黑色页岩风化的地球化学行为及力学特性研究

发布时间：2018-07-26 14:22

【摘要】：岩石风化是改变地球地表过程的一种主要方式,是控制元素地球化学循环的重要过程,也是影响岩石圈表层人类工程活动的方式之一。与花岗岩、玄武岩及碳酸盐岩等岩石类型相比,黑色页岩富含硫化矿物(黄铁矿为主)和有机质,在表生环境中极易被氧化而发生化学风化作用,并且生成的酸性水和硫酸盐矿物,对岩体造成溶蚀、膨胀等效应,加速黑色页岩的化学风化进程,破坏岩体结构,将造成一系列工程地质和环境地质问题。因此,黑色页岩化学风化的研究可提升岩石风化领域的理论知识,也对工程地质灾害与环境地质评价及预测具有重大意义。本论文以重庆城口地区下寒武统水井沱组黑色页岩为研究对象,选取位于山脊中部的A剖面、近山顶的B剖面和山谷的C剖面,围绕黑色页岩及风化物的物理性质、孔隙特征、显微观形态特征、元素及矿物成分等特征,对黑色页岩化学风化过程的孔隙演化、微观结构、风化程度、矿物风化序列、风化趋势及元素迁移、再分配、分异规律等问题进行系统研究,综合阐述了黑色页岩的风化驱动机制和演化机理;并利用不同pH值的流动态含氧型H2SO4酸性水,将黑色页岩浸泡于酸性水中来模拟页岩风化过程的水岩化学作用,分析了水岩化学作用下黑色页岩的化学-力学耦合特性,阐述了岩石风化的力学特性。通过研究,取得了如下几点主要成果和认识:(1)根据地质样品分析结果表明重庆城口(城巴断块)黑色岩层(页岩)形成于缺氧型的被动大陆边缘,沉积时期的古气候属于干热型气候,在沉积过程中具有明显的热液活动参与,其沉积所处的位置位于浅海陆棚相-斜坡过渡带。(2)基于黑色页岩及风化产物的物理化学性质,黑色页岩化学风化过程中,孔径分布曲线的最大峰值向右移,孔径直径随风化推进而增大,而孔隙分形维数随孔径增大而增大,由单一孔隙结构逐渐演变为多种孔隙结构;微观结构表明随化学风化推进,矿物颗粒间的胶结连接逐渐松散,大颗粒晶体演变为粉粒,呈不规则的多边形形状。(3)黑色页岩风化系统中氧化风化是基岩转为半风化层,再至风化层的关键过程。黑色页岩化学风化过程中,矿物风化的化学反应顺序为:硫化矿物、有机质氧化作用;碳酸盐矿物酸蚀溶解作用;硅酸盐矿物(长石系列)溶解、蚀变及黏土化作用;黏土矿物的溶解及向更稳定黏土矿物转变的过程。根据元素和矿物的质量迁移系数(τTi,j)和质量迁移通量(Mj,flux)显示黑色页岩风化过程中Ca、Mg和Na元素具有明显的贫化现象,近地表处存在Al元素的富集现象,元素的活动性随化学风化程度增大而增加,其活动顺序为:Ca Mg Na Fe Si K A1;根据 Na/K-CIA、K/Ca*-Al/Na、A-CN-K和A-CNK-FM图解显示A剖面处于脱Ca、Mg过程的初级风化阶段,B剖面处于脱Ca、Mg、Na初期的初等—中等风化阶段,C剖面已发生脱Ca、Mg、Na过程,并伴随脱Si作用的中等—强烈风化阶段,结合不同风化指数,各剖面的化学风化强弱程度依次为CBA。(4)微量元素中,Mn、Sr、Ba、Pb、U、V、Cr、Co、Ni、Cu和Zn元素的活动性较强而易发生迁移、再分配和分异现象,Sc、Rb和Th元素的活动性较弱,而高场强元素(HFSE)则发生共生迁移与再分配效应。稀土元素的迁移活动性与pH值相关,其pH值越小则活动性越大,且其活动性随化学风化程度(CIA)增强而增加,稀土元素的在黑色页岩风化过程中的活动性顺序为MREEHREELREE,导致各风化剖面稀土元素分异大小顺序为CBA,使LREE相对HREE呈富集现象;同时各风化剖面的δCeP1,呈铈正异常,指示各剖面环境处于氧化状态。(5)黑色页岩化学风化的本质是水岩化学作用过程,其化学风化主要受到硫化矿物和有机质的氧化作用、水岩化学/物理作用及微观力学作用的控制。运用非平衡态热力学和耗散结构理论,对黑色页岩风化过程进行分析,认为黑色页岩化学风化过程是以热传导、物质流、动量流(机械耗散)和化学反应来推动的不可逆过程,自发经历化学振荡周期,形成以耗散结构模式为框架的渐稳定风化历程的驱动风化机制。(6)利用不同pH值的非平衡流动态含氧型H2SO4酸性水浸泡黑色页岩来模拟酸性水-页岩化学作用过程。在酸性水化学作用下,黑色页岩的单轴抗压强度和弹性模量都有不同程度的降低,水岩化学作用对黑色页岩有由脆性破坏向延性破坏转化的趋势,且水岩化学作用受控于pH值,其pH值越小,水岩化学作用效应也越明显。化学腐蚀后的黑色页岩力学参数与基于次生孔隙率的化学损伤变量具有密切关系,基于次生孔隙率的化学损伤变量建立力学劣化表达式,可以描述酸性水-页岩化学作用过程的化学-力学耦合作用。
[Abstract]:Rock weathering is a major way to change the earth's surface process. It is an important process to control the geochemical cycle of elements. It is also one of the ways to influence human engineering activities on the surface of the lithosphere. Compared with rock types such as granite, basalt and carbonate rocks, black Ye Yanfu containing sulfide minerals (pyrite mainly) and organic matter are in the surface of the surface. The chemical weathering effect of the environment is very easy to be oxidized, and the acid water and sulphate mineral produced in the environment can cause corrosion and expansion to the rock mass, accelerate the chemical weathering process of the black shale and destroy the rock structure, which will cause a series of engineering geology and environmental geological problems. Therefore, the study of chemical weathering of black shale can improve the rock. The theoretical knowledge in the field of weathering is of great significance to the evaluation and prediction of engineering geological disasters and environmental geology. This paper takes the lower Cambrian black shale of the lower Cambrian in Chongqing Chengkou area as the research object, and selects the A section located in the middle of the ridge, the B section of the mountain and the C section of the valley, and the physical properties of the black shale and the weathered objects. The characteristics of quality, pore characteristics, microscopic morphological features, elements and mineral components, etc., have been systematically studied for the pore evolution, microstructure, weathering degree, mineral weathering sequence, weathering trend and element migration, redistribution and differentiation of black shale in chemical weathering process. The mechanism and evolution of the weathering drive of black shale are comprehensively expounded. The mechanism, and using the flow dynamic H2SO4 acid water with different pH values and immersing black shale in acid water to simulate the water rock chemical action of shale weathering process, the chemical mechanical coupling characteristics of black shale under the action of water rock chemistry are analyzed, and the force characteristics of rock weathering are expounded. Through the study, the following main points are obtained. (1) (1) according to the analysis results of geological samples, the black rock layer (Ye Yan) of Chengkou (city bar block) is formed in the passive continental margin of anoxic type, and the paleoclimate in the sedimentary period belongs to the dry and hot climate, and it is involved in the hydrothermal activity during the deposition process, and its location is located in the shallow sea shelf phase transition zone. 2) based on the physical and chemical properties of the black shale