Expanding the Capabilities of Ar-Ar Dating Using Ne Isotopes

扩展使用 Ne 同位素进行 Ar-Ar 测年的能力

• 批准号: 0609538
• 负责人: Chris Hall
• 金额: $ 7.22万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-07-01 至 2008-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0609538&HistoricalAwards=false
• 关键词: Expanding; Capabilities; Ar; Dating; Using

Isotopic dating is a critical tool in the earth sciences as it adds the essential dimension of time to a myriad of geological processes. Arguably the most versatile of all the modern dating methods uses the decay of an isotope of potassium into an isotope of argon. The most useful version of this dating method employs nuclear reactions to convert potassium, calcium and chlorine into a variety of argon isotopes. This so-called argon-argon dating method not only provides valuable time information but also gives us important chemical signals from the sample being analyzed. With investigators being able to analyze smaller and smaller mineral samples, it is possible to see that even the most pristine looking mineral often has tiny imperfections, which can be detected and interpreted using the extra chemical data available with the argon-argon method. However, by only looking at elements near argon in mass, there is a significant blind spot because other important major elements cannot normally be measured. This project is an attempt to extend the versatility of the argon-argon dating method by using neon isotopes which are created by nuclear reactions with sodium, magnesium and fluorine. The production of significant quantities of neon isotopes has been demonstrated and the project will do the important work of calibrating the system so that other researchers can adopt this extension to the method.Specifically, neutron irradiation produces large amounts of 20Ne from fluorine and 21Ne from magnesium. 22Ne is produced both from magnesium and sodium and it appears that sodium can be detected reasonably well for minerals with low magnesium content. Although there are procedural difficulties in analyzing neon and argon isotopes on the same material, modifications to equipment and analytical methods should be possible for virtually any modern argon-argon dating lab. Once calibrated, exploratory tests of the method will be done to demonstrate its potential. Obvious targets include feldspar samples which are made up of K, Ca and Na-rich end members. By adding Na to the two elements currently monitored, it will be possible to directly measure the out-gassing of different feldspar phases within a single crystal. Similarly, being able to monitor F as well as Cl will be a powerful tool for analyzing amphibole samples which typically have significant quantities of these halogens. In addition, the ability to analyze Mg will greatly improve our understanding of the degassing properties of whole-rock samples such as basalt where Mg-rich but Ca-poor minerals will be directly observable for the first time. Part of the project will also involve the dissemination of the results of these measurements and helping other researchers to be able to exploit the potential of this new extension to the already powerful Ar-Ar dating method.

同位素测年是地球科学中的一个重要工具，因为它为无数的地质过程增加了时间的基本维度。可以说，在所有现代测年方法中，最通用的方法是将钾的同位素衰变为氩的同位素。这种测年方法最有用的版本是利用核反应将钾、钙和氯转化为各种氩同位素。这种所谓的氩-氩定年法不仅提供了有价值的时间信息，而且还为我们提供了来自被分析样品的重要化学信号。随着研究人员能够分析越来越小的矿物样品，有可能看到即使是最原始的矿物也往往有微小的缺陷，可以使用氩-氩方法提供的额外化学数据来检测和解释。然而，通过只观察质量接近氩的元素，存在明显的盲点，因为其他重要的主要元素通常无法测量。该项目试图通过使用氖同位素来扩展氩-氩测年方法的多功能性，氖同位素是通过与钠、镁和氟的核反应产生的。大量氖同位素的生产已经得到证实，该项目将做校准系统的重要工作，以便其他研究人员可以采用这种方法的扩展。具体来说，中子辐照从氟中产生大量的20 Ne，从镁中产生大量的21 Ne。22 Ne是由镁和钠产生的，对于镁含量低的矿物，似乎可以合理地检测到钠。虽然在同一材料上分析氖和氩同位素存在程序上的困难，但几乎任何现代氩-氩测年实验室都可以修改设备和分析方法。校准后，将对该方法进行探索性试验，以证明其潜力。明显的目标包括由富K、Ca和Na端员组成的长石样品。通过将Na添加到目前监测的两种元素中，将有可能直接测量单晶中不同长石相的脱气。同样，能够监测F和Cl将是分析通常含有大量这些卤素的角闪石样品的有力工具。此外，分析Mg的能力将大大提高我们对玄武岩等全岩样品脱气性能的理解，其中富含Mg但贫Ca的矿物将首次直接观察到。该项目的一部分还将涉及传播这些测量的结果，并帮助其他研究人员能够利用这一新的扩展已经强大的Ar-Ar测年方法的潜力。