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Kurnosov et al. reply

Nature volume 564, pages E27–E31 (2018)Cite this article

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replying to J.-F. Lin, Z. Mao, J. Yang & S. Fu Nature 564, https://doi.org/10.1038/s41586-018-0741-7 (2018)

In our Letter1, we reported elastic properties for single crystals of Earth’s most abundant mineral, (Al,Fe)-bearing bridgmanite, at pressures of the lower mantle, measured by simultaneous Brillouin spectroscopy and X-ray diffraction. We used our data together with previously published results to model seismic wave velocities for Earth’s lower mantle. Contradicting previous work2, we showed that seismic wave velocities derived for a pyrolitic mantle containing (Al,Fe)-bearing bridgmanite are consistent with the seismic record in the lower mantle up to a depth of about 1,200 km. In the accompanying Comment, Lin et al.3 claim that our measurements are problematic because we measured insufficient velocity data and used insensitive crystal orientations to constrain the full elastic tensor and hence conclude that the uncertainties given in ref. 1 are underestimated. Here, we address their concerns3 and show them to be unwarranted.

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Fig. 1: Bulk and shear moduli obtained using the ‘global fit’ (grey squares, solid curves) in comparison to the results of fitting every pressure point individually (red diamonds).
Fig. 2: Elastic constants derived at 40.4 GPa by fitting the synthetic data.
Fig. 3: Uncertainty analysis for the ‘global fit’.

References

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Authors and Affiliations

  1. Bayerisches Geoinstitut BGI, University of Bayreuth, Bayreuth, Germany

    A. Kurnosov, H. Marquardt, D. J. Frost, T. Boffa Ballaran & L. Ziberna

  2. Department of Earth Sciences, University of Oxford, Oxford, UK

    H. Marquardt

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  1. A. Kurnosov
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  2. H. Marquardt
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  3. D. J. Frost
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  4. T. Boffa Ballaran
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  5. L. Ziberna
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Contributions

A.K., H.M., D.J.F. and T.B.B. discussed the content. A.K. performed the robustness test. H.M. wrote the paper draft. All authors commented on the manuscript.

Corresponding author

Correspondence to H. Marquardt.

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Declared none.

Extended data figures and tables

Extended Data Fig. 1 Raw data collected on single-crystal bridgmanite at two selected pressures and fits from our Letter.

The solid curves are fits to the grey data using the best-fit global model (the ‘global fit’ of ref. 1) and the red dashed curves are individual fits. a, c, Platelet 1. b, d, Platelet 2. a, b, Data collected at 11.8 GPa; c, d, data collected at 31.9 GPa. We note that the orientation of the crystals changed slightly during pressure increase, but was measured at every pressure in our experiment. A ‘tilt’ correction was employed for crystal platelet 1, as mentioned in our Letter1. The procedure is further explained in the Supplementary Information (containing the raw data).

Extended Data Fig. 2 Illustration of how the synthetic dataset at 40.4 GPa was generated using the elastic constants reported in our Letter.

For every pressure point and platelet, velocities in 18 propagation directions were calculated over an angular range of 360° to simulate in-plane rotations between individual measurements that are representative of our low pressure measurements where no overlap of peaks occurred (solid symbols). We randomly changed the velocity values by up to 0.5% to simulate errors typical for single velocity measurements by Brillouin spectroscopy in the diamond anvil cell13. a, Illustration of a complete velocity dataset, using crystal platelet 1 as an example. b, Illustration of a reduced dataset, using crystal platelet 2 as an example. This assumes limited data availability owing to peak overlap or elasto-optic coupling. The example in b corresponds to a situation where 20 directions have been measured in total (10 on each crystal). Solid and dotted curves are results from the ‘global fit’.

Supplementary information

Supplementary Information

This file contains a statement about the raw data presented in the Excel data file

Supplementary Data

This file contains the raw data as they were collected.

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Kurnosov, A., Marquardt, H., Frost, D.J. et al. Kurnosov et al. reply. Nature 564, E27–E31 (2018). https://doi.org/10.1038/s41586-018-0742-6

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