Determination And Geological Significance Of Gonglujing-sangejing Ductile Shear Zone In Beishan Area,Inner Mongolia

The Beishan Orogenic Belt is located at the key position of intersection of the four Plates:Siberia Plate,Tarim Plate,Kazakhstan Plate and North China Plate.The amalgamation between the Kazakhstan Plate and Tarim Plate took place,and a series of the collisional orogenesis occurred at the end of Late Carboniferous.At the same time,the oblique convergence and collisions were occurred between the Mingshui magmatic arc(C)which dominated by the Carboniferous granitoids in the Tarim Plate and the Gongpoquan(O-S)island arc which formed under the plate tectonic system of the Beishan orogenic belt in the Early Paleozoic.The collisional orogenesis were occurred along the contact zone.It is mainly characterized by strong right ductile shearing at the mid-deep level of the earth's crust,forming the Gonglujing-Sangejing ductile shear zone.The Gonglujing-Sangejing ductile shear zone suffered from the structural superposition of fracture fault at the shallow level of the earth's crust when the Beishan Orogenic Belt entered into the intracontinental evolution period.The overall performance is a brittle-ductile tectonic belt that spreads in the near NWW.The Gonglujing-Sangejing ductile shear zone in Beishan orogenic belt is the main ductile tectonic boundary which separates the Mingshui magmatic arc(C)from the Gongpoquan(O-S)island arc.The deformation style in the ductile shear zone is complex and diverse,in which foliations,lineations and asymmetric structures are well developed.Both the macro-and micro-structure shows characteristics of thrust-right-lateral and Strike-slip shear movement from SEE to NWW in the southwestern plate.Based on the field survey,combining with micro-macro structural,geophysical charactersitics,isotopic age and the regional geological correlation,describing structural deformation and formation age of ductile shear zone.The process of formation and evolution and the geological significance in the Late Paleozoic Collisional Orogenics of the Beishan orogenic belt were discussed,and the following conclusions are obtained.(1)Both the macro-and micro-structure shows characteristics of thrust-right-lateral and Strike-slip shear movement in the southwestern plate from SEE to NWW in the Gonglujing-Sangejing ductile shear zone.(2)The Gonglujing-Sangejing ductile shear zone experienced a process from early mid-high temperature brittle-ductile deformation to low temperature deformation and late superimposed brittle deformation.(3)Zircon U-Pb dating indicates that the crystallization age of 411±3Ma is obtained from diorite mylonite in the Gonglujing-Sangejing ductile shear zone,and the metamorphic age of partial metamorphic recrystallized zircon is 300±3Ma.The metamorphic age can be used as a reference for the time limit of ductile shear motion in the Gonglujing-Sangejing ductile shear zone.(4)The Gonglujing-Sangejing ductile shear zone in Beishan orogenic belt is the main ductile tectonic boundary which separates the Mingshui magmatic arc(C)from the Gongpoquan(O-S)island arc.It is also the product of the strike-slip shearing effect of the Late Paleozoic plate in the Beishan orogenic belt.The formation of the shear zone played an important role in decomposing the strain of the parallel boundary in the arc-arc oblique collision process.