Theses and Dissertations at Montana State University (MSU)
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Item Structural control of the Norris Hot Springs and associated geothermal system(Montana State University - Bozeman, College of Letters & Science, 2023) Wafer, Mia Peyton; Chairperson, Graduate Committee: Andrew K. LaskowskiMany active and productive geothermal systems are structurally controlled, suggesting that certain structural configurations have higher potentials for geothermal energy. Analyzing potential productive geothermal wells is known as geothermal play fairway analysis (PFA). Identifying these high potential structural configurations is another way to locate geothermal systems without surface expressions, which represent an unquantified natural resource for geothermal energy. By studying geothermal systems with surface expressions, I move closer to being able to locate additional natural resources. The Norris Hot Springs, located in the foothills of the Tobacco Root Mountains, Southwestern Montana, presents a novel study area to test structural control on geothermal system development. I combine geologic mapping, UAV-based photogrammetry, zircon U-Pb geochronology, seismic data, and 3D geologic modeling to date and interpret the multistage development of local structures and their influence on the geothermal system beneath the Norris Hot Springs. A comprehensive structural model suggests the geothermal system associated with the Norris Hot Springs is hosted by a deep network of faults and fractures in Precambrian gneiss basement. A nearby fault system primarily comprised of high angle NNW-SSE trending normal faults, which often display pervasive alteration and polymetallic vein mineralization, likely connects surficial features with deeper reactivated Laramide-era structures. A primary goal of this study was to investigate the benefits of supplementing traditional field work with novel methods. Results from this study demonstrate the utility of combining geologic mapping, 3D modeling, structural analysis, 3D modeling and UAV surveys for geothermal exploration and constrain the timing and influence of local faulting on geothermal activity at the Norris Hot Springs.Item The kinematics and dynamics of rifting in south-central Tibet(Montana State University - Bozeman, College of Letters & Science, 2023) Reynolds, Elizabeth Aislin Nicole; Chairperson, Graduate Committee: Andrew K. Laskowski; This is a manuscript style paper that includes co-authored chapters.Southern Tibet is a unique location to study complex interactions between continental collision and extension, or stretching, of the Earth's crust which forms linear structures called rifts. The study of rifts is important because the rocks they expose can record thermal changes in the Earth's crust related to large-scale processes such as shifts in tectonic plates which occur over long timescales and are difficult to observe. Rifts also interact with topography, can influence river systems, and cause changes in rainfall distribution across a landscape by forming topographic drainage divides. Despite their importance, the kinematics and dynamics of rifting, or processes that occur during rift formation and evolution, are not well understood. This study uses field and radiometric dating techniques to investigate the shape, orientation, and timing of extension in southern Tibet by testing kinematic models for two classes of rifts: (1) Tibetan rifts which are defined as rifts that are >150 km in length and crosscut the Lhasa Terrane, and (2) Gangdese rifts that are defined as rifts <50 km long that are isolated within the high topography of the Gangdese Range. Evaluation of rift age across the Tangra Yumco rift and three Gangdese rifts suggests the TYC rift formed through the linkage of smaller normal fault segments into larger and longer structures over time, while Gangdese rifts may have relatively constant lengths. Additionally, interactions between rifts and contractional structures have likely influenced the evolution of topography and drainage patterns in southern Tibet for at least the past sixteen million years. To further investigate structural interactions, a broader compilation of thermochronology ages expands results to include another Tibetan rift, the Lunggar rift. Trends in the data reveal all samples from Gangdese rifts and Tibetan rifts that spatially overlap the Gangdese Range yield ages between ~28-16 Ma, whereas samples north of the Gangdese Range yield ages between ~12-4 Ma. I interpret these results to reflect Gangdese rift initiation at ~28 Ma in conjunction with, and perhaps balancing, uplift driven by the India-Asia collision, while young ages North of the Gangdese Range (~12-4 Ma) reflect extension along Tibetan rifts.Item Addressing the state of Yellowstone National Park's geologic maps using traditional and novel approaches(Montana State University - Bozeman, College of Letters & Science, 2023) Kragh, Natali Ann; Chairperson, Graduate Committee: Madison MyersAccurate geologic mapping is especially important for public land, such as Yellowstone National Park, so land managers can mitigate safety risks, mindfully place infrastructure, and communicate scientific knowledge to the public. The geology of Yellowstone National Park (YNP) has been repeatedly mapped over the last century by multiple geologists with varying perspectives and mapping goals. The most recent efforts have resulted in a patchwork of twenty-one different scale maps (one 1:125,000, one 1:100,000, and nineteen 1:62,500). Presently, there exists significant promise of publishing a higher resolution, seamless map of YNP; however, it has become apparent that many of the current internal maps disagree along their shared boundaries. This study aims to address these discrepancies using both traditional and novel techniques and determine if mapping along boundaries is the best practice towards creating a seamless map. In total, 485 areas of disagreement, referred to here as boundary problems, were identified. During this study, 66 boundary problems were resolved. Each resolved boundary problem was aided by traditional mapping techniques (i.e., field mapping, field petrography, sample collection, and limited geochemistry and thin section work). However, some areas could not be addressed by field methods alone and required a more substantial analytical approach. Three "case studies" were chosen to highlight how geochemistry could aide in mapping in YNP: 1) a geochemical, textural, and age analysis of "dacite" units found throughout the north and northwestern portions of YNP and the Greater Yellowstone Region, 2) compiling a geochemical database to compare and correlate known rock units to unrecognized outcrops found in the field, 3) a novel technique using Pb isotopes in detrital plagioclase crystals from volcaniclastic units to establish a volcanic source for the units. These approaches resulted in varying success, but overall, lead to a better understanding of the work that needs to be done in YNP to publish an accurate, higher resolution geologic map. This work highlights the importance of reassessing older geologic maps and making necessary updates when the need is recognized, particularly along disagreeing shared boundaries using multiple techniques.