西藏阿里推覆构造与蛇绿岩构造侵位  

The Ngari thrust system and tectonic emplacement of ophiolites in western Tibet

作　　者：吴珍汉[1] 叶培盛[2] 杨艳[1] 

机构地区：[1]中国地质科学院.北京1000371 [2]中国地质科学院地质力学研究所,北京100081

出　　处：《中国地质》2013年第1期182-190,共9页Geology in China

基　　金：中国地质调查局青藏高原地质矿产调查评价专项(1212011221111、1212011120185);深部探测技术与实验研究专项(Sinoprobe-02)联合资助

摘　　要：通过野外观测和ETM遥感解译,结合1∶25区域地质调查相关资料,发现西藏阿里地区晚白垩世—古近纪发育自北向南长距离逆冲推覆构造运动,形成大型逆冲推覆构造系统,导致班公—怒江缝合带发生解体和蛇绿岩构造侵位。阿里逆冲推覆构造系统由大量逆冲断层、不同时代的构造岩片、不同规模的飞来峰和构造窗、不同方向的褶皱构造组成,前锋逆冲断层呈弧形分布于拉萨地块北部狮泉河—左左—革吉—麦岗沿线。沿主要逆冲断层,中生代蛇绿混杂岩、三叠纪和侏罗纪碎屑岩-碳酸盐岩、石炭纪板岩、二叠纪白云质灰岩自北向南逆冲推覆于早白垩世碎屑岩-碳酸盐岩、晚白垩世—古近纪红层之上,形成比较典型的薄皮双重推覆构造系统,估算最小推覆距离160～180 km。根据构造关系和同位素年龄资料,推断阿里薄皮推覆构造主要形成时代为75～20 Ma,对应自北向南逆冲推覆构造运动速率约2.91～3.28 mm/a。研究阿里逆冲推覆构造对深化认识班公—怒江缝合带及蛇绿混杂岩的构造属性、合理评价羌塘盆地西段油气资源潜力具有重要意义。Field profiling and ETM image interpretation as well as regional geological mapping at the scale of 1： 250000 led to the discovery of large scale Ngari thrust system caused by intense southward thrust in Late Cretaceous-Palaeogene and tectonic emplacement of ophiolite belts along the Bangoin-Nujiang suture in western Tibet. The Ngari thrust system mainly consists of regional thrust faults, tectonic slices of different epochs, nappes and tectonic windows of different scales, and accompanied folds of different orientations. In addition, the frontier thrusts were formed along Shiquanhe-Geji-Maigang arc belt in northern Lhasa block. Tectonic sheets of Mesozoic ophiolites, Carboniferous slate, Permian dolomite limestone, Triassic and Jurassic limestone and shale intercalated with sandstone were thrusted over Lower Cretaceous marine strata and Upper Cretaceous-Palaeogene red-beds, forming a typical thin-skin duplex with the minimal displacement of 160-180km in Ngari area. Such a thrust system was formed in 75-20 Ma according to available chronological data, corresponding to average slip rate 2.91-3.28 mm/a of southward thrust. The revelation of the Ngari thrust system is very important for better understanding tectonic evolution of ophiolites along Bangoin-Nujiang suture and reasonable evaluation of petroleum resources in western Qiangtang block.

关 键 词：薄皮双重推覆构造 逆冲断层 蛇绿岩构造侵位 班公-怒江缝合带 西藏阿里地区 

分 类 号：P588.125[天文地球—岩石学]