Acadian orogeny in west Newfoundland: Definition, character, and significance

Western Newfoundland underwent widespread deformation and metamorphism following emplacement of the Taconian allochthons but prior to deposition of onlapping Carboniferous sediments. Stratigraphic and isotopic data indicate that this deformation and metamorphism took place during the latest Silurian to early Devonian Acadian orogeny. Acadian deformation is characterized by an overall pattern of west-directed thrusting. Grenville basement is thrust above its carbonate cover sequence, and both are locally thrust over the Taconian allochthons. Between the Long Range and Indian Head inliers, cover and basement are probably delaminated with a series of east-verging folds and thrusts developed above an inferred west-directed passive roof duplex in Grenville basement. Metamorphism accompanying deformation locally reaches upper greenschist to lower amphibolite facies. West Newfoundland lies at the Acadian orogenic front. The intensity of deformation and metamorphism decreases and dies out westward. Structural and topographic relief across the frontal zone resulted in gravitational collapse and the generation of a series of extensional structures. The basal detachment of west Newfoundland ophiolites truncates Acadian compressive structures and probably reflects late-Acadian extensional tectonics rather than initial Taconian emplacement.