4:45 PM - 5:00 PM
[MIS17-12] New frontiers in fluid-rock interaction process
Chemical reactions (dissolution and precipitation reactions) in rocks affect the chemical composition of fluid, and the chemical composition of water in turn affects the chemical reactions in rocks. Fluid-rock interaction refers to the process by which rocks and water influence each other. Currently, fluid-rock interaction research is being actively conducted in a wide range of fields, including not only igneous processes, metamorphic processes, hydrothermal alteration of the ocean floor, element cycling, and life science both inside and outside the Earth, but also engineering fields (transport of contaminants in groundwater, circulation of geothermal fluids, formation of hydrothermal ore deposits, geological disposal of radioactive waste, CO2 storage, etc.).
Geochemical modeling evaluates the stability of chemical species at various temperatures, pressures, and redox states based on the thermodynamics of rocks and fluids, and provide quantitative interpretations and predictions of fluid-rock interaction. The geochemical modeling is based on equilibrium constants for minerals and aqueous species at high temperatures and pressures. The most common and widely used approach for predicting equilibrium constants is the HKF equation of state, which was developed by Helgeson et al. in the 1970s and 1980s. The subsequent development of the SUPCRT92 software (Johnson et al., 1992) made it possible for many researchers to use equilibrium constants based on the HKF equation for a wide range of temperature and pressure conditions. However, the HKF equation is applicable only to pressures below 0.5 GPa and water density above 0.35 g cm-1. As a result, application of geochemical modeling has been impossible for decades to evaluate fluid-rock interactions in subduction zones, as well as in specific geothermal reservoirs and ore deposits where low-density fluids are important.
However, in recent years, the application range of the HKF equation has been theoretically expanded, and quantitative interpretation and prediction of rock-water interactions based on geochemical calculations have become possible even in tectonic settings where they were previously impossible. Deep Earth Water (DEW) model was developed by Sverjensky et al. (2013), and the application pressure range of the HKF equation was extended to 6.0 GPa. Moreover, even under temperature and pressure conditions where the density of water is less than 0.35 g cm-1, recent study showed equilibrium constants can be obtained using empirical models (e.g., Okamoto et al. 2021). In this talk, I will introduce examples of geochemical calculations and the findings obtained in tectonic settings that can be called the frontier areas of fluid-rock interactions.
References
Johnson, J. W., Oelkers, E. H., & Helgeson, H. C. (1992). SUPCRT92: A software package for calculating the standard molal thermodynamic properties of minerals, gases, aqueous species, and reactions from 1 to 5000 bar and 0 to 1000 C. Computers & Geosciences, 18(7), 899-947.
Sverjensky, D. A., Harrison, B., & Azzolini, D. (2014). Water in the deep Earth: The dielectric constant and the solubilities of quartz and corundum to 60 kb and 1200 C. Geochimica et Cosmochimica Acta, 129, 125-145.
Okamoto, A., Ishii, H., Oyanagi, R., & Tsuchiya, N. (2021). Albite–K-feldspar–quartz equilibria in hydrothermal fluids at 400, 420° C and 20–35 MPa: Experimental measurements and thermodynamic calculations. Geothermics, 94, 102109.
Geochemical modeling evaluates the stability of chemical species at various temperatures, pressures, and redox states based on the thermodynamics of rocks and fluids, and provide quantitative interpretations and predictions of fluid-rock interaction. The geochemical modeling is based on equilibrium constants for minerals and aqueous species at high temperatures and pressures. The most common and widely used approach for predicting equilibrium constants is the HKF equation of state, which was developed by Helgeson et al. in the 1970s and 1980s. The subsequent development of the SUPCRT92 software (Johnson et al., 1992) made it possible for many researchers to use equilibrium constants based on the HKF equation for a wide range of temperature and pressure conditions. However, the HKF equation is applicable only to pressures below 0.5 GPa and water density above 0.35 g cm-1. As a result, application of geochemical modeling has been impossible for decades to evaluate fluid-rock interactions in subduction zones, as well as in specific geothermal reservoirs and ore deposits where low-density fluids are important.
However, in recent years, the application range of the HKF equation has been theoretically expanded, and quantitative interpretation and prediction of rock-water interactions based on geochemical calculations have become possible even in tectonic settings where they were previously impossible. Deep Earth Water (DEW) model was developed by Sverjensky et al. (2013), and the application pressure range of the HKF equation was extended to 6.0 GPa. Moreover, even under temperature and pressure conditions where the density of water is less than 0.35 g cm-1, recent study showed equilibrium constants can be obtained using empirical models (e.g., Okamoto et al. 2021). In this talk, I will introduce examples of geochemical calculations and the findings obtained in tectonic settings that can be called the frontier areas of fluid-rock interactions.
References
Johnson, J. W., Oelkers, E. H., & Helgeson, H. C. (1992). SUPCRT92: A software package for calculating the standard molal thermodynamic properties of minerals, gases, aqueous species, and reactions from 1 to 5000 bar and 0 to 1000 C. Computers & Geosciences, 18(7), 899-947.
Sverjensky, D. A., Harrison, B., & Azzolini, D. (2014). Water in the deep Earth: The dielectric constant and the solubilities of quartz and corundum to 60 kb and 1200 C. Geochimica et Cosmochimica Acta, 129, 125-145.
Okamoto, A., Ishii, H., Oyanagi, R., & Tsuchiya, N. (2021). Albite–K-feldspar–quartz equilibria in hydrothermal fluids at 400, 420° C and 20–35 MPa: Experimental measurements and thermodynamic calculations. Geothermics, 94, 102109.