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

分化是行星体根据天体的物理和化学特征分成几层的过程。根据温度、压力(或天体的大小)、氧逸度和撞击历史，天体将分成几层，最终产品将是一颗独特的行星、月球或小行星。在这一建议中，我们重点讨论硅酸盐地幔和金属核的区别。这一过程发生在类地行星、月球和许多小行星上，因为这些物体足够热，足够大，可以熔化金属，使其能够通过硅酸盐渗透。铁和亲铁元素下沉到中心形成核心，而硅酸盐和亲石元素形成地幔。利用稳定同位素探测行星整体化学成分的原理在于同位素分馏和元素在地核等看不见的储藏库中的封存相结合。具有不同键合环境的相间(如地球-S核和地幔)之间会存在同位素分馏，而储层之间元素的分离就是这种分馏的表现。在高压和高温下的实验可以揭示在行星物质中无法直接测量的平衡同位素分馏系数，当与在自然物质中发现的同位素比率相结合时，可以限制这些物质的形成条件。在这项建议中，我们关注的是铁与硫或碳等轻元素合金化时的平衡稳定同位素分馏。在过去的13年里，铁同位素领域取得了巨大的进展，然而，出现了一个不断增加的数据库，但缺少的是对这些可见的分馏是如何以及为什么形成的更系统的了解。我们打算研究的正是铁同位素分馏背后的机制。特别是，我们的目标是了解铁金属中的成键环境如何影响金属和硅酸盐之间的铁同位素分馏。

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.