Testing the Validity of Muscovite as a Continuous History Thermochronometer

温度变化对岩石的化学演化很重要。构造变形和侵蚀形成的景观引起的温度变化记录在岩石中。矿床存款的形成和烃类聚集的形成在一定程度上是温度驱动的。在过去的50年里，地质学家已经开发出了利用矿物中发现的放射性衰变产物来解码温度历史的方法。虽然衰变产物以众所周知的规律速率积累，但它们也可以在高温下从矿物中损失。在矿物颗粒的整个生命周期中，净剩余衰变产物以及由此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。研究对温度有不同反应的不同矿物可能是强大的。研究人员需要更广泛的抗蚀矿物质，以便在尽可能宽的温度范围内使用。这个小组将确定普通的白色云母是否可以用于温度历史研究。这种矿物很容易通过钾氩法测定年代，耐风化，并显示出能够在300摄氏度至400摄氏度的温度范围内工作的希望，这是其他矿物无法很好地覆盖的区间。 除了演讲和出版物外，该小组还将为学生和公众制作关于矿物测年及其如何支持地球基础研究的宣传视频。该项目的目标是开发一种新的方法，确定275摄氏度至425摄氏度范围内地壳岩石的温度历史。一些已发表的报告表明，矿物白云母的40 Ar/39 Ar分析可以解决这个范围。为了测试白云母不仅是一个测年目标，而且是一种在岩石冷却过程中测量温度的手段，研究人员将对一套具有已知温度历史的白云母样本进行扩散和测年实验，这些样本可以与实验预测进行比较。他们还将选择样品进行再加热实验，旨在检查白云母样品对更短时间尺度，更高温度的热脉冲的响应。是什么使白云母一个特别有吸引力的研究目标的建议，而不是作为一个简单的扩散系统的行为，白云母颗粒显示多扩散域的行为，这样的白云母的每一个颗粒实际上是一个集合的子样品具有部分重叠的保留氩。如果是这样的话，一个单独的样品可以记录一段连续的热历史，延伸到大约100摄氏度或更高。此外，有人提出，样品的具体信息白云母扩散性能可以得到作为副产品的40 Ar/39 Ar实验室步加热分析，这将支持恢复更准确的热历史比可能通过应用通用动力学数据从有限数量的已发表的扩散研究。这项研究将测试白云母分析可以揭示一系列热历史信息的建议，这些分析也可以产生准确的扩散动力学数据。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生的教学材料，这些材料涉及地质年代学主题，例如什么样的不同人可以做这种工作，为什么他们这样做，以及如何做。这些材料将与动画专业人士合作制作的一系列视频相结合，并在发布前在课堂上进行测试。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。

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.