Distribution of Ordovician and Devonian metamorphism in mafic and pelitic schists from northern Vermont

40 Ar/ 39 Ar range from 471 to 439 my and confirm that Ordovician metamorphism is recorded from the Canadian border south to the Precambrian core of the Green Mountain Anticlinorium (GMA). Medium-high pressure (P) facies series metamorphism in the north and medium-P metamorphism to the south. Similar metamorphic ages and compatible estimates of T and P indicate mafic and pelitic rocks were metamorphosed together. Medium-P Devonian metamorphism has overprinted the Ordovician metamorphism in northern Vermont east and probably west of the GMA axis, resulting in conventional K/Ar, 40 Ar/ 39 Ar total fusion and plateau ages of 386 to 355 my on muscovite, biotite, and amphibole.--Modified journal abstract.