TY - JOUR
T1 - H-D Interdiffusion in Single-Crystal Olivine
T2 - Implications for Electrical Conductivity in the Upper Mantle
AU - Sun, Wei
AU - Yoshino, Takashi
AU - Kuroda, Minami
AU - Sakamoto, Naoya
AU - Yurimoto, Hisayoshi
N1 - Funding Information:
As per AGU's Data Policy, the data in this study are listed in the references and supporting information. The authors appreciate D. Yamazaki and N. Tsujino for beneficial discussions and S. Yamashita for measurements by Fourier‐transform infrared spectroscopy. This work was supported by Grants‐in‐Aid for Scientific Research Grants JP15H05827 and 24244087 to T. Y. from the Japan Society for the Promotion of Science. We thank two anonymous reviewers who helped us improve the manuscript.
Publisher Copyright:
©2019. American Geophysical Union. All Rights Reserved.
PY - 2019/6
Y1 - 2019/6
N2 - 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: (Formula presented.). 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.
AB - 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: (Formula presented.). 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.
KW - electrical conductivity
KW - hydrogen
KW - interdiffusion
KW - olivine
KW - upper mantle
KW - water
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U2 - 10.1029/2019JB017576
DO - 10.1029/2019JB017576
M3 - Article
AN - SCOPUS:85068220870
VL - 124
SP - 5696
EP - 5707
JO - Journal of Geophysical Research
JF - Journal of Geophysical Research
SN - 0148-0227
IS - 6
ER -