Collaborative Research: RUI: Diffusion studies in baddeleyite and zircon

锆石（ZrSiO4）和斜锆石（ZrO2）虽然在大多数岩石中的含量很低，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。它们含有可用作地球化学指标的痕量和微量元素。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，是地球上已知的最古老的材料之一。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（原子的流动性）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限制。尽管对某些元素的研究还不够深入，但对锆石中几种化学元素的扩散已经有了广泛的研究。与此相反，有一个完整的斜锆石扩散数据，它可以产生补充信息，从锆石分析得到的缺乏。了解这些矿物中的扩散对于解释广泛的地质年代学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提供重要数据，供不同但相关领域的广大科学家使用。该项目还将为物理学、工程学和地球科学的本科生以及来自服务不足社区的高中生提供教育体验。拟议的实验建立在一个机构的工作测量扩散的各种元素的辅助矿物（矿物在岩石中一般丰度较小，但其中包含重要的元素作为地质年代或地球化学示踪剂），以获得更完整的地球化学图片这些关键矿物。这项工作还继续完善和应用加速器为基础的离子束技术（卢瑟福背散射光谱和核反应分析）在扩散研究，利用这些分析方法的上级深度分辨率，以访问这些材料中的许多物种的缓慢扩散特性。随着微分析技术在分析天然样品和获取精细尺度化学和同位素变化方面的应用越来越多，扩散数据是解释地质事件发生时间以及评估过去化学环境和热历史的关键参数。这些测量将产生关键的信息，解释同位素年龄和热历史的斜锆石，矿物的利益，但目前存在的扩散数据很少。五价阳离子在锆石中扩散的测量将提供有关可能用作地球化学示踪剂的元素的抗化学蚀变能力的信息，提供对替代机制和电荷平衡的洞察，为交互价阳离子的扩散。这些结果可能对更好地解释地球和月球样品中的氦同位素系统学和惰性气体行为，以及理解早期地球和太阳系的历史具有重要意义。氧化锆还可用作耐火材料和光学材料，因此更好地了解其特性可能具有技术意义。这项工作的更广泛影响将是提供重要数据，可供地球科学不同但相关领域的广泛科学家使用，包括热年代学、地质年代学以及早期地球和太阳系的研究。该项目将涉及本科生的研究，提供准备样品，晶体合成，进行实验，使用各种分析方法，分析和解释数据，并在研究会议上提出的经验。该项目还将支持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，该项目由岩石学&地球化学和地球科学司联合资助，以支持各种机构提高研究能力、能力和基础设施的项目，该奖项反映了NSF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.