The Mesozoic Thrust Fault And Ductile Deformation Characteristics Around Changping And Huairou County,Northern Beijing

Changping-Huairou district of Beijing is a part of western Yanshan mountain,which is located in east-western extending and north-eastern extending tectonic transition part.The study area has undergone the superposition and reconstruction of Paleo Asian tectonic system and Paleo Pacific tectonic system,Changping-Huairou area records the Yanshan orogenic belt tectonic evolution in Late Mesozoic.The tectonic deformation in study area has multi period and complexity.By field observation and laboratory study,doing the research of the thrust structure system in the district,analyzing the structure superposition,relationship of rock replacement with striking,to distinguish the relation between ductile shear zone and brittle deformation.And provide evidence for refining the background of regional dynamics.The Shisanling-Shangzhuang-Hongluosi thrust fault and Dapian-Tiekaungyu thrust fault constitute the basic structure of the study area.The characteristics of related structure(folds)indicate thrust faults are north-western extending movement.The Shisanling-Shangzhuang-Hongluosi thrust fault cuts down layer,which indicating the footwall had deformed before the fault appears.According to the age of the footwall of fault and t the fault is cut by the rock mass,the fault formed in Late Jurassic to early Cretaceous.Deformation planes(mylonitic foliation)developed around the boundary of the Chanyuan rock body,with weaken inward,and mylonitic foliation towards south direction.The microstructure shows they have left-slip movement.The orientation of mineral crystals is visible at the edges of the rock masses,indicate the emplacement mode of long rock mass is active emplacement of magma rising and extruding surrounding rock mass.The Changyuan rock mass intruded after the Shisanling-Shangzhuang-Hongluosi thrust fault formation,and cut in the fault plane.The Lianhuachi-Weidian ductile shear zone in the study area formed in the Changyuan rock mass late deformation stage,after the emplacement of the Xihouyu rock mass(148Ma),the ductile deformation is the dominant factor,and has the influence of brittle deformation by the later stage.