Studying Of The Self-Organized Criticality Of Tectonic-fluid-mineralization

Geological system is an extremely complex system which is open,far from equilibrium and interaction dissipative dynamic system in nature.It has the intrinsic basic properties of self-organized criticality,and its spatio-temporal behavior obeys the selforganized critical dynamics of geological processes.The ore-forming system is an important subsystem of the geological system.Its overall evolution follows the fractal dynamics of cascade,collapse-intermittent equilibrium,and ultimately evolute into the self-organized criticality and chaotic edge.Under the influence of the ore-controlling factors,the non-linear interaction between the internal factors of the system and mineralization process leads to the formation of self-organized criticality state in the tectonic-fluid-mineralization system.In such critical state,the chain reaction caused by small events may lead to a major disaster,and large(small)events are caused by the same mechanism.The general characteristics described by self-organizing criticality,such as the relative number of events,do not depend on the micro-mechanism,but a mathematical model that makes the whole theory applicable to dynamic systems.The aim of the nonlinearity and complexity theory is to discuss the overall nature of the mineralization system in a more general sense,without exploring its specific details.The application of non-linear theory and complexity theory,especially fractal/multifractal theory,self-organizing criticality and chaos theory in mineral deposits and ore-forming dynamics,is of great significance to reveal the complex process of mineralization and the element enrichment process.For ore-forming system,the numbersize of ore deposit,geochemical concentration-area,the thickness and number of veins,the length and thickness of veins can be measured by fractal/multifractal model.The selfsimilarity and scale-invariant characteristics of the end products of these ore-forming processes verify the self-organized critical process of the mineralization system.However,fractal models are often used to describe the self-similarity and scale-invariance of the phenomena,such as the aggregation of ore deposits,the inhomogeneity and generalized self-similarity of geological anomalies related to mineralization.Even if distributions of event sizes themselves are important and interesting,our view of nature is mostly based on our understanding of the processes that generate the patterns we observe in field.Therefore,the evolution mechanism of complex mineralization system can be studied by means of some simple ideal models which can reflect the basic characteristics of the real system.When these simple models are robust to various modifications,they can be extended to real systems,analogous to the spring-slider model for studying the selforganizing criticality of earthquakes.The principle of self-organizing criticality can be explained by the cellular automata model.Different from fractal model methods,the core of cellular automata in the application of complexity system is not to describe and explain the complex features of various phenomena,but to start from the law of phenomena,to construct a cellular automaton with specific meaning.The model to simulate and predict the complexity process is the key to revealing the evolutionary nature of the complexity system,which is also lacking in the complexity system research.The cells in cellular automata constitute the evolution of dynamic systems through the interaction of simple rules,which are very important for the construction of cellular automata.In recent years,scholars have proposed a large number of ore-forming dynamics mechanisms and models with the coupled interaction of tectonic-fluid.In this dissertation,taking the shear zone type gold deposit as an example,based on the fluid migration mechanism and the conceptual model of the fault valve,the evolution rules that can be used for the construction of the cellular automaton are extracted,and then the numerical simulation is carried out to study the complexity and self-organized criticality of fluid migration and the formation process of vein and shear zone type gold deposit within the interaction of coupled tectonic-fluid.To be specific,the main research contents and conclusions obtained in the dissertation are as follows:(1)The self-organized criticality of fracture system is analyzed from two aspects in the dissertation.On the one hand,the power law distribution of fault system in mining scale is introduced to verify the self-organized criticality dynamic features of fault system according to the fractal structure feature of self-organized criticality in space.On the other hand,the self-organized criticality of fault system is analyzed from the point of view of numerical simulation based on the variation of Olami-Feder-Christensen(OFC)seismic model.Based on the model,the isotropic,anisotropy and different disturbance strengths of the rock mass are discussed and analyzed.The results show that,as the disturbance strength increases,the fault frequency-size distribution change from power-law to Gaussian shapes.And also the power-law behavior of the frequency-size distribution is a feature of the model only in a limited region of the anisotropy parameter space,as concerns the effects of anisotropic transfer coefficients.(2)The fluid ascent and vein formation process within the interaction of coupled tectonic-fluid are simulated.Based on the conceptual model of mobile hydrofracture,the basic factors of fluid transport and capture in stepwise batches,which mainly consist of the generation mechanism of fault system,the ascent style along fault and the closure mechanism of fault,are extracted.Based on these factors,the cellular automaton is built.The cellular automaton is evolved as the follows: Rock fracture mechanism,the stress on each cell is increased at a uniform driving rate until exceeds the maximum static friction;The fluid is allowed to rise when any cell of the transport zone connected to the fluid source,and the fluid can only move from one fractured cell to an adjacent fractured cell;After the passage of individual fluid batches,the fractured cells close up,and trap the fluid they contain;If the fluid rises to the level of neutral buoyancy,the fluid may get arrested,start to solidify,and form veins.The scale-invariance exhibited by this system indicates that fluid ascent and the formation process of veins is a self-organized critical process and demonstrate that a cellular automaton and fractal model is suitable for capturing and quantifying the spatial and temporal evolution of complex veins;(3)The formation of the shear zone gold deposit with the interaction of coupled tectonic-fluid are simulated,thus a gold geochemical field is generated.Based on the dynamic mechanism of fluid pressure evolution and fault valve evolution in fault zone,a cellular automaton model for the formation of shear zone type gold deposits is established in this dissertation.The model evolution rules are: The fluid pressure in each cell within the impermeable fault zone is increased at a uniform driving rate at each time-step;Porosity reduction mechanisms(e.g.fault compaction and pressure solutions)and a direct fluid source(e.g.dehydration reactions)contribute to the increases of fluid pressure acting on discrete cells of a zero permeability fault plane until a cell fails.Once failure occurs,the failed cells and their immediate neighboring cells are labeled,and the fluid pressure instantaneously equilibrate with these hydraulically connected cells by conserving fluid mass;The fluid pressures in the failed cells are dropped rapidly due to rock ruptures which may induce repeated mineral deposition,and can generate geochemical field;The fracture cell seals,and the steps repeat.The cycles of fluid pressure increase – hydrofracture – fluid pressure decrease – rapid sealing from precipitation can lead the enrichment of geochemical elements,and thus generate a geochemical field with non-uniform distribution.The results suggest that cyclicity in the evolution of the fluid pressure system governed by local permeability is able to reproduce the repeated mineralization superposition process,and generate a complex geochemical pattern characterized by multifractal model.The nonlinear behavior shown in this model exhibits the scale-invariance property and has self-organized critical thresholds where mineral phase transitions are induced by fault failure.All of these results suggest that the simplified model can give a near-perfect expression of the singular mineralization process,and can generate complex multifractal geochemical structures.To sum up,the contribution of the thesis is mainly focused on the construction and parameter selection process of cellular automaton model of tectonic-fluid-mineralization system.Under the constraints of fluid pressure,permeability and density,the dynamic simulation of the mineralization process with the interaction of coupled tectonic-fluid is carried out by means of the cellular automata to analyze the self-organized criticality of the mineralization process,and to depict the migration and enrichment rules of the mineralization elements.The ore-forming cellular automaton provides a new idea and method for further understanding the self-organized criticality of mineralization process.