东昆仑东段晚古生代—中生代若干不整合面特征及其对重大构造事件的响应

Geological characteristics of Late Palaeozoic-Mesozoic unconformities and their response to some significant tectonic events in eastern part of Eastern Kunlun

地层不整合接触是研究地质发展历史和鉴定地壳运动特征的重要依据。通过大范围露头尺度和填图尺度不整合面的识别,结合不同时代地层沉积体系的特征及构造变形样式的对比研究,发现东昆仑造山带东段晚古生代—中生代地层由底到顶共发育有4个不同类型的不整合面,分别是上二叠统格曲组与上石炭统浩特洛哇组之间的角度不整合面、中三叠统希里可特组与闹仓坚沟组之间的微角度不整合面、上三叠统八宝山组与下伏不同时代地层之间的角度不整合面、下侏罗统羊曲组与上三叠统八宝山组之间的平行不整合面。这几个不同时代的不整合面分别代表了东昆仑东段晚古生代—中生代地质演化时期中特定的构造事件。其中,格曲组与浩特洛哇组角度不整合关系代表东昆仑造山带南缘阿尼玛卿—布青山古特提斯洋晚二叠世开始向北俯冲的构造事件;希里可特组与闹仓坚沟组微角度不整合关系与陆(弧)陆局部差异性初始碰撞的洋陆转换构造事件密切相关;八宝山组与下伏不同时代地层角度不整合关系是东昆仑地区分布较广、意义重大的一个不整合面,代表中三叠世晚期—晚三叠世早期东昆仑地区陆(弧)陆全面碰撞的主造山构造事件,同时该期碰撞造山事件铸就了东昆仑及其周缘地区的基本构造格架。羊曲组与八宝山组之间平行不整合面则与晚三叠世晚期—早侏罗世早期陆内演化过程中地壳垂向抬升事件相关。这些不整合面的厘定及其代表的相应构造事件对于合理建立东昆仑地区晚古生代—中生代构造演化过程具有重要意义。

The unconformities between strata can provide some important basis in the study of geological history and crustal movement.Combining the characteristics of sedimentary system and comparative study of deformation style,four different types of unconformities have been defined in Late Palaeozoic-Mesozoic strata in East Kunlun on basis of mapping and outcrop observation.From bottom to top of strata,these unconformities are angular unconformity between Upper Permian Gequ Formation and Upper Carboniferous Haoteluowa Formation,micro-angular unconformity between Middle Triassic Xilikete Formation and Naocangjiangou Formation,angular unconformity between Upper Triassic Babaoshan Formation and underlying strata,and parallel unconformity between Lower Jurassic Yanqu Formation and Upper Triassic Babaoshan Formation,respectively.These unconformities represent some specific tectonic events in the evolution history of the Late Palaeozoic-Mesozoic,respectively.The unconformity between Gequ Formation and Haoteluowa Formation represents the initial subduction event of Anemaqen-buqingshan Ocean in the late Permian.The micro-angular unconformity between Xilikete Formation and Naocangjiangou Formation is probably attributable to the initial collision between blocks.The angular unconformity between Babaoshan Formation and underlying strata is a significant tectonic interface,representing the main continental collision events in the late stage of Middle Triassic-the early stage of Late Triassic,which built up the basic tectonic framework in East Kunlun and its adjacent area.The parallel unconformity between the Yangqu Formation and Babaoshan Formation is interpreted as linking to the uplift movement of continent crust in the intracontinental tectonic stage in the late stage of Late Triassic-the early stage of Early Jurassic.These unconformities and their corresponding tectonic events have an important role in restoring the Late Palaeozoic-Mesozoic tectonic evolution history in East Kunlun.