Hydrogen incorporation mechanisms and diffusion of hydrous defects and silicon ions in olivine: the major rock-forming mineral of the Earth's upper mantle

Abstract

Water solubility of olivine was investigated with controlled pyroxene activity at 0.3 to 5 GPa and 1473 K. Its dependence on pyroxene activity and water fugacity with the activation volume was studies to place constraints on the hydrogen incorporation mechanisms in olivine. Results of water solubility in olivine indicate that hydrogen incorporated with metal vacancies is the dominant mechanism for samples buffered with pyroxene at all pressures. Hydration and dehydration experiments were carried out to study the kinetic properties of hydrogen ions in olivine to determine the diffusivity of hydrous defects associated with individual peaks in IR spectra. Results of diffusivity indicate that hydrogen diffuses in olivine as interstitial hydrogen ions regardless of the incorporation mechanisms. Silicon diffusivity was also study to better understand the point defect chemistry of olivine.