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Thesis (Ph. D.)--Miami University, Dept. of Geology, 2005. / Title from second page of PDF document. Document formatted into pages; contains [3], viii, 216 p. : ill. Includes bibliographical references (p. 151-159).

University, Diss., 2004--Kiel.

Long-lived and short-lived volcanic vents often form in close proximity to one another. However, the processes that distinguish between these volcano types remain unknown. Here, I investigate the differences of long-lived (shield volcano) and short-lived (cinder cone) magmatic systems using two approaches. In the first, I use melt inclusion volatile contents for shield volcanoes and compare them to published data for cinder cones to investigate how shallow magma storage conditions differ between the two vent types in the Oregon Cascades. In the second, I model the primitive magmas that fed shield volcanoes and compare these compositions to those of nearby cinder cones to determine if the volcanoes are drawing magma from the same sources. The volatile concentrations suggest that long-lived and short-lived magmatic plumbing systems are distinct. Modeling of parental magmas and differentiation processes further suggest that long-lived and short-lived volcanoes have erupted lava from the same mantle magma source.

Made available in DSpace on 2014-06-12T18:02:31Z (GMT). No. of bitstreams: 2 arquivo2589_1.pdf: 4302212 bytes, checksum: cd4f4248722b5820033caf825827a6d7 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2005 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / O Complexo Granítico Esperança (CGE) situa-se no Terreno Alto Pajeú (TAP), Domínio da Zona Transversal (DZT) da Província Borborema (PB), na porção centro-norte do Estado da Paraíba. Aflora em uma área de cerca de 500 Km2, encaixado em rochas Mesoproterozóicas alongadas no sentido SW-NE, limitadas a norte pelo Lineamento Patos transcorrente de cinemática dextral e a sul pela Zona de Cisalhamento Puxinanã-São Sebastião de Lagoa de Roça. Estas intrusões exibem petrografia, geoquímica, química mineral e isotópica distintas, sugerindo fontes distintas para pelo menos uma delas (Plúton Areial) e as demais intrusões (Puxinanã, Remígio, Pocinhos e Serrote da Cobra). São granitos metaluminosos a fracamente peraluminosos, cálcio-alcalinos de alto-K (Puxinanã, Remígio e Serrote da Cobra) a shoshoníticos (Areial), caracterizados geoquimicamente por elevados teores de álcalis (Na2O + K2O > 7%) e razões K2O/Na2O>1. Exibem coexistência e mistura parcial ou incompleta de magmas máficos e félsicos, com porções dos plútons apresentando hibridização em variados graus de combinações, com exceção de Pocinhos. Petrograficamente são biotita sienogranitos a monzogranitos associados a granodioritos, exibindo enclaves ou diques sin-plutônicos máficos (Areial, Puxinanã e Remígio), biotita tonalitos associados a diques tardi-plutônicos máficos (Serrote da Cobra) e biotita sienogranitos não-associados a enclaves ou diques máficos (Pocinhos). Estes plútons mostram características de granitos sin a tardi-orogênicos tipo I, menos o Plúton Pocinhos que possui características de granitos tipo A. Nas intrusões do CGE ocorrem as seguintes fases minerais: plagioclásio (oligoclásio a andesina), feldspato potássico (microclina pertítica), biotita (siderofilita a anita), anfibólio cálcico (edenita a ferro-edenita, com um fácies mostrando composições na série magnésiohornblenda a ferro-hornblenda no Plúton Areial), titanita e epidoto (com teor de pistacita variando de 0,25 a 0,24 para o Plúton Serrote da Cobra, e 0,28 a 0,31 para o Plúton Areial). Dados de química mineral, geotermometria e geobarometria mostraram condições de cristalização com temperaturas moderadas a altas (774 a 780° C) e pressões moderadas (5.6 e 6.0 Kbar) para o Plúton Areial do CGE. Geocronologia pelo método U/Pb em zircão forneceu idade de 581.3±7 Ma para o Plúton Puxinanã. Os dados isotópicos mostraram para o Plúton Areial valores fortemente negativos de εNd iniciais (-15.08 a -16.53) e idades modelo TDM Paleoproterozóicas (1.8 a 2.1 Ga), e para os demais plútons valores menos negativos de εNd iniciais (-7.19 a -3.46) e idades modelo TDM mistas de material Paleoproterozóico e Neoproterozóico (Brasiliano) ou Mesoproterozóico (Cariris Velhos), variando de 1.34 a 1.59 Ga. Os diagramas petrogenéticos de Patiño-Douce (1995) sugerem que os granitóides constituintes do CGE foram todos gerados a partir de fusões de rochas cálcio-alcalinas, possivelmente envolvendo fusão de rochas da crosta inferior, por ação do calor transmitido por magmas mantélicos alojados por underplating, seguido de assimilação das rochas encaixantes e armazenamento dos magmas híbridos em bolsões magmáticos, formados por mistura em profundidade de magmas mantélicos e crustais. Subsequente homogeneização química e isotópica dos magmas híbridos gerou as características cálcio-alcalinas das intrusões do CGE. Estes processos de mistura de magma em profundidade seriam responsáveis pela evolução das intrusões constituintes do CGE, exceto pelo plúton tipo A Pocinhos, originado a posteriori por fusão desidratada de um protólito granitóide cálcioalcalino portador de hornblenda e biotita, a baixas profundidades (inferiores a 15 Km), em condições de pressão ≤ 4 kbar

