Distinct Taconic, Salinic, and Acadian deformation along the iapetus suture zone, Newfoundland Appalachians

Structural mapping in central Newfoundland has identified seven distinct phases of deformation (D-1 to D-7), the most significant of which are D-1, D-2, and D-4. D-1 involved the formation of a Middle and Late Ordovician south-southeast-directed thrust belt and concomitant development of mylonite and phyllonite. A Late Ordovician to Early Silurian D-2 thrust and fold belt overprints D-1 mylonitic deformation and is the most distinctive deformation event in the study area. Late Silurian to Devonian D-4 is responsible for folds and north-northwest-directed dextral thrust and reverse faults that overprint D-1 to D-3 structures. D-4 structures in central Newfoundland include the Exploits-Gander boundary. Subsequent deformation is generally of local significance only. The are-back-arc complexes making up the various terranes in central Newfoundland are predominantly juxtaposed along D-1 shear zones, which include the Red Indian Line. Our data indicate that terrane boundaries initiated during D-1 may have protracted deformation histories spanning several deformation events. This has important implications for the interpretation of terrane boundaries in Newfoundland, as D-1 terrane boundaries may be interpreted as D-2 or D-4 shear zones depending on the intensity of overprinting or reactivation. The deformation history proposed in this paper corresponds closely to that of established Appalachian orogenic cycles. D-1 is correlated with the Ordovician Taconic orogeny and involved accretion of arc-back-arc complexes to the Laurentian margin. D-2 and D-4 are correlated with the Ordovician-Silurian Salinic and Silurian-Devonian Acadian orogenies, which involved the subsequent accretion of the Ganderia and Avalonia microcontinents to the Laurentian margin, respectively.