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- Title
Effect of Fe<sup>3+</sup> on Phase Relations in the Lower Mantle: Implications for Redox Melting in Stagnant Slabs.
- Authors
Sinmyo, Ryosuke; Nakajima, Yoichi; McCammon, Catherine A.; Miyajima, Nobuyoshi; Petitgirard, Sylvain; Myhill, Robert; Dubrovinsky, Leonid; Frost, Daniel J.
- Abstract
Recent studies have revealed that Earth's deep mantle may have a wider range of oxygen fugacities than previously thought. Such a large heterogeneity might be caused by material subducted into the deep mantle. However, high‐pressure phase relations are poorly known in systems including Fe3+ at the top of the lower mantle, where the subducted slab may be stagnant. We therefore conducted high‐pressure and high‐temperature experiments using a multi‐anvil apparatus to study the phase relations in a Fe3+‐bearing system at 26 GPa and 1573–2073 K, at conditions prevailing at the top of the lower mantle. At temperatures below 1923 K, MgSiO3‐rich bridgmanite, an Fe3+‐rich oxide phase, and SiO2 coexist in the recovered sample. Quenched partial melt was observed above 1973 K, which is significantly lower than the solidus temperature of an equivalent Fe3+‐free bulk composition. The partial melt obtained from the Fe3+‐rich bulk composition has a higher iron content than coexisting bridgmanite, similar to the Fe2+‐dominant system. The results suggest that strong mantle oxygen fugacity anomalies might alter the subsolidus and melting phase relations under lower mantle conditions. We conclude that (1) a small amount of melt may be generated from an Al‐depleted region of a stagnant slab, such as subducted former banded‐iron‐formation, and (2) Fe3+ is not transported into the deep part of the lower mantle because of its incompatibility during melting. Key Points: We determined phase relationships of Fe3+‐rich system at top of the lower mantleMelting temperature of Fe3+‐rich system is lower than Fe2+‐dominant systemFe3+ may not be transported into the deep lower mantle because of its incompatibility
- Subjects
HETEROGENEITY; BRIDGMANITE; OXIDATION-reduction reaction; FUGACITY; IRON
- Publication
Journal of Geophysical Research. Solid Earth, 2019, Vol 124, Issue 12, p12484
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2019JB017704