OBSERVED DEFORMATION AT MICROSTRUCTURE LEVEL IN QUARTZ AT THE COLTON-CARTHAGE SHEAR ZONE: ST. LAWRENCE COUNTY, NEW YORK

The Colton-Carthage shear zone in the Adirondack Mountains of upstate New York displays a contact between two distinct metamorphic events. The contact is between the Adirondack highlands (higher grade metamorphism) and Adirondack lowlands (lower grade metamorphism). The Grenville Orogeny (1.1 Ga) exposed parts of an ancient orogenic belt in the Northeastern portion of the United States, allowing observation of numerous metamorphic terrains separated by ductile shear zones. These continuous exposures aid in the understanding and timing of deformational events in the area, the Colton-Carthage shear zone being one of those ductile shear zones of great exposure. The Highlands are composed mainly of metaigneous rocks in the forms of foliated and lineated gneisses along with igneous rocks the likes of granite, anorthosites and gabbros, while the lowlands is mainly metasedimentary in the form of foliated and lineated quartzites. Both areas underwent extreme deformation but exact temperature ranges and deformation processes of the area are still not fully understood. In order to gain a more acute understanding of the geologic history of both events, the microstructues found in crystal grains of the area will be observed in both hand sample and thin section. Quartz was chosen to focus on due to its abundance in the rocks of the area along with its ability to display differing pressure and temperature ranges quite well, along with shear direction that general microstructures found in the samples can exhibit. Samples were taken along the Stone Valley trail as it cuts across the contact, giving easy access to exposures of the highlands and lowlands. Samples were taken at varying distances to the contact, along with directly on top, to see if deformation changed depending on proximity to the contact. EBSD will be used to observe the orientation of the crystals c-axis in the samples where microstructures are seen clearly as it provides orientation of individual grains, showing a preferred direction of pressure in one way or another. All things coupled together will provide a more precise history of the shear zone and the two different metamorphic events observed, in terms of shear direction, pressure and temperature.