Exploring the Effects of Light Elements on the Iron Isotope Fractionation between Metal and Silicate

Carnegie Institution Of Washington, Washington DC

Investigators

Abstract

Differentiation is the process with which a planetary body separates into layers based on the physical and chemical characteristics of the body. Based on the temperature, pressure (or size of body), oxygen fugacity, and impact history, the body will separate into layers and the final product will be a unique planet, moon or asteroid. In this proposal we focus on the differentiation of a silicate mantle and a metallic core. This process occurred on the terrestrial planets, the moon and on many asteroids, as these objects were hot and big enough to melt the metal so it could percolate through the silicate. The iron and siderophile elements sink to the center to form a core, while the silicates and lithophile elements form a mantle. The principle of using stable isotopes to probe the bulk chemical composition of planets lies with the combination of isotope fractionation and sequestration of elements in unseen reservoirs like the core. Isotope fractionation will exist between phases with distinct bonding environments (e.g., Earth?s core and mantle), and separation of elements between reservoirs manifests this fractionation. Experiments at high pressure and temperature can reveal the equilibrium isotopic fractionation factors that cannot be directly measured in planetary materials and when combined with isotopic ratios found in natural materials provide a constraint on the formation conditions of those materials. In this proposal we focus on the equilibrium stable isotopic fractionation of iron when it is alloyed to a light element such as sulfur or carbon. There has been enormous progress in the Fe isotope community in the past 13 years an ever-increasing database has emerged however, what is missing is a more systematic understanding of how and why these seen fractionations are formed. It is the mechanisms behind the iron isotopic fractionations that we are proposing to study. In particular, we aim to understand how the bonding environment in the iron metal effects the iron isotope fractionation between metal and silicate.