Effects of Fe spin transition on the elasticity of (Mg, Fe)O magnesiowüstites and implications for the seismological properties of the Earth's lower mantle

S. Speziale*, V. E. Lee, S. M. Clark, J. F. Lin, M. P. Pasternak, R. Jeanloz

*Corresponding author for this work

Research output: Contribution to journalArticle

43 Citations (Scopus)

Abstract

High-pressure x-ray diffraction of (Mg0.80 Fe0.20)O at room temperature reveals a discontinuity in the bulk modulus at 40 (±5) GPa, similar to the pressure at which an electronic spin-pairing transition of Fe2+ is observed by Mössbauer spectroscopy. We determine the zero-pressure bulk modulus of low-spin magnesiowüstite to be between K70=136 and 246 GPa, with a pressure derivative (∂Kτ/∂P)τ0 between 5.2 and 3.9. The best fit unit-cell volume at zero pressure, V0=71 (±5) Å, is consistent with past estimates of the ionic radius of octahedrally-coordinated low-spin Fe2+ in oxides. A spin transition at lower-mantle depths between 1100 and 1900 km (40-80 GPa) would cause a unit-cell volume decrease (ΔV) of 3.7 (±0.5) to 2.0 (±0.1) percent and bulk sound velocity increase (Δvø) of 7.6 (±4) percent at 40 GPa and 7.6 (±1.2) percent at 80 GPa. Even in the absence of a visible seismic discontinuity, we expect the spin transition of iron to imply correction to current compositional models of the lower mantle, with up to 10 mol percent increase of magnesiowüstite being required to match the seismological data.

Original languageEnglish
Article numberB10212
Pages (from-to)1-12
Number of pages12
JournalJournal of Geophysical Research
Volume112
Issue numberB10
DOIs
Publication statusPublished - 4 Oct 2007
Externally publishedYes

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