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

Abstract：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.