An experimental study of the diffusion of C and O in calcite in mixed CO2-H2O fluid
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T.C. Labotka
,
D.R. Cole
Abstract
The diffusivity of C and O in calcite in mixed CO2-H2O fluid was determined over the range in xCO₂ from 1.0 to about 0.2 at 700 °C, 100 MPa, with selected experiments conducted at pressures to 250 MPa and temperatures of 600 and 800 °C. The diffusivity of C, DC, varies little with xCO₂, although there is some evidence for a slight increase in DC from -5 × 10−18 to -5 × 10−17 cm2/s with decreasing xCO₂. Our data and those of others are consistent with a model for DC ∝ 1/fCO₂. Despite the large uncertainty, we observed that the diffusivity of O, DO, increases from ~2 × 10−16 to ~5 × 10−14 cm2/s with xCO₂ decreasing from 1.0 to 0. There is a good correlation at 700 °C between log DO and log fH₂O regardless of the total pressure, matching the observations of previous workers. The data are consistent with a simple two-component model for the diffusion of O in calcite, one component for diffusion in the presence of CO2 and one in the presence of H2O: DO = DOCO₂ + DOH₂O aH₂O. The activity of H2O is relative to the fugacity at 100 MPa, 700 °C. DOCO₂ is 3.45 × 10−16, and DOH₂O is 3.8 × 10−14 cm2/s. The data indicate that the rate of diffusion of C and O in calcite is controlled by reactions at the surface of calcite. Adsorption of H2O and the creation of vacancies at the surface account for the dependence of the diffusivity on the fugacity of the fluid components. There is little evidence that H itself diffuses into calcite. With this model and the values of DO in pure CO2 (Labotka et al. 2000) and in pure H2O (Farver 1994), the value of DO is predicted over the temperature range 600-800 °C and pH₂O up to 300 MPa, the range of the data. Calculated closure temperatures for diffusive exchange of O between calcite and fluid are reduced by about 150 °C in the presence of an aqueous fluid.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- High-pressure Raman spectroscopic studies of ulvöspinel Fe2TiO4
- Brearleyite, Ca12Al14O32Cl2, a new alteration mineral from the NWA 1934 meteorite
- The 3.65 Å phase in the system MgO-SiO2-H2O: Synthesis, composition, and structure
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- Mesoscale twinning and crystallographic registers in biominerals
- Radiation effects on cathodoluminescence of albite
- Structure refinement of high-pressure hexagonal aluminous phases K1.00Mg2.00Al4.80Si1.15O12 and Na1.04Mg1.88Al4.64Si1.32O12
- Elastic softening of metamict titanite CaTiSiO5: Radiation damage and annealing
- An experimental study of the diffusion of C and O in calcite in mixed CO2-H2O fluid
- Hydrochemical performance and mineralogical evolution of a dispersed alkaline substrate (DAS) remediating the highly polluted acid mine drainage in the full-scale passive treatment of Mina Esperanza (SW Spain)
- The effect of fO₂ on the partitioning and valence of V and Cr in garnet/melt pairs and the relation to terrestrial mantle V and Cr content
- An experimental study of OH solubility in rutile at 500–900 °C, 0.5–2 GPa, and a range of oxygen fugacities
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- Morphology and microstructure of magnetite and ilmenite inclusions in plagioclase from Adirondack anorthositic gneiss
- Thermodynamic properties of stishovite by low-temperature heat capacity measurements and the coesite-stishovite transition boundary
- Mechanisms of Cr and H incorporation in stishovite determined by single-crystal EPR spectroscopy and DFT calculations
- Paramagnetic interactions in the 31P NMR spectroscopy of rare earth element orthophosphate (REPO4, monazite/xenotime) solid solutions
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- Phase stability, elastic behavior, and pressure-induced structural evolution of kalsilite: A ceramic material and high-T/high-P mineral
- A new type of high-pressure low-flow metering valve for continuous decompression: First experimental results on degassing of rhyodacitic melts
- Substitution mechanisms and implications for the estimate of water fugacity for Ti-rich phlogopite from Mt. Vulture, Potenza, Italy
- Calibration for IR measurements of OH in apatite
- Electrolytic coloration and spectral properties of natural calcite crystals
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