(U-Th)/He Geochronometry and Thermochronometry

（U-Th）/He测年技术和应用在过去几年中迅速发展，这是由于这种新复兴的计时器具有较低的闭合温度和相对较高的分析精度。该提案寻求资金，以继续加州理工学院正在进行的广泛努力，以改进和扩展(U-Th)/He定年方法。在磷灰石热时计的情况下，几个重要的问题仍有待研究，以确保信心和可靠性的方法。此外，初步工作表明，其他矿物也可用于(U-Th)/He定年，并可能提供解决重要地质问题的新方法。这些是拟议工作要探讨的主要问题。更具体地说，该提案的目标是：1)开发和实施新的实验技术来评估He扩散系数，目的是建立对最终控制He扩散的因素的强有力的理解；2)理解为什么偶然的磷灰石样品会产生不稳定的He年龄，并测试新的分析方法来规避这些问题；3)利用新发展的激光加热技术探索磷灰石晶粒年龄非均质性的成因及意义；4)发展和初步应用极年轻火山样品（10年至几年）的测年方法，特别是评估u系列不平衡的后果；5)探索使用(U-Th)/He技术测定风化层中产生的铁和锰氧化物的测年。

FarleyEAR-0105981Techniques and applications of (U-Th)/He dating have grown rapidly in the last several years due to the low closure temperature and relatively high analytical precision of this newly revitalized chronometer. This proposal seeks funds to continue ongoing, broad efforts at Caltech to improve and expand methods of (U-Th)/He dating. In the case of apatite thermochronometry, several important questions remain to be investigated to assure confidence and reliability of the method. In addition, preliminary work indicates that other minerals may also be of use for (U-Th)/He dating and may provide new ways to address important geologic problems. These are the major issues to be explored by the proposed work. More specifically, the proposal objectives are 1) development and implementation of new experimental techniques for assessing He diffusion coefficients with the goal of establishing a robust understanding of what factors ultimately control He diffusion; 2) development of an understanding of why occasional apatite samples yield erratic He ages, and testing of new analytical methods by which to circumvent these problems; 3) exploration of the origin and significance of apatite grain-to-grain age heterogeneity using the newly developed laser heating technique; 4) development and initial application of methods for dating of extremely young volcanic samples (10's of kyr to few Myr), and in particular assessment of the consequences of U-series disequilibrium, and 5) exploration of the use of (U-Th)/He techniques for dating of Fe and Mn oxides produced in weathering horizons.