Structural constraints on the tectonic evolution of a late Archean greenstone belt in the northeastern Superior Province, northern Quebec (Canada)

Abstract

A detailed structural analysis shows that the Vizien greenstone belt of northeastern Superior Province records five generations (G 1 to G 5) of ductile deformation, as well as brittle faulting. G 1 is indicated by the local presence of a pre-G 2 foliation and is interpreted to be related to thrusting. G 2 is responsible for the main penetrative foliation (S 2), axial-planar to tight to isoclinal F 2 folds and subparallel to major boundaries between lithotectonic panels. It is concentrated in a thrust with sense of shear opposite to that interpreted for G 1. F 3 and F 4 folds are open to tight, with NNW-SSE- and E-W-trending axial surfaces, respectively. They warp the S 2 foliation and major panel boundaries and dominate the map pattern. G 5 is associated with dextral transcurrent movement along a NNW-SSE-trending shear zone. Through understanding of its geometry and deformation history, the Vizien belt has been unfolded into its much simpler pre-G 3 geometry. This greatly helps in the investigation of relationships between the different panels (proposed terranes), their tectonic settings and the kinematics of panel amalgamation. The structural study, in concert with geological and geochemical work, leads to a tectonic model for the evolution of the greenstone belt, which involves subduction of oceanic lithosphere and continental arc volcanism at ∼2724 Ma, intra-arc rifting at ∼2722 Ma, and collision between ∼2718 and ∼2693 Ma with associated obduction of oceanic plateau crust, formation of mélange and deposition in a possible foreland basin. The G 1 and G 2 deformations are interpreted to be related to synthetic thrusting and back thrusting, respectively, during the collision.