An experimental study of OH solubility in rutile at 500–900 °C, 0.5–2 GPa, and a range of oxygen fugacities
-
Clinton V. Colasanti
,
Elizabeth A. Johnson
Abstract
The solubility of OH in pure synthetic rutile was experimentally constrained at 0.5-2.0 GPa and 500-900 °C, in equilibrium with four oxygen fugacity (ƒO₂) buffering mineral assemblages: hematite-magnetite (HM), nickel-nickel oxide (NNO), cobalt-cobalt oxide (CCO), and iron-wüstite (IW). The hydroxyl concentration ([OH], in parts per million H2O by weight) of equilibrated rutile crystals was characterized by FTIR spectroscopy. Measurements at 1 GPa at individual ƒO₂ buffers demonstrate that [OH] in rutile depends strongly on temperature: at HM, [OH] increases from 48 to 267 ppm as temperature rises from 500 to 900 °C, whereas at NNO, [OH] increases from 108 to 956 ppm over the same temperature range. The [OH] in rutile also increases strongly with decreasing ƒO₂ at any pressure and temperature, and exhibits a slight, linear, positive dependence on pressure at a given temperature and ƒO₂. The observed systematic dependences on pressure, temperature, and ƒO₂ indicate that hydrogen substitutes into rutile as hydroxyl, (OH), via forward progress of the reaction Ti4+O2 + ½H2O = Ti3+O(OH) + ¼O2. Our measured [OH] values are significantly greater than those determined in previous studies on finer-grained, polycrystalline rutile, which likely suffered diffusive loss of H during quenching. This is supported by our observation of narrow, OH-depleted rims on otherwise high-OH run products, pointing to minor but important diffusive H loss from crystal rims during quenching. Fitting of isothermal variations in composition with ƒO₂ at 1 GPa and temperature indicates nearly ideal, multi-site mixing of the TiO2-TiOOH solid solution. A fit to the entire data set suggests standard volume, enthalpy, and entropy of the hydration reaction of, respectively, 1.90 ± 0.48 cm3/mol, 219.3 ± 1.3 kJ/mol, and 19.9 ± 1.4 J/(mol∙K) (1σ uncertainty). These constraints form the basis for use of [OH] in rutile as a thermobarometer and oxybarometer in experimental and natural systems. The moderate to high [OH] in nominally anhydrous rutile at all investigated temperatures, pressures, and ƒO₂ values imply that Ti3+ may be higher than previously suspected in some terrestrial geologic settings.
© 2015 by Walter de Gruyter Berlin/Boston
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- Structure refinement of high-pressure hexagonal aluminous phases K1.00Mg2.00Al4.80Si1.15O12 and Na1.04Mg1.88Al4.64Si1.32O12
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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
- Water in upper mantle pyroxene megacrysts and xenocrysts: A survey study
- 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
- The growth interval of garnet in the UHP eclogites from the Dabie orogen, China
- Structural studies of NH4-exchanged natrolites at ambient conditions and high temperature
- 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
- Garnet sector and oscillatory zoning linked with changes in crystal morphology during rapid growth, North Cascades, Washington
- 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
- Compositional dependent compressibility of dissolved water in silicate glasses
- In situ monitoring of lepidocrocite bioreduction and magnetite formation by reflection Mössbauer spectroscopy
- Direct determination of europium valence state by XANES in extraterrestrial merrillite: Implications for REE crystal chemistry and martian magmatism
