Transpressive tectonism in the eastern Penokean orogen, Canada: Consequences for Proterozoic crustal kinematics and continental fragmentation

Abstract

Results of a structural analysis of Archean basement, Huronian cover and various igneous rocks in the Sudbury area, Ontario, and regional tectonometamorphic correlations suggest that structures in the eastern Penokean orogen formed dominantly by dextral transpression. Bulk horizontal shortening started with the ca. 2.4 to 2.2 Ga Blezardian orogeny and was accompanied by peak metamorphism and local granitoid magmatism. During the 1.89 to 1.83 Ga Penokean orogeny, horizontal dextral shear parallel to the curved axis of the eastern Penokean orogen gained in importance, and is most likely related to docking of Proterozoic magmatic arc terranes to the Superior Province margin. This tectonic activity led to distributed, heterogeneous deformation of Archean basement rocks and exhumation of deep-crustal rocks in the Sudbury area and the Kapuskasing structural zone, but may have failed to accrete Paleoproterozoic terranes in the Lake Huron area. The lack of evidence for horizontal extension following Blezardian and Penokean contraction suggests that crustal fragmentation of the Archean supercontinent started at 2.45 Ga. Finally, the Great Lakes tectonic zone and the Murray fault, master dislocations in the Penokean orogen, may have acted as crustal weakness zones which influenced the orientation and development of 1.1 Ga Midcontinent Rift segments.