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In order to investigate bubble formation and growth at 1 atmosphere, degassing experiments using a Stromboli basalt with dissolved H2O or H2O + CO2 were performed in a custom furnace on a beamline at the Advanced Photon Source. The glasses were synthesized at 1250°C and 1000 MPa, with ~3.0 wt%, ~5.0 wt%, or ~7.0 wt% H2O or with mixtures of H2O + CO2, ~3.0 wt% H2O and ~440 ppm CO2, ~5.0 wt% H2O and 880 ppm CO2, ~7.0 wt% H2O and ~1480 ppm CO2, then heated on the beamline while recording the bubble growth. The 3D bubble size distributions in the quenched samples were then studied with synchrotron X-ray microtomography. / The experimental results show that bubble nucleation and growth are volatile-concentration dependent. Bubbles can easily nucleate in melts initially containing high volatile concentrations. CO2 has no significant effect on bubble formation and growth because of low CO2 concentrations. Multiple nucleation events occur in most of these degassing samples, and they are more pronounced in more supersaturated melts. Bubble growth is initially controlled by viscosity near glass transition temperatures and by diffusion at higher temperatures where melt viscous relaxation occurs rapidly. Bubble foam forms when bubbles are highly connected due to coalescence, and bubbles begin pop, 10 to 20 seconds after the foam is developed. The degree of bubble coalescence increases with time, and bubble coalescence can significantly change the bubble size distribution. Bubble size distributions follow power-law relations at vesicularities of 1.0% to 65%, and bubble size distributions evolve from power-law relations to exponential relations at vesicularities of 65% to 83%. This evolution is associated with the change from far-from-equilibrium degassing to near-equilibrium degassing. / The experimental results imply that during basaltic eruptions both far-from-equilibrium degassing and near-equilibrium degassing can occur. The far-from-equilibrium degassing generally generates the power-law bubble size distributions whereas the near-equilibrium degassing produces exponential bubble size distributions Bubbles begin to pop when the vesicularities attain 65% to 83%. Bubble expansion in the foam possibly accounts for the mechanism of magma fragmentation. / Afin d'étudier la formation et la croissance de bulle; sous pression d'une atmosphère, desexpériences de dégazage sur un basalte de Stromboli, avec HiO ou H20 + CO2 dissouts,ont été exécutées dans un four pilote sous rayonnement synchrotron à l'APS (AdvancedPhoton Source). Les verres ont été synthétisés à une température de 1250°C et unepression de 1000 MPa, avec des teneurs en eau dissoute de ~ 3.0, ~ 5.0 ou ~ 7.0% (enpoids), et des mélanges H20 + C02 à teneurs de ~ 3.0% H20 (en poids) et 440 ppm CO2,~ 5% H20 et 880 ppm CO2, et de ~ 7.0% H20 et 1480 ppm CO2. La croissance des bullesest enregistrée pendant le chauffage du mélange en utilisant le rayonnement synchrotron.Les distributions tridimensionnelles de la taille des bulles dans les échantillons trempésont été étudiées par microtomographie à rayon X synchrotron.

