Characteristics Of Structural Deformation And Its Controlling Factors Of Central And Western Segment In The Front Of The South Tian Shan

Structural deformation in fold and thrust belt controls accumulation of oil and gas, and a great number of hydrocarbon accumulates in the structural trap related to structural deformation.On the other hand,structural deformation of deposited strata makes it difficult to obtain ideal seismic data.The fold and thrust belt located in the front of the South Tianshan is a very important structural belt in West China,with particular tectonic setting,convenient observation in field and important significance in dynamics of inner plate,which has attracted many geologist from home and abroad to study its structural deformation.The structural belt has become an natural laboratory for studying intracontinental orogeny and its transverse dynamics and kinematics.There are abundant of oil and gas in the structural belt,and complicated structural deformation resulted from several times tectonic movement in Tianshan area makes it difficult to develop oil and gas exlploration.Research on structural analysis and formation mechanism of fold and thrust belt in the front of the South Tianshan is very crucial to oil and gas exploration.The stuy area in this thesis lies in the southern margin of the South Tianshan belonging to China,including Wushi fold and thrust belt,Keping fold and thrust belt and Artux fold and thrust belt.Research on structure analysis and formation mechanism of fold and thrust belt in the front of the South Tianshan is developed based on field geological,seismic and non-seismic data,by the technology of joint-inversion of gravity,magnetic,electric and seismic data,structure modeling of fold and thrust,structural balanced-section,and structural models of different segments are set up;controlling factors of structural deformation are pointed out. Through the research,the following new points are put forward:(1)The gravitational and magnetic data is merged and digitized for the first time. Combined with field geologic and seismic data,fault system of the fold and thrust belt is studied.According to characteristics of fault and deformation,central and western segments of southern margin of the South Tianshan are divided into three structural belts:Wushi structural belt,Keping structural belt and Artux structural belt.(2)It is put forward for the first time that Wushi Sag and Kuqa depression were connected in Mesozoic and separated in Cenozoic because of strike-slip of Kalayuergun fault.Structural frame and structural style of Wushi fold and thrust belt are set up which measures up to real condition much better.(3)Based on gravitational and magnetic data,Gaizi fault and West Yingan fault are recognized with activity since Palaeozoic,which is repectively the boundary between Artux and Keping fold and thrust belt,Keping and Wushi fold and thrust belt.(4)It is putforward that Structural deformation of central and western segment of South Tianshan are different in space and time.Basement-involved structure is the mainly structural style in Wushi fold and thrust belt,imbricate thrust structure in Keping fold and thrust belt,blind thrust structure in Artux fold and thrust belt.The period of structural deformation in Keping structural belt is late Miocene to Pliocene, and it is Pleistocene to Holocene in Wushi and Artux structural belt.(5)Through the research of structural balanced section,it was found that crustal shortening amount of central and western segments of southern margin of South Tianshan gradually becomes larger from east to west.The crustal shortening amount in Artux structural belt arrives at 50.5-63.8%,only 14.7-27.1%in Wushi structural belt.(6)Structural deformation model of the three fold and thrust belts in the southern margin of South Tianshan is set up and controlling factors of these structural belts are respectively analyzed.