(U-Th)/He Geochronometry and Thermochronometry

Farley EAR-0105981(U-Th)/He测年技术和应用在过去几年中得到了迅速发展，这是因为这种新恢复活力的计时器具有较低的闭合温度和相对较高的分析精度。这项提案寻求资金，以继续加州理工大学正在进行的、广泛的努力，以改进和扩大(U-Th)/He测年方法。在磷灰石热计时的情况下，仍有几个重要的问题有待研究，以确保该方法的可信度和可靠性。此外，初步工作表明，其他矿物也可能用于(U-Th)/He测年，并可能为解决重要的地质问题提供新的途径。这些都是拟议工作要探讨的主要问题。更具体地说，建议的目标是1)开发和实施评估He扩散系数的新的实验技术，目的是建立对最终控制He扩散的因素的可靠理解；2)发展对为什么偶尔的磷灰石样品产生不稳定的He年龄的理解，并测试绕过这些问题的新的分析方法；3)利用新开发的激光加热技术探索磷灰石颗粒对颗粒年龄不均的起源和意义；4)非常年轻的火山样品测年方法的发展和初步应用(KYR的10‘S到莱克迈尔)，特别是U系列不平衡的后果的评估，以及5)利用(U-Th)/He技术对风化层中产生的铁和锰氧化物进行测年的探索。

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.