Letter | Published:

The effect of water on the electrical conductivity of olivine

Nature volume 443, pages 977980 (26 October 2006) | Download Citation

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Abstract

It is well known that water (as a source of hydrogen) affects the physical and chemical properties of minerals—for example, plastic deformation1,2,3 and melting temperature4—and accordingly plays an important role in the dynamics and geochemical evolution of the Earth. Estimating the water content of the Earth’s mantle by direct sampling provides only a limited data set from shallow regions (<200 km depth)5. Geophysical observations such as electrical conductivity are considered to be sensitive to water content6, but there has been no experimental study to determine the effect of water on the electrical conductivity of olivine, the most abundant mineral in the Earth’s mantle. Here we report a laboratory study of the dependence of the electrical conductivity of olivine aggregates on water content at high temperature and pressure. The electrical conductivity of synthetic polycrystalline olivine was determined from a.c. impedance measurements at a pressure of 4 GPa for a temperature range of 873–1,273 K for water contents of 0.01–0.08 wt%. The results show that the electrical conductivity is strongly dependent on water content but depends only modestly on temperature. The water content dependence of conductivity is best explained by a model in which electrical conduction is due to the motion of free protons. A comparison of the laboratory data with geophysical observations7,8,9,10 suggests that the typical oceanic asthenosphere contains 10-2 wt% water, whereas the water content in the continental upper mantle is less than 10-3 wt%.

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Acknowledgements

Z. Jing, Z. Jiang and I. Katayama provided the technical assistance that made this research possible. T. Kawazoe was most helpful with the error estimates. This work was supported by the NSF of China and the NSF of the United States. Author Contributions S.-i.K. supervised the whole project and completed the paper. The experimental measurements of conductivity and the data analysis were made largely by D.W. and M.M. in collaboration with Y.X.

Author information

Affiliations

  1. Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China

    • Duojun Wang
  2. Institute of Geology, China Earthquake Administration, Beijing 100029, China

    • Duojun Wang
  3. Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA

    • Duojun Wang
    • , Mainak Mookherjee
    • , Yousheng Xu
    •  & Shun-ichiro Karato
  4. Department of Mathematics, University of Connecticut, Storr, Connecticut 06269, USA

    • Yousheng Xu

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Competing interests

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

Corresponding author

Correspondence to Shun-ichiro Karato.

Supplementary information

Word documents

  1. 1.

    Supplementary Notes 1

    A summary of experimental results. All experiments were conducted at 4 GPa. is water content, T is temperature and σis electrical conductivity.

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  1. 1.

    Supplementary Notes 2

    A broad peak at ~3,400 cm-1 from the original spectrum is used to estimate the water content in the grains in each sample.

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DOI

https://doi.org/10.1038/nature05256

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