Dissertations / Theses on the topic 'Basalt'

A erupção histórica de 1580 A.D. ocorreu ao sudoeste da Ilha de São Jorge, Açores recobrindo uma área total de 4 km². Este trabalho teve como objetivo caracterizar as diferentes morfologias de lava de 1580 A.D, juntamente com a definição de padrões petrográficos e geoquímicos. A erupção gerou quatro flow fields: Ribeira do Almeida, Queimada, Ribeira do Nabo I e Ribeira do Nabo II. A descrição detalhada das lavas permitiu identificar spiny, sheet, e slabby pahoehoe e derrames do tipo ‘a´ā. Próximo aos cones, derrames do tipo ‘a´ā são descritos. Com a constante erupção, estas lavas fluem em direção a costa formando deltas de lava ao entrar em contato com a água. Estes deltas geram um relevo sub-horizontal favorecendo a colocação de derrames do tipo sheet pahoehoe. A contínua alimentação interna favorece o espessamento dos derrames, podendo gerar o rompimento da superfície formando derrames slabby pahoehoe. Os estágios finais da erupção são marcados por derrames do tipo ‘a´ā canalizados lateralmente e sobre os derrames do tipo sheet pahoehoe. A variação na superfície dos derrames é controlada pelas taxas de efusão e pela topografia. Petrograficamente, todas as lavas da erupção de 1580 A.D. são olivina basaltos. Os dados geoquímicos indicam uma afinidade magmática alcalina com os termos menos diferenciados localizados na região de Ponta Queimada. Isto pode ser explicado por uma constante recarga de magma mais primitivo na câmara magmática. Os padrões de ETR normalizados sugerem que os basaltos estudados foram gerados a partir de um baixo grau de fusão de uma fonte profunda e enriquecida do tipo OIB. O estudo dos aspectos físicos dos derrames de 1580 juntamente com a petrografia e geoquímica permitiram compreender a história geológica deste evento.
The historic eruption of 1580 A.D. occurred in the southwestern of São Jorge Island, in the central Azores covering a total area of 4 km². This work provides a characterization of the distribution and morphology of the 1580 A.D. lava flows, integrated to petrography and geochemistry. The eruption formed four distinct flows fields: Ribeira do Almeida, Queimada, Ribeira do Nabo I and Ribeira do Nabo II. Detailed geological analysis allowed the identification of spiny, sheet and sllaby pahoehoe and ‘a´ā lava morphotypes. Near the vent, the flow fields are characterized by channelized ‘a´ā flows. With continuous eruption, these lavas flowed downwards forming fan-shaped lava deltas when entering the sea. Sheet pahoehoe flows overlay the ‘a´ā lavas and with continuous inflation the surface of the flows breaks generating slabby pahoehoe surface. The gradual increase in surface fragmentation form rubbly surfaces. In the late stages of the eruption channelized ‘a´ā flows were emplaced, depositing laterally and over the sheet pahoehoe flows. The variations in the lava surface are controlled by the effusion rates and the topography. Petrographically, all lava flows are olivine basalts. The chemistry of the basalts indicate an alkaline nature for the 1580 volcanism. The less-evolved compositions are found in Ribeira do Almeida and this fact can be related to continuous recharge of the magma chamber with more primitive melts. Normalized REE profiles show that the basalts were generated by low volumes of melt of an enriched OIB source. The study of the physical aspects of 1580 lava flows with petrography and geochemistry allowed understand the geologic history of this event.

