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

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1 Citation (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
JournalJournal of Geophysical Research: Solid Earth
DOIs
Publication statusAccepted/In press - 2017

Keywords

  • CF phase
  • Elastic anomalies
  • Lower mantle
  • Spin transition
  • Subducted MORB

ASJC Scopus subject areas

  • Geophysics
  • Oceanography
  • Forestry
  • Ecology
  • Aquatic Science
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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    Wu, Y., Qin, F., Wu, X., Huang, H., Mccammon, C. A., Yoshino, T., Zhai, S., Xiao, Y., & Prakapenka, V. B. (Accepted/In press). Spin transition of ferric iron in the calcium-ferrite type aluminous phase. Journal of Geophysical Research: Solid Earth. https://doi.org/10.1002/2017JB014095