9505742 Farley This research project is designed to be a definitive study of the applicability of the (U-Th)/He system for geochronology and thermochronology of common accessory minerals (particularly apatite). This system has significant potential to provide temporal constraints on geological events which are difficult to date with alternative techniques. The project involves laboratory diffusion experiments to constrain He retention characteristics, as well as measurement of He ages for intercomparison with ages determined by independent methods.