9406062 Cheney Laser Argon dating studies have established that substantial age variations occur within single muscovite crystals as a function of thermal history, size, and post-crystallization deformation. The core-to-rim age discordance of these crystals can have significant applications in studies of crustal development. This project will use the well-studied southwestern New England area as a field test area to develop a robust methodology for interpretation of such spectra. Successful results will have wide application to tectonic studies.