Solubility of hydrogen in olivine: Dependence on temperature and iron content

Yong Hong Zhao, S. B. Ginsberg, D. L. Kohlstedt

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The solubility of hydrogen in Mg-Fe olivines as a function of temperature and iron concentration was investigated by hydrothermally annealing single crystals of synthetic forsterite and San Carlos olivine. Experiments were performed at temperatures between 1,273 and 1,573 K on samples with compositions between Fa0 and Fa16.9 under a confining pressure of 300 MPa in a gas-medium apparatus with oxygen fugacity, fO2, buffered by the Ni:NiO solid-state reaction and silica activity, aSiO2, buffered by the presence of enstatite. Hydroxyl concentrations were determined from infrared spectra obtained from polished thin sections in crack-free regions ≤ 50 μm in diameter. Hydroxyl solubility increases systematically with increasing temperature and with increasing iron content. Combined with published results on the dependence of hydroxyl solubility on water fugacity and pressure, the present results can be summarized by the relation COH = AfH2O1exp [-(ΔE0{} + PΔV{}0 /RT] exp (αXFa/RT) with A = 90 ± 10 H/106Si/MPa, α = 97 ± 4 kJ/mol, ΔE0{} = 50 ± 2 kJ/mol, and ΔV{}0 = (10.0 ± 0.1 ×10-6 m3/mol. The subscript {} indicates the hydroxyl ions are incorporated primarily as defect pairs, probably of the type {(OHO - VMe - (OH)O}x ≡ (2H)Mex. Under similar thermodynamic conditions, the water content in olivine in the martian mantle and in olivine from gabbros may be as much as 5 to 25 times larger than in the less iron-rich olivine dominant in Earth's mantle.

Original languageEnglish (US)
Pages (from-to)155-161
Number of pages7
JournalContributions to Mineralogy and Petrology
Issue number2
StatePublished - Apr 2004

Bibliographical note

Funding Information:
Acknowledgments Financial support for this research was provided by the National Science Foundation through grant EAR-0106981 and the National Science Foundation of China through grants 10299040-1 and 40174028. The authors thank Shun Karato for providing the synthetic forsterite crystal, Steve Mackwell for invaluable comments and insights, and Mark Zimmerman for critical help with the design of the experiments.

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