Cette étude évalue expérimentalement et analytiquement le comportement au cisaillement des poutres en béton renforcé de fibres de basalte (BRFB) renforcées longitudinalement avec des barres en polymère renforcé de fibres de basalte (PRFB). Un nouveau type de macro-fibres de basalte a été ajouté au mélange de béton pour produire le mélange de BRFB. Quatorze poutres (152 x 254 x 2000 mm) sans armature transversale ajouté ont été testées sous une configuration de chargement à quatre points jusqu'à la défaillance. Les poutres ont été regroupés en deux groupes A et B en fonction de leurs rapports portée de cisaillement/profondeur, a/d. Les poutres du groupe A avaient un rapport a/d de 3,3 tandis que celles du groupe B avaient un rapport a/d de 2,5. Outre les rapports a/d, les paramètres étudiés comprenaient la fraction volumique des fibres ajoutées (0,75 et 1,5%) et le taux de renforcement longitudinal des barres en PRFB (0,31, 0,48, 0,69, 1,05 et 1,52). Les résultats des tests ont montré que l’ajout de macro-fibres de basalte au mélange de béton améliorait sa résistance à la compression. Une relation directe entre la fraction volumique de fibres, Vf, et la résistance à la compression a été observée. Les cylindres de béton coulés avec une Vf de 0,75 et 1,5% ont entraîné une augmentation de 11 et 30% de leur résistance à la compression par rapport à ceux moulés en béton standard (sans fibres), respectivement. L'ajout de fibres a également amélioré le mode de défaillance des poutres BRFB-PRFB que les poutres de contrôle coulées avec du béton standard. L’augmentation de la fraction volumique des fibres a réduit l’espacement entre les fissures et gêné sa propagation. Une amélioration significative des capacités de cisaillement des poutres testées a également été observée lorsque les macro-fibres de basalte ont été ajoutées à une fraction volumique Vf de 0,75. L'augmentation moyenne des capacités de cisaillement des poutres des groupes A et B, ayant les mêmes taux de renforcement, était respectivement de 45 et 44%, par rapport à celles des poutres de contrôle. Il a été noté que le gain en capacité de cisaillement des poutres testées était plus prononcé dans les poutres avec a/d= 3,3 que dans les poutres avec a/d = 2,5 lorsque le taux de renforcement augmentait. Au cours de la phase analytique, plusieurs modèles ont été utilisés pour prédire les capacités de cisaillement des poutres. Tous les modèles disponibles surestimaient les capacités de cisaillement des poutres testées avec un rapport moyen Vpre/Vexp compris entre 1,29 et 2,64. Cette observation a montré que ces modèles ne permettaient pas de prédire les capacités de cisaillement des poutres BRFB-PRFB. Un nouveau modèle modifié intégrant le type de renforcement longitudinal, le type de béton fibré et la densité du béton est proposé. Le modèle d’Ashour et al. -A (1992) a été modifié en utilisant un facteur égal au rapport entre le module des barres en PRF, Ef, et celui des barres en acier Es. Ce rapport prend en compte la différence de propriétés entre les barres en PRF et celles en acier, négligée par les modèles précédents. Le modèle proposé prédit bien les capacités de cisaillement des poutres BRFB-PRFB testées dans la présente étude avec des rapports moyens Vpre/Vexp = 0,82 ± 0,12 et 0,80 ± 0,01 pour les poutres des groupes A et B, respectivement. Les capacités de cisaillement des poutres en béton léger testées par Abbadi (2018) ont été prédites avec un rapport moyen Vpre/Vexp = 0,77 ± 0,05. De plus, le modèle prédit bien les capacités de cisaillement des poutres coulées avec du béton qui contient des fibres en acier testées par Awadallah et al. (2014) avec un rapport moyen Vpre/Vexp = 0,89 ± 0,07. Cela indique la large gamme d'applicabilité du modèle proposé. Cependant, il est recommandé d’évaluer le modèle proposé sur un ensemble de données plus large que celui présenté dans cette étude.
This study evaluates both experimentally and analytically the shear behavior of basalt fiber-reinforced concrete (BFRC) beams reinforced longitudinally with basalt fiber-reinforced polymer (BFRP) bars. A new type of basalt macro-fibers was added to the concrete mix to produce the BFRC mix. Fourteen beams (152 x 254 x 2000 mm) with no transverse reinforcement provided were tested under four-point loading configuration until failure occurred. The beams were grouped in two groups A and B depending on their span-to-depth ratios, a/d. Beams of group A had a ratio a/d of 3.3 while those of group B had a ratio a/d of 2.5. Besides the span-to-depth ratios, the parameters investigated included the volume fraction of the fibers added (0.75 and 1.5%) and the longitudinal reinforcement ratio of the BFRP reinforcing bars (0.31, 0.48, 0.69, 1.05, and 1.52). The test results showed that the addition of basalt macro-fibers to the concrete mix enhanced its compressive strength. A direct relationship between the fiber volume fraction, Vf, and the compressive strength was observed. Concrete cylinders cast with Vf of 0.75 and 1.5% yielded 11 and 30% increase in their