Collaborative Research: Experimental Determination of Iron (Fe) Isotope Fractionations in Sulfide Minerals

智力上的功绩。铁(铁)同位素地球化学领域发展迅速，目前的文献包括来自世界上20多个研究小组的75多篇论文中的数千种同位素分析。这些工作大多集中在自然系统上，只有少数实验确定的动力学和平衡分馏系数以及相关的交换动力学数据可用于地质相关的系统。地球上记录到的铁同位素组成变化最大的是硫化物，沉积黄铁矿的56Fe/54Fe比值几乎为5perm，高温热液硫化物的56Fe/54Fe比值为3perm，但水相和矿物Fe-S体系中的Fe同位素分馏机制尚不清楚。计划了一个全面的实验计划，以确定水中Fe-S物种和硫化物矿物之间的铁同位素分馏在最高温度范围至~250℃。该实验计划将探索三个系统中的同位素分馏，涵盖一些最常见的水和矿物物种。将对动力学和平衡Fe同位素分馏进行研究，包括探索不同的硫化物形成途径及其相关的同位素交换动力学，这些问题可能在确定硫化物矿物的Fe同位素组成方面发挥主要作用。除温度外，我们还将探讨pH和微量金属替代对Fe同位素分馏和交换动力学的影响。硫化物的铁同位素地球化学已被用于研究从生命起源和演化到热液矿床中金属来源的一系列问题。这项研究产生的同位素分馏机制的可用性将加强对这些数据的解释。此外，还将采用新的实验方法，这些方法将普遍适用于其他矿物合成的实验研究。研究小组融合了三个机构在同位素和实验地球化学方面的基本专业知识。该项目将支持和教育这三个机构的几名研究生和一名博士后。其中包括一名来自加纳的博士生和一名来自乌拉圭的女博士后科学家。此外，这项研究将包括一名职业生涯早期的助理教授。

Intellectual Merit. The field of Iron (Fe) isotope geochemistry has grown rapidly and the literature now contains several thousand isotopic analyses in over 75 papers from two-dozen research groups in the world. Most of this work has focused on natural systems, and only a handful of experimentally determined kinetic and equilibrium fractionation factors and associated exchange kinetic data are available for geologically relevant systems. The largest variations in Fe isotope compositions on Earth are recorded in sulfides, where almost a 5 permil range in 56Fe/54Fe ratios is found in sedimentary pyrite and a 3 permil range in high-temperature hydrothermal sulfides, and yet Fe isotope fractionation mechanisms in aqueous and mineral Fe-S systems poorly known. A comprehensive experimental program is planned for determining the Fe isotope fractionations among aqueous Fe-S species and sulfide minerals over the temperature range up to ~250 C. The experimental program will explore isotopic fractionations in three systems covering some of the most common aqueous and mineral species. Both kinetic and equilibrium Fe isotope fractionations will be investigated, including exploration of different sulfide formation pathways and their associated isotopic exchange kinetics, issues that may play a major role in determining the Fe isotope compositions of sulfide minerals. In addition to temperature, we will explore the effects of pH and trace metal substitution on Fe isotope fractionation and exchange kinetics.Broader Impacts. Iron isotope geochemistry of sulfides has been used to investigate problems ranging from the origin and evolution of life to the sources of metals in hydrothermal ore deposits. Interpretations of these data will be enhanced by availability of isotopic fractionation mechanisms generated by this study. In addition, new experimental approaches will be employed that will be generally applicable to other experimental studies of mineral synthesis. The research team blends essential expertise in isotope and experimental geochemistry from three institutions. The project will support and educate several graduate students and a post-doc from the three institutions. These include a Ph.D. student from Ghana and a female post-doctoral scientist from Uruguay. In addition, the research will involve an early-career Assistant Professor.