Structural Characteristics And Kinematic Significance Of Mylonites In Nanxiong And Tangdong Faults In Northern Guangdong

The Nanxiong and Tangdong faults are located in the Zhuguang Mine Concentrated Area of the South China Plate,it is one of the important fault zones for studying granite-type uranium deposits in South China.Widely distributed mylonite or mylonite breccia with characteristics,contained rich geological information,and recorded multiple tectonic events in the Zhuguang Mine Concentrated Area.This paper takes the Nanxiong and Tangdong faulted mylonites in the Zhuguang Mine Concentrated Area in northern Guangdong as the research object,on the basis of previous research,the method for combin field macrostructure observation with indoor microstructure.A detailed microstructural observation of the mylonite in the belt was carried out,there are fabric analysis of X-ray quartzite,estimation of ancient differential stress,finite strain measurement and muscovite Ar-Ar Chronology,I gained the following new understanding.1.Studied on the characteristics of field macrostructure,different types of mylonite or tectonic schist are developed in the Nanxiong and Tangdong fault zones,mylonite has rotating debris,?type rotating debris,stone sausage et al.,structure.These structures indicate that the shear direction of the fault zone is dominated by the left-line shear.2.The observation of the mylonite sample under the microscope showed that,the microstructural characteristics of Nanxiong and Tangdong fault zones are consistent,core mantle structure,quartz subgrainization,dynamic recrystallization of quartz or wave extinction,mica twisted belt,mechanical double crystal structure.Rotating Patch System,asymmetric pressure shadow,mica,S-C fabric and other microstructures indicates that the mylonite is sheared in the left direction,consistent with field observations.3.Through recrystallization method and creep equation calculation of quartz particles in mylonite,obtained paleo differential stress value of 45.8?106Mpa in the mylonite zone in the Nanguang and Tangdong mines.The strain rate?is 2.0×10^-9m/s?7.06×10^-11m/s,and the range of Fulin parameter k is 0.48?0.77,it indicates that the strain type is flattened strain.4.The structural analysis results of quartz minerals shows that the Nanxiong and Tangdong fault zones are in the process of shear deformation,quartz has two slip mechanisms:diamond slip and bottom slip,they are mainly left-handed.Deformation temperature is mainly based on medium and low temperature(250°C?350°C)ductile deformation,followed by medium and high temperature(350°C?450°C)ductile deformation.5.The ⁴⁰Ar/³⁹Ar chronology of muscovite in mylonite shows the ⁴⁰Ar/³⁹Ar plateau ages of the Nanxiong and Tangdong mylonite belts are 189.03±1.03Ma and 209.44±0.89Ma,respectively.It indicates that the Tangdong mylonite belt was formed in the late Indosinian period,and the Nanxiong mylonite belt was formed later,which is the early Yanshanian period.Combining the above microstructural and chronological results,This paper believes that the Tangdong mylonite zone of the fault zone was formed in the late Indosinian period,and the mylonite zone of the Nanxiong fault zone was formed in the Early Yanshanian period.During the formation process,the Nanxiong and Tangdong fault zones are mainly affected by the ductile deformation at low and medium temperatures,microscopic structures such as a rotating plaque system,a mica twisted belt,and S-C fabrics are formed,and the kinematics direction is left-handed.In the process of shear deformation,the strain type of Nanxiong and Tangdong fault zones is flattened strain...