AGE ADULARIA AND METAMORPHISM OUACHITA MOUNTAINS ARKANSAS

Adularias from quartz veins in Ouachita Mountains give isotopic ages that bracket time of crystallization between 287 and 214x10//6 yr ago; Middle Pennsylvanian age is excluded; combined isotopic, stratigraphic, and structural data suggest deposition in Late Pennsylvanian or Early Permian time and persistence of mild deformation and elevated temperatures related to low-grade regional metamorphism into and possibly somewhat after Middle Permian time; feldspars either highly ordered or highly disordered with respect to Al-Si distribution lose Ar at low temperature to extents that apparently do not differ significatly.