Displacement history of the Northern Arm Fault, and its bearing on the Post-Taconic evolution of north-central Newfoundland

Abstract

The Northern Arm Fault is a northeast trending late Paleozoic fault which, together with the Reach and Cape Ray Faults, separates the Exploits and Botwood tectontratigraphic zones of Newfoundland. Kinematic indicators reveal a dextral strike slip sense of motion. Although previous studies have suggested that the Northern Arm-Reach Fault system represents the suture marking the former position of an ocean which closed during the Devonian Acadian Orogeny, the presence of identical pre-Acadian lithologies and similar deformation histories on either side of the fault suggest otherwise. Alternatively, we suggest that the Northern Arm Fault system represents a major wrench zone, which developed within the Taconic- and Acadian-modified margin of North rn America in response to oblique subduction of the oceanic tract between North America and Gondwana. Analysis of Silurian sedimentary and volcanic sequences of the Botwood and Windsor Point Groups, which occur in right-steps along this fault system, suggests that they formed in pull-apart basins during an earlier episode of strike slip faulting. We relate this phase of motion to oblique subduction of the Acadian Ocean beneath North America during the Silurian and early Devonian, leading to the Acadian Orogeny.