Structural Characteristics And Evolution Of The Lushi-Luanchuan Area In Henan Province

The Lushi-Luanchuan area in Henan Province is located at the Sanmenxia-Lushan fault and the Zhuyangguan-Xiaguan fault.The south of the study area is located in the eastern part of the Qinling orogenic belt,and the north is located in the southern margin of the North China block.Predecessors have made great achievements in the crustal structure,evolution and dynamics of the Qinling orogenic belt,but the research on the structural characteristics of structural features such as faults and folds is still insufficient.In order to further explore the geometry,kinematics and dynamic mechanism of the geological structure in this area,based on the theory of structural geology and petrology,and combined with the data of predecessors,this paper makes a detailed structural analysis of the structural characteristics of faults and folds in the study area,and draws the following understandings and conclusions:1.The Lower Paleozoic Taowan Group mainly experienced three stages of fold structure deformation.The first stage is the homoclinic fold formed by the bedding as the deformation plane,the second stage is a series of tight-medium folds,and the third stage is the gentle fold formed by the axial plane of the tight fold,which is the product of late deformation.the fold in this period is reformed by the early stage and bent the axial plane of the early fold.Kuanping Group mainly experienced four stages of fold structural deformation.The first stage is soft-flow fold,forming schist and associated with remelting quartz vein-calcite pegmatite vein,which may be related to bedding shear deeply buried in plastic state during the formation of Kuanping rock group;the second stage is homoclinic fold;the third stage is tight-medium fold,which may be related to Triassic orogenic movement;the fourth stage is gentle fold,which is speculated to be formed at the end of Cretaceous.2.Four groups of fault structures are mainly developed in the study area,such as NWW-trending,NW-trending,NE-trending and NNE-trending fault structures.These four groups of faults were mainly formed in three periods: Caledonian,Indosinian and Yanshanian..Among them,NW-NWW-trending ductile-brittle-ductile faults are developed in Caledonian period,which belong to middle-deep structural level deformation;Indosinian period developed an NWW-trending southward imbricate thrust nappe structure,with NNE-trending right strike normal fault,which is brittle or brittle-ductile,which belongs to shallow structural level deformation;Yanshanian period is in extensional structural environment,developing NWW-trending and NE-trending brittle normal faults,which belongs to surface structural level deformation.3.According to the characteristics of sedimentary formation,structure and magmatic activity in the study area,combined with isotope chronological data,the history of geological tectonic evolution in this area can be divided into eight stages:(1)Neo-Archeancontinental core formation and accretion stage;(2)middle Paleoproterozoic subduction-collision stage;(3)early and late Paleoproterozoic-early Great Wall Epoch rift formation and development stage;(4)late early Great Wall Epoch-Sinian passive continental margin sedimentary stage;(5)early Paleozoic active terrigenous formation and evolution and collision orogenic stage;(6)Triassic Mianliuoyang closed orogenic stage;(7)Jurassic-Cretaceous littoral Pacific system tract convergence thickening and extension stage;(8)Cenozoic faulted basin development and evolution stage.