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Elasticity of lower-mantle bridgmanite

Nature volume 564, pages E18–E26 (2018)Cite this article

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A Brief Communications Arising to this article was published on 19 December 2018

The Original Article was published on 13 March 2017

arising from A. Kurnosov, H. Marquardt, D. Frost, T. Boffa Ballaran & L. Ziberna Nature 543, 543–546 (2017); https://doi.org/10.1038/nature21390

Bridgmanite ((Mg,Fe)(Fe,Al,Si)O3) is believed to be the most abundant mineral in Earth’s lower mantle, accounting for approximately 75% of the region by volume1,2. Recently, Kurnosov et al.3 reported on the single-crystal elasticity of (Al,Fe)-bearing bridgmanite up to 40 GPa and concluded that a Fe3+/Fe2+ ratio of about two is required to match Preliminary Reference Earth Model (PREM) seismic profiles4 at depths below 1,200 km. Here we use a sensitivity test between measured velocities and elastic constants (Cij) and a covariance matrix analysis to show that their derived elastic constants and velocities have large uncertainties at lower-mantle pressures. These uncertainties invalidate the assertion of ref. 3 of the existence of an Fe3+-rich pyrolitic lower mantle with (Al,Fe)-bearing bridgmanite, and therefore further experimental studies at relevant lower-mantle pressure–temperature conditions are required to reliably infer the mineralogical and geochemical properties of the deep mantle. There is a Reply to this Comment by Kurnosov, A. et al. Nature 564, https://doi.org/10.1038/s41586-018-0742-6 (2018).

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Fig. 1: Cij sensitivity to the velocities and number of measured phonon directions of single-crystal bridgmanite in two crystallographic orientations used in ref. 3 at 40.17 GPa.
Fig. 2: Derived full elastic constants of (Al,Fe)-bearing bridgmanite at high pressure.
Fig. 3: VP and VS profiles of the (Al,Fe)-bearing bridgmanite (Mg0.9Fe0.1Si0.9Al0.1)O3 in the lower mantle.

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Author information

Authors and Affiliations

  1. Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX, USA

    Jung-Fu Lin, Jing Yang & Suyu Fu

  2. Laboratory of Seismology and Physics of Earth’s Interior, School of Earth and Planetary Sciences, University of Science and Technology of China, Hefei, China

    Zhu Mao

  3. Geophysical Laboratory, Carnegie Institution for Science, Washington, DC, USA

    Jing Yang

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  1. Jung-Fu Lin
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Contributions

J.-F.L. initiated the project. Z.M. performed the data processing using the covariance matrix. J.Y. and S.F. performed the sensitivity test analysis. Z.M. and S.F. performed elasticity modelling and error analysis. S.F. prepared the draft Supplementary Information. J.-F.L. wrote the manuscript and all authors participated in the manuscript revision.

Corresponding author

Correspondence to Jung-Fu Lin.

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Declared none.

Extended data figures and tables

Extended Data Fig. 1 Relationship between the uncertainties of the reported elastic constants and our calculated sensitivity of wave velocities for a chosen crystallographic (100) orientation as well as the number of measured phonon directions.

a–d, The azimuthal angle between two adjacent phonon directions is 10°. Error bars in b–d represent standard deviations (1σ) of the elastic constants. Data on the elastic constants are from ref. 6.

Extended Data Fig. 2 Modelling the acoustic velocity of bridgmanite to derive Cij at 11.66 GPa.

Error bars are not shown when smaller than the symbols. Filled data points are the velocity data from Kurnosov et al.3; the dashed lines are velocity-fitting curves from Kurnosov et al.3; and the solid lines are velocity-fitting curves using the Cij derived from the covariance matrix analysis in this study. Red, VP; green, VS1; blue, VS2. The orientations of the crystal platelets are given in parentheses.

Extended Data Fig. 3 Modelling the acoustic velocity of bridgmanite to derive Cij at 31.76 GPa.

