Model Study Of The Tectonic-magmatic-metallogenical System In Tongling Ore Cluster Area

The tectonic-magmatic-metallogenic system of Tongling ore cluster area is appropriate for investigation of the intraplate metallogeny. The structural deformation, magmatic activities and ore-forming processes in this system show complex manifestations independently and close interrelationship among them. In order to determine the simple control mechanism for the complexity in the system and clarify the interrelationship among the three different geological events, the system was studied step by step via Model Study (MS), which is an effective analysis method for complex system. The structural deformation was studied from four interrelated aspects. Firstly, in virtue of the field observation, it is suggested that the complex deformation field of the caprocks in Tongling area was mainly developed during Indosinian-Yansanian epoch, and the caprocks had experienced two-stage deformation, the first stage of which is compression, and the second is shear. Secondly, mechanical analysis and analogue experiment not only verify the above view, but also qualitatively remolded 3D deformation field and drew some new knowledge about tectonic evolution and deformation characteristics of the caprocks with multi-layer structure. The detailed results showed that the area experienced four deformation processes, i.e. "compression-shearing-rotation-drag", therefore, drag basin developed at the opposite corners, the irregular boundaries and the complex 3D deformation field formed. In the 3D deformation field, two basic structural assemblages (SA) with the property of self-similarity were developed, one of which has the form of folding in the upper part and faulting in the lower part (SA1), while the other has the form of faulting in the upper part and folding in the lower part (SA2). Thirdly, trend surface analysis indicated that the middle part of Tongling area underwent jacking process due to the WE magmatic activity from the bottom besides buckling. Finally, 3D shape of strata was semi-qualitively recurred by numerical simulations. Ore-forming magma is characterized by low density, low viscosity and high volatile content. The statistics of the fractal calculation of structure, magma and ore deposits revealed that it was fold that controlled the emplacement of magma. Theoretical analysis and geological facts validated that the NE high-angle reverse faults and the basal faults were the flow channels for shallow magma. Furthermore, the study of "surplus space method"pointed the migration pattern of shallow magma could be expressed by "concentrating to the middle in depth and spreading all around in shallow". Based on the cognitions above, it was put forward that shallow magma in Tongling area intruded as "dyking/dike"model, and the variance of chemical compositions in different magmatic bodies was resulted from the impulsive motions of dikes. In general, the transporting and locating of dikes were controlled by SA1. The SA1 and the magma movement in this network constitute the "Cell", which was well developed in different scales and its specific form varied with the practical geological settings. According to the attributes of the "Cell"and its local geological background, it is deduced that the magma in the middle and lower crust transported as the mode of "mesoscale pervasive flow". It is confirmed that the metallization centralized mainly in Yanshanian epoch through the field observations, paleogeographic environment analysis, metallogenic chronology, stable isotopes and REE analysis of ores, cluster analysis of metallogenic elements of regional sedimentary rocks and principal component analysis of metallogenic elements of ores in typical ore deposits. Additionally, fluid physicochemical parameters and field phenomena made it clear that ore-forming fluid had the feature of multi-stage evolution. In the early stage, fluid activity was influenced by rapid decrease of magma external pressure, during which fluid immiscibility dominated; while in the late stage, fluid activity was affected by magma...