Hydrogen diffusion in spinel grain boundaries and consequences for chemical homogenization in hydrous peridotite

摘要: Hydrogen can be stored in the structure of nominally anhydrous minerals as point defects, and these impurities substantially modify many physical properties Earth’s mantle minerals. However, rocks are composed mineral grains separated by grain boundaries interphase boundaries. Therefore, a potential hydrogen reservoir, should given proper attention. Here, I report an experimental investigation into diffusion through polycrystalline aggregates. Sintering experiments were performed using gas-medium high-pressure vessel at under pressure 300 MPa over temperature range 900–1,250°C. The assembly consisted cylinder aluminous spinel + olivine crystals with talc main source. A Ni capsule was used to buffer oxygen fugacity Ni–NiO. Experimental durations varied from 5 min h. presence measured Fourier-transform infrared spectroscopy. calculation coefficients based on estimation characteristic distance. absence or recorded ‘hydrogen sensor’ olivines embedded aggregate allows bounds this Results presented here suggest that effective only one order magnitude faster (~10−9 m2s−1 1,000°C) than single crystal along [100] axis. Resulting for boundary four orders crystal, but diffusivity is not fast enough affect mobility sizes greater ~1 mm. Thus, very limited chemical homogenization would occur hydrous peridotite incompatible volatile element, such hydrogen.