The Ash Bay Gneiss Dome is located in the most northern part of Rainy Lake. The Quetico Fault and the Seine River-Rainy Lake Faults are located to the south of the dome. Rainy Lake is wedged between the Wabigoon Subprovince to the north and the Quetico Subprovince to the south, all being apart of the Superior Province. The mineralogy indicates that the rocks of the dome underwent amphibolite facies metamorphism at approximately 500°C and was emplaced during solid-state metamorphic flow by a diapiric inflation. The indicating minerals found in samples RL-01 - Rl-29 are mostly quartz and oligoclase, but sillimanite, epidote, and hornblende are also found within the samples in smaller amounts. There were no kinematic indicators located in the field, so a closer examination of the microstructures was necessary to understand the extent of the deformation of the crystals and their deformation mechanisms. In all, 29 oriented samples were studied that were taken from the eastern side of the Ash Bay dome by G. Borradaile and D. Gauthier. These samples were thin sectioned and quartz c-axis petrofabric studies were performed on them by the use of the universal stage. The petrofabric reveals a northeast-southwest orientation of the quartz crystals c-axes maximum compressive direction of the stress on the rocks, which is interpreted to be in a northwest-southeast direction. Anisotropy of magnetic susceptibility was also performed on the 29 oriented samples and was later compared with the petrofabrics. It was found that the quartz c-axis petrofabrics were strongly clustered and dipping at higher angles than the magnetic fabrics. This showed that the quartz fabrics were aligned before the magnetic fabrics and therefore record a longer period of shear. The magnetic fabrics could not have formed until the later stages of the domes inflation to result in nearly horizontal magnetic fabrics.
Amy is currently working as an exploration geologist
For more details about this thesis contact Dr. Graham Borradaile