Trace element partitioning in Fe-P-O-S alloy systems

An understanding of siderophile trace element partitioning between liquid and solid metal phases and between immiscible liquid metal phases is a key to studying the differentiation of planetary and asteroidal cores. Cores are thought to contain non-metallic 'light' elements like S, P, C and N and Si or / and O which may strongly affect the partitioning behavior of trace elements. In a complex system with multiple light elements, each of these non-metallic elements may have a different influence on the partitioning behavior of the trace elements. However, these influences have not been quantified in most cases. We investigated the partitioning behavior of trace elements within the Fe-P-O-S system with varying concentrations of P, O and S. The experiments were performed under pressures ranging from 1 atm to 2 GPa and temperatures varying from 1000°C to 1300°C. The influence of each light element (i.e. P, O, S) on trace element partitioning and their combined effects have been examined. Some highly siderophile elements including Os, Re, and Ir are strongly repelled by sulfur but even more strongly repelled by oxygen. It is possible that these elements could be fractionated significantly during crystallization of Earth's core, if it is oxygen-rich.