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H-D Interdiffusion in Single-Crystal Olivine: Implications for Electrical Conductivity in the Upper Mantle

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Title: H-D Interdiffusion in Single-Crystal Olivine: Implications for Electrical Conductivity in the Upper Mantle
Authors: Sun, Wei Browse this author
Yoshino, Takashi Browse this author
Kuroda, Minami Browse this author
Sakamoto, Naoya Browse this author
Yurimoto, Hisayoshi Browse this author →KAKEN DB
Keywords: electrical conductivity
upper mantle
Issue Date: Jun-2019
Publisher: American Geophysical Union
Journal Title: Journal of geophysical research. Solid earth
Volume: 124
Issue: 6
Start Page: 5696
End Page: 5707
Publisher DOI: 10.1029/2019JB017576
Abstract: Knowledge of water content and distribution in the Earth's mantle is critical to understanding the geochemical evolution and geodynamic processes of the Earth, since water can incorporate into nominally anhydrous minerals at high pressure and dramatically affect the chemical and physical properties of mantle minerals. Hydrogen diffusion controls the transport of water and electrical conductivity in the deep Earth but is not fully understood for olivine, the most abundant mineral in the upper mantle. Here we present new hydrogen self-diffusion coefficients determined from interdiffusion in H- and D-doped olivine single-crystal couples at the upper mantle conditions (3-13 GPa and 1,000-1,300 K). Present activation enthalpy for hydrogen migration is significant smaller than previous work determined within a limited measured temperature range. Parallel interdiffusion experiments with diversified water concentrations demonstrated that hydrogen diffusivity strongly accelerated by the water content in olivine. The geometric average diffusion coefficient on olivine is showed as a function of temperature and water content: DH=10-7.40.8*CH2O0.410.01expm2/s. Combined with the Nernst-Einstein relation, the present results can constrain the contribution of water to the electrical conductivity on olivine. It suggests that in situ conductivity measurements on hydrous olivine at low temperatures (<1,000 K) produced too low activation enthalpy to extrapolate to the higher temperatures. Comparison with previous results by conductivity measurements on single-crystal olivine suggests that the literature data except for Dai and Karato (2014) might overestimate water effect on conductivity because of heterogeneity of synthetic single crystals. Because of a change of dominant hydrogen diffusion mechanism at high temperature, this study suggests that the modeling of mantle conductivity with a high activation enthalpy from diffusion data is more trustworthy. Considering a reevaluated activation enthalpy on hydrogen diffusion and water solubility in olivine, comparisons between present conductivity model and geophysical observations suggest that hydration of olivine cannot account for extremely high conductive values (10(-2)-10(-1) S/m) observed in the oceanic asthenosphere.
Rights: An edited version of this paper was published by AGU. Copyright 2019 American Geophysical Union.
Type: article
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 圦本 尚義

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