Abstract
The kinetics of hydrogenation of dry synthetic forsterite single crystals was determined by performing experiments under hydrothermal conditions. The experiments were performed at 1.5 GPa, 1000 °C for 3 h in a piston-cylinder apparatus, or at 0.2 GPa, 900–1110 °C, for 3–20 h in TZM cold-seal vessels. The oxygen fugacity was buffered using Fe–FeO or Ni–NiO powders. Polarized Fourier transform infrared spectroscopy was utilized to quantify the hydroxyl distributions in the samples after the experiments. Hydrogenation rates were measured parallel to the three crystallographic axes from profiles of water content as a function of position in the samples. The chemical diffusion coefficients are marginally slower than in natural iron-bearing olivine for the same diffusion process, but the anisotropy of diffusion is the same, with the [001] axis the fastest direction of diffusion and [100] the slowest. Fits of the diffusion data to an Arrhenius law yield similar activation energies for each of the crystallographic axes; a global fit to all the diffusion data gave 211 ± 18 kJ mol−1, in reasonable agreement with the previous results for natural olivine. Thus hydrogenation most likely occurs by coupled diffusion of protons and octahedrally coordinated metal vacancies. The diffusion rates are fast enough to modify water contents within xenoliths ascending from the mantle, but probably too slow to permit a total equilibration of forsterite or olivine crystals.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Acknowledgments.
The authors thank Mervyn Paterson for supplying the Fo2 forsterite crystal, Hans Keppler and Burkhart Schmidt for their help with the infrared spectrometer and the TZM cold-seal vessels, Falko Langenhost for the TEM observations and Anke Markert for the ICP-AES analysis. The authors would like also to thank James Tyburczy and an anonymous reviewer for their constructive reviews. This work was supported by the European Community through the Human Potential Programme HPRN-CT-2000-00056, HydroSpec.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Demouchy, S., Mackwell, S. Water diffusion in synthetic iron-free forsterite. Phys Chem Minerals 30, 486–494 (2003). https://doi.org/10.1007/s00269-003-0342-2
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/s00269-003-0342-2