The Analysis Of Microstructure And Kinematics In The Wucheng-Tunxi Ductile Shear Zone Of South Anhui Province

The relationship between quartz crystallographic fabrics and strain date is complex in shear zones.The Wan-Zhe-Gan fault zone represents a typical region that records several tectonic events in the Yangtze Block of the South China Block.And we used a comprehensive structural and microstructural analysis,such as Electron Back-Scattered Diffraction(EBSD),3D strain analysis and multiple kinematic vorticity analysis,to the sheared rocks from the Wucheng-Tunxi ductile shear zone which belongs to Wan-Zhe-Gan fault zone and try to reveal this relationship.The analysis of microstructure under microscope indicates the rock deformation behavior included dislocation slip,dislocation climb,dynamic recrystallization,and we can observed the deformation twinning,wavy extinction,subgrain microstructure.The dynamic recrystallization was dominated by progressive bulging recrystallization,combined with grain boundary migration(GBM)which indicated the different deformation temperature.Vorticity analysis using strain-ratio/quartz c-axis fabric indicates a simple shear component of deformation(0.69 < Wn < 0.98)throughout the zone,and different methods suggested the simple shear was earlier than the pure shear.Moreover,the increase of the pure shear component towards the central domain is qualitatively inferred by the observed variation in the degree of asymmetry of quartz c-axis fabrics and flattening deformation according to the 3D strain analysis.Based on the analysis above,we found that later pure shear strongly affects the central domain of the shear zone in which the c-axis fabrics have been strongly modified after the early simple shear.However,in the southeast domain,the pure shear is not changed significantly,which is characterized by submaxima.The data indicate two major deformation episodes in the Wucheng-Tunxi ductile shear zone.A large-scale right-lateral shear was formed in the first deformation episode,which was characterized by a low-temperature simple shear,corresponding to the Early Paleozoic intracontinental orogeny.The latter was a high-temperature pure shear that was characterized by flattening deformation.This deformation was a remote effect which was the result of growing geothermal gradient and uplifting of mantle during the late Early Paleozoic orogeny in the Yangtze Block.In summary,the kinematic and dynamic characteristics of Wucheng-Tunxi ductile shear zone were determined primarily,and confirmed that the varied strain changed the quartz c-axis fabrics.Morever,it will guide the analysis of dynamics and kinematics.