A multi-prong approach was taken in this dissertation to understand volcanic processes from both a long-term and more immediate hazard perspective. In the long-term, magma sources within the crust may produce measurable surficial response and long-wavelength gravity anomalies that provide information about the extent and depth of this magma. Long-term volcanic hazard forecasting is also improved by developing as complete a record as possible of past events. In the short-term, a long-standing question has been on the casting of precursory volcanic activity in terms of future volcanic hazards. Three studies are presented in this dissertation to address these issues. Inversion of high-resolution ground magnetic data in Amargosa Valley, NV indicates that anomaly B could be generated by a buried shield volcano. This new information changes the event count in this region which in turn affects the overall volcanic hazard estimation. Through the use of Finite Element Models (FEM) an in-depth characterization of the surficial response to magma underplating is provided for the Tohoku Volcanic Arc, Japan. These models indicate that surficial uplift was dominantly driven by mid-crustal intrusions and the magnitude and wavelength of this uplift was mainly controlled by the elastic layer thickness. In Dominica, seismic data were used as weights in spatial intensity maps to generate dynamic volcanic hazard maps influenced by changes in seismicity. These maps show an increasing trend in the north that may be indicative of an increase in earthquake and volcanic hazards.

Tesis para optar al Grado de Magíster en Ciencias, Mención Geología / Los volcanes Michinmahuida y Chaitén son centros eruptivos vecinos que se ubican en la Zona Volcánica Sur-Sur de los Andes, en la Región de los Lagos, y presentan marcadas diferencias en sus características morfológicas, así como en las composiciones de sus productos y en sus estilos eruptivos. El volcán Chaitén presenta la capacidad de generar erupciones de mediana intensidad como la registrada durante el ciclo de 2008-09, y erupciones volumétricas como sus eventos de 10 ka y 5 ka. Por otro lado, el volcán Michinmahuida, se caracteriza por erupciones de mediana intensidad, pero que presentan mayor recurrencia que las del volcán Chaitén. En este trabajo se realizó un estudio en detalle de la tefroestratigrafía de la zona, que ha permitido identificar y describir en detalle los depósitos más representativos de la actividad Holocena de ambos centros eruptivos. Además, se han estimado parámetros eruptivos de dos erupciones Holocenas de estos volcanes: CHA2 de composición riolítica y edad estimada 5 ka, asociada al volcán Chaitén, para la que se ha estimado un volumen de entre 5.12-5.67 km3 de material eruptado, alcanzando un VEI de 5. La columna eruptiva de este evento habría alcanzado alturas de entre 26 y 28 km, con lo que se estima una tasa eruptiva de 1.5-2.1∙10^8 kg/s; y DAC MICH, de composición dacítica y edad estimada ~400 AP, asociada al volcán Michinmahuida, para la que se ha estimado una columna eruptiva de entre 8 y 13 km, con una tasa eruptiva estimada de 1.3-9.2∙10^6 kg/s. En este estudio se realizaron experimentos petrológicos sobre material juvenil de DAC MICH para constreñir las condiciones de presión y temperatura a las que se encontraba alojado el magma en el reservorio pre-eruptivo. Con ello se obtuvo que el material se estaba a una presión <125 MPa, y a una temperatura entre 825° y 900°C. Del mismo modo, se realizaron simulaciones numéricas con Confort 15, para estimar los parámetros que determinan las tasas eruptivas obtenidas a través del estudio de los depósitos de caída. Con ello se hicieron inferencias sobre la dinámica del ascenso del flujo, sobre cuáles son las variables que ejercen más efectos en los resultados estimados de tasas eruptivas, y sobre las dimensiones del conducto eruptivo. A partir de ello, se obtuvo un radio de entre 40 - 70 metros para CHA2, y de 5 - 28 metros para DAC MICH. Finalmente, se realizaron inferencias para estimar las intensidades que alcanzaron las erupciones reconocidas en sus registros geológicos. Con ello se obtuvo que para el volcán Chaitén, las erupciones siguen estilos plinianos, con tasas eruptivas en el orden de 2.7∙10^7-3.0∙10^8 kg/s con columnas eruptivas de entre 14 31 km de altura; mientras que el volcán Michinmahuida, tasas eruptivas en el orden de 1.0∙10^6- 5.4∙10^7 kg/s y alturas de columna eruptiva de entre 7-20 km, asociadas a un comportamiento sub-pliniano a pliniano.

