(U-Th)/He Geochronometry and Thermochronometry

California Institute Of Technology, Pasadena CA

Investigators

Abstract

Farley EAR-0105981 Techniques 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.