Microstructures and monazite geochronology suggest that the peak metamorphic assemblage of sillimanite+biotite+quartz+plagioclase+ilmenite+meltągarnetąmagnetite in the metasedimentary rocks from the Fosdick migmatite dome correspond to Carboniferous metamorphism. Constraints on the conditions of peak metamorphism are hindered by reequilibration of mineral compositions, but preliminary estimates based on mineral equilibria modeling suggest peak temperatures of 700-860°C and pressures of 5-10 kbar. Presence of coexisting garnet+magnetite is a function of bulk composition and constrains peak temperatures to 720-800°C using an assumed peak pressure of 8 kbar. Evidence for Cretaceous decompression includes cordierite replacing sillimanite and biotite, and cordierite rimming garnet. Estimates for Cretaceous metamorphism are P = 5.3-5.5 kbar and T = 700-740°C (Siddoway et al., 2004). Future studies will consider the effects of melting and melt loss, and localized compositional domains on the mineral equilibria, and the use of average thermobarometry and trace element thermometers.