Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Chemical interaction of Fe and Al2O3 as a source of heterogeneity at the Earth's core–mantle boundary

Nature volume 412, pages 527–529 (2001)Cite this article

Abstract

Seismological studies have revealed that a complex texture or heterogeneity exists in the Earth's inner core and at the boundary between core and mantle1,2,3,4. These studies highlight the importance of understanding the properties of iron when modelling the composition and dynamics of the core and the interaction of the core with the lowermost mantle5,6,7. One of the main problems in inferring the composition of the lowermost mantle is our lack of knowledge of the high-pressure and high-temperature chemical reactions that occur between iron and the complex Mg–Fe–Si–Al-oxides which are thought to form the bulk of the Earth's lower mantle. A number of studies6,8,9,10,11,12 have demonstrated that iron can react with MgSiO3-perovskite at high pressures and high temperatures, and it was proposed6,8 that the chemical nature of this process involves the reduction of silicon by the more electropositive iron. Here we present a study of the interaction between iron and corundum (Al2O3) in electrically- and laser-heated diamond anvil cells at 2,000–2,200 K and pressures up to 70 GPa, simulating conditions in the Earth's deep interior. We found that at pressures above 60 GPa and temperatures of 2,200 K, iron and corundum react to form iron oxide and an iron–aluminium alloy. Our results demonstrate that iron is able to reduce aluminium out of oxides at core–mantle boundary conditions, which could provide an additional source of light elements in the Earth's core and produce significant heterogeneity at the core–mantle boundary.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Get just this article for as long as you need it

$39.95

Learn more

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Schematic diagram of electrical heating assemblage.
Figure 2: Examples of X-ray diffraction patterns collected after heating of iron and corundum at different pressures and temperatures.
Figure 3: Mössbauer spectra obtained at room temperature and different pressures before and after laser heat treatment at 2,000(150) K.

References

  1. Vidale, J. E. & Earle, P. S. Fine-scale heterogeneity in the Earth's inner core. Nature 404, 273–275 (2000).

    Article  ADS  CAS  Google Scholar 

  2. Vidale, J. E., Dodge, D. A. & Earle, P. S. Slow differential rotation of the Earth's inner core indicated by temporal changes in scattering. Nature 405, 445–448 (2000).

    Article  ADS  CAS  Google Scholar 

  3. Breger, L., Romanowicz, B. & Rousset, S. New constraints on the structure of the inner core from P′P′. Geophys. Res. Lett. 27, 2781–2784 (2000).

    Article  ADS  Google Scholar 

  4. Carnero, E. J. & Jeanloz, R. Fuzzy patches on the Earth's core–mantle boundary? Geophys. Res. Lett. 27, 2777–2780 (2000).

    Article  ADS  Google Scholar 

  5. Stixrude, L. & Brown, J. M. The Earth's core. Rev. Mineral. 37, 262–283 (1998).

    Google Scholar 

  6. Knittle, E. & Jeanloz, R. Simulating the core–mantle boundary: an experimental study of high-pressure reactions between silicates and liquid iron. Geophys. Res. Lett. 16, 609–612 (1989).

    Article  ADS  CAS  Google Scholar 

  7. Poirier, J. P., Malavergne, V. & Le Mouël, J. L. in The Core–Mantle Boundary Region (eds Gurnis, M., Wysession, M. E., Knittle, E. & Buffet, B. A.) 131–137 (AGU, Washington, 1998).

    Book  Google Scholar 

  8. Knittle, E. & Jeanloz, R. Earth's core–mantle boundary: Results of experiments at high pressures and high temperatures. Science 251, 1438–1443 (1991).

    Article  ADS  CAS  Google Scholar 

  9. Goarant, F., Guyot, F., Peyroneau, J. & Poirier, J. P. High-pressure and high-temperature reactions between silicates and liquid iron alloys in the diamond anvil cell, studied by analytical electron microscopy. J. Geophys. Res. 97, 4477–4487 (1992).

    Article  ADS  CAS  Google Scholar 

  10. Song, X. & Ahrens, T. J. Pressure-temperature range of reactions between liquid iron in the outer core and mantle silicates. Geophys. Res. Lett. 21, 153–156 (1994).

    Article  ADS  CAS  Google Scholar 

  11. Malavergne, V. Etude experimentale à haute pression et haute température du partage des éléments de transition entre les phases du manteau et du noyau de la Terre. Thesis, Univ. Paris 7, (1996).

