Deep Structure Analysis And Metallogenic Prediction Of Gangdese Metallogenic Belt Based On Gravity And Magnetic Data

The Gangdese metallogenic belt is a complex tectonic-magmatic-metallogenic belt which is formed in the background of the collision between the Indian continent and Eurasia.It has always been a hot spot in geoscience research.Over the years,a large number of geologists have conducted in-depth research on the deep structure,geodynamic background and regional mineralization of the Gangdese metallogenic belt,which greatly promoted the geological understanding of the Gangdese metallogenic belt.As the only two geophysical data with area constraints in this area,gravity and magnetic data play an important role in interpreting the overall tectonic framework,delineating the horizontal position of intrusive rock mass and describing the deep three-dimensional physical structure.It can also provide a basis for the division of regional metallogenic prospects.In order to extract more reliable and effective information from gravity and magnetic data,the two-dimensional empirical mode decomposition(EMD)potential field separation method combined with power spectrum analysis is studied,and the effectiveness of this method for superposition anomaly separation is verified by model tests.Then,for the factors affecting the edge detection effect,the application effect of different edge detection methods are discussed,and the best combination of edge detection method is obtained.Finally,in order to alleviate the problem of low vertical resolution in gravity and magnetic inversion,a reasonable three-dimensional gravity and magnetic inversion process based on prior information constraints is proposed in this thesis.The above methods are applied to the processing,inversion and interpretation of gravity and magnetic data in the study area,and the main results are as follows.(1)The bouguer and the RTP magnetic anomalies can be divided into three anomalies which are induce by three equivalent layer sources from shallow to deep.Deep gravity and magnetic fields are characterized by north-south zoning and east-west partitioning.The north-south zone is bounded by about 31°N,while the East-West zone is bounded by about 88 °E and 93°~95°E.The low-density bodys are basically consistent with the low speed and high conductor explained by the MT inversion and the seismic receiver function respectively.(2)Integrated edge detection method is applied to gravity and magnetic anomalies.The distribution of basicultrabasic(mixed)and intermediate-acid intrusive bodies are delineated by combining geological data,and the main fracture structures are inferred.(3)The results of gravity and magnetic three-dimensional inversion show that the local residual density in the study area is mainly caused by sedimentary depression,fluctuation of crystalline basement and intrusion of magmatic rocks.Strong magnetic bodies are widely and continuously distributed in the South Gangdese Zone.After analyzing the above results,the following conclusions are drawn.Tibet Plateau is formed by splicing the terrains along the north-south direction and after its formation,it is continuously pushed northward by the Indian plate unevenly,which makes the material properties of the Himalayan terrain and the Gangdese terrain have significant differences in deep from east to west.The east-west direction of low-density bodies in the lower and middle crust of the southern Tibet Plateau is discontinuous.The Bangong Co-Nujiang oceanic crust may have subducted northward and southward subsequently in the west of the northern Gangdese in the range of 84°E ~ 88°E.The oceanic crust subducted northward to the Qiangtang terrane and southward to the Gangdese terrane.Finally,the relationship between the above results and the distribution of deposits is comprehensively analyzed.We have summarized the mineralization factors related to gravity and magnetic and then delineated 21 mineralization prospects.