Collaborative Research: Experimental Determination of Abiologic and Inorganic Iron and Oxygen Isotope Fractionation

合作研究：非生物和无机铁和氧同位素分馏的实验测定

• 批准号: 0106611
• 负责人: Paul Braterman
• 金额: $ 11.54万
• 依托单位: University of North Texas
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-15 至 2004-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0106611&HistoricalAwards=false
• 关键词: Collaborative; Research; Experimental; Determination; Abiologic

BratermanEAR-0106611Isotopic variations of transition metals have attracted attention in the last year or two, in large part because such elements may be isotopically fractionated by biological processes. So far, clear biologically produced isotopic fractionation has been measured in the laboratory only for Fe, and this led to the proposal that Fe isotopes may be a useful "biosignature" that may be applied to tracing the role of organisms in modern and ancient environments, and may help in understanding the origin and evolution of life on Earth or other planetary bodies. However, because significant Fe isotope variations (3-4 per mil [/] in 56Fe/54Fe) are found only in fluids, rocks, and minerals from low temperature environments, it is possible that inorganic or abiologic Fe isotope fractionation may at least in part explain the range of Fe isotope compositions measured for natural samples. Support for inorganic or abiologic Fe isotope fractionation comes from experimental data and theoretical calculations, involving both mineral and fluid systems. Data from the U.W. Madison group on oxide and carbonate minerals from sedimentary rocks, as well as initial experimental results from mineral-fluid and Fe(II)-Fe(III) aqueous systems, indicate inorganic Fe isotope fractionations on the order of 1-3 / for some (but not all) systems, similar to those calculated from theory for a few cases, but also pointing to significant discrepancies between experiments and theory.The proposed research involves an extensive set of experimental determinations of Fe isotope fractionation factors between coexisting aqueous Fe species, between minerals and fluids, and between coexisting minerals. In all of the proposed experiments, distinction between kinetic and equilibrium isotope fractionations will be accomplished through use of the "three isotope method" or use of enriched isotope tracers. One phase of the proposed research will focus on determining the equilibrium Fe isotope fractionation between coexisting Fe(II) and Fe(III) complexes as a function of temperature, ionic strength, pH, and ligand chemistry, including aquo, chloro, and cyanide complexes, as well as mixed complexes. Another phase of the planned work will involve determining mineral-mineral and mineral-fluid isotope fractionation factors over the T-P range 200-600 degrees C and 1-20 kbar; in many cases, this work will involve determination of both O and Fe isotope fractionation factors from the same run products so that the relative isotopic exchange rates of these two elements may be compared. Initially, the goal will be to determine isotopic fractionations between siderite, magnetite, hematite, and fluid, given the importance of these minerals in the low-temperature rock record, but our work may be extended to other minerals (such as sulfides) depending upon the results. Ultimately, combined O and Fe isotope analysis of natural minerals may provide important cross-checks of attainment of isotopic equilibrium and the sources of fluids from which they precipitated. A number of experimental strategies are outlined in the proposal, which are aimed at addressing known experimental issues, but are intended to be flexible enough so that different approaches may be tried depending upon initial results. An important component to the viability of the planned experimental program is the very high precision that is now attainable using new instrumentation at U.W. Madison, where Fe isotope compositions may be determined on real samples to an external precision of plus or minus 0.05 / in 56Fe/54Fe ratios on very small (~ 100-300 ng) quantities of Fe. Given the great potential that Fe isotope geochemistry has for addressing problems that cut across several disciplines, the proposed experimental determinations of Fe isotope fractionation factors are viewed as essential before the field of Fe isotope geochemistry can move forward.

过渡金属的Bratermanear-0106611异位变化在过去一两年中引起了人们的关注，在很大程度上是因为这些元素可能会通过生物学过程对同位素分离。 到目前为止，仅在实验室中才在实验室中测量了清晰的生物学产生的同位素分馏，这导致提出的提议是，Fe同位素可能是一种有用的“生物签名”，可以应用于生物体在现代和古老环境中的作用，并且可能有助于理解地球或其他地球上生命的生命和其他地球上的生命和进化。 但是，由于仅在低温环境中的流体，岩石和矿物质中发现了显着的Fe同位素变化（56FE/54FE中的每Mil [/]），因此至少可以在自然样品中测量的Fe同位素组合物的无机或物质Fe同位素分馏。 对无机或原始FE同位素分馏的支持来自实验数据和理论计算，涉及矿物和流体系统。 来自U.W.的数据麦迪逊在沉积岩上的氧化物和碳酸盐矿物质组，以及矿物流体和Fe（II）-FE（III）水的最初实验结果表明，在某些（但不是所有）的系统中，与某些（但不是所有）的研究相似，与某些案例相似的研究和理论相似，根据1-3 /相似的研究表明，根据1-3 /相似的无机Fe同位素分馏，并指出了一些差异。 Fe同位素分级因子在共存水性物种，矿物质和流体之间以及共存矿物质之间的广泛实验确定。 在所有提出的实验中，动力学和平衡同位素分馏之间的区别将通过使用“三种同位素方法”或使用富集的同位素示踪剂来实现。 拟议的研究的一个阶段将重点侧重于确定共存的Fe（II）和Fe（III）复合物之间的平衡同位素分馏，这是温度，离子强度，pH和配体化学的函数，包括Aquo，Chloro，Chloro和Cyanide Complectes，以及混合复合物。 计划工作的另一个阶段将涉及确定在200-600摄氏度和1-20 kbar的T-P范围内的矿物矿物和矿物流体同位素分馏因子；在许多情况下，这项工作将涉及从同一运行产品中确定O和Fe同位素分级因子，以便可以比较这两个元素的相对同位素汇率。 最初，鉴于这些矿物质在低温岩石记录中的重要性，目标是确定铁矿，磁铁矿，赤铁矿和流体之间的同位素分馏，但根据结果，我们的工作可能会扩展到其他矿物（例如硫化物）。 最终，天然矿物质的O和Fe同位素分析可能会提供重要的同位素平衡的达到的交叉检查以及它们沉淀的流体来源。 该提案中概述了许多实验策略，旨在解决已知的实验问题，但旨在足够灵活，因此可以根据初始结果尝试不同的方法。 计划中实验计划的生存能力的重要组成部分是现在可以使用U.W.的新仪器来实现的很高的精度。麦迪逊，可以在实际样品上确定Fe同位素组合物的外部精度为Plus或负0.05 / 56FE / 54FE的比率，而Fe的量很小（〜100-300 ng）。 鉴于FE同位素地球化学对解决跨多个学科的问题的巨大潜力，因此在Fe同位素地球化学领域可以向前发展之前，提出的Fe同位素分馏因子的实验确定被认为是必不可少的。