The north-east Atlantic margin (NEAM) is important for hydrocarbon exploration because of the growing evidence of hydrocarbon reserves in the region. However, seismic exploration of the sub-surface is hampered by large deposits of flood basalts, which cover possible hydrocarbon-bearing reservoirs underneath. There are several hypotheses as to why imaging beneath basalt is a problem. These include: the high impedance contrast between the basalt and the layers above; the thin-layering of the basalt due to the many flows which make up a basalt succession; and the rough interfaces on the top-basalt interface caused by weathering and emplacement mechanisms. I perform forward modelling to assess the relative importance of these factors for imaging of sub-basalt reflections. The boundary element method (BEM) is used for the rough-interface modelling. The method was selected because only the interfaces between layers need to be discretized, in contrast to grid methods such as finite difference for which the whole model needs to be discretized, and so should lead to fast generation of shot gathers for models which have only a few homogeneous layers. I have had to develop criteria for accurate modelling with the boundary element method and have considered the following: source near an interface, two interfaces close together, removal of model edge effects and precise modelling of a transparent interface. I have improved efficiency of my code by: resampling the model so that fewer discretization elements are required at low frequencies, and suppressing wrap-around so that the time window length can be reduced. I introduce a new scheme which combines domain decomposition and a far-field approximation to improve the efficiency of the boundary element code further. I compare performance with a standard finite difference code. I show that the BEM is well suited to seismic modelling in an exploration environment when there are only a few layers in the model and when a seismic profile containing many shot gathers for one model is required. For many other cases the finite difference code is still the best option. The input models for the forward modelling are based on real seismic data which were acquired in the Faeroe-Shetland Channel in 2001. The modelling shows that roughness on the surface of the basalt has little effect on the imaging in this particular area of the NEAM. The thin layers in the basalt act as a low-pass filter to the seismic wave. For the real-data acquisition, even the topbasalt reflection is a low frequency event. This is most likely to be due to high attenuation in the layers above the basalt. I show that sea-surface multiple energy is considerable and that it could mask possible sub-basalt events on a seismic shot gather, but any shallow sub-basalt events should still be visible even with the presence of multiple energy. This leaves the possibility that there is only one major stratigraphic unit between the base of the basalt and the crystalline basement. The implication of the forward modelling and real data analysis for acquisition is that the acquisition parameters must emphasize the low frequencies, since the high frequencies are attenuated before they even reach the top-basalt interface. The implication for processing is that multiple removal is of prime importance.

The study of magmatic processes and their location in the crustal profile is fundamental for the understanding of the volcanic systems and their associated hazards. Changes and continuities in magma storage zones, fractional crystallization and crustal contamination are studied over a time span of 300 ka in Puyehue Volcano in the Southern Volcanic Zone, Chile. Using thermobarometric models outlined in Putirka (2008), bulk assimilationand fractional crystallization modelling this study show that: a) fractional crystallization of plagioclase and clinopyroxene in Puyehue Volcano occurs in the upper 20 km of the crust with plagioclase preceding clinopyroxene in the crystallization sequence, b) fractional crystallization of basaltic andesites is dominated by plagioclase with a break in th e geochemical trend at around 55 wt% SiO2caused by an increased share of pyroxene fractionation and the onset of significant magnetite fractionation, c) both old and young Puyehue volcanics are contaminated by a gabbroic lithology of the lower crust as suggested previously by Jicha et al. (2007) and d) the Anticura Group lavas and a single Puyehue Volcano sample reflect magma-metasediment interaction with likely in the middle to upper crust. / El estudio de los procesos magmáticos y su ubicación en el perfil de la corteza terrestre es fundamental para la comprensión de los sistemas volcánicos y sus riesgos asociados. Cambios y continuidades en las zonas de almacenamiento de magma, cristalización fraccionada y contaminación