Expanding the Capabilities of Ar-Ar Dating Using Ne Isotopes

同位素定年是地球科学的一个重要工具，因为它为无数的地质过程增加了时间的基本维度。可以说，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。这种所谓的氩-氩测年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我们提供了重要的化学信号。随着研究人员能够分析越来越小的矿物样本，有可能看到，即使是最原始的矿物通常也有微小的缺陷，这些缺陷可以使用氩氩法提供的额外化学数据来检测和解释。然而，如果只观察质量接近氩的元素，就会有一个明显的盲点，因为其他重要的主要元素通常无法测量。这个项目试图通过使用氖同位素来扩展氩-氩测年法的多功能性，氖同位素是由钠、镁和氟的核反应产生的。已经证明了大量氖同位素的生产，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该方法的扩展。具体来说，中子辐照从氟中产生大量的20Ne，从镁中产生大量的21Ne。ne是由镁和钠两种物质产生的，而且对于镁含量低的矿物质，钠似乎可以很好地检测出来。虽然在同一材料上分析氖和氩同位素存在程序上的困难，但对设备和分析方法进行修改应该是可能的，几乎任何现代氩氩测年实验室。校准后，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钾、富钙和富钠端元组成的长石样品。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出气。同样，能够监测F和Cl将是分析通常含有大量卤素的角闪洞样品的有力工具。此外，分析镁的能力将大大提高我们对整个岩石样品（如玄武岩）脱气特性的理解，在玄武岩中，富镁贫钙矿物将首次被直接观察到。该项目的一部分内容还包括传播这些测量结果，并帮助其他研究人员能够利用这种已经强大的Ar-Ar测年方法的新扩展的潜力。

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.