and weathering products, the maximum peak of the pore size distribution curve is shifted to the right in the chemical weathering process of the black shale, and the diameter of the pore size increases with the wind, and the pore fractal dimension increases with the increase of the pore size, and the single pore structure gradually evolves into a variety of pore structures, and the microstructure indicates that the pore structure is characterized by chemistry. The cementing connection between mineral particles is gradually loosened by weathering, and the large granular crystals evolve into particles and irregular polygon shapes. (3) the oxidation weathering of the black shale weathering system is the key process of turning the bedrock to semi weathered layer and then to the weathering layer. In the chemical weathering process of black shale, the chemical reaction order of mineral weathering is vulcanized ore The oxidation of organic matter, organic matter oxidation; acid dissolution and dissolution of carbonate minerals; dissolution, alteration and clay mineralization of silicate minerals (feldspar Series); the dissolution of clay minerals and the process of changing to more stable clay minerals. According to the mass transfer coefficient of elements and minerals (tau Ti, J) and mass transfer flux (Mj, flux), C is shown in the weathering process of black shale. The elements of a, Mg and Na have obvious dilution, and there is a enrichment of Al elements in the near surface. The activity of elements increases with the degree of chemical weathering. The sequence of activities is Ca Mg Na Fe Si K A1. In the initial moderate weathering stage of Ca, Mg and Na, the C section has taken off Ca, Mg, Na process, and accompanied with the moderate strong weathering stage of the deactivation of Si, and the chemical weathering intensity of each section is in turn CBA. (4) trace elements. The activity of migration, redistribution and differentiation, the activity of Sc, Rb and Th elements is weak, and the high field strength element (HFSE) has the effect of symbiotic migration and redistribution. The mobility of rare earth elements is related to the pH value. The smaller the pH value is, the greater the activity is, and its activity increases with the degree of study wind (CIA), and the rare earth element is in black shale. The order of activity in the weathering process is MREEHREELREE, which leads to the sequence of different size of rare earth elements in each weathering section of CBA, which makes LREE relatively rich in relative HREE; at the same time, the delta CeP1 of each weathering section shows positive anomalies of cerium, indicating that the environment in each section is in oxidation state. (5) the nature of chemical weathering of black shale is the chemical process of water rock chemistry. The study of weathering is mainly caused by the oxidation of sulphide minerals and organic matter, the chemical / physical action of water rock and the control of the micromechanical action. The process of the weathering of black shale is analyzed by using the theory of non equilibrium thermodynamics and dissipative structure. It is considered that the chemical weathering process of black shale is based on heat conduction, material flow, momentum flow (mechanical dissipation) and chemical process. The irreversible process, driven by the learning reaction, spontaneously experiences the chemical oscillation cycle, and forms the weathering mechanism of the gradual weathering process with the dissipative structure mode as the framework. (6) the chemical process of acid shale chemical action is simulated by soaking the black shale with the dynamic oxygen type H2SO4 acidic water with different pH values to simulate the acid shale chemical process. The uniaxial compressive strength and modulus of elasticity of black shale are reduced in varying degrees. The chemical action of water rock has a tendency to transform from brittle failure to ductile damage to the black shale, and the chemical action of water rock is controlled by the pH value. The smaller the pH value, the more obvious the chemical effect of water rock is. The mechanical parameters of the black shale after chemical corrosion and the mechanical parameters of the black shale after chemical corrosion. The chemical damage variable based on secondary porosity is closely related. The mechanical deterioration expression is established based on the chemical damage variable of secondary porosity, which can describe the chemical mechanical coupling effect of the acid shale chemical process.
【学位授予单位】：西南交通大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P584

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