Metamophic-Deformation Characteristics Of Tuanliangzi-Daxinshan Metamorphic Zone, In Lancang River Region, Yunnan

Tectonic position of the study area is located in the south of Three-River orogenic zone, the junction between the Gangdise-Nianqing Tanggula fold system and Tanggula-Qamdo-Lanping-Simao fold system. Along the Lancang River deep fault, there are two tectonic units of gradeⅠ: the east side for Tanggula-Qamdo-Lanping-Simao fold system, which is an important component of the Paleo-Tethys orogenic belt; the west side for Gangdise- Nianqing Tanggula fold system, which is the northern margin of Gondwana land . There are many faults in the study area, most N-S ternding faults. The two important faults are the Lancang River and Jiufang fault zones, which are made of a series of imbricated thrust-nappe structures.Tuanliangzi-Daxinshan metamorphic belt is made of phyllite and shallow metamorphic-clastic rocks, with a low greenschist facies, a regional low-temperature dynamic metamorphism type, which belongs to one part of Lancang Group in keeping with Lancang metamorphic depression belt proposed by Zhaojing etal. The belt to form was connected with Paleo-Tethys subducting from west to east along Changning-Shuangjiang metamorphic belt.Tuanliangzi rock formation extensive development of quartz veins with the regional foliation S2 as the result of progressive tectonic deformation. Its formation mechanism is the progressive shear deformation under the pressure solution differentiation. Based on primary fluid inclusions of quartz micro-temperature data, the formation of quartz veins come to the temperature and pressure conditions: T = 290-340℃, P = 125-141MPa, the formation of metamorphic facies reached a low greenschist facies. Tuanliangzi rock formation experienced twice metamorphism: Caledonian, the late Variscan-the early Indosinian and Daxinshan rock formation experienced only the later one.There are many structures with the instructions in the multi-phase deformation and third-stage quartz veins in the metamorphic belt. Through cleavages and lineations statistics and the stereographic analysis: the metamorphic belt experienced Indosinian northeast-southwest tectonic extrusion and Himalayan strike-slip shearing extrusion.Movement direction of the structure of the instructions such as the "σ-type quartz broken line spots" testify that the shear zone north righted-incline thrust from the southwest to northeast. And the sericite "S-C" fabric left under a microscope showed that they are subject to Lancang Jiang fault zone late strike-slip.Tuanliangzi rock formation experienced three tectonic deformations: Caledonian, the late Variscan-the early Indosinian and Himalayan. And Daxinshan rock formation experienced the later two deformations.