Reassignment of the Lowland Creek Volcanics to Eocene Age

Abstract

Recent potassium-argon age determinations of 48 and 50 m.y. for biotite in rocks of the Lowland Creek Volcanics in southwestern Montana agree with previous K-Ar age of 49 m.y. for biotite of a dike rock correlated with lavas of the upper part of the volcanics. Together, these determinations establish the age of the volcanics as early Eocene rather than late Oligocene, as they had been tentatively designated.