Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 46-51). Also available on the World Wide Web.

abstract: Primitive arc magmas provide a critical glimpse into the geochemical evolution of subduction zone magmas, as they represent the most unadulterated mantle-derived magmas observed in nature in these tectonic environments and are the precursors of the more abundant andesites and dacites typical in arcs. To date, the study of primitive arc magmas has largely focused on their origins at depth, while significantly less is known about pre-eruptive crustal storage and ascent history. This study examines the crustal storage and ascent history of the Mt. Shasta primitive magnesian andesite (PMA), the demonstrated dominant parent magma for the abundant mixed andesites erupted at Mt. Shasta. Petrographic and geochemical observations of the PMA identify a mid-crustal magma mixing event with a less evolved relative of the PMA recorded in multiple populations of reversely zoned clinopyroxene and orthopyroxene phenocrysts. Prior phase equilibrium experiments and thermobarometric calculations as part of this study suggest the PMA experienced storage, mixing with a less evolved version of itself, and subsequent crystallization at 5kbar and 975°C. Modeling of Fe-Mg interdiffusion between the rims and cores of the reversely-zoned clinopyroxene and orthopyroxenes suggest this mixing, crystallization and subsequent ascent occurred within 10 years, or ~2.9 (+6.5 / -2.5) years, prior to eruption. Ascent from 5kbar or ~15 km, with no meaningful shallower storage, suggests minimum crustal transit rates of ~5 km/year. This rate is comparable to only a couple of other similar types of crustal transit rates (and slower than the much faster, syn-eruptive ascent rates measured through methods like olivine-hosted melt embayment volatile gradients and U-series isotope measurements on other arc magmas). The results of this study help to constrain the pre-eruptive history and ascent rates of hydrous primitive arc magmas, illuminating their magmatic processes during ascent. When combined with geophysical signals of magma movement, mixing to eruption timescales such as this have the power to inform volcanic hazard models for monogenetic, cinder cone eruptions in the Southern Cascades. / Dissertation/Thesis / Masters Thesis Geological Sciences 2019

Ceratomyxa shasta infects salmonids in the Pacific Northwest (PNW) of North America, occasionally causing losses in wild and captive populations. Host-specific parasite genotypes (O, I, II, III) were previously characterized molecularly using markers in the ribosomal DNA and phenotypically by type host in the Klamath River, CA/OR. This thesis sough to re-examine the composition of the parasite population elsewhere in the PNW and to further evaluate the host specificity of each genotype. I surveyed salmonids native to the PNW primarily from the Fraser, the Columbia and the Sacramento River basins. I also conducted sentinel studies on the Willamette and Deschutes Rivers that exposed native and non-native salmonids to parasite populations above and below migration barriers. These studies expanded upon the known host range of each genotype: O was specific to rainbow/steelhead (Oncorhynchus mykiss) and coastal cutthroat trout (O. clarkii); I was specific with Chinook salmon (O. tshawytscha); II was non-specific, being detected in six species, but predominating in coho (O. kitsuch), chum (O. keta), and pink (O. gorbuscha) salmon; and III was also non-specific infecting many native and non-native salmonids. Hosts infected with genotype III were considered “adequate” if myxospore development occurred, and included brook char (Salvelinus fontinalis), brown (Salmo trutta), rainbow, cutthroat, and steelhead trout; but Chinook, kokanee/sockeye (O. nerka) and Atlantic salmon (Salmon salar) were less suitable. The distribution, life history, and phylogenetic traits of each salmonid host are factors that potentially explain the host specificity and the spatial and temporal patterns of each genotype. Data collected in this thesis provide evidence that host-specific C. shasta coevolved with Pacific salmonids, adapting unique host-parasite relationships over time. / Graduation date: 2012

No description available.

Les éléments volatils, principalement l'eau, sont enrichis dans les magmas d'arcs. Ils jouent un rôle prépondérant dans le magmatisme de zone de subduction, que ce soit en permettant la fusion du manteau ou en influençant l'explosivité des éruptions en surface. L'objectif de cette étude est la caractérisation (en éléments majeurs, traces, volatils et isotopes du bore) des liquides primaires des magmas d'arcs et de leurs sources, afin de discuter de l'influence des phases mobiles issues du slab dans leur genèse. L'approche adoptée est l'analyse des inclusions magmatiques piégées dans les olivines magnésiennes de quatre volcans répartis dans trois zones de subduction : Vulcano, dans l'arc Eolien (Italie), le Mont Shasta, dans l'arc des Cascades (Californie, Etats-Unis), le Pichincha et le Pan de Azucar, dans l'arc Equatorien. Les inclusions primaires étudiées contiennent des liquides basaltiques sous-saturés en silice, plus ou moins riches en CaO, dérivant d'une source mantellique veinée de zones riches en amphiboles (±clinopyroxène, ±phlogopite) et ayant subi un degré variable de métasomatisme. Leurs compositions en éléments traces illustrent l'enrichissement de leurs sources mantelliques par des composés mobiles issus du slab et de compositions contrastées. Il existe d'importantes variations des compositions en éléments volatils entre les inclusions provenant de plusieurs échantillons d'un même volcan (le Mont Shasta), celles provenant de plusieurs volcans d'une même zone de subduction (le Pichincha et le Pan de Azucar) ainsi qu'entre les inclusions des trois zones de subduction étudiées (arc Eolien, arc Equatorien et arc des Cascades). L'étude de l'évolution des teneurs en éléments volatils en fonction des pressions de saturation indique que seules les teneurs en Cl et F des inclusions magmatiques sont représentatives des teneurs du magma primitif. Le dégazage précoce et la formation de globules de sulfure affectent les teneurs en H2O, CO2 et S, qui peuvent être utilisées en tant qu'estimations minimales des teneurs des magmas primitifs. Les compositions en Cl des sources mantelliques des inclusions étudiées varient de 3±1 ppm à 450±125 ppm et celles en F varient de 16±6 ppm à 147±32 ppm (Cl/F de 0,2±0,1 à 3,6±1,2). L'association des rapports Cl/F des sources avec l'enrichissement en Nb (par rapport aux MORB) des inclusions et leurs valeurs isotopiques en bore suggère la participation de deux principaux composés mobiles dans la source de ces inclusions : (1) un liquide silicaté issu de la fusion des sédiments déshydratés (principal agent métasomatique de la source des inclusions du Pan de Azucar, qui possèdent des faibles δ11B ainsi qu'un fort enrichissement en Nb par rapport aux MORB) ; (2) un fluide aqueux formé lors de la déshydratation de la croûte océanique (principal agent métasomatique de la source des inclusions du Pichincha). Selon les propriétés physico-chimiques des différentes zones de subduction, ce fluide peut avoir les caractéristiques d'un fluide supercritique et être plus ou moins riche en éléments traces. Les compositions des inclusions de la Sommata (Italie) et de l'échantillon 95-15 du Mont Shasta montrent des enrichissements intermédiaires de leurs sources comparé à celles des inclusions du Pichincha et du Pan de Azucar. Leurs sources semblent avoir été métasomatisées par un mélange entre les deux composés métasomatiques décrits ci-dessus.

The freshwater polychaete Manayunkia speciosa was identified as an obligate host of the salmonid parasite Ceratomyxa shasta in 1997, prompting increased research on the small benthic invertebrate. Ceratomyxa shasta infection in fish can cause mortality, and presents a disease risk for both hatchery and wild salmon and trout. Ceratomyxa shasta is endemic to rivers of the Pacific Northwest, and its effects have been particularly well documented in the Klamath River, Oregon and California. One option for managing C. shasta impacts is by decreasing densities of M. speciosa through habitat manipulation, thus decreasing amplification of the parasite. The Klamath River is regulated by irrigation and hydropower dams, thus manipulating the hydrograph to destabilize habitat is a possibility. Decreasing habitat through flow manipulation requires a thorough understanding of the hydraulic environment of polychaete habitat, and how that environment changes with discharge. This thesis proposes an influence diagram of physical variables driving M. speciosa density, and investigates several of them. Samples were collected for enumerating M. speciosa density from nine sites in the Klamath River over 15 months, and seasonal density changes were examined, as were the relationships between density and hydraulic variables (depth, average velocity, substrate size, Reynolds number, Froude number). Density increased directly with depth and inversely with velocity, and was greater on small (silt, sand) and large (boulder, bedrock) substrate relative to medium substrate (gravel, cobble). Density was highest in the summer (July, August, September), and there was evidence that summer densities were influenced by spring discharges through the mechanism of substrate mobilization. Differences in infection prevalence among seasons and habitats were also investigated; however, very low overall incidence of infection limited any conclusions. Based on these results, it is recommended that habitat modeling for management of M. speciosa populations include a habitat stability component that incorporates s whether peak discharge the previous year surpassed a stability threshold. / Graduation date: 2013