The Vermont Appalachians expose metamorphosed magmatic rocks ranging in age from Late Proterozoic to Cretaceous. Geochemistry, in concert with stratigraphic, structural, and metamorphic studies, reveals the origins of the magmatic rocks. Late Proterozoic–Early Cambrian dikes and greenstones in western Vermont formed during rifting of the Laurentian continent to form the Iapetus Ocean. Cambrian serpentinized peridotite represents forearc suprasubduction zone ophiolitic fragments. Cambrian to Ordovician amphibolites and felsic gneisses were formed as part of the Shelburne Falls volcanic arc. The Early Ordovician Mount Norris intrusive suite formed in an extensional setting in the vicinity of the Shelburne Falls arc. Silurian extensional...