The Tectonic Rock’s Metamorphic And Evolutionary Process Of The Ailaoshan Fault Belt In Western Yunnan

Sanjiang region of Yunnan province has always been a hot spot researched by geological experts of each domain. The Ailaoshan fault zone is one of the important linear structures of the southeast margin of Qinghai-tibet plateau in this region. Because of its unique line extension, complex and multiphase tectonic evolution, as well as the obvious geological evolution differencese on both sides of the structural belt, plus as the important place of plate collision regulation and composite of Indian-Eurasian plate since Cenozoic era, Ailaoshan fault belt has long been one of the tetonic zones, which are wildly concerned and researched.Ailaoshan fault belt is located in southeast margin of Tethys Sanjiang orogenic belts and the integration of plate tectonics, with its complex background and structural feature development of multiple levels and periods. The study area is located in the northern section of Ailaoshan fault belt, its overall distribution is from north west to south east. Ailaoshan fault belt is a tectonic deformation zone, of which western north and south eastern side is wide and middle is relatively narrow.Ailaoshan fault zone spread over the range of Maanshan-HongshuijingMeiziqing-Azhaluxiaocun-Tuantianshan, and it’s the boundary of the Yangtze plate of Chuxiong basin and Lanping-Simao basin. The contact relationship between it and its east and west Mesozoic stratas is of the fault, with only scattered on the upper tertiary middle and unconformity. It consists of three fractures and two metamorphic belts. The three faults are Honghe fault, Ailaoshan fault and Jiujia-Andingfault from north east to south west. Two metamorphic zones are divided into deep metamorphic zone and shallow metamorphic zone, and the deep metamorphic zone is clamped by the Ailaoshan fault and the Honghe fault and the shallow metamorphic zone is located between the Ailaoshan fault and the Jiujiang fault. Previous divided Ailaoshan terrain of north Ailaoshan into Along terrain, Qingshuihe terrain and Xiaoyangjie terrain in turns from east to west, and divided Ailaoshan terrain of south Ailaoshan into Wudukeng terrain, Fenggang terrain, Along terrain, Xiaoyang terrain.The structure experienced old ancient Tethys stage, ancient Tethys stage, new Tethys stage and intracontinental evolution stage. Especially in Paleozoic-Cenozoic period, collision, collage and intracontinental convergence of the west margin of the Yangtze continental block(including stretching, contraction, napping, overthrusting of the lithosphere), make its tectonic evolution history long and complex.Deformation-metamorphism of the Ailaoshan terrain is very strong, the ductile deformation performance especially significantly, and the phenomenon of mylonitization is common. The early formed crystal schistosity, gneissic schistosity has fully replaced original bedding, and the deformation of multiple periods is obvious. Therefore, now see "layer" structure can not represent the original rock construction characteristics. Thus, we cannot tell the succession of stratas of Ailaoshan terrain.Dahebian terrain has experienced Chengjiang, Hercynian-Indosinian movement and Himalayan movement of tectonic deformation, metamorphism and transform. fold occurs in early recumbent folds in rock, forming vertical or inclined slanting fold, and associated with axial plane cleavage, which replaced the early foliation structure.Carbonatite of P2 b and coal-bearing formation of delta facies of P3 y were deposited from middle Permian to late Permian. With the westward pushing of the oceanic crust and the expansion of back-arc basin, Paleozoic stratas in basin were all surfered deformation and metamorphism. Varying degrees of low greenschist facies regional and low temperature dynamic metamorphism were generated. Under the background of stretching structure, regional penetration foliation and schistosity plane stretching lineation were formed, foliation and inclined fold were developed in recumbent fold. They are obvious thermal metamorphism formed in the shallow tectonic level and resulted from heat flux of upwelling.According to geological survey in the study area and comprehensive analysis in combination with regional geological data, the tectonic evolution in the study area roughly divided into three stages: Ocean basin formation; Ocean basin closed; continent-continent collision. Ocean basin formed in the late Devonian- early Permian. Ocean basin closed in the later stage of Early Permian to late stage of Middle Triassic. It includes two stages: subduction and back-arc basin formation; Ocean basin closed and back-arc foreland basin formation. Continent continent collision formed from the late Triassic to Paleogene.