compressive strengths over those cast with plain concrete, respectively. The addition of fibers greatly enhanced the shear capacity of BFRC-BFRP beams compared to their control beams cast with plain concrete. The increase of the fiber volume fraction decreased the spacing between cracks and hindered its propagation. A significant enhancement in the shear capacities of the tested beams was also observed when the basalt macro-fibers were added at a volume fraction Vf of 0.75%. The average increase in the shear capacities of beams of group A and B, having the same reinforcement ratios, were 45 and 44%, respectively, in comparison with those of the control beams. It was noticed that the gain in shear capacities of the tested beams was more pronounced in beams with a/d = 3.3 than in beams with a/d = 2.5 when the reinforcement ratio increased. In the analytical phase, several models were used to predict the shear capacities of the beams. All of the available models overestimated the shear capacities of the tested beams with average ratio Vpre/Vexp ranging between 1.29 to 2.64. This finding indicated that these models were not suitable to predict the shear capacities of the BFRC-BFRP beams. A new modified model incorporating the type of the longitudinal reinforcement, the type of FRC used, and the density of concrete is proposed. The model of Ashour et al. –A (1992) was calibrated using a calibration factor equal to the ratio of modulus of FRP bars used, Ef, and that of steel bars, Es. This ratio takes into consideration the difference in properties between the FRP and steel bars, which was overlooked by previous models. The proposed model predicted well the shear capacities of the BFRC-BFRP beams tested in the current study with average ratios Vpre/Vexp = 0.82 ± 0.12 and 0.80 ± 0.01 for beams of groups A and B, respectively. The shear capacities of the lightweight concrete beams tested by Abbadi (2018) were predicted with an average ratio Vpre/Vexp = 0.77 ± 0.05. Moreover, the model predicted well the shear capacities of the SFRC beams reinforced with BFRP bars tested by Awadallah et al. (2014) with an average ratio Vpre/Vexp = 0.89 ± 0.07. This indicates the wide range of applicability of the proposed model. However, it is recommended that the proposed model be assessed on larger set of data than that presented in this study

La concentration croissante de CO2 dans l'atmosphère et les dangers potentiels qu'elle représente pour la terre au travers des changements climatiques, l'acidification des océans et l'élévation du niveau de la mer a conduit à un certain nombre de projets qui tentent de trouver un moyen sûr et inoffensifs pour capturer et stocker le CO2 dans des formations géologiques. Une de ces tentatives se déroule actuellement en Islande à la centrale géothermique Hellisheiði, située à proximité de la capitale, Reykjavik (le projet CarbFix). Le dioxyde de carbone et d'autres gaz comme H2S, N2, H2, CH4, et Ar sont des sous-produits de l'exploitation de l'énergie géothermique et l'objectif est de stocker tout ce CO2 dans les formations basaltiques qui se situent sous Hellisheiði. Le CO2 est dissous dans un courant d'eau injecté par pompage dans puits jusqu'à à 350 mètres de profondeur et qui s'écoule ensuite au sein d'horizons mixtes de verre basaltique et de basalte cristallin. Les roches basaltiques sont caractérisées par des teneurs élevées en cations divalents comme Mg2+, Fe2+ et Ca2+ et des vitesses de dissolution relativement rapides. L'eau acide chargée en CO2 dissout le basalte, libérant ainsi des cations qui peuvent réagir avec les ions carbonates pour former des minéraux carbonatés (magnésite, sidérite, calcite, ankérite ainsi que des solutions solides (Ca-Mg-Fe)CO3)). Si on admet que c'est la dissolution des roches basaltiques qui contrôle ce processus de séquestration du carbone, on peut en déduire que tout ce qui pourra limiter cette dissolution sera préjudiciable à l'ensemble du processus de confinement du CO2. Mon rôle dans le projet CarbFix a été d'examiner les effets de la formation de revêtements de carbonate de calcium sur la dissolution des phases primaires de basalte. Je me suis concentrée sur le verre basaltique et le clinopyroxène, diopside, afin de comparer des phases cristallines et non cristallines. En outre, une série d'expériences ont été menées pour étudier l'effet de la structure du minéral primaire sur la nucléation de calcite. Ces expériences ont été faites pour vérifier si les différentes structures de silicate conduiraient à une différente étendue de la nucléation et croissance de la calcite à la surface des silicates. Enfin, de nombreuses expériences de dissolution de verre basaltique ont été menées en présence de bactéries hétérotrophes mortes et vivantes, Pseudomonas reactans, afin de déterminer l'effet des bactéries sur la dissolution des roches dans le système des eaux souterraines du site Hellisheiði. Les expériences de dissolution de verre basaltique et de diopside ont été réalisés à 25 et 70 °C pour un pH de 7-8 dans des réacteurs à circulation