Brittney Swoffer HBSc thesis abstract

Thesis Title: 
The Deformation History of the Ivanhoe Lake Structure

Ivanhoe Lake is located 220km east of Wawa, Ontario, Canada. The Ivanhoe Lake structure strikes northeast to southwest and is the boundary between the high grade metamorphism of the Kapuskasing structural zone and the low grade metamorphism of the Abitibi subprovince. This difference in grade of metamorphism is what makes the Ivanhoe Lake structure so interesting to study. Through analysis of the microstructures seen in thin section a long deformation history was revealed. Ductile deformation, characteristic of deep burial, as well as deformation at or near the brittle-ductile transition zone were evident. This affects a wide area that extends to either side of the structure. This was followed by brittle fracturing at a shallower depth of burial. The brittle deformation is confined to a narrow zone found along Ivanhoe Lake. Examples of ductile deformation within the thin sections include: undulatory extinction in quartz, subgrains in quartz and feldspars, deformation twins in plagioclase and microcline, as well as irregular grain boundaries for all grains. The brittle-ductile transition zone is documented by the existence of pseudotachylites. These glassy rocks are characteristic of large faults. The brittle history is documented by quartz or calcite filled fractures found at both the outcrop and microscopic scale. These brittle structures always crosscut the ductile features. This crosscutting relationship suggests that the structure has had a long history which began with ductile deformation and progressed into brittle deformation.