Letter | Published:

A perovskitic lower mantle inferred from high-pressure, high-temperature sound velocity data

Nature volume 485, pages 9094 (03 May 2012) | Download Citation

Abstract

The determination of the chemical composition of Earth’s lower mantle is a long-standing challenge in earth science. Accurate knowledge of sound velocities in the lower-mantle minerals under relevant high-pressure, high-temperature conditions is essential in constraining the mineralogy and chemical composition using seismological observations1, but previous acoustic measurements were limited to a range of low pressures and temperatures. Here we determine the shear-wave velocities for silicate perovskite and ferropericlase under the pressure and temperature conditions of the deep lower mantle using Brillouin scattering spectroscopy2. The mineralogical model that provides the best fit to a global seismic velocity profile1 indicates that perovskite constitutes more than 93 per cent by volume of the lower mantle, which is a much higher proportion than that predicted by the conventional peridotitic mantle model. It suggests that the lower mantle is enriched in silicon relative to the upper mantle, which is consistent with the chondritic Earth model. Such chemical stratification implies layered-mantle convection with limited mass transport between the upper and the lower mantle.

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Acknowledgements

We greatly appreciate the comments by I. Jackson. Suggestions from E. Ohtani, C. Bina, S. Karato and S.-H. Shim improved the manuscript. We also thank N. Sata and Y. Asahara for their experimental assistance at SPring-8. This study was performed under the approval of SPring-8 (proposals no. 2008B0099 and 2009A0087).

Author information

Affiliations

  1. Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, Sendai, Miyagi 980-8578, Japan

    • Motohiko Murakami
  2. Japan Synchrotron Radiation Research Institute, Sayo, Hyogo 679-5198, Japan

    • Yasuo Ohishi
    •  & Naohisa Hirao
  3. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan

    • Kei Hirose
  4. Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Kanagawa 237-0061, Japan

    • Kei Hirose

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Contributions

M.M. planned the research and did experimental and analytical work. M.M. and K.H. wrote the paper. All authors were involved in the experiments and discussed the results.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Motohiko Murakami.

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https://doi.org/10.1038/nature11004

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