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Efficacy of the post-perovskite phase as an explanation for lowermost-mantle seismic properties

Nature volume 438, pages 1004–1007 (2005)Cite this article

Abstract

Constraining the chemical, rheological and electromagnetic properties of the lowermost mantle (D″) is important to understand the formation and dynamics of the Earth's mantle and core. To explain the origin of the variety of characteristics of this layer observed with seismology, a number of theories have been proposed1, including core–mantle interaction, the presence of remnants of subducted material and that D″ is the site of a mineral phase transformation. This final possibility has been rejuvenated by recent evidence for a phase change in MgSiO3 perovskite (thought to be the most prevalent phase in the lower mantle2) at near core–mantle boundary temperature and pressure conditions3. Here we explore the efficacy of this ‘post-perovskite’ phase to explain the seismic properties of the lowermost mantle through coupled ab initio and seismic modelling of perovskite and post-perovskite polymorphs of MgSiO3, performed at lowermost-mantle temperatures and pressures. We show that a post-perovskite model can explain the topography and location of the D″ discontinuity, apparent differences in compressional- and shear-wave models1 and the observation of a deeper, weaker discontinuity4,5. Furthermore, our calculations show that the regional variations in lower-mantle shear-wave anisotropy are consistent with the proposed phase change in MgSiO3 perovskite.

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Figure 1: Phase boundary7 and calculation points for the perovskite and post-perovskite polymorphs of MgSiO3.
Figure 2: Seismic properties interpolated from ab initio calculations.
Figure 3: Comparison between real and synthetic S-wave seismograms predicted from the velocity/density profiles shown in Fig. 2.
Figure 4: Fast shear-wave orientation predicted for single-crystal perovskite and post-perovskite polymorphs of MgSiO 3 as a function of azimuth.

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Acknowledgements

We thank D. Dobson for discussions. This work was supported by the Deep Earth System NERC consortium grant.

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Author notes

  1. James Wookey

    Present address: Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ, UK

Authors and Affiliations

  1. School of Earth and Environment, University of Leeds, LS2 9JT, Leeds, UK

    James Wookey

  2. Department of Earth Sciences, University College London, Gower Street, WC1E 6BT, London, UK

    Stephen Stackhouse, John Brodholt & G. David Price

  3. Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, BS8 1RJ, Bristol, UK

    J-Michael Kendall

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Correspondence to James Wookey.

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This file contains Supplementary Methods, Supplementary Tables 1 and 2 and Supplementary Figures 1–4. (PDF 638 kb)

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Wookey, J., Stackhouse, S., Kendall, JM. et al. Efficacy of the post-perovskite phase as an explanation for lowermost-mantle seismic properties. Nature 438, 1004–1007 (2005). https://doi.org/10.1038/nature04345

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