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Experimental study of reaction between perovskite and molten iron to 146 GPa and implications for chemically distinct buoyant layer at the top of the core

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Abstract

Partitioning of oxygen and silicon between molten iron and (Mg,Fe)SiO3 perovskite was investigated by a combination of laser-heated diamond-anvil cell (LHDAC) and analytical transmission electron microscope (TEM) to 146 GPa and 3,500 K. The chemical compositions of co-existing quenched molten iron and perovskite were determined quantitatively with energy-dispersive X-ray spectrometry (EDS) and electron energy loss spectroscopy (EELS). The results demonstrate that the quenched liquid iron in contact with perovskite contained substantial amounts of oxygen and silicon at such high pressure and temperature (P–T). The chemical equilibrium between perovskite, ferropericlase, and molten iron at the P–T conditions of the core–mantle boundary (CMB) was calculated in Mg–Fe–Si–O system from these experimental results and previous data on partitioning of oxygen between molten iron and ferropericlase. We found that molten iron should include oxygen and silicon more than required to account for the core density deficit (<10%) when co-existing with both perovskite and ferropericlase at the CMB. This suggests that the very bottom of the mantle may consist of either one of perovskite or ferropericlase. Alternatively, it is also possible that the bulk outer core liquid is not in direct contact with the mantle. Seismological observations of a small P-wave velocity reduction in the topmost core suggest the presence of chemically-distinct buoyant liquid layer. Such layer physically separates the mantle from the bulk outer core liquid, hindering the chemical reaction between them.

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Acknowledgments

We thank S. Tateno, R. Sinmyo, and E. Takahashi for technical support and discussions. The manuscript was remarkably improved by comments from two anonymous reviewers and the Editor. X-ray diffraction measurements were conducted at SPring-8 (proposal no. 2007A0099 and 2007B0099). This research was supported by grant from JSPS to K.H. and Nanotechnology Network Project.

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Authors and Affiliations

  1. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551, Japan

    Haruka Ozawa & Kei Hirose

  2. Japan Agency for Marine-Earth Science and Technology, Institute for Research on Earth Evolution, 2-15 Natsushima-cho, Yokosuka, Kanagawa, 237-0061, Japan

    Kei Hirose & Nagayoshi Sata

  3. Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, Japan

    Masanori Mitome & Yoshio Bando

  4. Japan Synchrotron Radiation Research Institute, 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo, 679-5198, Japan

    Yasuo Ohishi

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  1. Haruka Ozawa
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  2. Kei Hirose
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  3. Masanori Mitome
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  4. Yoshio Bando
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  5. Nagayoshi Sata
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  6. Yasuo Ohishi
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Correspondence to Haruka Ozawa.

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Ozawa, H., Hirose, K., Mitome, M. et al. Experimental study of reaction between perovskite and molten iron to 146 GPa and implications for chemically distinct buoyant layer at the top of the core. Phys Chem Minerals 36, 355–363 (2009). https://doi.org/10.1007/s00269-008-0283-x

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  • DOI: https://doi.org/10.1007/s00269-008-0283-x

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