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Author ORCID Identifier
Open Access Dissertation
Doctor of Philosophy (PhD)
Year Degree Awarded
Month Degree Awarded
Michael L. Williams
Geology | Tectonics and Structure
The eastern Adirondack Mountains contain abundant exposures of high-grade metamorphic rocks. These exposures are interpreted to be a window into the mid/deep crust of an ancient, large, hot, long-duration orogen, allowing the Adirondack Mountains to be used as an analogue to the deep processes of modern orogens. Currently interpreted thermo-tectonic events in the eastern Adirondack Mountains include the ca. 1245-1220 Ma Elzevirian orogeny, the ca. 1190-1150 Ma Shawinigan orogeny, emplacement of the ca. 1150 Ma AMCG igneous suite, the ca. 1090-1050 Ma Ottawan orogeny, and a ca. 1050-1020 Ma extensional collapse phase. This dissertation focuses on six migmatite domains within the eastern Adirondack Mountains, utilizing in-situ petrochronology, kinematic analysis, whole rock geochemistry, and forward petrologic modeling to constrain the character, timing, and significance of partial melting in these domains. Combining petrochronology with geochemistry links monazite growth timing to biotite-dehydration melting reactions in migmatitic samples. Melt reaction timing was found to vary between the six migmatite domains, splitting them roughly into the northern and southern regions. Melt timing in the northern region was generally ca. 1160 Ma, associated with the late Shawinigan orogeny and AMCG emplacement. Melt timing in the southern region was generally ca. 1050 Ma, associated with the late Ottawan orogeny. At least one of the migmatite domains in the northern region shows evidence for both melt timings within a single sample. Analysis of conflicting kinematic indicators within the Shelving Rock quadrangle illustrates the significance of late melting events on the overprinting or preservation of deformational textures and fabrics from earlier tectonometamorphic events. Feldspar kinematic indicators here show a compressional shear sense interpreted to be syn-melting while garnet kinematic indicators show an extensional shear sense interpreted to be post-melting. Whole rock geochemistry and forward petrologic modeling illustrates the compositional variability and melt loss variability of the migmatites. These variabilities had a significant effect on the timing and number of melting events recorded by each migmatite sample. The melting history of the eastern Adirondack Mountains is important in understanding the evolution of large ancient orogens and in applying this understanding to large modern orogens.
Pless, Claire Rose, "Implications and Significance of Partial Melting on the Tectonic History of the Eastern Adirondack Mountains" (2020). Doctoral Dissertations. 2071.
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