Spin transition of ferric iron in the calcium-ferrite type aluminous phase

Ye Wu, Fei Qin, Xiang Wu, Haijun Huang, Catherine A. McCammon, Takashi Yoshino, Shuangmeng Zhai, Yuming Xiao, Vitali B. Prakapenka

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

Abstract

We investigated Fe-free and Fe-bearing CF phases using nuclear forward scattering and X-ray diffraction coupled with diamond anvil cells up to 80 GPa at room temperature. Octahedral Fe3+ ions in the Fe-bearing CF phase undergo a high-spin to low-spin transition at 25–35 GPa, accompanied by a volume reduction of ~2.0% and a softening of bulk sound velocity up to 17.6%. Based on the results of this study and our previous studies, both the NAL and CF phases, which account for 10–30 vol % of subducted MORB in the lower mantle, are predicted to undergo a spin transition of octahedral Fe3+ at lower mantle pressures. Spin transitions in these two aluminous phases result in an increase of density of 0.24% and a pronounced softening of bulk sound velocity up to 2.3% for subducted MORB at 25–60 GPa and 300 K. The anomalous elasticity region expands and moves to 30–75 GPa at 1200 K and the maximum of the VΦ reduction decreases to ~1.8%. This anomalous elastic behavior of Fe-bearing aluminous phases across spin transition zones may be relevant in understanding the observed seismic signatures in the lower mantle.

Original languageEnglish
Pages (from-to)5935-5944
Number of pages10
JournalJournal of Geophysical Research: Solid Earth
Volume122
Issue number8
DOIs
Publication statusPublished - Aug 2017

Keywords

  • CF phase
  • elastic anomalies
  • lower mantle
  • spin transition
  • subducted MORB

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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