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

ABSTRACT: Nominally anhydrous minerals formed deep in the mantle and transported to the Earth's surface contain tens to hundreds of ppm wt H₂O, providing evidence for the presence of dissolved water in the Earth's interior. Even at these low concentrations, H₂O greatly affects the physico-chemical properties of mantle materials, governing planetary dynamics and evolution. The diffusion of hydrogen (H) controls the transport of H₂O in the Earth's upper mantle, but is not fully understood for olivine ((Mg, Fe)₂SiO₄) 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 m²/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 ?_H?=?10^2.12S/m·C_H2O·exp^{-187kJ/mol/(RT)}. Comparisons between the model presented in this study and magnetotelluric measurements suggest that plausible H₂O 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.

SUBMITTER: Novella D 

PROVIDER: S-EPMC5509734 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature