xv, 108 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / Studies on seismic attenuation are an important complement to those on seismic velocity, especially when interpreting results in terms of temperature. But estimation of attenuation (t*) is more computationally involved and prone to contamination by noise, especially signal-generated noise. We have examined the effects of various forms of synthetic noise on t* estimation using time and frequency domain methods with varying window lengths and data frames of reference. We find that for S-waves, error due to noise can be reduced by rotating the data into the estimated polarization direction of the signal, but unless the exact nature of the noise is known, no method or window size is clearly preferable. We recommend the use of multiple estimation methods including a careful assessment of the uncertainty associated with each estimate, which is used as a weight during inversion for 1/Q. Our synthetic tests demonstrate that the misfit between actual and estimate-predicted traces or spectra correlates with t* error, and a similar relationship is suggested for real data. Applying this approach to data from the Yellowstone Intermountain Seismic Array, we employ two important constraints during inversion. First, we scale the misfit values so that the resulting weights are comparable in magnitude to the squares of the eventual data residuals. Second, we smooth the model so that the maximum attenuation (1/Q) does not exceed a value which would totally explain the observed velocity anomaly. The tomographic models from all the estimation methods are similar, but in the vicinity of the Yellowstone mantle plume, S-wave models show greater attenuation than do P-wave models. We attribute this difference to greater focusing by the plume of S-waves. All models show relatively high attenuation for the plume at depth, but above 250 km attenuation in the plume drops rapidly to values less than those of the surrounding mantle. We attribute this drop to the onset of partial melting, which dehydrates the olivine crystals, suppressing dislocation mobility and thereby attenuation. These attenuation models suggest excess plume temperatures at depth which are too low to support a plume origin in the lower mantle. This dissertation includes unpublished co-authored material. / Committee in charge: Eugene Humphreys, Chairperson, Geological Sciences; Emilie Hooft Toomey, Member, Geological Sciences; Douglas Toomey, Member, Geological Sciences; James Isenberg, Outside Member, Mathematics

Cenozoic tectonics of the Pacific Northwest (PNW) and the associated mantle structures are remarkable, the latter revealed by EarthScope seismic data. In this thesis we model teleseismic body waves constrained by ambient-noise surface waves and teleseismic receiver function analysis in order to recover better-controlled higher resolution images of the PNW continuously from the surface of the crust to the base of the upper mantle. We focus on and have clearly imaged two major upper mantle structures: (1) the high-velocity Farallon slab (the "Siletzia curtain") extending vertically beneath the Challis-Kamloops-Absaroka volcanic flareup (~53-47 Ma) of western Idaho and central Washington; and (2) a high-velocity anomaly beneath the Wallowa Mountains of northeast Oregon associated with the main Columbia River flood basalts source region. The proximity of these two structures along with the tectono-magmatic history of the PNW leads us to reexamine the origin of the Columbia River Basalts ~ 16 Ma. This thesis includes co-authored material submitted for publication.

No description available.

abstract: Volcanic eruptions are serious geological hazards; the aftermath of the explosive eruptions produced at high-silica volcanic systems often results in long-term threats to climate, travel, farming, and human life. To construct models for eruption forecasting, the timescales of events leading up to eruption must be accurately quantified. In the field of igneous petrology, the timing of these events (e.g. periods of magma formation, duration of recharge events) and their influence on eruptive timescales are still poorly constrained. In this dissertation, I discuss how the new tools and methods I have developed are helping to improve our understanding of these magmatic events. I have developed a method to calculate more accurate timescales for these events from the diffusive relaxation of chemical zoning in individual mineral crystals (i.e., diffusion chronometry), and I use this technique to compare the times recorded by different minerals from the same Yellowstone lava flow, the Scaup Lake rhyolite. I have also derived a new geothermometer to calculate magma temperature from the compositions of the mineral clinopyroxene and the surrounding liquid. This empirically-derived geothermometer is calibrated for the high FeOtot (Mg# = 56) and low Al2O3 (0.53–0.73 wt%) clinopyroxene found in the Scaup Lake rhyolite and other high-silica igneous systems. A determination of accurate mineral temperatures is crucial to calculate magmatic heat budgets and to use methods such as diffusion chronometry. Together, these tools allow me to paint a more accurate picture of the conditions and tempo of events inside a magma body in the millennia to months leading up to eruption. Additionally, I conducted petrological experiments to determine the composition of hypothetical exoplanet partial mantle melts, which could become these planets’ new crust, and therefore new surface. Understanding the composition of an exoplanet’s crust is the first step to understanding chemical weathering, surface-atmosphere chemical interactions, the volcanic contribution to any atmosphere present, and biological processes, as life depends on these surfaces for nutrients. The data I have produced can be used to predict differences in crust compositions of exoplanets with similar bulk compositions to those explored herein, as well as to calibrate future exoplanet petrologic models. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2020

