Testing the Validity of Muscovite as a Continuous History Thermochronometer

测试白云母作为连续历史测温计的有效性

• 批准号: 2223700
• 负责人: Peter Zeitler
• 金额: $ 17.3万
• 依托单位: Lehigh University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-03-01 至 2025-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2223700&HistoricalAwards=false
• 关键词: Testing; Validity; Muscovite; Continuous; History

Temperature change is important to a rock's chemical evolution. The tectonic deformation and erosion that shape landscapes cause temperature changes that are recorded in rocks. Ore deposit formation and the creation of hydrocarbon accumulations are in part temperature-driven. Over the past 50 years, geologists have developed ways use radioactive decay products found in minerals to decode temperature histories. While decay products accumulate at a well-known regular rate, they can also be lost from minerals at elevated temperatures. Over the life span of a mineral grain, the net remaining decay product and thus the measured mineral age represents the outcome of these competing processes of steady gain and temperature-dependent loss. Studying different minerals with different responses to temperature can be powerful. Researchers need a broader range of alteration-resistant minerals to use for as wide a range of temperatures as possible. This team will determine whether the common white mica can be used for temperature-history studies. This mineral is easily dated by the potassium-argon method, is resistant to weathering, and shows promise in being able to work over the 300 ˚C to 400˚C temperature range, an interval not well covered by other minerals. In addition to presentations and publications, this team will develop outreach videos for students and the general public about mineral dating and how it supports basic research about the Earth.The goal of this project is to develop a new means of determining the temperature histories of crustal rocks across the range 275˚C to 425˚C. Several published reports suggest that 40Ar/39Ar analyses of the mineral muscovite can address this range. To test how useful muscovite might be as not just a dating target but also as a means to measure temperatures during rock cooling, the researchers will carry out diffusion and dating experiments on a suite of well characterized muscovite samples that have known temperature histories that can be compared to predictions from their experiments. They will also choose samples for reheating experiments designed to examine the response of muscovite samples to shorter timescale, higher-temperature thermal pulses. What makes muscovite a particularly appealing target for study are suggestions that rather than behaving as a simple diffusing system, muscovite grains show multi-diffusion-domain behavior, such that each grain of muscovite is in effect a collection of subsamples having partially overlapping retentivities for argon. If so, an individual sample could record a continuous segment of a thermal history that extends over some 100˚C or more. Moreover, it has been proposed that sample-specific information about muscovite diffusion properties can be obtained as a byproduct of 40Ar/39Ar laboratory step heating analysis, which would support the recovery of more accurate thermal histories than would be possible by applying generic kinetic data obtained from a limited number of published diffusion studies. The research will test both the proposal that muscovite analyses can reveal a range of thermal-history information and that these analyses can also yield accurate diffusion-kinetics data. The work involved will form part of a Ph.D. dissertation as well as an undergraduate project. To convey their work broadly, the team will develop instructional materials targeted at the undergraduate level on such geochronology topics as what sort of diverse people can do this kind of work, why they do it, and how. These materials will be integrated with a series of videos prepared in collaboration with animation professionals, and tested in classes before release.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.

温度变化对于岩石的化学演化很重要。塑造景观的构造变形和侵蚀会导致岩石中记录的温度变化。矿石沉积的形成和碳氢化合物积累的产生是部分温度驱动的。在过去的50年中，地质学家开发了使用矿物质中发现的放射性衰减产品来解码温度历史的方法。尽管衰减产品以众所周知的固定速度积累，但在升高温度下，它们也可能因矿物质而丢失。在矿物谷物的寿命中，剩余的衰减产物以及测得的矿物年龄代表了这些稳定增益和温度依赖性损失的竞争过程的结果。研究不同矿物质具有不同反应温度的矿物可能会很强大。研究人员需要更广泛的抗改变矿物质，以尽可能多地使用多种温度。该团队将确定是否可以将普通的白云母用于温度历史研究。该矿物很容易通过钾 - 阿尔贡法的日期，具有抗风化性，并有望在300°C至400°C温度范围内工作，这间隔不被其他矿物覆盖。除演讲和出版物外，该团队还将为学生和公众开发有关矿物约会的外展视频及其如何支持有关地球的基础研究。该项目的目的是开发一种新的手段，以确定跨范围275˚C至425°C的地壳岩石的温度历史。几份已发表的报告表明，矿物白云母的40AR/39AR分析可以解决此范围。为了测试穆斯科特的有用程度不仅是一个约会目标，而且是在岩石冷却过程中测量温度的一种手段，研究人员将在一系列具有良好表征的麝香木样本的套件上进行扩散和约会实验，这些样本具有已知的温度历史，这些温度历史可以与实验的预测进行比较。他们还将选择样品进行重新加热实验，旨在检查棉绒样品对更短时，温度较高的热脉冲的响应。使穆斯科特人成为研究的特别吸引人的是，暗示，而不是表现为简单的扩散系统，而是表现出多延伸域的行为，因此，每种麝香木晶体实际上是一组质量部分的子样本的集合。如果是这样，单个样本可以记录一个在100°C或更多以上的热史的连续段。此外，已经提出，可以作为40AR/39AR实验室步骤加热分析获得有关麝香木扩散特性的样本特异性信息，这将支持比采用从有限发表的差异研究中获得的通用动力学数据来恢复更准确的热历史。这项研究将测试马云分析可以揭示一系列热历史信息的提案，并且这些分析也可以产生准确的扩散 - 金属学数据。所涉及的工作将构成博士学位的一部分。论文以及本科项目。为了广泛地传达他们的工作，该团队将开发针对本科级别的教学材料，这些材料是关于地年代学主题的，例如哪种不同的人可以做这种工作，为什么做这类工作以及如何做。这些材料将与一系列与动画专业人员合作准备的视频，并在发布前进行了测试。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子优点和更广泛影响的评估审查标准来通过评估来支持的。