    Google Scholar 

  12. Tschauner, O. et al. Partitioning of nickel and cobalt between silicate perovskite and metal at pressures up to 80 GPa. Nature 398, 604–607 (1999).

    Article  ADS  CAS  Google Scholar 

  13. Anderson, D. L. Theory of the Earth (Blackwall Scientific, Boston, 1989).

    Google Scholar 

  14. Allègre, C. J., Poirier, J.-P., Humler, E. & Hofmann, A. W. The chemical composition of the Earth. Earth Planet. Sci. Lett. 134, 515–526 (1995).

    Article  ADS  Google Scholar 

  15. Ruff, L. J. & Anderson, D. L. Core formation, evolution, and convection; a geophysical model. Phys. Earth Planet. Inter. 21, 181–201 (1980).

    Article  ADS  CAS  Google Scholar 

  16. McCammon, C. A. Perovskite as a possible sink for ferric iron in the lower mantle. Nature 387, 694–696 (1997).

    Article  ADS  CAS  Google Scholar 

  17. Lauterbach, S., McCammon, C. A., van Aken, P., Langenhorst, F. & Seifert, F. Mössbauer and ELNES spectroscopy of (Mg,Fe)(Si,Al)O3 perovskite: a highly oxidised component of the lower mantle. Contrib. Mineral. Petrol. 138, 17–26 (2000).

    Article  ADS  CAS  Google Scholar 

  18. Hillgren, V. J., Drake, M. J. & Rubie, D. C. High-pressure and high-temperature experiments on core–mantle segregation in the accreting Earth. Science 264, 1441–1445 (1994).

    ADS  Google Scholar 

  19. Li, J. & Agee, C. B. Geochemistry of mantle–core differentiation at high pressure. Nature 381, 686–689 (1996).

    Article  ADS  CAS  Google Scholar 

  20. Fabrichnaya, O. B. & Sundman, B. The assessment of thermodynamic parameters in the Fe–O and Fe–Si–O systems. Cosmochim. Acta 61, 4539–4555 (1997).

    Article  ADS  CAS  Google Scholar 

  21. Dubrovinsky, L. S., Saxena, S. K., Lazor, P. & Weber, H.-P. Structure of β-iron at high temperature and pressure. Science 281, 11–12 (1998).

    Article  ADS  Google Scholar 

  22. Yoo, C. S., Akella, J., Campbell, A. J., Mao, H. K. & Hemley, R. J. Phase diagram of iron by in situ X-ray diffraction: implications for Earth's core. Science 270, 1473–1475 (1995).

    Article  ADS  CAS  Google Scholar 

  23. El Goresy, A., Dubrovinsky, L., Sharp, T. G. & Chen, M. A new monoclinic post-stishovite polymorph of silica in the SNC meteorite Shergotty. Science 288, 1632–1634 (2000).

    Article  ADS  CAS  Google Scholar 

  24. Dubrovinsky, L. S. et al. Stability of ferropericlase in the lower mantle. Science 289, 430–432 (2000).

    Article  ADS  CAS  Google Scholar 

  25. Dubrovinsky, L. S. & Saxena, S. K. Emissivity measurements on same metals and oxides using multiwavelength spectral radiometry. High Pressure High Temp. 31, 393–399 (1999).

    Article  CAS  Google Scholar 

  26. Mao, H. K., Bell, P. M. & Hadidiacos, C. in High-Pressure Research in Mineral Physics (eds Manghnani, M. H. & Syono, Y.) 135–138 (Terra Scientific, Tokyo, and American Geophysical Union, Washington DC, 1987).

    Google Scholar 

  27. Dubrovinsky, L. S., Saxena, S. K. & Lazor, P. High-pressure and high-temperature in situ x-ray diffraction study of iron and corundum to 68 GPa using internally heated diamond anvil cell. Phys. Chem. Minerals 25, 434–441 (1998).

    Article  ADS  CAS  Google Scholar 

  28. Dubrovinskaia, N. A., Dubrovinsky, L. S., Karlsson, A., Saxena, S. K. & Sundman, B. Experimental study of thermal expansion and phase transformations in iron-rich Fe–Al alloys. Calphad 23, 69–84 (1999).

    Article  CAS  Google Scholar 

  29. Pasternak, M. P. et al. High pressure collapse of magnetism in Fe0.94O: Mössbauer spectroscopy beyond 100 GPa. Phys. Rev. Lett. 79, 5046–5049 (1997).

