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Hydrous olivine unable to account for conductivity anomaly at the top of the asthenosphere

Nature volume 443, pages 973976 (26 October 2006) | Download Citation

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Abstract

The oceanic asthenosphere is observed to have high electrical conductivity, which is highly anisotropic in some locations1,2. In the directions parallel and normal to the plate motion, the conductivity is of the order of 10-1 and 10-2 S m-1, respectively, which cannot be explained by the conductivity of anhydrous olivine2. But because hydrogen can be incorporated in olivine at mantle pressures3,4,5, this observation has been attributed to olivine hydration, which might cause anisotropically high conductivity by proton migration1,2,6,7. To examine this hypothesis, here we report the effect of water on electrical conductivity and its anisotropy for hydrogen-doped and undoped olivine at 500–1,500 K and 3 GPa. The hydrous olivine has much higher conductivity and lower activation energy than anhydrous olivine in the investigated temperature range. Nevertheless, extrapolation of the experimental results suggests that conductivity of hydrous olivine at the top of the asthenosphere should be nearly isotropic and only of the order of 10-2 S m-1. Our data indicate that the hydration of olivine cannot account for the geophysical observations2, which instead may be explained by the presence of partial melt elongated in the direction of plate motion.

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Acknowledgements

We thank K. Baba, K. Fujita, M. Ichiki, T. Koyama, E. Ito and D. Yamazaki for discussions, D. Kohlstedt for comments and suggestions that improved manuscripts, and C. Oka for technical assistance.

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Affiliations

  1. Institute for Study of the Earth’s Interior, Okayama University, Misasa, Tottori 682-0193, Japan

    • Takashi Yoshino
    • , Takuya Matsuzaki
    • , Shigeru Yamashita
    •  & Tomoo Katsura

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Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.

Corresponding author

Correspondence to Takashi Yoshino.

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  1. 1.

    Supplementary Notes

    This file contains Supplementary Methods, Supplementary Discussion (a cause of lower activation energy for proton conductivity) and Supplementary Figure 1 (Electrical conductivity of hydrous olivine single crystals as a function of reciprocal temperature).

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https://doi.org/10.1038/nature05223

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