Tectonic Deformation Characteristics Of Faults In The Eastern Margin Of Xichang Basin

The eastern margin of the Xichang Basin is located on the western margin of the Yangtze block.Since the Cenozoic Himalayan movement,the Asian plate collided with the Indian plate,which caused violent fracture and compression activities in the region,which continued to this day,ultimately retaining the complex geological structure.The Xichang Basin and the Sichuan Basin have similar reservoir-forming conditions,and they also have good prospects for oil and gas exploration.The study of the influence of fractured structural deformation in the eastern margin of the Xichang Basin on the formation and evolution of hydrocarbons and oil and gas preservation conditions has a guiding role.In this paper,guided by structural geology and other geological theories,using analytical structural methods,summarizing the geometric model and multi-stage kinematic properties of fault structures in the eastern margin of the Xichang Basin,and comprehensively analyze the tectonic evolution of this area,and discuss the effects of fault structural deformation on oil and gas preservation conditions.(1)The main faults in the study area are the Yuexi River-Heishui River Fault,the Puxiong River-Sikai Fault,and the Zhaojue Fault.They form an imbricate structure.The main structural deformation features are: 1)The Yuexi River-Heishui River fault is roughly in the north-south direction,starting from Yuexi and Puxiong in the north,passing through Mishidong and Jiefang Township in the middle,and reaching Puge and Ningnan in the south.It is a high-angle reverse fault with a tendency generally eastward.The fault zone mainly develops cleavage,lens,cataclasication rock and tectonic breccia.2)The Puxiong River-Sikai fault is divided into three sections: north,middle and south.The northern section of the study area is mainly exposed in the Xinjigu area.The fault strikes roughly from north to south to NNW-SSE,which appears as a thrust fault.The section dips to the east with a dip angle of 70-80°.The rocks on both sides are strongly broken.The middle section is mainly distributed in Sikai,Feidiajiao and Boluo Township.The fault strikes roughly NNW-SSE.The surface shows that the section is generally inclined to the west,and the underground shows a tendency to move to the east,mostly with high-angle thrusts.The southern section is mainly distributed in the Wuku Township and Yepu area on the west side of Butuo County.There are many parallel branch faults.The strikes are generally NNW-SSE.The cross section tends to the east,followed by the west dip,and the fault movement is reversed.Extrusion is dominant,and normal faults are occasionally seen.The entire fault zone develops cleavage,lens,fault gouge,compression-fold zone,cataclasication rock and tectonic breccia.3)The Zhaojue fault in the Zhuhe area is characterized by a relatively upright fault,with fault gouge,tectonic breccia and granulite developed in the fault zone.The fragmented dolomite in the Ganluo area in the northern section showed obvious two stress compression tectonic movements.(2)The formation and evolution of the fault structure on the eastern margin of the Xichang Basin are as follows: 1)The first phase of activity should originate from the northeast force exerted by the Indian plate on the Asia-Europe plate in the middle Cenozoic,induced by the east side of the Qinghai-Tibet area Caused by the lateral squeezing force from west to east.In this paper,the compression stress in the E-W direction caused the east-west compression of the near-south-trending reverse fault in the east margin of the basin to form a compression fracture zone,and a series of breccia belts and cleavage lens belts developed.The folds on the east and west sides of the fault on the eastern margin of the basin are not the same.The east side of the fault is inverted and closed,while the west side is gentle and open.2)In the second phase of this article,it can be inferred that calcite veins developed after east-west extrusion,and they showed a rightward movement.Based on previous analysis,after east-west stress compression to form a fault,NE-SW compression stress developed to form a north-west restricted fold.In this context,the right-handed movement in the NE-SW direction of this issue may be superimposed.3)The third phase of this article should originate from the activities caused by the tectonic stress site in the evening of the Himalayan movement.Since the activity in the middle and late Quaternary period,the region has formed a regional compressive stress in the direction of NW-SE,prompting the major fault zones in the study area.Resurrected and existed in the form of left-handed strike-slip.The movement of the left-lateral strike-slip characteristic of NW-SE extrusion to the maximum principal stress summarized in this paper should be derived from the tectonic stress field,affected by the regional strike-slip and continue to this day,and the newly developed fault gouge in the area Belt,it is speculated that it should be the result of stress in this period,making the original fault activity more complicated.(3)The structural deformation strength of the Xichang Basin is generally strong at the basin margin,while the deformation within the basin is relatively weak.The fault system composed of various faults in the eastern margin of the Xichang Basin.The fault structure completely destroyed the oil and gas preservation in this belt,and the preservation conditions were poor.Units with better preservation conditions should be located in the gentle fold belt of Mishi-Qiliba in Mishi area far away from the influence of the eastern margin fault,which can be used as a favorable preservation area for oil and gas in the Xichang Basin.