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- Title
Spin transition of ferric iron in the calcium-ferrite type aluminous phase.
- Authors
Wu, Ye; Qin, Fei; Wu, Xiang; Huang, Haijun; McCammon, Catherine A.; Yoshino, Takashi; Zhai, Shuangmeng; Xiao, Yuming; Prakapenka, Vitali B.
- 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.
- Publication
Journal of Geophysical Research. Solid Earth, 2017, Vol 122, Issue 8, p5935
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1002/2017JB014095