Evidence is presented to support the conclusion that pore fluid pressures tresses PF during regional metamorphism are generally greater than or equal to the minimum principal compressive stress S3. The resultant very low effective stresses σ lead to significantly increased porosity and permeability, even at moderate to high metamorphic temperatures. Permeabilities between 10−18 and 10−15 m2 and are considered to be common, resulting in rapid fluid migration and the dominance of advective (infiltrative) over diffusive mass transport, even over relatively small distances. In view of the importance of intergranular mass transport to rock deformation during metamorphism, a mobile, high-pressure fluid will have substantial rheological effects, especially in polyphase rocks. The fluid is capable of influencing the rate of dislocation creep in a number of ways. More importantly, advective mass transport along fluid pressure gradients can give rise to a solution transfer deformation mechanism that competes with conventional pressure solution. The rate of deformation by advective mass transport could be controlled by a number of processes, including dissolution kinetics, advective transport rates, and the rate of crack growth. A specific deformation model, based on advective transport rate control,is developed, which can produce strain at competitive rates but with stress and temperature dependences of unusual form.

High fluid pressures during regional metamorphism and deformation: Implications for mass transport and deformation mechanisms

The solubility of quartz in H2O in the lower crust and upper mantle

Synthetic fluid inclusions in natural quartz. III. Determination of phase equilibrium properties in the system H2O-NaCl to 1000°C and 1500 bars

Geochemical modeling based on equilibrium and irreversible thermodynamics has, in the last 20 years, become a well recognized tool for understanding the processes of water-rock interactions and predicting their consequences. SOLMINEQ.88 is the latest version of the 1973-computer program code SOLMNEQ and its various updated versions. This program is general and comprehensive, but is particularly useful for modeling geochemical interactions in sedimentary basins and petroleum reservoirs where petroleum, aqueous organic species, and subsurface pressure play an important role. SOLMINEQ.88 is written in FORTRAN-77 and has an improved algorithm over that in previous versions for faster execution. This version has a revised thermodynamic database, more inorganic (260) and organic (80) aqueous species and minerals (220), computes the activity coefficients in brines using Pitzer equations, and computes pH and mineral solubilities at subsurface temperatures (0° to 350° C) and pressures (1 to 1,000 bars). New modeling options in SOLMINEQ.88 can be used to study the effects of boiling, mixing of solutions and partitioning of gases between water, oil and gas phases. SOLMINEQ.88 has several mass transfer options that can be used to predict the effects of ion exchange, adsorption/desorption, and dissolution/precipitation of solid phases. A user-friendly interactive code SOLINPUT is available for use to generate and update the input file for SOLMINEQ.88. The numerous assumptions and limitations of geochemical models like SOLMINEQ.88 are described in detail because they indicate the range of conditions where the models can be used successfully. The limitations may be related to incomplete and/or unreliable chemical and mineral data as well as to uncertainties in equilibrium constants for aqueous species and minerals. The modeling capabilities and the limitations of the various options in this code are described with output from selected examples. Alberta Research Council Oil Sands and Hydrocarbon Recovery Department Edmonton, Alberta, Canada Battelle Memorial Institute Columbus, Ohio

https://pubs.usgs.gov/wri/1988/4227/report.pdf

Robert W. Potter

Papers

An equation correlating the solubility of quartz in water from 25° to 900°C at pressures up to 10,000 bars