The Overflow Pond Granite intrudes deformed sedimentary and volcanic sequences in the central part of the Dunnage Zone of the Newfoundland Appalachians. Zircon and biotite in the pluton record similar ages (U–Pb and 40Ar/39Ar, respectively), which suggest an emplacement date of ca. 390 Ma. The concordant isotopic systems require relatively rapid post-magmatic cooling and indicate intrusion at shallow crustal levels. The metasedimentary rocks show a marked increase in grade in the vicinity of the pluton. Biotite within the higher grade terrane records 40Ar/39Ar ages identical to those within the pluton and suggests that the high-grade assemblages developed in response to emplacement of the granite. Whole-rock phyllite samples from lower grade portions of the sequence display variable discordant 40Ar/39Ar release spectra. These indicate a complex tectonothermal history, including formation of a pressure solution cleavage at ca. 410 Ma (with associated folding) and a contact-metamorphic overprint by the Overflow Pond Granite.