Event Title

Microstructural analysis of centimeter scale shear zones within the Grassy Portage Sill, Ontario, Canada.

Presenter Information

Joshua Reed

Mentor 1

Dyanna M. Czeck

Location

Union Wisconsin Room

Start Date

27-4-2018 1:00 PM

Description

The Grassy Portage Sill (GPS), located in the Rainy Lake region of northwestern Ontario, is an approximately 2.7 billion year gabbroic intrusion that was caught within a major deformation zone related to granite-greenstone terranes formation. Deformation in the GPS was localized into some prime examples of local (cm scale) shear zones. Understanding the microscopic structure and mineralogy of these shear zones will provide a better understanding of shear zone dynamics. The Rainy Lake region is bounded by the Quetico Fault to the north which runs mostly east west, and the Rainy Lake – Seine River Fault to the south which runs diagonal of the Quetico Fault. Past research in the Rainy Lake Region show complex structural dynamics within the area of interest and show a overall dextral (right-lateral) zone with a component of shortening. Of interest to us are the localized shear zones, and as such we are analyzing a small scale shear zone within a previously recovered sample of a metagabbro from the Grassy Portage Sill. The shear zone of interest is approximately 1 cm in width and shows strong mineral banding inside the zone with isotropic mineral fabric outside of the shear zone. Fabric is the preferred orientation and alignment of the mineral crystals that make up a rock. Our sample was prepared into petrographic thin sections that span the deformation from outside the shear zone gradually into the deformed shear zone. Mineral abundance and microstructural features of the samples can be identified through thin section analysis. Comparing the mineral composition from one thin section to the next across the deformation gradient will indicate how the mineralogy and fabric of a rock reacts during shear zone formation.

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Apr 27th, 1:00 PM

Microstructural analysis of centimeter scale shear zones within the Grassy Portage Sill, Ontario, Canada.

Union Wisconsin Room

The Grassy Portage Sill (GPS), located in the Rainy Lake region of northwestern Ontario, is an approximately 2.7 billion year gabbroic intrusion that was caught within a major deformation zone related to granite-greenstone terranes formation. Deformation in the GPS was localized into some prime examples of local (cm scale) shear zones. Understanding the microscopic structure and mineralogy of these shear zones will provide a better understanding of shear zone dynamics. The Rainy Lake region is bounded by the Quetico Fault to the north which runs mostly east west, and the Rainy Lake – Seine River Fault to the south which runs diagonal of the Quetico Fault. Past research in the Rainy Lake Region show complex structural dynamics within the area of interest and show a overall dextral (right-lateral) zone with a component of shortening. Of interest to us are the localized shear zones, and as such we are analyzing a small scale shear zone within a previously recovered sample of a metagabbro from the Grassy Portage Sill. The shear zone of interest is approximately 1 cm in width and shows strong mineral banding inside the zone with isotropic mineral fabric outside of the shear zone. Fabric is the preferred orientation and alignment of the mineral crystals that make up a rock. Our sample was prepared into petrographic thin sections that span the deformation from outside the shear zone gradually into the deformed shear zone. Mineral abundance and microstructural features of the samples can be identified through thin section analysis. Comparing the mineral composition from one thin section to the next across the deformation gradient will indicate how the mineralogy and fabric of a rock reacts during shear zone formation.