| The bottleneck constraints of resources and environment have become the main contradiction of social and economic development.It is still a major task of China's geological work to ensure the safety of China's strategic mineral resources and achievemajor breakthroughsin geological prospecting in the new development stage.Guided by "ecological priority and green development",conducting research on three-dimensional exploration techniques for deep mineral resources,strengthening deep prospecting and expanding the deep "second prospecting space" are the main directions for the high-quality development of China's future mineral resource prospecting.It is well-known that there are many mineral resourcesin Guangxi,e.g.precious metals,nonferrous metals,rare metals,rare earth and radioactive minerals,all of which are genetically correlated to granite intrusion.At present,many of the large and medium-sized deposits discovered in Guangxi are spatially controlled by the distributing feature of magmatic intrusions.The known ore-controlling outcropped or semi-buriedmagmatic intrusions are Dachang(Longxianggai),Damingshan,West Damingshan,Qinjia,Kunlunguan.This fully demonstrates that it is of great significance to predict and search for concealed deposits related to magmatic intrusions by exploring and studying the spatial distribution of these intrusions.Therefore,based on the research of the lithospheric structure and tectonic which restrict the temporal and spatial distribution,andthe study on the distribution characteristics of magmatic rocks in Guangxi as bridges and links,this thesis mainly solves the problems of ore-controlling structures and geological bodies that restrict deep prospecting andprovidestheoretical and technical support for realizing breakthroughs in deep prospecting in Guangxi by grasping the key link of magmatic rock.Based on the systematic analysis of the characteristics of gravity and magnetic anomalies and the inversion of gravity and magnetic data,combined with the lithospheric velocity structure,this paper infers the lithospheric structure characteristics and main structures,establishes the deep geological structure framework,and divides the deep geological structure units of Guangxi.On this basis,the relationship between lithospheric structure and magmatic rocks in Guangxi is studied,the gravity and magnetic anomaly characteristics of magmatic provinces in the region are analyzed,and the development and emplacement characteristics of typical magmatic rocks are discussed,which provides new evidence for further study on the genesis and spatial relationship between magmatic rocks and mineralization.The main content and research results of the thesis include:1.This paper systematically summarizes the previous geological and geophysical survey of magmatic rocks,and sorts out the problemsof magmatic rocks in Guangxi to be solved.2.According to the characteristics of satellite gravity and magnetic anomalies and the analyses of upper mantle velocity structure and density distribution,combined with the crust-upper mantle velocity structure of southeast Asia deduced from the full waveform inversion of seismic waves,this thesis carried out lithosphere and upper mantle structural feature analysis in Guangxi region.The thesis argued that the lithosphere in Guangxi region has a different velocity structure from the crust,with the former is composed of western,northeastern,central and southern blocks,and deduced that there may be an intra-crustal detachment layer in the depth of 20-30 km in the lithosphere.The bottom detachment layer of lithosphere mainly occurs in the depth of40-80 km,it possibly becomes the main channel of magmatic activity in southeastern China since Yanshanian,which is the manifestation of lithospheric thinning process in South China.Accordingly,the lithosphere in Guangxi has formed a deep tectonic framework composed of several blocks under the background of lithospheric thinning in South China in Mesozoic-Cenozoic.3.The thesis used regional gravity and aeromagnetic data to inverse the lithospheric density and magnetic susceptibility structures,and analyzed the causes of lithospheric density and magnetic anomalies and their correlation with surface regional structures based on the obtained results.Combined with the recent research achievements on crust-upper mantle structure and thermal state of coastal areas in south and southeast China,the thesis argued that there is a structural discontinuity between the lower crust and upper mantle in Guangxi,and as reveal by the magnetic susceptibility structure,there may be different extents and degrees of decoupling of middle and lower curst in different regions,which result in the limited upper curst invasion of mantle-derived materials since Mesozoic.This may be the main reason for the “dislocation” between the upper mantle structure and the crust structure in Guangxi.4.In order to improve the resolution of gravity and magnetic anomalies and highlight more useful information,the thesis used wavelet transform to multi-analyze the regional gravity and magnetic anomalies in Guangxi and discussed its geological implications.Based on the features of gravity and magnetic anomalies and their linear distributions,the thesis inferred fault structures and concealed and semi-concealed intrusions in Guangxi and divided eight magmatic rock belts.It is considered that they are basically distributed in the low-density anomaly belt(zone)of the upper crust,and developed in the deep fault near the low-density anomaly zone side,i.e.the front of deep structural steep slope belt.The closer the fault is,the higher the positioning of magmatic rock is.5.Combined with the new achievements and new understanding of geology,two different magmatic rock belts,Xidamingshan intrusionand Qiaoxu medium-basic intrusion with high degree exploration of geophysics and geochemistry,are selected for interpretation and comprehensive analysis.Their distribution form,positioning characteristics,and metallogenic relationship are discussed.In conclusion,based on the lithospheric structure of Guangxi,and research of the magmatic rocks through multi-dimensions and multiple methods,this paperdelineates the concealed rock mass and discusses its spatial distribution,which can not only be used as a direct or indirect prospecting method,but also provide an important geophysical basis for the selection and work deployment of deep prospecting and mineral resources investigation and evaluation.The research results have reference value and significance for basic geological research and deep prospecting in Guangxi. |
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