Pseudotachylyte is a type of fault rock consisting of a heterogeneous mixture of finely cominuted wall rock and melt likely caused by high transient frictional heating during fault movement. Although very complex material, it does theoretically offer the possibility of dating active faulting, assuming that it is produced during faulting and that some radiometric clock system is reset during pseudotachylyte formation. This project will address this problem by investigating several isotopic dating systems, theoretical diffusion models and calibration techniques using natural and artificial material. Results are expected to help understand pseudotachylyte formation and to provide insight into how it might be used to date fault movements. ***