Date of Award
Honors Thesis (Open Access)
Colby College. Geology Dept.
Walter A. Sullivan
Robert A. Gastaldo
Robert E. Nelson
Mylonite formation and development is dependent on a number of factors including temperature, strain rate, and fluid fugacity. All three factors affect flow stress and viscosity; thus, a variance in each will affect the development of mylonites. This study focuses on factors leading to the formation of mylonite surrounded by ultramylonite of the same protolith, along-strike to one another at the center of a fault zone. The rocks in question are from the Deblois granite cut by the Kellyland fault zone, a ductile strike-slip fault zone within the larger Norumbega fault system in eastern Maine. The Deblois granite as a whole experienced three stages of deformation within the Kellyland fault zone: a primary high-temperature phase, a second brief brittle phase, and a third long-lived ductile phase. The brittle phase prompted the widespread development of ultramylonite in the center of the shear zone; the zone of mylonite records no evidence for this brittle phase. The lack of brittle deformation in the mylonites was probably due to prolonged locally elevated temperatures and to a high fluid content during later stages of deformation. The implications for this study are that even in a setting of prolonged high-strain shearing, ultramylonites may not form without a primary brittle phase to weaken the overall rheology, and may not form in the presence of a fluid.
mylonite, deformation mechanisms, kellyland fault zone, norumbega fault system, dynamic recrystallization, microstructure
Recommended CitationBoyd, Ariana S., "Deformation mechanisms in mylonites at Fletcher Peak, Washington County, ME" (2014). Honors Theses. Paper 727.
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