摘要:

The important role of pore pressure in promoting such brittle processes as cataclasis, hydraulic fracturing, large‐scale faulting, and earthquakes within the crust is widely accepted in geology and geophysics [Hubbert and Willis, 1957;Hubbert and Rubey, 1959;Handin, 1958;Handin et al., 1963;Brace and Martin, 1968;Healy et al., 1968;Raleigh et al., 1976;Sibson, 1973, 1980;Raleigh and Evernden, 1981]. Provided that fluid pressure is fully communicated with rock pore space, the effective normal stresses that control crack growth, macroscopic fracture, and friction are reduced by the magnitude of the fluid pressui'e. Beyond this physical effect of pore fluids, there are chemical effects of water on the strength of rocks that are also important in governing differential stresseg and flow in the continental crust. Some of these chemical effects of water on rock deformation have long been recognize

ISSN:0148-0227    

DOI:10.1029/JB089iB06p03991

年代:1984

数据来源: WILEY

摘要:

Water and electrolytes cause significant changes in brittle fracture strength and subcritical fracture propagation velocities in quartz and quartz rocks. The changes may be caused, in part, by changes in surface free energy. Experimental fracture surface energies of quartz range from about 400 mJ m−2to about 11.5 J m−2. Thermodynamic surface free energies are likely to be lower than fracture surface energies owing to dissipative energy losses and failure to achieve equilibrium surface structure. Thermodynamic surface free energies are sensitive to environmental composition. Reaction of water vapor with pristine fracture surfaces reduces surface energy by hydroxylation, but the extent of reduction is not known. Adsorption of water vapor on the hydroxylated surface and immersion in liquid water reduce surface energy by 75–230 and 72 mJ m−2respectively. In an electrolyte, the surface free energy is maximum at the point of zero charge, where adsorption of ionic solutes is least. Adsorption of hydrogen ion, hydroxide ion, and electrolytes reduce surface energy as concentration increases, by tens of mJ m−2. All of these surface energy changes are qualitatively consistent with changes in fracture behavior caused by the same

ISSN:0148-0227    

DOI:10.1029/JB089iB06p03997

年代:1984

数据来源: WILEY

摘要:

The recent literature on the kinetics of water‐rock interactions is reviewed. The data are then extended to provide a quantitative framework for the description of weathering and alteration. The available experimental data on dissolution of silicates verifies quantitatively the usual mineral stability series in sedimentary petrology. The rate of hydration of carbonic acid is shown to be a possible limiting factor in water‐rock interactions. The framework is developed to enable use of laboratory dissolution experimental results and thermodynamics to arrive at a rate law applicable up to equilibrium and therefore applicable to natural systems. The kinetic justification for the significance of a water‐rock ratio is discussed. With a proper treatment of fluid flow, the equations are applied to the weathering profile leading to the development of bauxites from nepheline sye

ISSN:0148-0227    

DOI:10.1029/JB089iB06p04009

年代:1984

数据来源: WILEY

摘要:

The kinetics of rock/water interactions are sufficiently rapid that most hydrothermal systems in nature will be in equilibrium with the adjacent rock mass. The bulk rock chemistry buffers the fugacity of oxygen, which in turn fixes the fugacities of water and of hydrogen for a given pressure and temperature. Systems in which only water, oxygen, and hydrogen are present as fluid phases are considered here. Variations in the fugacity of oxygen by several orders of magnitude are possible locally, controlled by variations in local rock chemistry; these lead to relative small variations in the fugacity of water. Incorporation of a hydrogen defect that is capable of acting as an acceptor into silicates leads to a strong dependence of point defect chemistry upon the fugacities of both water and oxygen. The strong dependence on the fugacity of water is capable of explaining the hydrolytic weakening effect, but in view of the strong dependence on oxygen fugacity, the question should also be raised whether it is an oxygen effect that is observed in the classical hydrolytic weakening process or solely a dependence on changes in the fugacity of water. Examples are given for impure natural quartz, olivine, and albite with trace amounts of calcium.

ISSN:0148-0227    

DOI:10.1029/JB089iB06p04026

年代:1984

数据来源: WILEY

摘要:

Diffusional oxygen exchange between quartz and water was studied by determining18O profiles in the quartz using an ion microprobe. Inverse error function plots of the data are linear as required for a diffusion mechanism. One natural and two synthetic samples were used, and although they had different impurity concentrations (OH−, Na, and Al per 106Si atoms are 7–4000, 35–835, and 67–127, respectively), theDvalues were the same within experimental uncertainty. Diffusion parallel tocis about 2 orders of magnitude faster than that normal tocat 700°C, and diffusion normal to the rhombohedron is intermediate. The data indicate a change in slope on an Arrhenius plot at the α‐βboundary. At 100‐MPa (1 kbar) water pressure the preexponential factors (Do, in square centimeters per second) and activation energies (Q, in Kilojoules per mole) for α quartz (500°–550°C) are as follows:Do= 190 andQ= 284 parallel toc, andDo= 8 × 10−2andQ= 238 normal to the rhombohedron. Forβquartz (600°–800°C),Do= 4 × 10−7andQ= 142 parallel toc,Do= 9 × 10−7andQ= 155 normal to the rhombohedron; andDo= 1 × 10−4andQ= 234 normal toc.Dincreases withPH 2 O, and between 25 and 350 MPa logDversus logƒH 2 Ohas a slope of approximately 1.1. TheseDvalues are all several orders of magnitude larger than previously reported values for o

