Structural Characteristics And Evolution Of Yilan Area In Yishu Graben

Yilan area is located in the northeast of Harbin City,Heilongjiang Province.Its tectonic position is in the north of Fangzheng fault depression,in Yishu graben,in the north extension of Tanlu fault to Yilan-Yitong fault zone.Influenced by the evolution process of the northern extension of the Tanlu fault,Yilan area has experienced many stages of strike-slip transition since the Cenozoic.Taking the geological,seismic and logging data of Yilan third coal mine as the research object,this paper studies the structural characteristics of Yilan area by using three-dimensional seismic structural interpretation and structural geometry,and infers its evolution process in combination with the evolution history of Tanlu fault.In this paper,SMT and paradigm full three-dimensional interpretation systems are applied to analyze and interpret the three-dimensional data volume of the delimited research area.Many methods,such as automatic fault identification technology and guided filtering technology,are used.The medium coal seam with large thickness,wide range,obvious characteristics and easy identification is taken as the research target layer to complete the pretreatment of logging data,the production of synthetic records and horizon calibration,the identification of breakpoints and horizon tracking Velocity analysis and structural mapping are used to identify and describe fault related structures.According to the results of three-dimensional seismic structure interpretation,this paper considers that the structural styles in Yilan area have 8 forms,including breakthrough type fault propagation fold,high-angle thrust structure,imbricate thrust structure and multiple structure,thrusting and extrusion structure,structural wedge,detachment structure,thin-skin flower structure and derived extensional structure.According to the study of structural geometry,this paper holds that the structural framework in Yilan area is divided into three layers from the basement to the caprock,bounded by the two detachment planes F081 and F082;The upper layer is dominated by strike slip compression torsion formed by breakthrough type fault propagation folds and high-angle thrust faults.The middle layer is formed by overlapping multiple structures of imbricate thrust nappe.The lower layer is a multiple structure composed of a large number of structural wedgesThe target layer in this study area is generally divided into two parts: southwest and northeast.The southwest side is a southwest inclined monocline with folds,and the northeast side is a south inclined monocline separated by complex faults.In this paper,it is considered that the structural form of the fault assemblage in Yilan area can be divided into four parts.The southwest side is mainly composed of breakthrough type fault propagation folds and strike-slip faults moving in the NE direction,the northwest side is mainly composed of high-angle thrust faults and strike-slip faults moving in the WS direction,and the middle part is composed of strike-slip faults moving in the NE direction with the strike-slip faults as the boundary,The east-southeast part is a combination of strike-slip faults with strike-slip faults as the boundary and relatively moving in WS direction.The fracture of the coal seam in the study area is a non syndepositional fracture,which does not control the thickness of the coal seam.Based on the analysis of the structural styles,structural framework,fault assemblage and its activity in Yilan area and the evolution model of Tanlu north extension,this paper believes that Yilan area was mainly in the strike slip background in the Cenozoic,and the existing residual structural pattern experienced two tectonic evolution stages: the Neogene left-handed strike slip and the Quaternary right-handed strike slip.