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

Results of a structural analysis of Archean basement, Huronian cover and va rious igneous rocks in the Sudbury area, Ontario, and regional tectonometam orphic correlations suggest that structures in the eastern Penokean orogen formed dominantly by dextral transpression. Bulk horizontal shortening star ted with the ca. 2.4 to 2.2 Ga Blezardian orogeny and was accompanied by pe ak metamorphism and local granitoid magmatism. During the 1.89 to 1.83 Ga P enokean orogeny, horizontal dextral shear parallel to the curved axis of th e eastern Penokean orogen gained in importance, and is most likely related to docking of Proterozoic magmatic are terranes to the Superior Province ma rgin. This tectonic activity led to distributed, heterogeneous deformation of Archean basement rocks and exhumation of deep-crustal rocks in the Sudbu ry 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 suggest s that crustal fragmentation of the Archean supercontinent started at 2.45 Ga. Finally, the Great Lakes tectonic zone and the Murray fault, master dis locations in the Penokean orogen, may have acted as crustal weakness zones which influenced the orientation and development of 1.1 Ga Midcontinent Rif t segments. (C) 1999 Elsevier Science B.V. All rights reserved.