Hydrogen self-diffusion in single crystal olivine and electrical conductivity of the Earth’s mantle

• Published in: Scientific reports 2017-07, Vol.7 (1), p.5344-10, Article 5344
• Main Authors: Novella, Davide, Jacobsen, Benjamin, Weber, Peter K., Tyburczy, James A., Ryerson, Frederick J., Du Frane, Wyatt L.
• Format: Article
• Language: English
• Subjects: 704/2151/2809; 704/2151/431; Chemical properties; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Crystals; Diffusion; Diffusion coefficient; Earth; Electrical conductivity; GEOSCIENCES; Humanities and Social Sciences; Hydrogen; Minerals; multidisciplinary; Physicochemical properties; Science; Science (multidisciplinary); Upper mantle
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-05113-6

Nominally anhydrous minerals formed deep in the mantle and transported to the Earth’s surface contain tens to hundreds of ppm wt H 2 O, providing evidence for the presence of dissolved water in the Earth’s interior. Even at these low concentrations, H 2 O greatly affects the physico-chemical properties of mantle materials, governing planetary dynamics and evolution. The diffusion of hydrogen (H) controls the transport of H 2 O in the Earth’s upper mantle, but is not fully understood for olivine ((Mg, Fe) 2 SiO 4 ) the most abundant mineral in this region. Here we present new hydrogen self-diffusion coefficients in natural olivine single crystals that were determined at upper mantle conditions (2 GPa and 750–900 °C). Hydrogen self-diffusion is highly anisotropic, with values at 900 °C of 10 −10.9 , 10 −12.8 and 10 −11.9 m 2 /s along [100], [010] and [001] directions, respectively. Combined with the Nernst-Einstein relation, these diffusion results constrain the contribution of H to the electrical conductivity of olivine to be σ H  = 10 2.12 S/m·C H2O ·exp −187kJ/mol/(RT) . Comparisons between the model presented in this study and magnetotelluric measurements suggest that plausible H 2 O concentrations in the upper mantle (≤250 ppm wt) can account for high electrical conductivity values (10 −2 –10 −1  S/m) observed in the asthenosphere.