Structural Deformation Characteristics And Its Significance In Huo BuHaer Of EjNaQi,Inner Mongolia

Take the Carboniferous-Permian geological bodies deformation characteristics as the research object in Huo Bu Haer and Sheng Ge Gashun which in the middle segment that on the southern margin of the central Asian orogenic belt,Carboniferous-Permian geological bodies formed different level,different tectonic style of tectonic deformation phenomenon in different time.through the system structure and chronology research,it has important significance for the reconstruction of late Paleozoic tectonic evolution in the study area,in this paper,guided by the theory of plate tectonics,use the method of structural analysis technology,based on the large scale field geological mapping of structure and lithology,combining indoor comprehensive test and analysis of geologic bodies in carboniferous-Permian tectonic deformation system,main innovation and understanding obtained as follows:Ductile shear deformation is common in the late Paleozoic magmatic rocks in the study area,the macroscopic mylonitic bedding is distributed in the northeast-southwest direction,The Stretching line of mylonitic bedding is nearly horizontal,macroscopic and microscopic fabric?such as S-C fabric,rotating speckle system,etc.?indicates left shear deformation.Through detailed structural analysis and Structural chronology research,it is believed that the ductile shear zone fabric has superimposed two-stage ductile shear deformation characteristics,the ²⁰⁶Pb/²³⁸U weighted mean age of myolitic rhyolites zircon is 287.0±2.7Ma and 273.1±6.8 Ma,the ²⁰⁶Pb/²³⁸U weighted mean age of a group of metamorphic zircons in mylonitic rhyolites is 259±4.4 Ma,and the ductile shear is the same time as the emplacement cooling process of the rhyolites.Therefore,it is believed that theductile zone was formed in273-259Ma?middle-late Permian?.The ⁴⁰Ar/³⁹Ar plateau age of sericite-schist in ductile shear band was 216.21±2.56 Ma,this indicates that the left ductile shear zone was active again in the late Triassic.The outcome of quartz c-axis EBSD of mylonite oriented slices shows:the early mylonite formation environment was medium high temperature?450-550^oC?and the late mylonite formation environment was medium low temperature?250-350^oC?.It is concluded that the formation of the ductile shear zone is related to oblique subduction of regional oceanic crust and the late ductile shear activity is related to intracontinental convergence.Carboniferous-Permian strata in the study area underwent two stages of superimposedfold deformation,for the first phase of the fold deformation under the action of buckle folding formation,north east-south west distribution of complex fold,complex foldformed obvious structure displacement phenomenon,on the macro performance for north east,south west distribution of axial plane cleavage,analysis indicates the formation of complex fold related to NW-SE direction compression.The strongly developed axial plane cleavage are the products of the orogenic period when the ancient Asian ocean basin entered the land-land convergencing stage after the closure of the yagan area.The second phase fold deformation transformed the first phase complex fold that make the axial plane cleavage plane formed in the first phase tectonic displacement show an"S"curve,and the"S"curve reflects the anti-clockwise shear action in the regional.The ³⁹Ar/⁴⁰Ar plateau age of oriented sericite minerals in the phyllite with axial plane cleavage is 215.45±2.11 Ma,It is believed that the first stage of fold deformation was formed in the late Triassic,The second period time?216Ma?of ductile shear activity is highly consistent with the time?215 Ma?of axial plane cleavage,which reflects that ductile shear activity is dominant in the northern part of the study area,while the complex anticline and multiple syncline with related axial plane cleavage are dominant in the southern part of the study area,all of which are formed in the middle structural level,indicating that the yagan area has entered the strong orogenic stage of land-land convergencing.The weighted mean zircon U-Pb age of monzogranite in Sheng Ge Gashun is 206.8±4.2 Ma?MSWD=10.8?,indicating that the rock mass was formed in the late Triassic.Combined with comprehensive research shows that:in the late Permian,kazakhstan plate has been collided with the northeastern margin of Tarim plate,late Triassic is still in the orogenic period,and then entered the Crustal extensional deformation stage.