Research On Deformation Characteristics Of Fold Structure In Xichang Basin

The Xichang Basin is located on the western edge of the Yangtze Block,and the basin is distributed in a rhombic shape.Many superimposed folds are developed in the basin.Superimposed folds are important for determining multi-stage deformation and tectonic movement stages exploring tectonic evolution history,and determining oil and gas preservation conditions.However,there are few studies on the evolution characteristics of superimposed folds in Xichang Basin.Therefore,in this paper,basic geological theories such as structural geology and tectonic composite principles are used as guidance,and structural analysis methods are used to conduct in-depth analysis and research on superimposed folds to determine each superimposed fold type in Xichang Basin,and inversion of its tectonic evolution characteristics using the balanced profile technique,and discuss the effect of superimposed folds on oil and gas preservation.This paper mainly achieved the following results:(1)The stacking modes of the main folds in the Xichang Basin include cross-folding,shifting,strengthening,limiting,turning and other stacking modes.The stacking modes of the folds are mostly strengthened in the closed-closed fold belt of the basin,and the gentle fold belt in the west of the Xichang Basin It is more biased towards migrating and spanning superimposed folds.(2)The evolution of the superimposed fold structure in the Xichang Basin can be generally divided into the following three stages: The first stage is the squeezing movement after Paleogene.The main compressive stress direction is near EW direction.Due to the influence of the fault structure in the basin,NE direction folds are formed in the north of the west of the basin,and NW direction is formed in the south of the west of the basin.Folds form folds towards S-N in the east of the basin.The second stage is the squeezing movement after the Pleistocene,the principal stress direction is NE-SW,and the folds formed in the first stage are superimposed and reformed,the NE-oriented folds are superimposed on the NW-oriented fold structure in the northern part of the west of the basin,and the NS-oriented folds are on the east Wrinkle strengthening occurs.The third stage is the Holocene squeezing movement,the principal stress direction is NW-SE,compound superposition of the folds in the southwest of the basin,twisting of the fault zone in the basin,and the formation of joints inside the folds.The east of the Xichang Basin is dominated by tightly closed folds and shingled thrusts.Fractures and micro-fissures are developed,destroying the preservation conditions,and its fold superposition is strengthened.It is difficult to form a large anticline trap and its preservation conditions are poor.The Tanshan anticline in the west of the basin,the secondary anticline in the Mishi syncline,and the Qiliba anticline formed in the south of the basin through migration and crossover folds formed by fold superposition all form good structural traps,which is good Save unit.