Structural evolution of a major fault zone: the Cape Ray Fault Zone, southwestern Newfoundland, Canada

Abstract

The Cape Ray Fault Zone is a major Paleozoic structure in southwestern Newfoundland, and occurs at or close to the boundary between two major continental blocks, Laurentia and Avalonia. A detailed structural analysis demonstrates that the fault records early reverse-sinistral thrusting of the Grand Bay Complex at amphibolite grade (D2), followed by a protracted event (D3) characterized by reverse-dextral thrusting of the Grand Bay Complex rocks on top of the supracrustal rocks of the Windsor Point Group and retrogression to greenschist facies, as well as a pre-384 Ma orogen-parallel dextral transcurrent mylonite (D4) during the later stages of the collision. Regional-scale strain partitioning induced heterogeneity of strain both along and across the strike of the Cape Ray Fault Zone. The east–west-oriented segment of the Cape Ray Fault Zone is a tear fault that accommodated differential displacement along the length of the fault. Later stages of the deformation include post-384 Ma sinistral transcurrent reactivation of the dextral mylonite and extension. The reverse-sinistral thrusting and the reverse-dextral motion occurred between 415 and 386 Ma and correspond to the two-phase Acadian orogeny recognized at the scale of the orogen and believed to be related to collision between Laurentia and Avalonia. The Cape Ray Fault Zone preserves evidence of large-scale geodynamic processes affecting rocks where the kinematics and the timing are well constrained.