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Science 31 July 2009:
Vol. 325. no. 5940, pp. 605 - 607
DOI: 10.1126/science.1174156
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Reports

Water and the Oxidation State of Subduction Zone Magmas

Katherine A. Kelley1,*,{dagger} and Elizabeth Cottrell2,*

Mantle oxygen fugacity exerts a primary control on mass exchange between Earth’s surface and interior at subduction zones, but the major factors controlling mantle oxygen fugacity (such as volatiles and phase assemblages) and how tectonic cycles drive its secular evolution are still debated. We present integrated measurements of redox-sensitive ratios of oxidized iron to total iron (Fe3+/{Sigma}Fe), determined with Fe K-edge micro–x-ray absorption near-edge structure spectroscopy, and pre-eruptive magmatic H2O contents of a global sampling of primitive undegassed basaltic glasses and melt inclusions covering a range of plate tectonic settings. Magmatic Fe3+/{Sigma}Fe ratios increase toward subduction zones (at ridges, 0.13 to 0.17; at back arcs, 0.15 to 0.19; and at arcs, 0.18 to 0.32) and correlate linearly with H2O content and element tracers of slab-derived fluids. These observations indicate a direct link between mass transfer from the subducted plate and oxidation of the mantle wedge.

1 Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA.
2 National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA.

* These authors contributed equally to this work.

{dagger} To whom correspondence should be addressed. E-mail: kelley{at}gso.uri.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Ironing Out the Oxidation of Earth's Mantle.
M. M. Hirschmann (2009)
Science 325, 545-546
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