Diffusion rates of hydrogen defect species associated with site-specific infrared spectral bands in natural olivine

We investigated hydrogen transport in naturally occurring, iron-bearing samples of San Carlos olivine that were hydrogenated at confining pressures 200 or 300 MPa and 1173 to 1303 K dehydrogenated room pressure 1191 1358 K. Chemical diffusion coefficients determined from profiles for individual O-H-stretching bands series infrared spectra orthogonal directions across each sample. Within experimental uncertainty, the diffusivities associated with all are good agreement one another both hydrogenation dehydrogenation experiments. Hydrogenation proceeds by two mechanisms, as reported previously. The faster process involves interstitial protons coupled a counter-flux polarons, proton rate-limiting hydrogenation. For this mechanism, is along [100] direction than [010] [001], consistent anisotropy conductivity olivine. slower parallel flux metal vacancies, vacancy [001] [010], previously cations Diffusivities our new experiments identical magnitude those earlier This demonstrates validity studies used results analyze xenocrysts mantle xenoliths determine rates magma ascent source regions Earth's interior.