cortical correspondientes a un lapso de 300 ka se estudiaronen Volcán Puyehue en la Zona Volcánica Sur, Chile. Utilizando modelos termobarométricos descritos en Putirka (2008) más un modelamiento de la asimilación y cristalización fraccionada este estudio muestra que: a) la cristalización fraccionada de plagioclasa y clinopiroxeno en el Volcán Puyehue se produce en los 20 Km superiores de la corteza y que la plagioclasa precede al clinopiroxeno en la secuencia de cristalización, b) la cristalización fraccionada de andesitas basálticas está dominada por plagioclasa con un quiebre en la tendencias geoquímicas en torno al 55 wt%SiO2causado por un aumento relativo delfraccionamiento piroxeno y ael comienzo de un fraccionamiento significativo de magnetita, c) las rocas volcánicas del Volcán Puyehue, tanto lasantiguas como las recientes, están contaminadas por una litología de gabro de la corteza inferior como se ha sugeridoanteriormente por Jicha et al. (2007) y d) las lavas del Grupo Anticura además de una sola muestra Volcán Puyehue evidencian interacción entre magma y metasedimentos que probablemente ocurrió en la corteza media o superior / Studiet av magmatiska processer och deras placering i jordskorpans profil är väsenlig för förståelsen av den vulkaniska system och dithörande risker. I denna studie granskas förändringar och kontinuiteter i lagringszoner för magma, fraktionerad kristallisation och jordskorpsföroreningar över en tidsperiod på 3 00 ka i Puyehue vulkan i den Södra Vulkaniska Zonen, Chile. Till denna ändamål användes termobarometriska modeller beskrivna i Putirka (2008) och andra modeller för assimilering och fraktionerad kristallisation som visar att: a) fraktionerad kristallisation av plagioklas och klinopyroxen i Puyehue vulkanen sker i de övre 20 km av jordskorpan och att plagioklas föregår clinopyroxene i kristallisations följden, b) fraktionerad kristallisering av andesitiska basalterförhärskas av plagioklas samt att den geokemiska utvecklingen förändras omkring 55 wt% SiO2på grund av en ökad fraktioneringsandel av pyroxen plus uppkomsten av betydande magnetit fraktionering, c) både gamla och unga Puyehue vulkaniter är förorenade av ett gabbroisk litologi från den undre kontinentalskorpanså som detföreslagits tidigare av Jicha et al. (2007) och d) Anticura Group lavornasamt ett enda Puyehue-prov reflekterar magma-metasediment interaktion som sannolikt sker i mitten eller övre delenav kontinentalskorpan.

The Kemess North porphyry Au-Cu-Mo deposit (300 Mt resource @ 0.30 g/t Au and 0.16% Cu)i s situated in the Toodoggone district, along the eastern margin of the Stikinia terrane in British Columbia. Mineralization is genetically related to the ca. 202 Ma, moderately SE-plunging, Kemess North diorite and is also hosted by proximal Takla Group basalt country rock. The nearby 202.7 ± 1.9 Ma Sovereign diorite has a comparable emplacement age, mineralogy, and chemistry to the Kemess North diorite, but is unmineralized. Toodoggone Formation volcaniclastic rocks (199.1 ± 0.3 Ma) crop out as prominent N-trending ridges or as isolated, fault-bounded blocks within Takla Group basalt. The unmineralized, (197.3 + 1.1/0.9 Ma) Duncan pluton intrudes Takla Group basalt. Seven vein types are separated into four stages of formation with respect to Au-Cu-Mo mineralization. Early-stage veins include magnetite stringer veins and later quartz-magnetite-pyrite + chalcopyrite + molybdenite veins. These veins are restricted mainly to the diorite, are associated with locally preserved potassic (biotite) alteration, and resulted in most of the Au-Cu-Mo mineralization at Kemess North. Main-stage quartz-pyrite + chalcopyrite ± molybdenite veins are the most abundant vein type and are present in the diorite and proximal Takla Group basalt. The veins are associated with phyllic (sericite-quartz) alteration and have a Re-Os molybdenite age of 201.8 ± 1.2 Ma. Late-stage pyrite-chalcopyrite and anhydrite ± pyrite ± chalcopyrite veins and associate phyllic (sericite-chlorite-pyrite) alteration occur in diorite and Takla Group country rocks. Lastly, post-mineralizationan hydrite and carbonate-zeolite veins cut all rocks. Fluid inclusion studies indicate that early-and main-stage ore fluids deposited Au-Cu-Mo at similar temperatures (about 400°C to 375°C) and pressures (0.9 to 3.0 kbar), corresponding to crustal depths of 3 to 10 km. Sulfur and Pb isotope compositions suggest that metals from the early-stage fluid were derived from the Kemess North diorite; metals in the main-stage fluid were derived from the diorite and probably Takla Group country rock and meteoric fluids. An E-striking, steeply S-dipping fault truncates the northern extremity of the ore body. Late NW- to NE-striking normal faults vertically displace the deposit resulting in graben-and-horst block shuffling of the stratigraphy.

