Open AccessThe valence state and partitioning of iron in the Earth's lowermost mantle
Author(s) -
Sinmyo Ryosuke,
Hirose Kei,
Muto Shunsuke,
Ohishi Yasuo,
Yasuhara Akira
Publication year - 2011
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2010jb008179
Subject(s) - geology , mantle (geology) , geophysics , valence (chemistry) , astrobiology , physics , quantum mechanics
While iron occurs predominantly in the form of Fe 2+ in the Earth's upper mantle and transition zone, Al‐bearing (Mg,Fe)SiO 3 perovskite (Pv), a primary mineral in the lower mantle, contains a large proportion of ferric iron (Fe 3+ ). It has been demonstrated that such Fe 3+ strongly affects physical and chemical properties of Pv. On the other hand, the iron substitution mechanism and valence state of iron in postperovskite (PPv) are still unclear. Here we determined the valence state of iron in PPv with changing Al 3+ content, on the basis of electron energy‐loss near‐edge structure spectroscopy measurements. The results show that PPv includes a small amount of Fe 3+ , which is independent from the Al 3+ content. This indicates that Fe 3+ in Pv and coexisting metallic iron recombine to form Fe 2+ upon phase transition from Pv to PPv in pyrolitic mantle. Such Fe 2+ partitions preferentially into (Mg,Fe)O ferropericlase (Fp), and therefore PPv is depleted in iron compared to Pv. Such a marked change in the valence state of iron and resulting iron depletion in PPv have broad implications for seismic and transport properties in the lowermost mantle. Phase transition from Pv to Fe‐poor PPv occurs in a much narrower pressure range than that for a fixed iron content.