Collaborative Research: RUI: Diffusion studies in baddeleyite and zircon

矿物锆石（ZrSiO4）和坏辉石（ZrO2），虽然在大多数岩石中只以低浓度存在，但在地质年代学（测量岩石、陨石和地质事件的年龄）中是重要的相。它们含有作为地球化学指标有用的微量元素和微量元素。特别是锆石是非常坚固的矿物颗粒，因为它们可以在许多类型的地质事件中幸存下来，是地球上已知最古老的物质之一。它们保存了44亿年前发生的地质过程的信息。了解这些矿物中关键元素的扩散（原子的迁移）行为为我们如何解释测量的年龄、岩石的化学特征和古代地质事件提供了主要的限制。人们对锆石中几种化学元素的扩散进行了广泛的研究，尽管有些元素还没有得到充分的研究。相比之下，坏辉石的扩散数据完全缺乏，这可以获得与锆石分析相补充的信息。了解这些矿物中的扩散对于解释广泛的地质年代数据，以及评估和解释这些矿物在地质时间框架内保留的化学和同位素特征至关重要。这项工作的主要广泛影响将是重要数据的贡献，这些数据可以被广泛的科学家在不同但相关的领域使用。该项目还将为物理、工程和地球科学专业的本科生以及来自服务欠缺社区的高中生提供教育体验。拟议的实验建立在一系列测量辅助矿物（岩石中通常含量较少的矿物，但含有地质计时器或地球化学示踪剂等重要元素）中各种元素扩散的工作基础上，以获得这些关键矿物的更完整的地球化学图像。这项工作还继续改进和应用基于加速器的离子束技术（卢瑟福后向散射光谱和核反应分析）在扩散研究中，利用这些分析方法的优越深度分辨率来获取这些材料中许多物种的慢扩散特性。随着微分析技术越来越多地应用于分析自然样品和获取精细尺度的化学和同位素变化，扩散数据成为解释地质事件时间、评估过去化学环境和热历史的关键参数。这些测量将为解释坏辉石的同位素年龄和热历史提供关键信息，坏辉石是一种令人感兴趣的矿物，但目前几乎没有扩散数据。对锆石中五价阳离子扩散的测量将提供有关元素对化学变化的抵抗力的信息，这些元素可能作为地球化学示踪剂有用，并为替代阳离子扩散的取代机制和电荷平衡提供见解。Xe扩散结果可能有助于更好地解释地球和月球样品中的Xe同位素系统和稀有气体行为，以及了解早期地球和太阳系的历史。氧化锆还可以作为耐火材料和光学材料，因此更好地了解其性质可能具有技术意义。这项工作的更广泛的影响将是作为重要数据的贡献，这些数据可以被广泛的科学家在不同但相关的地球科学领域使用，包括热年代学，地质年代学，以及早期地球和太阳系的研究。该项目将让本科生参与研究，提供制备样品、晶体合成、进行实验、使用各种分析方法、分析和解释数据以及在研究会议上发表报告的经验。该项目还将支持一项旨在向当地高中生介绍科学研究方法和地球科学的社区外展工作。该项目由岩石与地球化学和地球科学部共同资助，以支持在各种机构类型中提高研究能力、能力和基础设施的项目，如GEO EMBRACE DCL所述。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The minerals zircon (ZrSiO4) and baddeleyite (ZrO2), although present only in low concentrations in most rocks, are important phases in geochronometry (measuring ages of rocks, meteorites, and geologic events). They incorporate trace and minor elements useful as geochemical indicators. Zircons in particular are very robust mineral grains and, since they can survive many types of geological events, are some of the oldest known materials on Earth. They have preserved information about geological processes that were occurring up to 4.4 billion years ago. Understanding the diffusion (mobility of atoms) behavior of key elements inside these minerals provides major constraints on how we interpret the measured ages, and chemical signatures of rocks and ancient geological events. There has been extensive study of diffusion of several chemical elements in zircon, even if some elements have been understudied. In contrast, there is a lack of diffusion data entirely for baddeleyite, which can yield complementary information to that gained from zircon analysis. Understanding diffusion in these minerals is essential for interpreting a wide range of geochronometric data, and evaluating and interpreting the chemical and isotopic signatures retained in these minerals over geologic timeframes. The main broader impacts of this work will be a contribution of important data that can be used by a wide range of scientists in diverse, but related, fields. The project will also provide an educational experience for undergraduate students in physics, engineering, and geosciences, as well as high school students from underserved communities. The proposed experiments build on a body of work measuring diffusion of a variety of elements in accessory minerals (minerals in generally minor abundance in rocks, but which incorporate elements important as geochronometers or geochemical tracers), to obtain a more complete geochemical picture of these critical minerals. The work also continues the refinement and application of accelerator-based ion beam techniques (Rutherford Backscattering Spectroscopy and Nuclear Reaction Analysis) in diffusion studies, exploiting the superior depth resolution of these analytical methods to access the slow diffusivities characteristic of many species in these materials. With the increasing application of microanalytical techniques to analyze natural samples and access fine-scale chemical and isotopic variations, diffusion data are a critical parameter in interpreting timing of geologic events, and evaluation of past chemical environments and thermal histories. These measurements will yield critical information for interpreting isotopic ages and thermal histories for baddeleyite, a mineral of interest but for which little diffusion data currently exist. The measurements of pentavalent cation diffusion in zircon will provide information about the resistance to chemical alteration of elements potentially useful as geochemical tracers, provide insight into substitutional mechanisms and charge balance for diffusion of altervalent cations. The Xe diffusion results may have implications for better interpreting Xe isotope systematics and noble gas behaviors in terrestrial and lunar samples, and understanding histories of the early Earth and Solar System. Zirconia also has utility as a refractory and optical material, so better understanding of its properties may have technological implications. The broader impacts of this work will be as a contribution of important data that can be used by a wide range of scientists in diverse, but related, fields in the geosciences, including thermochronology, geochronology, and studies of the early Earth and Solar System. The project will involve undergraduate students in research, providing experience in preparing samples, crystal synthesis, conducting experiments, using various analytical methods, and analyzing and interpreting data and presenting at research conferences. The project will also support a community outreach effort aimed at introducing local high school students to scientific research methods and Earth science.This project is jointly funded by Petrology & Geochemistry and Division of Earth Sciences to support projects that increase research capabilities, capacity and infrastructure at a wide variety of institution types, as outlined in the GEO EMBRACE DCL.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.