The Atherton Tablelands basalt aquifer is a major source of groundwater supply for irrigation and other agricultural use. The Tertiary to Quaternary age basaltic aquifer can be regarded as a generally unconfined, layered system, comprising numerous basalt flows separated by palaeo-weathering surfaces and minor alluvial gravels of palaeo-drainage channels. Layers of massive basalt and clay-rich weathered zones act as local aquitards, with some local perched aquifers also present. The aquifer is regarded as a system in which several factors interact to produce the overall characteristics of the hydrogeochemistry of the groundwaters. They include the mineralogical composition of both the basalt aquifer and the thick overlying weathered zone, the porosity and permeability of the basalt aquifer, its thickness, bedrock composition, and climate and topography. The hydrogeochemical processes operating in this aquifer system have been investigated though the analysis of 90 groundwater samples collected from October 1998 to October 1999, groundwater chemistry data provided by the Queensland Department of Natural Resources & Mines for more than 800 groundwater samples, rain water samples collected during 1999 by CSIRO, stream chemistry data provided by CSIRO and James Cook University, and mineralogical and whole rock geochemistry data of drill chip samples. The methods used in this research study include the assessment of groundwater major ion chemistry data and field physico-chemical parameters using hydrochemical facies and statistical approaches, investigation of the mineralogical composition of the aquifer, assessment of concentrations and activities of the ions in solution, the degree of saturation with respect to both primary and secondary minerals, and hydrogeochemical modelling to determine the likely controls on the chemical evolution of these groundwaters. The basaltic groundwaters are mostly Mg-Ca-Na, HCO3 type waters, with electrical conductivities generally less than 250 μS/cm and pH values from 6.5 to 8.5. Dissolved silica (H4SiO4) comprises a large proportion of the total dissolved load, with average concentrations of around 140 mg/L. Concentrations of potassium, chloride and sulphate are low, that is, generally less than 3 mg/L, 15 mg/L and 10 mg/L, respectively. Despite the very low salinity of the Atherton Tablelands basalt groundwaters, the relative concentrations of the major ions are comparable to groundwaters from other basaltic regions, and are consistent with expected waterrock interactions. A variety of multivariate statistical techniques may be used to aid in the analysis of hydrochemical data, including for example, principal component analysis, factor analysis and cluster analysis. Principal component factor analyses undertaken using the hydrochemical data for the Atherton groundwaters has enabled the differentiation of groundwaters from various lithological formations, the underlying geochemical processes controlling groundwater composition in the basalt aquifer to be inferred, relative groundwater residence and flow directions to be inferred and mapping of the estimated thickness of the basalt aquifer. The limitations of multivariate statistical methods have been examined, with emphasis on the issues pertinent to hydrochemical data, that is, data that are compositional and typically, non-normally distributed. The need to validate, normalize and standardize hydrochemical data prior to the application of multivariate statistical methods is demonstrated. Assessment of the saturation states of the Atherton basalt groundwaters with respect to some of the primary minerals present indicate that the groundwaters are mostly at equilibrium or saturated with respect to K-feldspar, and approach equilibrium with respect to the plagioclase feldspars (albite and anorthite) with increasing pH. These groundwaters are at equilibrium or saturated with respect to the major secondary minerals, kaolinite, smectite (Ca-montmorillonite) and gibbsite. They also tend to be saturated with respect to the oxidation products, goethite and hematite, common accessory minerals in the Atherton Tablelands basalt sequence. Silicate mineral weathering processes are the predominant influence on the composition of these basalt groundwaters. These weathering processes include the weathering of pyroxenes, feldspars and other primary minerals to clays, aluminium and iron oxides, amorphous or crystalline silica, carbonates and zeolites, releasing ions to solution. The contribution of substantial organic carbon dioxide to the groundwater is an important factor in the extent to which silicate mineral weathering occurs in this aquifer system. Evaporative enrichment of recharging waters, oxidation and ion-exchange reactions and the uptake of ions from, and decomposition of, organic matter, are processes that have a minor influence on the composition of the basalt groundwaters. The relationships observed between mineralogical compositions, basalt character and groundwater occurrence in the Atherton Tablelands region improved the understanding how groundwater is stored and transmitted in this basalt aquifer system. Groundwater is mostly stored in vesicular basalt that may be fresh to highly weathered, and movement of this water is facilitated by pathways through both vesicular and fractured basalt. Related work undertaken as part of this research project showed that the groundwater flow patterns defined by the hydrogeochemical interpretations correspond well with the spatial trends in water level fluctuations, and response to recharge events in particular. Groundwater baseflow to streams and discharge to topographic lows in the Atherton Tablelands region is indicated by the relationships between the major cations and anions in the stream waters. Fracture zones are likely to be preferred pathways of groundwater movement. Recharge estimates, based on a chloride mass balance, range from 310 mm/yr in the north-western part of the study area (north of Atherton) to 600 mm/yr in the wetter southern and eastern parts of the study area. These recharge estimates should be treated with caution however, due to the low groundwater chloride concentrations and the high variability in rainfall chloride concentrations. The findings of this research project have improved the understanding of the hydrogeochemical processes controlling the composition of the low salinity basalt groundwaters in the Atherton Tablelands region, and are applicable to other basalt groundwater systems, particularly those in high rainfall environments.

