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Effect of Fe 3+ on Phase Relations in the Lower Mantle: Implications for Redox Melting in Stagnant Slabs
Author(s) -
Sinmyo Ryosuke,
Nakajima Yoichi,
McCammon Catherine A.,
Miyajima Nobuyoshi,
Petitgirard Sylvain,
Myhill Robert,
Dubrovinsky Leonid,
Frost Daniel J.
Publication year - 2019
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2019jb017704
Subject(s) - mantle (geology) , mineral redox buffer , partial melting , subduction , geology , slab , silicate perovskite , solidus , peridotite , transition zone , oxygen , geochemistry , mineralogy , analytical chemistry (journal) , materials science , geophysics , chemistry , alloy , metallurgy , tectonics , paleontology , organic chemistry , chromatography
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 Fe 3+ 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 Fe 3+ ‐bearing system at 26 GPa and 1573–2073 K, at conditions prevailing at the top of the lower mantle. At temperatures below 1923 K, MgSiO 3 ‐rich bridgmanite, an Fe 3+ ‐rich oxide phase, and SiO 2 coexist in the recovered sample. Quenched partial melt was observed above 1973 K, which is significantly lower than the solidus temperature of an equivalent Fe 3+ ‐free bulk composition. The partial melt obtained from the Fe 3+ ‐rich bulk composition has a higher iron content than coexisting bridgmanite, similar to the Fe 2+ ‐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) Fe 3+ is not transported into the deep part of the lower mantle because of its incompatibility during melting.

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