Analysis Of Deformation Characteristics,Kinematics And Rheology In The Ductile Shear Zone Of Ejiumai,Nima,Tibet

The ductile shear zone of Ejiumai is located at the north margin of the Longmucuo-Shuanghu subduction and proliferating complex belt.It is an important part of the central part of the Qiangtang Basin and records the evolutionary history of this area.Combined with regional geological background,this study tries to discuss possible tectonic evolution of the shear zone through deformation characteristics,characteristics of kinematics and rheological characteristics.Macro-phenomena in the field,micro-structure and crystal preferred orientation of quartz indicate that the shear zone is normal-right lateral shear;The characteristics of quartz dynamic recrystallization,crystal preferred orientation of quartz,relation diagram of fractal dimension and deformation temperature indicate that the deformation temperature is about 400?-600?,which is in the low green schist facies to the low amphibolite facies;The instantaneous vorticity values at each point range between 0.49 to 0.96,the average vorticity values are 0.76 to 0.99,and 0.49 is the value of the later kinematics vorticity with the measurement of C',and the kinematics vorticity values of the other points are all greater than 0.76.The above data show that the process is greatly affected by the early general shear.They indicate that the shear zone is affected by general shear,which is mainly simple shear in the early stage and pure shear in the later stage.The toughness thinning rate?between 82%and 92%?,strain rate(between 10^-10.23 and 10^-15.30 s^-1)and the vorticity of kinematics at each point,indicate that D1604-DB1 and D1607-DB1 are located at the area of the strong shear,basing the position of each point;The crystal preferred orientation of quartz at D1604-DB1 shows that the main period is the bottom slip of?a?,the second period is the rhombus slip of?a?.The Preferred azimuth of quartz crystallography at D1607-DB2 shows the main period is the rhombus slip of?a?,the second period is the bottom slip of?a?.They show that they retain two deformation temperatures.The combination of outcrop observation,microstructural characteristics,analysis of EBSD,the vorticity of kinematics,and strain rate estimation of the shear zone indicate that there are at least two stages of deformation in the ductile shear zone of Ejiumai.The first stage of deformation is the early detachment of the early Yanshan period with the right lateral shearing of NWW-SEE.Due to the continental tectonic stress field in the early Yanshan period,the shear zone extended nearly north-south.Due to the near-horizontal shortening of the NWW-SEE in this period,the right direction of NWW-SEE shear occurs in the shear zone.The second stage of deformation occurred in the late Yanshan period,with the detachment and the right shearing,the crust of the overlying crust is thinned.The shear zone is affected by general shear and the general shear changes from mainly simple shear in early stage to Mainly pure shear in later period.Its source of power is equalizing compensation and magma upwelling.The location of the core of the magma upwelling is exactly where D1604-DB1 and D1607-DB1 are located,causing the shear zone to rise rapidly.