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

分化是一个行星体根据其物理和化学特性分成不同层的过程。根据温度、压力（或物体的大小）、氧气逸度和撞击历史，物体将分成几层，最终的产物将是一颗独特的行星、月球或小行星。在这个建议中，我们着重于硅酸盐地幔和金属地核的区分。这一过程发生在类地行星、月球和许多小行星上，因为这些天体温度高、体积大，足以熔化金属，使其渗透到硅酸盐中。铁元素和亲铁元素向中心下沉形成地核，硅酸盐元素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结合同位素分馏和在岩心等看不见的储集层中封存元素。同位素分馏将存在于具有不同键合环境(例如，地球？储集层之间的元素分离体现了这种分馏作用。在高压和高温下的实验可以揭示行星物质中无法直接测量的平衡同位素分馏因子，当与天然物质中的同位素比率相结合时，可以对这些物质的形成条件提供约束。在这个建议中，我们将重点放在铁与硫或碳等轻元素合金时的平衡稳定同位素分馏上。在过去的13年里，铁同位素群落已经取得了巨大的进步，一个不断增加的数据库已经出现，然而，缺少的是对这些可见分馏是如何以及为什么形成的更系统的理解。这是铁同位素分馏背后的机制，我们建议研究。特别是，我们旨在了解铁金属中的键合环境如何影响金属与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.