Study On The Tectonic Characteristics Of Central Yili Basin Based On Comprehensive Interpretation Of Gravity And Magnetic Data

Yili basin is a superimposed basin,which is clamped in the Tianshan orogenic belt,central Asia.There are good prospects for oil and gas but not yet a breakthrough.The region centered Baishidun subarch is a prospective area of oil and gas.Due to the structural units located in a plurality of the intersection area,the geological structure is more complex and the exploration work is few,which restricts the further deployment of exploration and delineation of favorable exploration area.Determining the position of geological faults and boundaries of units,inferring the extent and distribution of igneous rocks,identifying geological structural framework are the basis of the further work on this area.This thesis studied and improved some gravity and magnetic data processing methods,including the signal and noise separation method based on energy threshold using two-dimensional wavelet,a comparative study of a variety of potential field separation methods and some boundary identification methods.The high-precision gravity and magnetic data of the area were processed by using a preferable combination of a lot of methods.The gravity and magnetic anomalies and other processing results were obtained based on research objectives and the actual situation.This thesis also had a research on the three-dimensional inversion theory of gravity and magnetic data and a data processing technique of actual data of three-dimensional inversion was summarized.It focused on the data preprocessing,the various parameters setting,the priori information adding and the evaluation standard of results and improved the accuracy of the solution model significantly.Under the constraints of a variety of prior information,the three-dimensional density and magnetic models under the study area of about 11 km deep were built.Based on high-precision gravity and magnetic data processing results,three-dimensional inversion results,combined with 4 MT sections inversion results and other prior information,60 faults and boundaries location which were mainly in NE were divided and 44 of them were new.It focused on the morphological characteristics and tectonic units impact of 6 deep faults that control sedimentary structures.It redefined 5 boundaries location and clarified the contact relationship of the 5 tectonic units in study area,in which the 2 boundaries location of Wusunshan area and Southern slope change larger than others.Baishidun subarch was thought belongs to Yining depression because of features of gravity and magnetic field and geological structure.It also delineated 6 areas within 20 igneous rocks which were mainly mafic igneous rocks and got three-dimensional morphology.According to the distribution characteristics of faults zone and tectonic units,combined with processing and inversion results,main geological structure characteristics were summarized.This dissertation thought there was an asymmetry north-south depression which had thicker sediment in north than south in the Baishidun subarch centered region.The southern boundary of Awulale may be overthrust and the south of study area overlapped on Wusunshan area.Hydrocarbon-generating center was controlled by faults and the depth was gradually shallower from north to south.Based on structural characteristics and the distribution of igneous rock and faults,this thesis delineated 2oil and gas favorable storage areas— the Southern slope of Yining depression favorable area and Baishidun subarch favorable area.