Journal Article

PUBDB-2019-00242

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Oxidized iron in garnets from the mantle transition zone

Kiseeva, E. S. (Corresponding author) ; Vasiukov, D. M. ; Wood, B. J. ; McCammon, C.Extern* ; Stachel, T. ; Bykov, M.Extern* ; Bykova, E.DESY* ; Chumakov, A. ; Cerantola, V. ; Harris, J. W. ; Dubrovinsky, L.Extern*

2018
Nature Publ. Group London

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Please use a persistent id in citations: doi:10.1038/s41561-017-0055-7  doi:10.3204/PUBDB-2019-00242

Abstract: The oxidation state of iron in Earth’s mantle is well known to depths of approximately 200 km, but has not been characterized in samples from the lowermost upper mantle (200–410 km depth) or the transition zone (410–660 km depth). Natural samples from the deep (>200 km) mantle are extremely rare, and are usually only found as inclusions in diamonds. Here we use synchrotron Mössbauer source spectroscopy complemented by single-crystal X-ray diffraction to measure the oxidation state of Fe in inclusions of ultra-high pressure majoritic garnet in diamond. The garnets show a pronounced increase in oxidation state with depth, with Fe$^{3+}$/(Fe$^{3+}$+ Fe$^{2+}$) increasing from 0.08 at approximately 240 km depth to 0.30 at approximately 500 km depth. The latter majorites, which come from pyroxenitic bulk compositions, are twice as rich in Fe$^{3+}$ as the most oxidized garnets from the shallow mantle. Corresponding oxygen fugacities are above the upper stability limit of Fe metal. This implies that the increase in oxidation state is unconnected to disproportionation of Fe$^{2+}$ to Fe$^{3+}$ plus Fe$^0$. Instead, the Fe$^{3+}$ increase with depth is consistent with the hypothesis that carbonated fluids or melts are the oxidizing agents responsible for the high Fe$^{3+}$ contents of the inclusions.

Note: © Macmillan Publishers Limited, part of Springer Nature.

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Contributing Institute(s):

1. DOOR-User (DOOR)
2. Experimentebetreuung PETRA III (FS-PE)

Research Program(s):

1. 6211 - Extreme States of Matter: From Cold Ions to Hot Plasmas (POF3-621) (POF3-621)
2. 6G3 - PETRA III (POF3-622) (POF3-622)

Experiment(s):

1. PETRA Beamline P02.2 (PETRA III)

Appears in the scientific report 2018

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