| Bangong- Nujiang suture zone is the main suture zone of the collision between Indian continentand the Asian continent, which also is the the largest suture zone on the Qinghai-Tibet Plateau, being sandwiched between the Qiangtang and Lhasa block, extending 2000 km from west to east across the plateau, by which the Meo-Tethys basin represented. The Meo-Tethys basin, either as initial ocean that splits Gondwana land and Laurasia land or as a limitation of back-arc basin, has a vital tectonic evolution that are related to the fate of the entire Tibetan plateau. We take the Jurassic Muga Kangri group which exposed in the western part of the Bangong- Nujiang suture zone as research object, combining field geological survey, thin section analysis, geochemical analysis, detrital zircon U-Pb dating, rock zircon LA-ICP-MS and comprehensive study, we make the tectonic attribute and age of Muga Kangri group clear and bring new limitation of the formation and evolution of Bangong-Nujiang suture zone. we achived following understanding:1. Muga Kangri group is mainly composed of two parts, matrix and rock. Matrix is a set of bathyal flysch deposits from deep sea and half deep sea, composing of a pale yellow lithic sandstone, quartz sandstone, yellow-gray calcareous sandstone, slate, shale, thin black chert and limestone. The rock consist of rock sandstone, limestone rock, andesite rock and basalt rock.2. By the development position, rock composition and regional comparison analysis of Muga Kangri Group,we infer that Muga Kangri group belonging to the accretionary wedge basin, and the basalt and limestone rock belong to the redeposited products of the early rock or the same period of oceanic island materials.3. Despite the fact that Muga Kangri group as a whole had suffered a strong shear and even some rock itself has been subjected to intense shear deformation, we still come recognized that the Muga Kangri group is a set of sedimentary melange suffered strong shear extrusion.4. Muga Kangri group has the main feature of diffuse the intense shearing and closed recumbency- pour vertical fold, reflecting the strong compression and strike-slip deformation.5. Through geochemical analysis, the basalt rock and andesite rock are all belong to sub-alkaline rocks, where basalt belongs to tholeiitic basalt. Basalt samples has a flat-type REE patterns with no Eu apparent anomaly. Andesite rare earth elements has a right-tilt standardized schema curve of, LREE has an enrichment, LREE, HREE fractionation obviously, belongs to a LREE enrichment-style, δEu exhibit negative anomaly.6. We conducted detrital zircon LA-ICP-MS dating for the matrix, amone which, the youngest zircon age is 204 ± 2Ma, thus can indicate that the matrix of Muga Kangri group forms later than this age, indicating that the sleeve belongs to Jurassic strata.7. Through the discriminant of tectonic environment of Muga Kangri group we figured out that the initial environment for the formation of the group belongs to oceanic island arc environment. |
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