The effect of oxygen as a light element in metallic liquids on partitioning behavior

Abstract

Oxygen has been considered a potentially important light element in metallic liquids during a range of planetary processes, yet the influence of O in a metallic melt on element partitioning behavior is largely unknown. To investigate the effect of O in such systems, we conducted experiments in the Fe-S-O system, doped with 25 trace elements, which produced two immiscible metallic liquids. Our results indicate that the presence of O in the metallic liquid produces a distinctive chemical signature for W and Ga in particular. Tungsten shows an affinity for O in the metallic liquid and partitions more strongly into the metallic melt in the presence of O. The partitioning of Ga is relatively constant despite the presence of O, which is in contrast to the majority of the other siderophile elements in the study. Our experiments from 1400 to 1600°C show no significant effect from temperature on the partitioning behavior of any trace elements over this limited temperature range. This distinctive chemical signature due to the presence of O in the metallic liquid has potential implications for modeling core formation, evaluating isotopic signatures produced by core crystallization, and interpreting chemical assemblages observed in meteorites.

Experimental constraints on the fate of H and C during planetary core-mantle differentiation. Implications for the Earth

“…The addition of ~10% of light elements (S, Si, O, C and H) is required to account for the density deficit observed between pure Fe and core models (e.g Poirier, 1994;Chabot et al, 2015). It has been shown that H or C can easily be combined with iron at high pressures (HP) and high temperatures (HT) and could explain such a density deficit (e.g.…”

Highly Siderophile Elements in Earth, Mars, the Moon, and Asteroids

“…Examples of such processes include asteroidal core formation (e.g., Jones and Drake 1982;Wasson 1999), or the separation of metallic core from silicate mantle during core formation (e.g., Righter and Drake 1997;Li and Agee 1996). Distributions of the HSE between a liquid metal phase and solid metal restite during partial melting in the Fe-Ni-S system are strongly dependent on the S-content of extracted melts, and on C and P that enter the metallic phase (e.g., Chabot and Jones 2003;Chabot et al 2014). Parameterization of solid-metal-liquid-metal D-values has been established by several authors as a function of the metallic liquid composition, with the most commonly used iteration derived from Chabot and Jones (2003).…”

“…Conceptually, this process leads to segregating metal concentrating more compatible HSE, including Os, Ir, Ru, Rh, and Re, from Pt, Pd, and Au (e.g., Scott 1972;Pernicka and Wasson 1987;Walker et al 2008;Goldstein et al 2009;McCoy et al 2011). Studies of the magmatic iron groups have also emphasized the importance of non-metal components, including S, C, Si, P, and O in affecting the solid-metal-liquid-metal partitioning (e.g., Chabot and Drake 1999;Chabot and Jones 2003;Chabot et al 2014), consistent with the requirement of a light element component in terrestrial planetary cores to satisfy cosmochemical constraints (e.g., Dreibus and Wanke 1985;McSween 1994;McDonough 2003).…”

Siderophile element systematics of IAB complex iron meteorites: New insights into the formation of an enigmatic group

“…crystallization. For our CS model, initial S, P, and C contents were iteratively chosen by applying the parameterization of Chabot and Jones (2003) and Chabot et al (2014) so that D Ir was also 3.0 (IP-MG CS ; Table 3). The parameterization was then used to calculate the corresponding D values for the other HSE (Table 4).…”

“…For the modeling conducted here, the solid metal-liquid metal D values were calculated using a "parameterization method" which uses empirical parameters derived from experimental partitioning data (supplementary material; Jones and Malvin, 1990;Chabot and Jones, 2003;Chabot et al, 2014). In brief, the parameterization depends on the mole fractions of S, P, and C (X S , X P , and X C ); an "Fe domains" variable, which constitutes the availability of light elementfree domains into which siderophile elements prefer to partition; and β, which is the slope of the fit to experimental data for a given element on a plot of the natural log of D vs. the natural log of Fe domains.…”