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A young marine island called Heard Island is located in the southern Kerguelen Plateau in the Indian Ocean, a large igneous province created by the Kerguelen mantle plume. The two major geographic regions on Heard Island have two principal volcano-magmatic suites. Basanites, alkali basalts, and trachybasalts make up one group, the Big Ben Series (BBS), while basanitic to trachytic rocks make up the Laurens Peninsula Series (LPS). The most recent eruption at Big Ben volcano occurred in October 2022. To better understand magma evolution in the underlying plumbing system, clinopyroxene, feldspar, and olivine, mineral chemistry, clinopyroxene thermobarometry, and olivine thermometry were used.      The main phenocrysts from Heard Island are olivine, clinopyroxene, and feldspar. All phenocrysts share the characteristics of sieve textures and fractures. The mineral chemistry of clinopyroxene, zonation, and variation of core and rim of Mg#, Al2O3, TiO2, and Cr2O3, provides insight into the magmatic evolution of magma. Results from clinopyroxene-liquid thermobarometry suggest that clinopyroxene crystallization occurs at depths of 1 to 39 km for the cores and 1 to 47 km for the rims, with corresponding temperatures of 1098 to 1208°C and 1099 to 1254°C respectively. Comparison with olivine thermometry shows concordance in temperature estimates. The Mohorovičić discontinuity, or Moho, which marks the boundary between the Earth's crust and mantle, is believed to lie between 18 and 26 km deep at Heard Island. This study suggests that magma pockets can be found below the Moho between 51 and 18 km, and in the upper and lower crust between 18 and 2 km. Additionally, the density difference between various crustal layers determines where magma storage is located. The evidence from petrology and geochemistry points to common processes of magma mixing, recharge, and fractional crystallization during magma evolution.

Widespread base- and precious-metal anomalies, altered porphyry intrusions and oxidized veins occur in a portion of the Sulphur Springs Range, Nevada (adjacent to the Au-producing Carlin Trend). Some of the Eocene-Oligocene intrusions and cogenetic volcanic rocks in the range exhibit evidence of magma mixing and invite comparisons with other mineralized, Eocene mixed magma systems like the Bingham porphyry Cu deposit 300 km farther to the east. The Sulphur Springs igneous suite ranges compositionally through rhyolite, dacite, andesite and basaltic andesite but is less alkaline than the Bingham volcanic suite. However, the alkali content of the Sulphur Springs suite is similar to other Eocene igneous rocks along the Carlin Trend. The unusual geochemical signature of the Bingham igneous suite, enrichment in Cr, Ni, and Ba, is generally not found in the unaltered Sulphur Springs suite, with the exception of a set of altered mafic and intermediate dikes found in the core of the Sulphur Springs Range. The Bingham and Sulphur Springs volcanic suites both show extensive mixing of mafic magma with more silicic magma to create magma with intermediate compositions. The Bingham suite demonstrates mixing mineralogically by the presence of altered olivine and pyroxene in intermediate composition rocks. One of the disequilibrium Sulphur Springs rocks vividly expresses magma mixing as “andesite" - containing plagioclase, biotite, clinopyroxene, orthopyroxene, olivine, and amphibole coexisting with heavily resorbed megacrysts of quartz and K-feldspar. The Sulphur Springs mixed magma also contains abundant late-stage accessory magnetite and resorbed and oxidized garnet. The most likely parental magmas for this rock are a garnet-bearing quartz porphyry and olivine-bearing basaltic andesite which are both present in the range. Questions these data raise include: 1) Was there an unusual tectonic setting during the Eocene of the western United States that promoted both magma mixing and base- and precious-metal mineralization? 2) How vital might mixing processes and mafic magma be in delivering large amounts of S and chalcophile metals from deeper magmas to the shallow crust and eventual ore deposits?