Vertical lines represent standard deviations (+1σ) and are not shown when smaller than symbols. Solid data points are velocity data from Kurnosov et al.3; the dashed lines are velocity-fitting curves from Kurnosov et al.3; and the solid lines are velocity-fitting curves using the Cij derived from the covariance matrix analysis in this study. Red, VP; green, Vs1; blue, Vs2. The orientations of the crystal platelets are given in parentheses.

Extended Data Fig. 4 Adiabatic bulk modulus and shear modulus of bridgmanite (Mg0.9Fe0.1Si0.9Al0.1)O3 at high pressure.

a, KS; b, G. Red data points are results using our obtained full elastic constants (Cij); black data points are data reported in Kurnosov et al.3. Black and red dashed lines are the best fits to data from Kurnosov et al.3 and this study, respectively. Error bars represent standard deviations (1σ) and are not shown when smaller than the symbols. In this study, the adiabatic bulk modulus at ambient conditions (KS0) is 250(1) GPa, with the pressure derivative of KS at 300 K (KS′) = 3.2(2), while the shear modulus at ambient conditions (G0) is 159(1) GPa, with the pressure derivative of G0 at 300 K (G′) = 2.2(1).

Extended Data Fig. 5 Comparison of elastic constants of single-crystal bridgmanite as a function of pressure.

Bgm, MgSiO3 bridgmanite; Fe10-Al10-Bgm, (Al,Fe)-bearing bridgmanite with a composition of (Mg0.9Fe0.1Si0.9Al0.1)O3. Error bars represent standard deviations (1σ) and are not shown when smaller than the symbols. Symbols indicate experimental results from the literature; lines indicate theoretical calculations3,6,7,16,17,18,19,20. The filled red circles represent the derived elastic constants in this study using the raw velocity data in Kurnosov et al.3.

Extended Data Fig. 6 Comparison of aggregate compressional and shear wave velocities of single-crystal and polycrystalline bridgmanite at high pressure.

Symbols and solid lines represent experimental results from the literature; dashed lines indicate theoretical calculations3,6,7,8,9,10,11,16,17,18,21,22. The solid red circles are the calculated velocities of (Al,Fe)-bearing bridgmanite using the elastic constants derived in this study (Extended Data Fig. 5), while open black circles are from Kurnosov et al.3. Error bars represent standard deviations (1σ) and are not shown when smaller than the symbols.

Supplementary information

Supplementary Methods

The Supplementary Methods consist of calculation on the sensitivity of wave velocity to variation of elastic constants, uncertainty evaluation on the derived elastic constants, derivations of elasticity from single crystals to aggregates

Supplementary Table 1

Derived full elastic constants of bridgmanite (Mg0.9Fe0.1Si0.9Al0.1)O3 at high pressure in this study using the raw velocity data in Kurnosov et al.3 and the covariance matrix analysis

Supplementary Table 2

Covariance matrix (in GPa2) of elastic constants at 0.48 GPa

Supplementary Table 3

Covariance matrix (in GPa2) of elastic constants at 11.66 GPa

Supplementary Table 4

Covariance matrix (in GPa2) of elastic constants at 15.89 GPa

Supplementary Table 5

Covariance matrix (in GPa2) of elastic constants at 21.25 GPa

Supplementary Table 6

Covariance matrix (in GPa2) of elastic constants at 25.06 GPa

Supplementary Table 7

Covariance matrix (in GPa2) of elastic constants at 31.76 GPa

Supplementary Table 8

Covariance matrix (in GPa2) of elastic constants at 35.44 GPa

Supplementary Table 9

Covariance matrix (in GPa2) of elastic constants at 40.17 GPa

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Lin, JF., Mao, Z., Yang, J. et al. Elasticity of lower-mantle bridgmanite. Nature 564, E18–E26 (2018). https://doi.org/10.1038/s41586-018-0741-7

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