Iron isotopic systematics of oceanic basalts Fang-Zhen Teng a,b,⇑ , Nicolas Dauphas b , Shichun Huang c , Bernard Marty d a Isotope Laboratory, Department of Geosciences and Arkansas Center for Space and Planetary Sciences, University of Arkansas, 113 Ozark Hall, Fayetteville, AR 72701, USA b Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA c Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA d Centre de Recherches Pe ´trographiques et Ge ´ochimiques, CNRS, 15 Rue Notre-Dame-des-Pauvres, 54501 Vandoeuvre-le ` s-Nancy, France Received 10 June 2012; accepted in revised form 24 December 2012; available online 4 January 2013 Abstract The iron isotopic compositions of 93 well-characterized basalts from geochemically and geologically diverse mid-ocean ridge segments, oceanic islands and back arc basins were measured. Forty-three MORBs have homogeneous Fe isotopic com- position, with d 56 Fe ranging from +0.07& to +0.14& and an average of +0.105 ± 0.006& (2SD/ p n, n = 43, MSWD = 1.9). Three back arc basin basalts have similar d 56 Fe to MORBs. By contrast, OIBs are slightly heterogeneous with d 56 Fe ranging from +0.05& to +0.14& in samples from Koolau and Loihi, Hawaii, and from +0.09& to +0.18& in samples from the Soci- ety Islands and Cook-Austral chain, French Polynesia. Overall, oceanic basalts are isotopically heavier than mantle peridotite and pyroxenite xenoliths, reflecting Fe isotope fractionation during partial melting of the mantle. Iron isotopic variations in OIBs mainly reflect Fe isotope fractionation during fractional crystallization of olivine and pyroxene, enhanced by source het- erogeneity in Koolau samples. Ó 2012 Elsevier Ltd. All rights reserved. 1. INTRODUCTION The magnitude of equilibrium isotope fractionation de- creases with increasing temperature and atomic mass, and is likely to be small for isotopes of heavy elements during high-temperature processes (Bigeleisen and Mayer, 1947; Urey, 1947). On the other hand, isotope fractionation asso- ciated with kinetic processes such as chemical diffusion, Soret effect, or evaporation/condensation can remain sig- nificant at high temperatures (Richter et al., 2009). Recent high-precision isotopic analyses of natural samples have shown that measurable Fe isotope fractionation could oc- cur at both whole-rock (>0.2&) and mineral scales (>1.6&) during mantle melting (Williams et al., 2004, 2005, 2009; Weyer et al., 2005; Weyer and Ionov, 2007; Dauphas et al., 2009a; Zhao et al., 2010, 2012; Huang et al., 2011c; Hibbert et al., 2012) and igneous differentia- tion (Poitrasson and Freydier, 2005; Heimann et al., 2008; Teng et al., 2008, 2011; Schoenberg et al., 2009; Schuessler et al., 2009; Weyer and Seitz, 2012; Telus et al., 2012). The fractionation of Fe isotopes at high temperatures could be produced by kinetic or equilibrium processes and may be associated with changes in the oxidation state of Fe. Studying the mechanism associated with high-tempera- ture Fe isotope fractionation is important to further our understanding of the theory on stable isotope fractionation and to use Fe isotopes as tracers of petrogenetic processes. For example, compared to chondrites (Poitrasson et al., 2005; Schoenberg and von Blanckenburg, 2006; Dauphas et al., 2009a; Craddock and Dauphas, 2010), terrestrial and lunar basalts have heavy Fe isotopic compositions (Beard et al., 2003; Poitrasson et al., 2004; Schoenberg and von Blanckenburg, 2006; Weyer and Ionov, 2007; Teng et al., 2008; Schuessler et al., 2009; Dauphas et al., 2009a; 0016-7037/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.gca.2012.12.027 ⇑ Corresponding author. Present address: Department of Earth and Space Sciences, University of Washington, Johnson Hall Rm- 070, Box 351310, 4000 15th Avenue NE, Seattle, WA 98195, USA. E-mail address: fteng@uw.edu (F.-Z. Teng). www.elsevier.com/locate/gca Available online at www.sciencedirect.com Geochimica et Cosmochimica Acta 107 (2013) 12–26