Volcanism associated with the onset of Karoo flood basalt eruptions (c. 180 Ma) at Sterkspruit, South Africa, began with emplacement of thin lava flows before abruptly switching to phreatomagmatic and magmatic activity that formed a nest of craters, spatter and tuff rings and cones that collectively comprise a crater complex >40 km� filled by 9-18 km� of volcaniclastic debris. Phreatomagmatic activity driven by interaction of Karoo magma with groundwater hosted in country rock and crater-filling debris quarried broad, mainly shallow craters (hundreds of metres, but not kilometers deep) into wall-rock. Closely spaced individual vents, the consequence of magma emplaced over a broad area through a network of feeder dikes and stocks, were active at the same time or over short periods of time. Highly ephemeral access of external water to vents drove repeated and reversible switches between explosive to effusive magmatic and explosive phreatomagmatic activity, resulting in vents and craters that grew laterally and vertically into adjacent ones through quarrying and vent migration. Deposits within the Sterkspruit crater complex are dominated by 7-15 km� of massive, unsorted polymict lapilli tuff and tuff breccia juxtaposed with localised fountain-fed lava and strombolian spatter deposits. Transport within the complex was dominated by jets and fountains of volcaniclastic debris and by mass movement. Country-rock breccias indicate that craters grew via a combination of mechanical fragmentation, granulation and mass-movement of 7-12 km� of wall-rock, adding mass and previously locked-up pore-water to the volcanic system. Ash and lapilli, the deposits of plumes 5-15 km high, form a 50-110 m-thick ejecta blanket mantling Clarens Formation country rock that thins gradually away from the crater-complex margins. Explosive volcanism was succeeded by brief fluvial and eolian reworking of volcaniclastic debris and formation of a shallow crater lake 12 km� in extent, and then by voluminous effusion of flood basalt that inundated the Sterkspruit crater complex with lava. Flood basalt magmas involved in Sterkspruit eruptions were chemically heterogenous. This study documents the rapid (perhaps simultaneous) eruption of multiple, chemically distinct basaltic magmas, which cannot be simply related to one another, from one vent site, and possibly many others, within the Sterkspruit crater complex. Five distinct magma types were involved in eruptions at Sterkspruit, indicating that in the early stages of flood basalt eruption (i) magma batches may be small and not simply related to one another, (ii) heterogeneities in the magma source region may be close to each other in time and space, and (iii) eruptions of chemically distinct magmas may take place over short intervals of space and time without significant hybridisation. Formation of the Sterkspruit Complex, and many others like it in South Africa, confirms that the opening phases of Karoo flood basalt volcanism were explosive, and that the volume of the products of explosive volcanism may have important implications for climate change and landscape development associated with the emplacement of large igneous provinces.

Thesis (M.S.)--Baylor University, 2007. / Includes bibliographical references (p. 95-98).

Thesis (Ph. D.) -- University of Tennessee, Knoxville, 2005. / Vita. Includes bibliographical references (p. 57-76). Also available via World Wide Web.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 475-517). Available also in a digital version from Dissertation Abstracts.