ISSN:0148-0227    

DOI:10.1029/JB089iB06p04039

年代:1984

数据来源: WILEY

摘要:

Oxygen self‐diffusion, Dox, has been monitored in single‐crystal quartz in the temperature range 515°–850°C under hydrothermal conditions. In the beta field, between 700° and 850°C, the data are represented by two linear Arrhenius relations for transport parallel and perpendicular to c. Values for Do(m2s−1) are 2.09×10−11parallel to c and 3.16×10−10perpendicular to (101¯0). Values for ΔH (kJ mol−1) are 138.54 parallel to c and 203.72 perpendicular to (101¯0). At 700°C, in the total pressure range 11.5–100 MPa, Doxis independent of water (f(H2O)) and oxygen (f(O2)) fugacities between the Ni‐NiO and Fe3O4‐Fe2O3buffers. The results are consistent with diffusion via a simple charged vacancy mechanism under an extrinsic point defect regime. Further experiments are required to confirm the nature of the mobile oxygen defect. A key aspect of the results is the observation that at the low water fugacities of the present experiments a hydrogen‐containing defect appears to play no role in the oxygen transport mechanism. This is in contrast to other published sets of data and leads directly to the requirement for detai

ISSN:0148-0227    

DOI:10.1029/JB089iB06p04047

年代:1984

数据来源: WILEY

摘要:

The study of water in minerals with infrared spectroscopy is reviewed with emphasis on natural and synthetic quartz. Water can be recognized in minerals as fluid inclusions and as isolated molecules and can be distinguished from hydroxide ion. The distinction between very small inclusions and aggregates of structurally bound molecules is difficult. New studies of synthetic quartz using near‐infrared spectroscopy are reported. These demonstrate that water molecules are the dominant hydrogen containing species in synthetic quartz but that this water is not in aggregates large enough to form ice when coole

ISSN:0148-0227    

DOI:10.1029/JB089iB06p04059

年代:1984

数据来源: WILEY

摘要:

This paper presents a review of our current understanding of environmentally induced slow crack growth in glasses, single crystals, and polycrystalline ceramics. It is shown that the rate of crack growth is controlled by the chemical activity of the active species in the environment as well as by the stress intensity at the crack tip. A recently developed molecular model of stress‐induced chemical reaction between vitreous silica and water is described. The implications of this model for the effects of other chemical species on crack growth are discussed. Finally, the complications introduced by the presence of grain boundaries in polycrystalline ceramics are pointed ou

ISSN:0148-0227    

DOI:10.1029/JB089iB06p04072

年代:1984

数据来源: WILEY

摘要:

A review is presented of the experimental data on subcritical crack growth in geological materials. The main parameters describing subcritical crack growth are the critical stress intensity factor Kc, the subcritical crack growth limit Ko, and the stress intensity factor‐crack velocity (K‐v) relationship between Koand Kc. The K‐v data are presented in terms of an equation in which the crack velocity depends on stress intensity factor raised to a power n because this is common practice in experimental studies. These data are presented as tables and in synoptic diagrams. For silicates the value of n increases as the environment becomes depleted in hyroxyl species and with increase in the microstructural complexity of the solid. Values of n as low as 9.5 have been found for tensile cracking of quartz in basic environments and as high as 170 for tensile cracking of basalt in moist air. Insufficient experimental data are available to predict subcritical crack growth behavior at depth in the earth's crust without major extrapolations of the data base. Schematic outlines are presented, therefore, of the probable influence on subcritical crack growth of some key parameters in the crustal environment. These include stress intensity factor, temperature, pressure, activity of corrosive environmental agent, microstructure, and residual strains. In addition, a discussion is presented of the likely magnitude of the subcritical crack growth limit. For stress corrosion tensile crack growth of quartz a limit of approximately 0.2 of the critical stress intensity factor is inferred from theoretical calculations. Further problems discussed with regard to the extrapolation of experimental data to crustal conditions include the choice of a suitable equation to describe crack growth and the magnitude of parameters in these equations. A brief discussion of the double torsion testing method is presented in order to aid the interpretation of experimental results because it is almost the sole method used to study subcritical cracking in

ISSN:0148-0227    

DOI:10.1029/JB089iB06p04077

年代:1984

数据来源: WILEY

摘要:

The chemical role of water and other aqueous environments in crack propagation was examined in a series of crack propagation tests in natural and synthetic quartz. The potential roles of surface free energy reduction and zeta potential (surface electrostatic potential) in chemical weakening were specifically examined by running the crack propagation tests in the presence‐of six surface active aqueous environments which varied sub‐stantially in these parameters with respect to quartz. Calorimetric and electrophoresis tests were also undertaken in order to determine the degree of reduction of the surface energy of quartz produced by each chemical environment and the zeta potential between each environment and quartz. It was found that there was a moderate correlation between reduction of the crack propagation stress of quartz and the degree by which the surface energy was reduced in the presence of a particular environment. No such correlation was found with respect to zeta potential. It was also observed that some of the chemical environments appeared to produce highly branched cracks in quartz. This branching effect is probably related to the velocity of crack propagat

ISSN:0148-0227    

DOI:10.1029/JB089iB06p04115

年代:1984

数据来源: WILEY