Program > Browse abstracts by speaker > Demouchy Sylvie

The effect of pressure on hydrogen diffusivity in San Carlos olivine (Fo90) single crystals was determined by performing experiments under hydrothermal conditions at high pressures and high temperatures. The experiments were performed in a multi-anvil press at 6, 9 and 12 GPa, for temperatures between 900 and 1300 °C and for various durations. As in previous studies, gem-quality San Carlos olivines were used and hydrogenated under controlled oxygen fugacity (Ni-NiO) and silica activity (10% natural San Carlos othropyroxene, in equilibrium with the olivine). Polarized Fourier transform infrared spectroscopy was used to quantify the hydroxyl distributions in the samples along crystallographic axes. At 12 GPa and 1100 °C, the resulting chemical diffusion coefficients are slower only by one order of magnitude than in olivine hydrogenated at lower pressure (3 GPa) for the same diffusion mechanism. Under the given experimental conditions, diffusion along the [001] axis is slightly faster than along the [100] or [010]. However, anisotropy fades away at 9 and 12 GPa. We conclude that diffusivity of hydrogen can fairly be estimated by a single mechanism which is controlled by coupled diffusion of protons with trivalent ions. The diffusion coefficients remain rapid when compared with other ionic species in olivine. Nonetheless, the time scale inherent to ionic diffusion also implies the preservation of H enriched reservoirs at kilometer scale within Earth's upper mantle if melting and melt migration do not occur.