Material Composition Characteristics And Tectonic Evolution Of The Ailao Shan Tectonic Belt In Najian Areas, Yunnan Province

The Ailao Shan tectonic belt, expanding from northeast to southwest, which hassuccessively experienced the evolution of Tethys from Late Paleozoic to Mesozoic eraand the Indian plate and Eurasian plate collision in the new generation.It is animportant tectonic transform the response.The Ailao Shan tectonic belt displated anddismembered Ailao Shan ophiolitic melange belt.The involvement of all kinds ofrocks with different age lead to the internal composition which is quite complicated.Those caused the Ailao Shan tectonic belt different material composition in differentpositions with. To clear up with material composition is of great significance toexplore Ailao Shan tectonic belt tectonic evolution.Ailao Shan tectonic belt in the study area was holding by three regional deepfault. Honghe fault, Ailao Shan fault and Jiujia-Anding fault distribute from thenortheast to the southwest in turn. In this paper, through three geological sectionsacross tectonic belt, two sections of rock mass, as well as the route geological survey,combined with identification of rock and minerals and the analysis of chemical data,the author thinks Ailao Shan tectonic belt is a typical tectonic melange belt.Composition in Ailao Shan tectonic belt is made up of two parts which are the matrixand rock mass. The matrix is the Madeng group composed of shallow metamorphicrock and sedimentary rock. Rock mass is comprised of the Ailao Shan group rockmass, sedimentary rock mass, magmatic rock mass. The Madeng group and rockblocks possessing different degree of deformation later formed at different times, indifferent tectonic environment and from different source. Different sizes of varioustectonic massif (piece) form a unified mixed material field today, which haveoverlapped or displaced or missed. The premise of tectonic evolution model of the Ailao Shan tectonic belt is tofigure out different tectonic environment of tectonic evolution. Tectonic environmentdiscrimination is mainly starting from the sedimentary facies, tectonic deformationand metamorphism, magmatic activity and other aspects.In the paper, a more detailedgeochemical analysis is made the quartz diorite porphyrite rock and the granite rock inthe study area, in order to distinguish tectonic environment. The quartz dioriteporphyrite being changing extrusion to stretch between arc-continental collision orcontinent continent collision and post-collision，formed from the later stage of MiddleTriassic to the end of Late Triassic. Granite rock in stretching stage after the collisionmass formed in the Eocene.According to geological survey in the study area and comprehensive analysis incombination with regional geological data, The tectonic evolution in the study arearoughly divided into three stages: Ocean basin formation; Ocean basinclosed;continent continent collision. Ocean basin formed in the late devonian-earlyPermian. Ocean basin closed in the later stage of Early Permian to late stage ofMiddle Triassic. It includes two stages: subduction and back-arc basin formation;Ocean basin closed and back-arc foreland basin formation. Continent continentcollision formed from the late Triassic to Paleogene.