Adularias from quartz veins give isotopic ages which bracket crystallization between 287 and 214 m.y. ago. A Middle Pennsylvanian age is excluded. Isotopic, stratigraphic, and structural data suggest deposition in Late Pennsylvanian or Early Permian and persistence of mild deformation and elevated temperatures related to low-grade regional metamorphism into and possibly somewhat after Middle Permian. The metamorphism may coincide with the 250 m.y. heating event in the southern Appalachians. Feldspar data suggest continuous Ar diffusional loss activated by very slow Al-Si ordering toward the stable structural state of maximum microcline. Feldspars in intermediate structural states are more prone to such ordering and give lower ages.