Mesozoic Deformation Characteristics And Tectonic Evolution In Qinglong Area,the Eastern Segment Of The Yanshan Belt

Throughout the Yanshan area,both the Pre-Tiaojishan Period(Pre-165Ma)deformation and the Pre-Zhangjiakou Period(Pre-136Ma)deformation have been widely recognized,but the Pre-Jurassic deformation has been reported rarely.In this paper,we select Qinglong,Hebei to southern region of western Lingyuan,Liaoning as researth priorities,to explore Mesozoic deformation characteristics and tectonic evolution in the eastern segment of the Yanshan belt.Based on the study on the structural geometry and kinematics in the Qinglong area,the eastern segment of the Yanshan belt,combining with related research in tectonic chronology,this paper has identified three contraction deformation(Dl-D3)before late Triassic,two contraction deformation(D4-D5)during late Triassic,and continuous contraction deformation(D6)during Late Jurassic to Early Cretaceous.Meanwhile,through the construction of a series of multiple structural sections,this paper has restored six tectonic evolution process.Phase I deformation,mainly represented by NW-NNW trending isoclinal overturned folds,with the kinematic characteristics towards the southwest direction.Phase II deformation,mainly represented by NE trending ramp-flat thrust faults and associated folds,with the kinematic characteristics towards the northwest direction.Phase III deformation,mainly represented by a series of NE trending folds and associated faults,with the kinematic characteristics towards the southeast direction.Phase IV deformation,mainly represented by vertical uplift deformation as block-type.Phase V deformation,mainly represented by NE trending thrust faults,with the kinematic characteristics towards the southeast direction.Phase VI deformation,mainly represented by NE trending folds that deforming continuously,and associated faults,such as the forelimb thrust and the back thrust.And Archean was involved in all six tectonic deformation.In addition,this paper collects four samples derived from Dashizhuzi composite pluton for zircon U-Pb dating,the results show porphyritic granite emplacement age of 214.31 ± 0.5Ma,biotite-hornblende monzonite granite emplacement age of 211.23± 0.7Ma,granodiorite emplacement age of 226.8±1.7Ma,fine K-feldspar granite emplacement age of 218±1.0Ma.Therefore,the time of Phase III and Phase IV tectonic activity can be limited by the reliable chronological evidence,because of the emplacement of Dashizhuzi pluton destroyed Phase III deformation,as well as the destruction of Dashizhuzi pluton which was made by Phase IV tectonic activity.