Mehdi Tavakoli Yaraki, MSc

M. Tavakoli Yaraki¹, B. Lafrance¹, R. Sherlock¹

¹Mineral Exploration Research Centre (MERC), Harquail School of Earth Sciences, Laurentian University, Sudbury, Ontario, Canada

The Atikokan area, located approximately 175 km west of Thunder Bay, Ontario, lies along the Neoarchean boundary between the Quetico metasedimentary subprovince to the south and Mesoarchean greenstone belts and TTG suites of the Wabigoon subprovince to the north within the western Superior Province. This crustal-scale boundary is defined by the east–west–trending Quetico Fault system, which hosts numerous structurally controlled gold and base-metal prospects. This study presents new detailed structural mapping and kinematic analysis along an Atikokan transect, focusing on the Quetico subprovince and the Quetico and Rawn fault zones, to better constrain the deformational evolution and tectonic regime responsible for strain localization and mineral prospectivity. Field observations and structural measurements document a polyphase deformation history involving two principal events. An early D2 event was dominated by north–south shortening and resulted in the development of a previously unrecognized, regional-scale, east–west–trending tight to isoclinal syncline with a steep axial plane within the Quetico metasedimentary rocks. This structure is associated with a pervasive, bedding-parallel S2 foliation that transposes primary layering across much of the study area. D2 deformation is further characterized by boudinaged quartz veins, tight folding of veins, and strong flattening of clasts within fine-grained monomictic conglomerates, indicating significant pure shear strain under ductile conditions. This contractional architecture was subsequently overprinted by a D3 dextral transpressional event. D3 deformation is marked by the development of a steep S3 foliation that obliquely overprints S2, localized Z-shaped F3 drag folds, and abundant kinematic indicators, including dextrally sheared quartz veins, tension-gash arrays, and well-developed S-C-C’ fabrics. Within the Quetico and Rawn fault zones, deformation is concentrated into high-strain corridors characterized by steeply dipping foliations, asymmetric strain shadows, and shallow to steeply plunging stretching lineations, reflecting non-coaxial ductile flow. The presence of oblique and locally doubly plunging lineations, together with the oblique relationship between stretching lineations and the vorticity vector, indicates triclinic transpressional flow involving variable extrusion directions rather than simple monoclinic transpression. These relationships are consistent with along strike variations in transpression documented elsewhere along the Quetico-Wabigoon boundary. The results highlight the fundamental role of progressive dextral transpression and the reactivation of earlier contractional fabrics in localizing deformation and fluid pathways along this major Archean transcurrent fault, providing an important structural framework for mineralization in the Atikokan area and analogous settings.