Transpression-Induced Ductile Shear in the Boundary Region of the Quetico and Wawa Subprovinces, NE Minnesota — A Response to Local Strain Partitioning

Abstract

Evidence from shear zone geometries, finite strains, and the kinematics of shear indicate that well-developed ductile to brittle-ductile shear zones concentrated in the boundary region of the Quetico and Wawa subprovinces are a result of regional dextral transpression. However, the local concentration of shear in the subprovince boundary region is interpreted as a response to local partitioning of shear and shortening strains rather than a response to local suturing or accretion along this segment of the subprovince boundary. The shear zones are concentrated primarily in metasedimentary rocks that are interlayered with steeply dipping basaltic flows in the northern Wawa subprovince near the sub-province boundary. This association suggests that shear strains developed during the transpression were concentrated in the subprovince boundary region as a result of local rheological contrasts between steeply dipping mafic flows and associated metasedimentary rock, not in response to accretion along the subprovince boundary.