The influence of carbon on trace element partitioning behavior Nancy L. Chabot a, * , Andrew J. Campbell b,1 , John H. Jones c , Munir Humayun d , H. Vern Lauer Jr. e a Johns Hopkins Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA b Department of the Geophysical Sciences, The University of Chicago, 5734 S. Ellis Ave., Chicago, IL 60637, USA c Mail Code KR, NASA Johnson Space Center, Houston, TX 77058, USA d National High Magnetic Field Laboratory, Department of Geological Sciences, Florida State University, Tallahassee, FL 32310, USA e ESCG/Barrios Technology, P.O. Box 58477, Houston, TX 77258, USA Received 14 June 2005; accepted in revised form 10 November 2005 Abstract Carbon has been proposed as a potential light element in planetary cores, included in models of planetary core formation, and found in meteoritic samples and minerals. To better understand the effect of C on the partitioning behavior of elements, solid/liquid partition coefficients (D = (solid metal)/(liquid metal)) were determined for 17 elements (As, Au, Co, Cr, Cu, Ga, Ge, Ir, Ni, Os, Pd, Pt, Re, Ru, Sb, Sn, and W) over a range of C contents in the Fe–Ni–C system at 1 atm. The partition coefficients for the majority of the elements increased as the C content of the liquid increased, an effect analogous to that of S for many of the elements. In contrast, three of the elements, Cr, Re, and W, were found to have anthracophile (C-loving) preferences, partitioning more strongly into the metallic liquid as the C content increased, resulting in decreases to their partition coefficients. For half of the elements examined, the prediction that partitioning in the Fe–Ni–S and Fe–Ni–C systems could be parameterized using a single set of variables was not supported. The effects of S and C on elemental partitioning behavior can be quite different; consequently, the presence of different non-metals can result in different fractionation patterns, and that uniqueness offers the opportunity to gain insight into the evolution of planetary bodies. Ó 2005 Elsevier Inc. All rights reserved. 1. Introduction The separation of metal from silicate occurred during the early evolution of numerous planetary bodies in our solar system (e.g., Kleine et al., 2002; Schoenberg et al., 2002; Yin et al., 2002). The evolution of that separated metal continues today, as the central metallic cores of planets, like Earth, solidify (e.g., Jeanloz, 1990; Labrosse et al., 2001). The composition of the metal during these planetary processes affects how elements partition be- tween the metallic core and the silicate mantle or be- tween the solid inner core and the liquid outer core. Previous work has demonstrated that the presence of a ‘‘light’’ element in the metal, like S, P, or C, can espe- cially influence the elemental partitioning behavior (Willis and Goldstein, 1982; Jones and Drake, 1983; Jones and Malvin, 1990). The effects of S, and to a lesser extent the effects of P, on solid metal/liquid metal partitioning have been examined by previous studies (compiled in Chabot et al., 2003; Chabot and Jones, 2003). Carbon has been suggested as a potentially important light element in the central metallic cores of larger-than-as- teroid-sized planetary bodies (Wood, 1993). Models of core formation in the Earth have included a variable to account for effects due to the presence of C in the segregating metal (Righter and Drake, 1999). Cohenite ((Fe,Ni) 3 C) and graphite have been found in differentiated meteorites (e.g., Buchwald, 1975; Goodrich, 1992), which is evidence that C was present during the evolution of these materials. It is thus of interest to understand the influence of C on ele- mental partitioning behavior. www.elsevier.com/locate/gca Geochimica et Cosmochimica Acta 70 (2006) 1322–1335 0016-7037/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.gca.2005.11.011 * Corresponding author. Fax: +1 240 228 8939. E-mail address: Nancy.Chabot@jhuapl.edu (N.L. Chabot). 1 Present address: Department of Geology, University of Maryland, College Park, MD 20742, USA.