Modeling trace element partitioning in multi-component iron alloy systems
Abstract
Iron alloys play a key role in the differentiation of planetary bodies, both during core formation and during the subsequent crystallization of the core. Siderophile trace elements are fractionated during these processes and thus have the potential to provide information on the conditions of differentiation. It is well known that the partitioning of trace elements between metallic phases, and between metal and silicate, depends strongly on the concentration of non-metallic "light" elements, such as sulfur, carbon, silicon, oxygen and phosphorus, in the liquid metal. These effects have been well characterized in many cases, for metallic systems that contain a single light element. Many trace elements have been shown to have variable affinities (and/or repulsions) for different light elements dissolved in iron alloys, and the combined effects of these interactions in complex systems containing multiple light elements have not yet been effectively parameterized. Here we present one possible solution to this problem, which is based on an activity model that is commonly used in metallurgy. The activity coefficient for the trace element of interest is expanded in a Taylor series about the infinitely dilute reference state, with first- and second-order interaction coefficients describing the influence of different light elements and their combinations. The model provides a good fit to the available experimental database for solid/liquid and liquid/liquid partitioning of more than 20 siderophile trace elements in binary (e.g. Fe-S) and ternary (e.g. Fe-S-C) iron alloy systems at ambient pressure. It should provide a useful framework for parameterizing trace element partition coefficients in metallic systems containing many light elements, and for evaluating the influence of pressure on trace element partitioning.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.P14A..03V
- Keywords:
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- 1015 GEOCHEMISTRY / Composition of the core;
- 1060 GEOCHEMISTRY / Planetary geochemistry;
- 3630 MINERALOGY AND PETROLOGY / Experimental mineralogy and petrology