Compressibility of ferropericlase at high-temperature: evidence for the iron spin crossover in seismic tomography

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1016/j.epsl.2023.118296. This is version 2 of this Preprint.

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Authors

Viktoria Elisabeth Trautner , Stephen Stackhouse, Alice Turner, Paula Koelemijer, D. Rhodri Davies, Alba San José Méndez, Niccolo Satta, Alexander Kurnosov, Hanns-Peter Liermann, Hauke Marquardt

Abstract

The iron spin crossover in ferropericlase, the second most abundant mineral in Earth’s lower mantle, causes changes in a range of physical properties, including seismic wave velocities. Understanding the effect of temperature on the spin crossover is essential to detect its signature in seismic observations and constrain its occurrence in the mantle. Here, we report the first experimental results on the spin crossover-induced bulk modulus softening at high temperatures, derived directly from time-resolved x-ray diffraction measurements during continuous compression of (Mg0.8Fe0.2)O in a resistive-heated dynamic diamond-anvil cell. We present new theoretical calculations of the spin crossover at mantle temperatures benchmarked by the experiments. Based on our results, we create synthetic seismic tomography models to investigate the signature of the spin crossover in global seismic tomography. A tomographic filter is applied to allow for meaningful comparisons between the synthetic models and data-based seismic tomography models, like SP12RTS. A negative anomaly in the correlation between Vs variations and Vc variations (S-C correlation) is found to be the most suitable measure to detect the presence of the spin crossover in tomographic models. When including the effects of the spin crossover, the misfit between the synthetic model and SP12RTS is reduced by 63%, providing strong evidence for the presence of the spin crossover, and hence ferropericlase, in the lower mantle. Future improvement of seismic resolution may facilitate a detailed mapping of spin state using the S-C correlation, providing constraints on mantle temperatures, thanks to the temperature sensitivity of the spin crossover.

DOI

https://doi.org/10.31223/X5GH2P

Subjects

Earth Sciences, Geophysics and Seismology, Mineral Physics

Keywords

Ferropericlase, lower mantle, Spin crossover, Elastic softening, Ab initio computations, Seismic tomography

Dates

Published: 2023-04-06 08:13

Last Updated: 2023-07-14 21:49

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License

CC-By Attribution-NonCommercial-NoDerivatives 4.0 International

Additional Metadata

Conflict of interest statement:
None

Data Availability (Reason not available):
Data will be deposited as separate tables on the figshare online repository after acceptance by a peer-reviewd journal.