Stability of ferrous-iron-rich bridgmanite under reducing midmantle conditions

Sang-Heon Shim, Brent Grocholski, Yu Ye, E. Ercan Alp, Shenzhen Xu, Dane Morgan, Yue Meng, Vitali B. Prakapenka

Research output: Contribution to journalArticle

20 Scopus citations

Abstract

Our current understanding of the electronic state of iron in lowermantle minerals leads to a considerable disagreement in bulk sound speed with seismic measurements if the lower mantle has the same composition as the upper mantle (pyrolite). In the modeling studies, the content and oxidation state of Fe in the minerals have been assumed to be constant throughout the lower mantle. Here, we report high-pressure experimental results in which Fe becomes dominantly Fe2+ in bridgmanite synthesized at 40-70 GPa and 2,000 K, while it is in mixed oxidation state (Fe3+/∑Fe = 60%) in the samples synthesized below and above the pressure range. Little Fe3+ in bridgmanite combined with the strong partitioning of Fe2+ into ferropericlase will alter the Fe content for these minerals at 1,100- to 1,700-km depths. Our calculations show that the change in iron content harmonizes the bulk sound speed of pyrolite with the seismic values in this region. Our experiments support no significant changes in bulk composition for most of the mantle, but possible changes in physical properties and processes (such as viscosity and mantle flow patterns) in the midmantle.

Original languageEnglish (US)
Pages (from-to)6468-6473
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume114
Issue number25
DOIs
StatePublished - Jun 20 2017

Keywords

  • Bridgmanite
  • Bulk sound speed
  • Lower mantle
  • Oxidation state
  • Spin transition

ASJC Scopus subject areas

  • General

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