Structural Deformation Characteristics Of The Machaoying Fault Zone In The Northern Margin Of The East Qinling Mountains

The study region is located in the southern margin of the North China plate,which between the Sanmenxia-Lushan fracture and the Zhu Yangguan-Xiaguan fracture,and it is belongs to the eastern section of the QinqianKun orogenic belt.The fracture zone of MaChaoying is located in the central and northern part of the research area,which is the eastern part of the Panhe-Luchouying fracture zone,and is the largest NWW to near EW major fracture on the southern slope of Xionger Mountain.It has complex geological tectonic characteristics and a long history of evolution,and it has obvious control over sedimentary formation,magmatic activity,tectonic deformation and migration of useful components in this area.The work of the predecessors in the area mainly focused on tectonic ore-control,but the research of tectonic deformation in the MaChaoying fracture zone is still insufficient and divergent.Therefore,this paper takes the tectonic deformation characteristics of the Ma Chaoying fracture zone as the title,and relying on the project of “Investigation on regional geology and mineral resources of 1:50,000 Lushi County,Baitu Street,Hengjian and Sanchuan regions in Henan Province ”.This paper starts with field survey and previous geological data collection.,to study the tectonical deformation characteristics of each stage of the Machaoying fracture zone,and to analyze the tectonic evolution of each stage according totectonical deformation.Through the interpretation of regional geophysical data and remote sensing images,it is considered that the Ma Chongying fault zone has a small depth of crust cutting and is only a large basement fault on the southern margin of the North China block.On the basis of large scale geological mapping and fine structural analysis,it is considered that the distribution of strong and weak deformation fields in the Machaoying fracture zone is characterized by the phase distribution,and the dominant movement direction of the fracture zone is nearly north-south and and the dominant motion direction of the fractue zone is determined to be near-north-north direction,and the geometric and kinematic features are matched with the macroscopic and microscopic deformation features.The microscopic observation according to the oriented specimen the dynamic recrystallization of the rock and the grain size of the quartz sub-particles were measured.The average paleo-stress value of the Majiaoying fracture zone was estimated to be 81.31 MPa.By means of finite strain measurement,it is found that the K value coefficient of the fault zone is 0 < K < 1,whichbelongs to the general flattened strain,the strain intensity is about 2.4,and the direction of the principal stress of the fracture zone is NE-SW,and the closer it is to the fracture zone,the greater the strain intensity is.Through the study of the tectonical deformation characteristics of the fracture zone and summarizing the predecessor data,it is determined that the tectonical deformation of the Ma Chaoying fracture zone can be divided into four stages:during the Paleozoic period,the tectonic deformation was dominated by the SN extrusion deformation,which produced a series of extrusion lithology and tectonic schist,forming a NNE ductile deformation zone.In the early Mesozoic,the early formation of the pleats occurred folds,deflections and structural lens bodies,and produced brittle-ductile shear zone and ductile-brittle shear zone,the local area developed a bedding shearing effect.The zircon U-Pb age obtained in the penetrating syenite vein is 206±39 Ma,which indirectly represents the age of ductile-brittle shear zone formation;In the middle and late Mesozoic,the activity was the strongest,characterized by the thrust nappe structure,the gravity slip structure,and the metamorphic core complex;In the Cenozoic,the major activity was brittle deformation,and the initial formation of structural rock was broken,and the NNE fracture surface was formed,and sag,horst and graben structures were formed,and the previously developed graben basin continued to develop.