Theses and Dissertations at Montana State University (MSU)
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Item Orogens of Big Sky Country: reconstructing the deep-time tectonothermal history of the Beartooth Mountains, Montana and Wyoming, USA(Montana State University - Bozeman, College of Letters & Science, 2021) Ronemus, Chance Baylor; Chairperson, Graduate Committee: Devon A. Orme; Devon A. Orme, William R. Guenthner, Stephen E. Cox and Christopher A. L. Kussmaul were co-authors of the article, 'Orogens of Big Sky Country: reconstructing the deep-time tectonothermal history of the Beartooth Mountains, Montana and Wyoming, USA' submitted to the journal 'MDPI Geosciences Special Issue: Evolution of Modern and Ancient Orogenic Belts' which is contained within this thesis.The southwestern Montana region has experienced a protracted history of orogeny, burial, and erosion recording the development of the western margin of Laurentia, the core of the North American continent. This > 2.5 Gyr record contains clues about the nature of Precambrian tectonism, the development of economic mineral and hydrocarbon reserves, and the long-term geodynamic evolution of Earth. However, aspects of this history remain enigmatic, with events in the geologic record obscured by erosion and thermal overprinting. The manuscript presented herein, bound by introductory and concluding chapters, comprises a deep-time thermochronologic investigation of the Beartooth Mountains. New biotite 40 Ar/39 Ar, and zircon U-Pb and (U-Th)/He data are presented from 14 samples collected from the Montana part of the range. These data indicate that thermal effects of Paleoproterozoic thermotectonism associated with the Big Sky orogeny (ca. 1.8-1.71 Ga) and/or related mantle metasomatism or mafic underplating penetrated into the core of these mountains. Thermal history model results indicate that this region of the craton experienced multi-phase Proterozoic cooling. The first phase of this cooling is generally coeval with the collapse of the Big Sky orogen. A second phase of Proterozoic cooling culminated in the development of the Great Unconformity surface, across which > 2 Gyr is regionally 'missing' from the stratigraphic record. Constraints placing this latter phase between 1.4 Ga and 0.8 Ga preclude mechanisms predicting later Neoproterozoic-Cambrian cooling, such as erosion associated with Snowball Earth glaciation, and support diachronous development of the Great Unconformity surface in Laurentia. Thermal models resolve a Phanerozoic thermal history involving maximum burial temperatures by late Pennsylvanian time and cooling throughout Mesozoic time. This Phanerozoic thermal history, broadly out of sync with nearby basins, underscores the effects of interactions between far-field tectonism and inherited crustal weaknesses in the Beartooth Mountains and reconciles previous interpretations of pre-Late Cretaceous cooling with other evidence only constraining later phases of uplift. Finally, model results suggest Cenozoic reheating--likely due to burial by volcanics--and later cooling to surface temperatures due to erosional removal of these rocks--potentially related to encroachment of the Yellowstone hotspot and/or regional Basin and Range extension.Item Geothermal systems of the Corwin Springs-Gardiner area, Montana : possible structural and lithologic controls(Montana State University - Bozeman, College of Letters & Science, 1976) Struhsacker, Eric MitchellItem The geology and geothermal potential of the upper Madison Valley between Wolf Creek and the Missouri Flats, Madison County, Montana(Montana State University - Bozeman, College of Letters & Science, 1976) Weinheimer, Gerald JosephItem The Structural, volcanic, and hydrothermal geology of the Warm Springs Creek Area, eastern Garnet Range, Powell County Montana(Montana State University - Bozeman, College of Letters & Science, 1984) Callmeyer, Thomas J.Item Hydrogeology and geothermal potential of the Radersburg Valley, Broadwater County, Montana(Montana State University - Bozeman, College of Letters & Science, 1984) Wyatt, Glen MiltonItem Qualitative hydrogeologic model of thermal springs in fractured crystalline rock(Montana State University - Bozeman, College of Letters & Science, 1977) Galloway, Michael J.Item Geothermometry of selected Montana hot spring waters(Montana State University - Bozeman, College of Letters & Science, 1974) Kaczmarek, Michael BernardItem Geology and geothermal system near Jackson, Beaverhead County, Montana(Montana State University - Bozeman, College of Letters & Science, 1983) Black, Geoffrey Alan