Investigations into ophiolite from California demonstrated that these ultramafic rocks formed within the mantle wedge of a subduction zone. Fore-arc locales are dominated by highly refractory peridotite, formed by hydrous-fractional partial melting that began in the garnet stability field and ended in the spinel stability field. These ophiolites also displayed enriched fluid-mobile element concentrations. Based on melt models, these elements should have extremely low concentrations, yet all pyroxenes display enriched compositions. A new algorithm was derived to model this fluid enrichment process, which represents the total addition of material to the mantle wedge source region and can be applied to any refractory mantle peridotite that has been modified by melt extraction and/or metasomatism. Investigations into the interaction of a mantle plume with continental lithosphere demonstrated that Yellowstone-Snake River Plain olivine tholeiites are compatible with genesis from a deep-seated mantle plume and were modeled via mixing of three components. The variable age, thickness, and composition of North American lithosphere guide this process. Drill core near Twin Falls, ID was examined to assess (1) the chemical evolution of olivine tholeiite, (2) how basalt evolves in continental settings, and (3) the dominant fractionation process, e.g., fractional crystallization, Raleigh fractional crystallization, or assimilation fractional crystallization.

Eutrophication is of interest in the field of water quality. Eutrophic lakes, when used as sources for drinking water, can cause problems during the treatment process, for example algae blooms can clog filters, requiring more water and energy to be used during the cleaning and backwashing of the filters. Excess nutrient loading and eutrophication can also harm fish and aquatic life habitats. Certain species of algae and cyanobacteria can be toxic to humans as well. Since 1998, Dr. A. Woodruff Miller has collected water samples from 46 lakes and ponds in Yellowstone National Park. The Carlson Trophic State Index, the Vollenweider Model, the Larsen Mercier Model, the Burns Trophic Level Index, and the Naumann Trophic Scale were then used to assign each lake or pond to a trophic state classification (Oligotrophic, Mesotrophic, Eutrophic, and Hyper-Eutrophic). Of the 46 total lakes and ponds that have been tested over the past 14 years, five lakes are classified as slightly oligotrophic, implying that the waters are relatively clear and free from nutrient pollution. Of the 46 lakes, 19 are classified as slightly mesotrophic, mesotrophic, or strongly mesotrophic. These classifications imply that the waters are moderately clear and contain some nutrient pollution. Of the 46 lakes, 14 are classified as slightly eutrophic, eutrophic, or strongly eutrophic. This implies that the waters have high turbidity and nutrient content. Of the 46 lakes, 8 are classified as slightly hyper-eutrophic or hyper-eutrophic. These lakes are noticeable for their high algae content with very high nutrient content. These classifications are based on the most recent year sampled.

No description available.

A key component to conservation is an accurate understanding of genetic subdivision within a species. Despite their ecological and economic importance, relatively little is understood about the genetic structuring of Yellowstone cutthroat trout in Yellowstone National Park. Here, we use traditional (Fst, Rst, Nm, and AMOVA) and modern (Bayesian assignment tests, coalescent theory, and nested clade analysis) analytical approaches to describe the population genetic subdivision of cutthroat trout spawning populations in Yellowstone Lake and to identify genetically distinct population segments throughout Yellowstone National Park. Evidence for restricted gene flow between spawning populations within Yellowstone Lake was detected using nested clade analysis. This is the first molecular evidence for restricted gene flow between spawning populations in Yellowstone Lake. In contrast, traditional methods such as Fst and Rst as well as the Bayesian clustering program STRUCTURE v2.0 failed to detect evidence for restricted gene flow. Across our sampling range within Yellowstone National Park, eleven genetically distinct cutthroat trout population segments were detected. These showed a general pattern of small, isolated populations with low genetic diversity in headwater streams and wide-spread, genetically diverse populations in higher-order rivers. We recommend populations be managed to maintain current levels of genetic diversity and gene flow. Based on the recent decline of and distinct morphological, behavioral, and genetic nature of cutthroat trout in Yellowstone Lake, we recommend the Yellowstone Lake spawning populations collectively be recognized as an evolutionarily significant unit.

Le geyser d'Old Faithful dans le Parc National de Yellowstone, aux États-Unis, est l'undes geysers les plus connus au monde. La cyclicité de ses éruptions est étudiée depuis lesannées 60 a_n de comprendre sa dynamique. En e_et, le caractère bimodal de la fréquencede ses éruptions intriguent les scienti_ques qui cherchent à en connaître les causes.Les enregistrements sismiques réalisés à la surface du geyser démontrent des signauximpulsionnels dont l'origine fut identi_ée par Sharon Kedar. Ainsi, en 1992, S. Kedar etses collègues ont déployé plusieurs capteurs sismiques dans le but d'étudier la source dessignaux sismiques de type tremor enregistrés à la surface du dôme. Ils ont ainsi identi_éla source du signal sismique enregistré à la surface du geyser comme étant des signauxde cavitation de bulles. La cavitation se produisant à la surface du niveau de l'eau dansle conduit, les localisations des sources sismiques réalisées à partir des enregistrements desurface peuvent être reliées au niveau de l'eau dans le conduit.Dans un premier temps nous avons proposé de localiser les sources sismiques desenregistrements à partir de la méthode du Matched Field Processing (MFP) provenantde l'acoustique sous-marine. Plusieurs algorithmes du MFP ont été testés pour pouvoirlocaliser au mieux les sources sismiques. La bonne concordance des résultats obtenus avecchacun des algorithmes a permis d'obtenir un grand nombre de localisations des sourcesau cours du cycle. Les positions déterminées avec les di_érents algorithmes du MFP ontpermis de mettre en évidence deux zones d'activité hydrothermale du geyser associéesà di_érentes périodes du cycle éruptif, telles que le remplissage du conduit avant leséruptions et l'alimentation du geyser en eau une fois la vidange du conduit e_ectuée.Dans un second temps, l'analyse des variations de vitesse des signaux sismiques estproposée pour suivre des changements des propriétés du dôme du geyser, comme des variationsde pression avant l'éruption. Pour cela, une nouvelle méthode basée sur les mesuresde phases instantanées est suggérée. Les résultats obtenus montrent des faibles changementsde vitesse, pouvant être associés à la mise en pression du dôme ou à l'augmentationde la température du milieu avant l'éruption en surface. / The geyser of Old Faithful in the National Park of Yellowstone, in USA, is one of themost famous geysers in the world. The cyclic behavior of the geyser is studied since the60's with the aim to understand its dynamics. In fact, the bimodal nature of the frequencyof the eruptions raises questions and scientists want to know the causes of this behavior.The seismic signals recorded at the surface of the geyser present pulses whose origin wasidenti_ed by Sharon Kedar. Thus, in 1992, S. Kedar and his colleagues deployed severalseismic sensors in order to study the source of the seismic signals, which are tremor-like,recorded at the surface of the edi_ce. They identi_ed the source of the seismic signalrecorded at the surface of the geyser that they related to bubbles collapse. The bubblescollapse takes place at the surface of the water level in the conduit, thus the localizationsof the seismic sources determined with the records made at the surface would be relatedto the water level in the conduit.In a _rst time we proposed to locate the seismic sources of the records using theMatched Field Processing (MFP), a method used in ocean acoustics. Several algorithmsof the MFP were tested to better localize the seismic sources. The good agreement ofthe di_erent results obtained with each technique allowed to obtain a big number oflocalizations of the sources through the cycle. The locations determined with di_erentalgorithms of MFP allowed to highlight two areas of hydrothermal activities of the geyserlinked to di_erent periods of the eruption's cycle, as the _lling-up of the conduit beforeeruptions and the feeding of the geyser with water once the discharge of the conduitaccomplished.In a second time, the analysis of velocity's changes of the seismic records is proposedto follow changes in the properties of the edi_ce of the geyser, and pressure changes beforean eruption for example. To do that, a new technique based on the measurement of theinstantaneous phases is suggested. The results obtained show weak changes of velocity,that can be related to the pressure buildup of the edi_ce or to the increase of temperaturein the medium before an eruption.

Master of Science / Department of Geology / Matthew E. Brueseke / Previous studies of the northern Great Basin have indicated that mid-Miocene epithermal gold and silver ore deposits distributed regionally are temporally related to the magmatic activity associated with the onset of widespread extension and the Yellowstone hotspot (Saunders and Crowe, 1996; Kamenov et al., 2007). This study is focused on the volcanic rocks and ore deposits from the Silver City district (SCD), ID to address the petrogenesis and magmatic evolution that was influential in forming local precious metal deposits. The goal is to understand the tectonomagmatic conditions that contributed to the petrogenesis of the volcanic suite in the Silver City district, which can be used to provide details on the relationship between coeval mid- Miocene magmatism and mineralization across the northern Great Basin and Oregon Plateau. In order to better constrain the magmatic evolution of the SCD and potential sources of the precious metals, we have undertaken detailed sampling of local crust and mid-Miocene volcanic units to constrain their physical, geochemical, isotopic, and geochronological characteristics, as well as provide constraints on the petrogenesis of the mid-Miocene volcanic package. Prior studies of the local volcanism have yielded K-Ar and [superscript]40Ar/[superscript]39Ar ages of ~16.6 to 14 Ma (Bonnichsen, 1983), while others have dated adularia from one SCD mineral vein and obtained [superscript]40Ar/[superscript]39Ar ages of between 15.6 and 16.3 Ma (Hames et al., 2009; and Aseto et al., 2011). Field observations are consistent with earlier work (Lindgren, 1900; Asher, 1968; Pansze, 1975; Halsor et al., 1988; Bonnichsen and Godchaux, 2006; Camp and Ross, 2009) and reveal a sequence of basalt consisting of regionally prevalent Steens Basalt that pre-dated precious metal mineralization. Some of the basalt appears to have been erupted locally, based on the presence of mafic dikes and thick pyroclastic deposits similar to other regional mid-Miocene magmatic systems. Stratigraphically overlying this lower basalt suite is a complex package of rhyolite flows and domes, thin silicic pyroclastic units, additional basaltic lava flows, intermediate lava flows, and mafic/silicic shallow intrusives. Geochemical analysis indicates that the basaltic and basaltic andesite lava flows are locally erupted flows of Steens Basalt while the intermediate and silicic volcanism in SCD can be classified into nine distinct units including two andesites, one dacite, four rhyolites and two rhyolite tuffaceous units. Geochemical modeling suggest that the intermediate and silicic magmas were formed by a combination of open system processes, including low pressure partial melting and assimilation of mid to upper crustal granitoid basement rock, and magma mixing between silicic and basaltic endmembers. The formation of silicic volcanism in the SCD is similar to other regional mid-Miocene silicic volcanic systems (e.g. Santa Rosa-Calico volcanic field and Jarbidge Rhyolite). Based on new [superscript]40Ar/[superscript]39Ar geochronology of both volcanic units and epithermally emplaced mineralization, SCD volcanism appears to have erupted over a relatively short amount of time that overlaps with local epithermal Au-Ag mineralization.