The Ackley granite was intruded into variably deformed and metamorphosed rocks within the Gander and Avalon Zones of the Newfoundland Appalachians. Biotite and hornblende from the pluton record internally concordant 40Ar/39Ar age spectra that define total-gas dates of 352–356 Ma. These are similar to a previously reported 355 ± 5 Ma Rb–Sr whole-rock isochron age, and indicate relatively rapid post-magmatic cooling, a feature consistent with the post-kinematic character of the pluton.In the western Avalon Zone, recrystallized, sericitic metavolcanic rocks from the Late Precambrian Love Cove and Marys-town Groups display variably discordant, whole-rock 40Ar/39Ar age spectra. However, the samples yield well defined plateau ages of 353–400 Ma (11 samples), which are interpreted to closely date the regional metamorphism and associated deformation in the western Avalon Zone. This chronology is similar to that of the easternmost Gander Zone, indicating that deformation and metamorphism in the western Avalon Zone occurred simultaneously with tectonic juxtaposition of the Gander and Avalon terranes during the Acadian Orogeny. Geochronological evidence of previously described Precambrian (Avalonian) tectonothermal activity has not been documented in this study.

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