Date of Award
Bachelor of Science (BS)
Reconstructing the assembly of the Middle Proterozoic Adirondack Mountains and surrounding regions is difficult due to high-grade metamorphism, igneous intrusions, faulting, erosion, and dense cover. A 2008/2009 Keck Geology Consortium Project devoted itself to collecting petrological and structural data in the Adirondack Lowlands and into the Frontenac terrane of Ontario with the hypothesis that a shear zone near the St. Lawrence River, the Black Lake Shear Zone (BLSZ), may be a tectonic boundary representing the welding of the Adirondacks onto the rest of the Precambrian core. In this study, to determine if or if not the BLSZ is a discontinuity, we used garnet-biotite, Ti-in-biotite, and two-feldspar geothermometry and we examined the geochemistry of Adirondack Lowlands and Frontenac terrane pelites. Rare-earth elements and trace element concentrations reveal a shale protolith for the Adirondack Lowlands pelites and most likely for the Frontenac terrane pelites. The mineralogy reflects upper amphibolite facies conditions in the Adirondack Lowlands and granulite facies conditions in the Frontenac terrane. Geothermometry from all three thermometers confirmed higher temperatures in the Frontenac terrane than in the Adirondack Lowlands, but lack of samples due to cover near the BLSZ makes it difficult to determine if this temperature difference is gradual or abrupt. Temperature results varied greatly between geothermometers with Ti-in-biotite results being approximately 200°C higher than two-feldspar temperature results. These inconsistencies between geothermometers may be due to problems with calibrations or fluid infiltration in association with the shear zone. The region requires more work as every new study helps to construct the history of the Adirondack Mountains.
Russell, Ashley, "Recent two-feldspar, Ti-in-biotite, and garnet-biotite geothermometry of the Frontenac terrane and Adirondack Lowlands, Grenville Province, Canada and the United States" (2009). Undergraduate Theses and Senior Projects. 102.