Enabling the (U-Th)/Ne Thermchronometer: Ne Diffusion in Zircon and Titanite

启用 (U-Th)/Ne 测温计：锆石和钛矿中的 Ne 扩散

• 批准号: 0910983
• 负责人: Kip Hodges
• 金额: $ 19.85万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-15 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0910983&HistoricalAwards=false
• 关键词: Enabling; Th; Ne; Thermchronometer; Diffusion

Intellectual Merit: Thermochronology - the study of temperature histories for geologic samples using the tools of isotope and nuclear geochemistry - has evolved into a fundamental part of earth system research. This proposal contributes to that broader initiative by addressing issues that are important obstacles to (U-Th)/Ne thermochronology. Proposed just a few years ago, this method derives from the fact that alpha particles produced by the radioactive decay of U and Th in accessory minerals produce 21Ne via reaction with 18O. Empirical evidence suggests that 21Ne lattice diffusion is slower than that for 4He in accessory minerals, such that the (U-Th)/Ne and (U-Th)/He methods might be used together to probe more deeply into the temperature-time evolution of a sample than by using (U-Th)/He alone. While the basic theory of (U-Th)/Ne thermochronology has been developed, it is currently impossible to interpret the geologic significance of (U-Th)/Ne dates because we have no quantitative measure of 21Ne diffusivity in minerals that might be useful for thermochronometry. Thus, it is proposed to conduct a series of nucleogenic 21Ne diffusion experiments on proton-irradiated zircon and titanite. In addition to 21Ne, proton bombardment of these materials also will produce nucleogenic 3He. This nuclear reaction forms the basis for another powerful new method, 4He/3He thermochronology. A key assumption in that technique is that proton irradiation produces a spatially uniform distribution of 3He in minerals. Prior to the diffusion experiments that are at the core of the proposed study, we will test this assumption by mapping the spatial distribution of 3He (as well as 21Ne) in our irradiated samples using laser microprobe methods recently developed at Arizona State University.Broader Impacts: This project provides an opportunity for undergraduate students to become involved in the fabrication and testing of new analytical instrumentation. In keeping with the emphasis of ASU's new School of Earth and Space Exploration on integrated science and engineering education, the proposed work will involve the development of engineering practica for geoscience undergraduates. Informal discussions at professional meetings in recent years suggests that there is a need for noble gas geochronology short-courses aimed at graduate students and professionals who are users but not providers of thermochronologic data. In conjunction with this project, a web-based short course (including modules on laser microprobe applications) will be developed, using the well-received MIT OpenCourseWare structure as a model.

智力优点：热量教学 - 使用同位素和核地球化学工具对地质样品的温度历史研究 - 已演变为地球系统研究的基本部分。该提案通过解决（U-TH）/NE热量学的重要障碍的问题来促进更广泛的倡议。仅几年前提出的，这种方法源于以下事实：辅助矿物质中U和TH的放射性衰变产生的α颗粒通过与18O的反应产生21Ne。经验证据表明，在辅助矿物中4HE的21ne晶格扩散慢，因此（u-th）/NE和（u-th）/He方法可以一起使用，以更深入地探测温度时间的演化。样本比使用（u-th）/单独使用。虽然已经开发了（u-t​​h）/NE热量计划的基本理论，但目前不可能解释（u-th）/NE日期的地质意义，因为我们在矿物质中没有21NE扩散率的定量度量，这可能是有用的用于热化学计。因此，建议对质子辐照的锆石和钛矿进行一系列核源21Ne扩散实验。除了21Ne，这些材料的质子轰击还将产生核苷3HE。该核反应构成了另一种强大的新方法4HE/3HE热量体的基础。该技术的一个关键假设是，质子辐照在矿物质中产生3HE的空间均匀分布。在进行拟议研究核心的扩散实验之前，我们将使用最近在亚利桑那州立大学开发的激光微探针方法在我们的辐照样品中绘制3HE（以及21Ne）的空间分布来测试这一假设。 ：该项目为本科生提供了一个机会，可以参与新的分析仪器的制造和测试。为了强调ASU新的地球和太空学院对综合科学和工程教育的探索，拟议的工作将涉及地球科学本科生的工程实践。近年来在专业会议上的非正式讨论表明，旨在涉及针对用户的研究生和专业人士，但不是热力学数据提供者的崇高气体地球体学缩写。与该项目一起，将使用良好的MIT Opencouseware结构作为模型来开发基于Web的简短课程（包括激光微探针应用程序的模块）。