonic evolution and mineralization.