Structural style and tectonic significance of the Jianglang dome in the eastern margin of the Tibetan Plateau, China

The Jianglang Tectonic Dome (JTD) lies on the eastern margin of the Tibetan Plateau and consists of three tectono-stratigraphic units separated by two extensional detachment faults: a schist complex, a middle ductile slab and an overlying sedimentary unit. The schist complex is composed of quartz–mica schists and amphibolites of possible Mesoproterozoic age and exhibits two early foliations (S1 and S2) overprinted by two later foliations (S3 and S4). The ductilely deformed middle slab consists of Paleozoic quartzite, phyllite, marble, amphibolite and meta-basalt. It is characterized by pervasive intrafolial and intraformational recumbent folds with a penetrative axial foliation S′1 (an equivalent of S3 in the basement rocks). The cover unit, the Triassic Xikang Group of flysch sedimentary rocks, experienced shallow level buckling and flattening deformation with an axial cleavage defining S″1 (an equivalent of S4 in the middle slab and basement rocks). D appears to have experienced three stages of extension immediately after orogeny. The earliest (D1), recorded by an axial surface S1 of S0 intrafolial folds and sub-parallel to S0 in the schist complex, probably occurred prior to the collision between the South China and North China Blocks. This extensional event was followed by subduction of the Yangtze Block to the west towards the eastern margin of the Tibetan Plateau. The two detachment faults are characterized by structures formed by ductile–brittle to brittle shear deformation, which are sub-parallel to the layer of S2 in the lower detachment and to S0 in the upper detachment. These faults mark the second stage of extension and may have caused thinning and selective removal of the Sinian and Paleozoic strata, as well as exhumation of the schist complex and the middle slab in the middle Jurassic (177 Ma). The final stage of extension (D5), shown by brittle deformation and thermo-metamorphism from the lower detachment to the Xikang Group, was associated with the Indian–Eurasia collision.