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Oxidized iron in garnets from the mantle transition zone

Title data

Kiseeva, Ekaterina S. ; Vasiukov, Denis M. ; Wood, Bernard J. ; McCammon, Catherine ; Stachel, Thomas ; Bykov, Maxim ; Bykova, Elena ; Chumakov, Aleksandr I. ; Cerantola, Valerio ; Harris, Jeff W. ; Dubrovinsky, Leonid:
Oxidized iron in garnets from the mantle transition zone.
In: Nature. Vol. 11 (2018) Issue 2 . - pp. 144-147.
ISSN 1476-4687

Abstract in another language

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 Fe3+/(Fe3++ Fe2+) 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 Fe3+ 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 Fe2+ to Fe3+ plus Fe0. Instead, the Fe3+ increase with depth is consistent with the hypothesis that carbonated fluids or melts are the oxidizing agents responsible for the high Fe3+ contents of the inclusions.

Further data

Item Type: Article in a journal
Refereed: Yes
Institutions of the University: Research Institutions > Research Centres > Bavarian Research Institute of Experimental Geochemistry and Geophysics - BGI
Research Institutions
Research Institutions > Research Centres
Result of work at the UBT: Yes
DDC Subjects: 500 Science > 550 Earth sciences, geology
Date Deposited: 28 Aug 2018 06:17
Last Modified: 01 Jun 2022 09:28