Expanding the Capabilities of Ar-Ar Dating Using Ne Isotopes

同位素测年是地球科学中的一个关键工具，因为它为无数的地质过程增加了重要的时间维度。可以说，在所有现代测年方法中，最通用的方法是利用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Ar-Ar测年方法不仅提供了宝贵的时间信息，而且还从被分析的样品中给出了重要的化学信号。随着调查人员能够分析越来越小的矿物样本，我们有可能看到，即使是看起来最原始的矿物，也往往有微小的缺陷，这可以通过使用Ar-Ar方法获得的额外化学数据来检测和解释。然而，如果只观察质量接近Ar的元素，就有一个明显的盲点，因为其他重要的主要元素通常不能被测量。这个项目是通过使用钠、镁和氟的核反应产生的霓同位素来扩展Ar-Ar测年方法的多功能性的一次尝试。已经证明了大量Ne同位素的产生，该项目将完成校准系统的重要工作，以便其他研究人员可以采用这种扩展方法。具体地说，中子辐照从氟产生大量的20Ne，从镁产生大量的21Ne。22Ne是由镁和钠产生的，对于镁含量较低的矿物，钠似乎可以很好地被检测出来。尽管在同一种材料上分析氦和氩的同位素存在程序上的困难，但对设备和分析方法的改进对于几乎任何现代的氩-氩测年实验室来说都是可能的。一旦校准，将对该方法进行探索性测试，以证明其潜力。明显的目标包括由富K、Ca和Na端元组成的长石样品。通过在目前监测的两种元素中添加钠，将有可能直接测量单晶中不同长石相的出气。同样，能够监测氟和氯将是分析闪石样品的有力工具，角闪石样品通常含有大量此类卤素。此外，分析镁的能力将极大地提高我们对全岩样品(如玄武岩)的脱气性能的了解，在那里将首次直接观察到富镁但贫钙的矿物。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开发这一新的扩展到已经很强大的Ar-Ar测年方法的潜力。

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.