GNEISSIC DOMES IN AN ARCHEAN TERRANE: STRUCTURAL MAPPING & KINEMATIC ANALYSIS

The Rice Bay Dome (RBD) and Northeast Bay Dome (NEBD) are gneissic bodies within the Archean Rainy Lake District in northwestern Ontario, Canada. These domes are some of the oldest units in the area (emplaced 2.7 Ga), and experienced a significant dextral transpression event shortly thereafter, which formed a pervasive fabric over the whole region. Although deformation was concentrated along the bounding shear zones (the Quetico to the north and Rainy Lake-Seine River to the south), much deformation was also accommodated in the central portions of the Rainy Lake zone. The Rainy Lake District is comprised of a heterogeneous lithological assembly, and deformation was partitioned differently in each unit based largely on spatial distribution and relative competence. A structural study was undertaken to further understand how deformation manifested itself within the domes. Foliations within the RBD generally strike roughly east-west, and follow the shape of a NE/SW-E/W trending arch, while dipping moderately-steeply to both the north and south. Lineations in the RBD are subhorizontal, and plunge either east or west. Foliations in the NEBD strike NE, and dip moderately-steeply to either the NW or SE. Unfortunately the outcrop in this area did not lend itself to lineation measurements. Shear zones are concentrated within the center of the domes, while features such as deformed mafic enclaves are concentrated towards the edges of the domes. Within the RBD, many shear zones, both sinistral and dextral, strike roughly east-west with moderate to steep dips. Shear zones within the NEBD are oriented in a similar manner, but are of primarily dextral sense. The difference in sense of shear between domes is likely due to their spatial distribution. The NEBD is proximal to the Quetico shear zone, and has accommodated a significant amount of dextral strike-slip motion, while the RBD has accommodated more of the contractional component of the transpression.