Detrital and metamorphic Ar-40/Ar-39 ages from muscovite and whole-rock samples, Meguma Supergroup, southern Nova Scotia

Ar-40/Ar-39 dates from eight muscovite separates and two whole-rock samples of slate, siltstone, and sandstone provide detrital, metamorphic, and post -metamorphic overprinting ages for the low-grade metamorphic rocks of the M eguma Supergroup in the Mahone Bay region of southern Nova Scotia. Variably reset detrital muscovite ages of 600-550 Ma agree with previously obtained U-Pb dates from detrital zircon. Separates of foliation-parallel muscovite yield precise Ar-40/Ar-39 ages of 395-388 Ma. Petrographic and metamorphic data indicate that these are metamorphic mica growth ages. The range overl aps with the younger limit of previously reported whole-rock ages (410-380 Ma), but is more tightly constrained. An apparent inconsistency between pre vious Ar-40/Ar-39 whole-rock ages as old as 410 Ma and regional deformation that affected sedimentary rocks as young as 385 Ma has been resolved by th e younger ages reported here and by recent adjustments to the early Paleozo ic time scale which suggest that the Lochkovian to Emsian Torbrook Group wa s deposited between 419 and 394 Ma. A muscovite plateau age of 376 Ma from one sample may be related to late-stage flexural slip deformation in the Ov ens gold district.