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Science 11 June 2004:
Vol. 304. no. 5677, pp. 1656 - 1659
DOI: 10.1126/science.1095679
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Reports

Iron Isotope Fractionation and the Oxygen Fugacity of the Mantle

Helen M. Williams,1* Catherine A. McCammon,2 Anne H. Peslier,3 Alex N. Halliday,1 Nadya Teutsch,1 Sylvain Levasseur,1 Jean-Pierre Burg1

The oxygen fugacity of the mantle exerts a fundamental influence on mantle melting, volatile speciation, and the development of the atmosphere. However, its evolution through time is poorly understood. Changes in mantle oxidation state should be reflected in the Fe3+/Fe2+ of mantle minerals, and hence in stable iron isotope fractionation. Here it is shown that there are substantial (1.7 per mil) systematic variations in the iron isotope compositions ({delta}57/54Fe) of mantle spinels. Spinel {delta}57/54Fe values correlate with relative oxygen fugacity, Fe3+/{Sigma}Fe, and chromium number, and provide a proxy of changes in mantle oxidation state, melting, and volatile recycling.

1 Department of Earth Sciences, ETH-Zürich, Sonneggstrasse 5, CH-8092 Switzerland.
2 Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany.
3 Texas Center for Superconductivity, University of Houston, Houston, TX 77204, USA.

* To whom correspondence should be addressed. E-mail: williams{at}erdw.ethz.ch

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