Deformation Characteristics And Chronological Analysis Of The Sanjiang Ductile Shear Zone In Area Of Northern Guangxi

The Hunan-Guangxi junction is located in the southwestern part of the South China continent,just in the intersection of the early Paleozoic Yangtze block and the southwestern part of the Cathaysia block junction.Strong ductile shear deformation and related ductile shear zones are important manifestations of early Paleozoic tectonic events in this area,and have important indications for revealing the assembly process of the Early Paleozoic Yangtze Block and Cathaysia Block and its tectonic background.Based on field geological survey and microstructural research,this paper uses magnetic fabric measurement,quartz microfabric analysis,and zircon U-Pb dating methods to analyze the deformation characteristics of the Sanjiang ductile shear zone in the Xiang-Guangxi junction area.And the cause mechanism was studied.The Sanjiang ductile shear zone develops in the NNE trend along the Changjie line of Longji to Xiangxi Channel in Sanjiang County,northern Guangxi,superimposed on Neoproterozoic metamafic-ultramafic rocks,as well as regional metamorphic rocks of the Danzhou Group and Nanhua System Above it,the length exceeds 42.6 km,the width is3.7~7.7 km,and the dominant position is 295°?69°.It generally shows the nature of left-handed thrust and also has the characteristics of right-handed and positive slip.Macroscopically,the ductile shear zone has developed mylonite,dense penetrating flakes,"A" type folds,stretch lineage,and "SC" fabric formed by syntectonic quartz lenses;microscopically,developed There are book oblique structure,quartz wave-like extinction,quartz dynamic recrystallization,calcite mechanical double crystal,etc.The magnetic fabric characteristics and kinematic vorticity calculations(or diagrams)show that the Sanjiang ductile shear zone is dominated by flattening strain and accompanied by a certain tensile strain.The kinematic vorticity is characterized by simple shearing.Mainly;strain intensity also has obvious inhomogeneity.Vertically,the strain intensity presents the characteristics of structural deformation that is strong in the middle section and gradually weaker to the south and north sections;in the horizontal direction,there are strong and weak strain bands alternately spreading in parallel.Characteristics,and generally present the structural deformation characteristics of strong in the middle and weak on both sides.Quartz recrystallization form and EBSD fabric analysis results show that the formation temperature of the Sanjiang ductile shear zone is 380?~650?,and the quartz C-axis fabric generally has rhombohedral <a> slip and cylindrical <a> slip.The shift and different shear directions suggest that it is a ductile shear zone with multiple periods of activity or may have undergone different secondary transformations and superimpositions.U-Pb dating results of hydrothermal zircons in ultramafic mylonites show that the ductile shear zone was formed at 441.0±11.0 Ma,which is highly consistent with the early Paleozoic deformation age of the NNE-trending ductile shear zone in the region.In terms of tectonic system,the Sanjiang ductile shear zone was generally formed in the NWW-SEE compression,which was coordinated with the EW compression and shear in the Caledonian period.Its formation was controlled by the long-range tectonic events in the Eastern South China during the Early Paleozoic.The effect is formed by the diagonal extrusion of the Cathaysia Block to the Yangtze Block,and is the product of the Early Paleozoic Yangtze Block and the Cathaysia Block's intracontinental orogeny.