Abnormal Elasticity of Fe-Bearing Bridgmanite in the Earth's Lower Mantle

Suyu Fu, Jing Yang, Yanyao Zhang, Takuo Okuchi, Catherine McCammon, Hyo Im Kim, Sung Keun Lee, Jung Fu Lin

    Research output: Contribution to journalArticlepeer-review

    15 Citations (Scopus)

    Abstract

    We measured the effect of pressure on the compressional and shear wave velocity (VP, VS) as well as density of Fe-bearing bridgmanite, Mg0.96(1)Fe2+ 0.036(5)Fe3+ 0.014(5)Si0.99(1)O3, using impulsive stimulated light scattering, Brillouin light scattering, and X-ray diffraction, respectively, in diamond anvil cells up to 70 GPa at 300 K. A drastic softening of VP by ~6(±1)% is observed between 42.6 and 58 GPa, while VS increases continuously with increasing pressure. A significant reduction in Poisson's ratio from 0.24 to 0.16 occurs at ~42.6–58 GPa, while VS increases by ~3(±1)% above ~40 GPa compared to MgSiO3-bridgmanite. Thermoelastic modeling of the experimental results shows that the observed elastic anomaly of Fe-bearing bridgmanite is consistent with a spin transition of octahedrally coordinated Fe3+ in bridgmanite. These results challenge traditional views that Fe enrichment will reduce seismic velocities, suggesting that seismic heterogeneities in the mid-lower mantle may be due to a spin transition of Fe in Fe-bearing bridgmanite.

    Original languageEnglish
    Pages (from-to)4725-4732
    Number of pages8
    JournalGeophysical Research Letters
    Volume45
    Issue number10
    DOIs
    Publication statusPublished - May 28 2018

    Keywords

    • bridgmanite
    • elasticity
    • lower mantle
    • spin transition

    ASJC Scopus subject areas

    • Geophysics
    • Earth and Planetary Sciences(all)

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