Spin transition, substitution, and partitioning of iron in lower mantle minerals

Spin transition and substitution of Fe3+ in Fe3+AlO3-bearing MgSiO3 perovskite (Pv) and post-perovskite (PPv) were examined up to 200 and 165 GPa, respectively, at room temperature by X-ray emission spectroscopy (XES) and XRD. The results of XES and XRD indicate that in Pv high spin (HS) Fe3+ at the dodecahedral (A) site replaces Al at the octahedral (B) site and becomes low spin (LS) between 50 and 70 GPa with pressure, while in PPv LS Fe3+ occupies the B-site and Al occupies the A-site above 80–100 GPa. The Fe3+–Al coupled substitution seems to be at work in both Pv and PPv. Combining these results on Fe3+ with the recent first-principles calculations on Fe2+ in Pv and PPv, the spin transition and substitution of iron in pyrolitic lower mantle minerals are proposed. Further, their effects on iron-partitioning among the lower mantle minerals are discussed.

•Spin states of Fe3+ in Al-bearing perovskite and post-perovskite were clarified.•Fe3+-Al exchange reaction between A and B sites strongly affects the Fe3+ spin state.•The model of the spin transitions of iron in lower mantle minerals is proposed.•Effect of spin transition on iron-partitioning in lower mantle minerals is discussed.