The climactic, middle Paleozoic event that affected the Newfoundland Appalachians has been referred to traditionally as Acadian orogeny. The latest Field studies and isotopic ages indicate that it began in the Early Silurian and continued into the Devonian. It affected the Newfoundland Humber, Dunnage, and Gander zones and western parts of the Avalon Zone. Intensities of the effects of the orogeny decrease westward across the Humber Zone (Appalachian miogeocline) and eastward across the onland Avalon Zone. Offshore, the wide Avalon Zone is virtually unaffected by Paleozoic deformation.

The most intense regional metamorphism coincides mainly with the Gander Zone. Plutonism affected...