Experimental Investigation of Non-Traditional Stable Isotope Fractionation in Geological Materials

地质材料非传统稳定同位素分馏实验研究

• 批准号: 0711411
• 负责人: Edward Young
• 金额: --
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-06-01 至 2011-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0711411&HistoricalAwards=false
• 关键词: Experimental; Investigation; Non; Traditional; Stable

Stable isotopes (i.e., isotopes that do not undergo radioactive decay) of different elements comprising rocks are used as tracers of redistribution of mass in Earth. The present study plans to exploit a new methodology for measuring accurately the stable isotope ratios of many important rock-forming elements to improve our knowledge of several geological processes. As part of the research plan, it is to establish the fundamental parameters necessary to use the isotopes of iron and magnesium as tracers of the movement of these important elements between different geological reservoirs. Whereas in past decades investigations of stable isotope fractionation in geological materials meant mainly studies of the isotopes of the lighter elements carbon, hydrogen, oxygen, nitrogen, and sulfur (of these, only oxygen is a major rock-forming element), the advent of multiple-collector inductively-coupled plasma-source mass spectrometry (MC-ICPMS) has allowed geoscientists to examine the distribution of isotopes of major rock-forming elements such as iron, magnesium, and silicon. At the same time, advances in computational chemistry have afforded the capacity to make quantitative predictions for the partitioning of isotopes between materials of geological interest. In this work, the investigators outline a research program that takes advantage of both of these advances. The ultimate goal is to determine equilibrium distribution of the isotopes of iron and magnesium in mineral materials of geological significance, and to compare these distributions in the laboratory to the distributions of the stable isotopes of these major rock-forming elements in natural systems. The investigators intend to test theoretical predictions of iron (Fe) and magnesium (Mg) isotope fractionation among mineral phases experimentally. Iron and Mg were selected as the focus of the study because of the importance of these rock-forming elements in many geochemical and biogeochemical cycles. The research is composed of three related facets: 1) prediction of the ways that Fe and Mg isotopes partition themselves between different minerals; 2) implementation of so-called three-isotope experiments designed to determine equilibrium isotope partitioning of isotopes among minerals of interest; and 3) high-precision measurement of stable isotope ratios in the experimental products. The experiments involve subjecting minerals of interest to high temperatures and pressures in a heated "piston cylinder" until isotopic equilibrium is achieved. The three isotope technique, by which samples are artificially enriched ("spiked") with a particular isotope, permits quantitative assessment of the degree to which the experimental products achieved equilibrium.This project will take advantage of several sub-disciplines in the geological sciences to further our understanding of how elements move deep within Earth. A benefit is the highly unusual interdisciplinary training afforded a Ph.D. student associated with the project. Communication between members of the disparate groups of geoscientists is expected to have a lasting positive impact on the field. The project promotes participation of underrepresented groups in the sciences by including members of such groups (women, African American) on the research team.

组成岩石的不同元素的稳定同位素（即不经历放射性衰变的同位素）被用作地球质量再分配的示踪剂。目前的研究计划开发一种新的方法来精确测量许多重要的岩石形成元素的稳定同位素比率，以提高我们对几种地质过程的认识。作为研究计划的一部分，它将建立必要的基本参数，以便使用铁和镁的同位素作为这些重要元素在不同地质储层之间运动的示踪剂。在过去的几十年里，对地质材料中稳定同位素分选的研究主要是对较轻元素碳、氢、氧、氮和硫的同位素进行研究（其中只有氧是主要的岩石形成元素），而多收集器电感耦合等离子体源质谱法（MC-ICPMS）的出现使地球科学家能够检查主要岩石形成元素（如铁、镁和硅）的同位素分布。与此同时，计算化学的进步使人们能够对具有地质意义的物质之间同位素的分配进行定量预测。在这项工作中，研究人员概述了一个利用这两种进步的研究计划。最终目标是确定具有地质意义的矿物材料中铁和镁同位素的平衡分布，并将实验室中的这些分布与自然系统中这些主要造岩元素的稳定同位素分布进行比较。研究人员打算对矿物相中铁（Fe）和镁（Mg）同位素分馏的理论预测进行实验验证。铁和镁在许多地球化学和生物地球化学循环中具有重要作用，因此选择铁和镁作为研究重点。研究工作主要包括三个方面：1)预测铁、镁同位素在不同矿物间的分配方式；2)实施所谓的三同位素实验，旨在确定感兴趣矿物之间同位素的平衡同位素分配；3)实验产品稳定同位素比值的高精度测量。实验包括将感兴趣的矿物置于加热的“活塞缸”中的高温高压下，直到达到同位素平衡。三同位素技术是用一种特定的同位素对样品进行人工富集（“加标”），可以定量评估实验产品达到平衡的程度。这个项目将利用地质科学的几个分支学科来进一步了解元素如何在地球深处移动。一个好处是，与该项目相关的博士生可以获得非常不同寻常的跨学科培训。不同地球科学家群体成员之间的交流有望对该领域产生持久的积极影响。该项目通过将这些群体的成员（妇女、非洲裔美国人）纳入研究小组，促进代表性不足的群体参与科学。