    Article  ADS  CAS  Google Scholar 

Download references

Acknowledgements

We thank D. C. Rubie for comments and discussions. This work was supported by the Swedish Science Foundation (NFR), the Wallenberg and Göran Gustafssons Stiftelse Funds.

Author information

Authors and Affiliations

  1. Department of Earth Sciences, Uppsala University, Uppsala, S-753 36, Sweden

    L. Dubrovinsky, H. Annersten, N. Dubrovinskaia, F. Westman & H. Harryson

  2. Max Planck Institut für Metallforschung, Stuttgart, D 70569, Germany

    O. Fabrichnaya

  3. European Synchrotron Radiation Facility, Grenoble, 38043, France

    S. Carlson

Authors
  1. L. Dubrovinsky
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. H. Annersten
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. N. Dubrovinskaia
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. F. Westman
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. H. Harryson
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. O. Fabrichnaya
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. S. Carlson
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to L. Dubrovinsky.

Supplementary information

Figure 1a

(JPG 72.4 KB)

Diffraction pattern of the sample electrically heated at 59(2) GPa and 1450(50) K processed with GSAS program. The pattern is completely explained as a mixture of two phases – corundum (lower ticks, a=4.4966(6) Å, c=12.286(2) Å) and e -Fe (upper ticks, a=2.3606(3) Å, c=3.7719(4) Å). Background is subtracted.

Figure 1b

(JPG 64.7 KB)

Diffraction pattern of the sample electrically heated at 63(5) GPa and 2200(50) K processed with GSAS program. The pattern could not be described just as a mixture (b) of corundum and e -Fe, but a mixture (c) of corundum (lower ticks, a=4.4915(6) Å, c=12.256(2) Å), e -Fe (middle ticks, a=2.3533(2) Å, c=3.7564(4) Å), and rhombohedral wustite (upper ticks, a=2.843(1) Å, a =58.56(2)o) explain the pattern. Background is subtracted.

Figure 1c

(JPG 68.5 KB)

Diffraction pattern of the sample electrically heated at 63(5) GPa and 2200(50) K processed with GSAS program. The pattern could not be described just as a mixture (b) of corundum and e -Fe, but a mixture (c) of corundum (lower ticks, a=4.4915(6) Å, c=12.256(2) Å), e -Fe (middle ticks, a=2.3533(2) Å, c=3.7564(4) Å), and rhombohedral wustite (upper ticks, a=2.843(1) Å, a =58.56(2)o) explain the pattern. Background is subtracted.

Figure 1d

(JPG 31.7 KB)

Diffraction pattern of the sample laser-heated at 56(2) GPa and 2000(150) K, collected at ID30 beam line at ESRF. Blue bars show calculated intensities of the wustite reflections, and red ones - intensities of Fe3Al reflections.

Figure 2a

(JPG 55 KB)

Schematic diagram of the high-pressure assemblage used for microprobe analysis of the product of the reaction between iron and corundum. Specially shaped stainless steel gasket of 300 m m thickens was indented to 50 m m between diamonds with 300 m m culets. Pure corundum was loaded in to the indentation, covered by a 2 m m thick iron foil and NaCl with several small ruby chips were placed on the top. Pressure was measured by ruby fluorescence. The sample was heated by a Nd:YAG laser at pressures between 68 and 74 GPa and temperatures between 2200 and 2350 K. After complete decompression NaCl was washed out and the chemical composition of the heated foil was analysed.

Figure 2b

(JPG 169 KB)

Backscattered electron images of the recovered sample (dark color corresponds to iron-rich, and light area – to aluminum-rich parts). White circle marks indentation. Chemical composition of heated part of the foil varied from 2 wt.% Al to 10 wt.% Al in good agreement with X-ray data. White areas corresponds to higher Al content, and dark one to higher Fe content. Chemical analyses were obtained using the CAMECA SX-50 electron microprobe, employing a PAP correction program. The operating conditions were: accelerating voltage 20 kV, beam current 50 nA, and 1-2 m m beam diameter. Penetration depth of the beam is less than 2 m m. Counting times were 10 s. The following analyzing crystals were used: TAP for Al Ka and LiF for Fe Ka.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Dubrovinsky, L., Annersten, H., Dubrovinskaia, N. et al. Chemical interaction of Fe and Al2O3 as a source of heterogeneity at the Earth's core–mantle boundary. Nature 412, 527–529 (2001). https://doi.org/10.1038/35087559

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/35087559

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing