CSEDI: Determination of Equilibrium Iron Isotope Fractionation Factors at High Pressure

CSEDI：高压下平衡铁同位素分馏因子的测定

• 批准号: 1464008
• 负责人: Anat Shahar
• 金额: $ 7.81万
• 依托单位: Carnegie Institution of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-04-15 至 2019-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1464008&HistoricalAwards=false
• 关键词: CSEDI; Determination; Equilibrium; Iron; Isotope

Understanding the composition of the Earth is crucial to constraining under which conditions it formed along with the rest of the solar system. The more we can learn about the Earth, the better suited we are to understanding how planets form in general and why the planets are all so different. Many elements that are abundant on Earth have stable isotopes (same number of protons, different number of neutrons) that have been studied extensively for their use as tracers for physical and chemical processes. However these isotopes have largely not been explored for how they can trace processes occurring at high pressure, such as during the formation of our planet's core. This proposal is aimed at studying the composition of the core of the Earth through experiments at high pressure and theoretical calculations of the isotopic ratios. The goal is to place an independent constraint on the composition of the core, which has critical implications on the formation and evolution of our planet. 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 inaccessible reservoirs like the Earth's core. 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. The principal aim of this proposal is to understand how the light elements bonded to iron in the core can affect the distribution of isotopes during core formation. Ths Pis will do this by determining how various phases (Fe3C, FeO, FeS, FeHx) isotopic fractionation factors are affected by pressure. This study relies on mineral physics techniques and experiments (DAC experiments at the synchrotron using nuclear resonant inelastic x-ray scattering) combined with isotope geochemistry calculations and analyses. It is a truly interdisciplinary project that can only be accomplished with the right expertise and has the potential to make a large imprint on several fields of geoscience. The main research goals of this proposal are to: reveal how iron stable isotope ratios under extreme pressure conditions can be used to understand planet formation and differentiation; determine the effect of bonding partners on iron stable isotope fractionation so as to investigate the light element in cores of differentiated objects; and calculate theoretical iron isotopic fractionation factors based on high pressure NRIXS synchrotron experiments.

了解地球的组成对于确定地球与太阳系其他部分在何种条件下形成至关重要。我们对地球了解得越多，我们就越能理解行星是如何形成的，以及为什么行星如此不同。地球上丰富的许多元素都有稳定的同位素（质子数相同，中子数不同），这些同位素作为物理和化学过程的示踪剂被广泛研究。然而，这些同位素在很大程度上还没有被探索过，它们是如何追踪在高压下发生的过程的，比如在地球核心形成的过程中。这一建议旨在通过高压实验和同位素比值的理论计算来研究地核的组成。目标是对地核的组成进行独立的约束，这对我们星球的形成和演化具有关键意义。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地球核心等难以接近的储集层中元素的隔离相结合。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。这项提议的主要目的是了解在岩心形成过程中，与铁结合的轻元素如何影响同位素的分布。该Pis将通过确定压力如何影响不同相（Fe3C, FeO, FeS, FeHx）同位素分馏因子来实现这一点。这项研究依靠矿物物理技术和实验（利用核共振非弹性x射线散射在同步加速器上进行的DAC实验）结合同位素地球化学计算和分析。这是一个真正的跨学科项目，只有正确的专业知识才能完成，并有可能在地球科学的几个领域留下巨大的印记。该提案的主要研究目标是：揭示极端压力条件下铁稳定同位素比率如何用于理解行星的形成和分化；确定成键伙伴对铁稳定同位素分馏的影响，以研究分馏物岩心中的轻元素；并基于NRIXS高压同步加速器实验计算理论铁同位素分馏因子。