alimentés en solutions de forces ioniques > 0,03 mol / kg contenant CaCl2 ± NaHCO3. Deux séries d'essais ont été menés simultanément, une série appelée essais de 'précipitations' au cours de laquelle la solution dans le réacteur était sursaturée par rapport à la calcite, et l'autre série appelée essais de 'contrôle', pour laquelle la modélisation PHREEQC ne prévoyait pas formation de minéraux secondaires. Ainsi, il a été possible de comparer les vitesses de dissolution du verre basaltique et du diopside à 25 °C avec et sans la formation de carbonate de calcium et d'autres minéraux secondaires afin d'en déduire leur effet sur les vitesses de dissolution. Les images de microscopie électronique à balayage ont montré que des quantités importantes de carbonate de calcium ont précipité au cours des expériences de 'précipitations' mais, dans le cas du verre basaltique la croissance primaire se présente sous forme gros amas discrets de calcite et d'aragonite qui ne se forment pas sur le verre lui-même. Par contre, plusieurs des cristaux de diopside ont été largement envahis par des revêtements de calcite sans aragonite décelable. Dans les deux cas, la présence de calcite / aragonite n'a pas eu d'incidence sur les vitesses de dissolution du verre basaltique et de diopside qui sont les mêmes que celles mesurées dans la série 'contrôle'. Il semblerait que la couverture discontinue et poreuse de carbonates permet aux ions des phases primaires de continuer à diffuser sans entrave à travers la couche secondaire. Pour mieux évaluer l'effet de la surface des silicates sur la nucléation de la calcite, les vitesses de dissolution de six minéraux et roches silicatés ont été mesurées à 25 °C dans des réacteurs à circulation en présence de solutions de pH ~ 9,1 sursaturées par rapport à la calcite. Les phases silicatées étaient les suivantes: olivine, enstatite, augite, labradorite, verre basaltique et péridotite. Les résultats montrent que le temps d'induction pour la nucléation de calcite et l'étendue de la couverture de carbonatée avec le temps varient selon la phase silicatée. Dans un même laps de temps l'olivine, l'enstatite et la péridotite (principalement composé d'olivine riche en Mg) étaient les plus couvertes par les précipitations de calcite, suivis par l'augite, la labradorite et enfin le verre basaltique. Toute la croissance de calcite a eu lieu sur la surface du silicate, y compris sur le verre basaltique. La cinétique favorise la croissance de calcite par nucléation sur les minéraux orthorhombiques (enstatite et olivine) par rapport aux minéraux monocliniques et tricliniques. Les plus faibles quantités de calcite ont été trouvées sur le verre qui n'a pas de structure silicatée ordonnée. Des bactéries hétérotrophes, Pseudomonas reactans ont été extraites de l'un des puits de contrôle à Hellisheiði et ont ensuite été séparées, purifiées et cultivées en laboratoire. Avec le bouillon de culture utilisé, les conditions de croissance optimales de cette bactérie sont 5-37 °C et un pH de 7,0 à 8. Cette bactérie, très commune dans l'eau et le sol, est une bonne candidate pour tester l'impact des bactéries hétérotrophes en général lors de la séquestration du CO2 dans un aquifère naturel comme en Islande. Les vitesses de dissolution du verre basaltique ont été mesurés à 25 °C dans des nouveaux réacteurs à circulation permettant d'opérer en présence de bactéries (BMFR) dans des solutions tamponnées transportant 0,1 à 0,4 g/L de bactéries mortes et 0,9 à 19 g/L de bactéries vivantes à 4 = pH = 10. Les résultats ont montré que la présence de ces bactéries n'avait quasiment pas d'effet effet sur la vitesse de dissolution. La conclusion générale de cette étude est que ni les revêtements de carbonate, ni les bactéries n'ont d'impact majeur sur les vitesses de dissolution des phases primaires silicatées. Ainsi, leur effet devrait être négligeable sur le processus de séquestration du CO2 sur le site Hellisheiði en Islande. Le basalte cristallin pourrait être recouvert plus rapidement en carbonate de calcium, mais le verre basaltique pourrait aussi servir de support pour la nucléation de calcite
The increasing levels of CO2 in the atmosphere and the potential dangers this pose to the Earth through climate change, ocean acidification and sea-level rise has lead to a substantial number of projects attempting to find a safe and benign way to capture and store CO2 in geological formations, also referred to as the CCS (Carbon Capture Storage) technology. One of these CCS attempts is currently taking place in Iceland at the geothermal power plant Hellisheiði, located close to the capital Reykjavik (the CarbFix project). CO2 and other gasses (H2S, N2, H2, CH4) are waste products of the geothermal energy exploitation and the aim is with time to store all of this anthropogenic-made CO2 in the basaltic formations underlying Hellisheiði. The CO2 is dissolved in groundwater as it is pumped down to 350 meters depth and then injected into mixed horizons of basaltic glass and crystalline basalt. The basaltic rocks are characterized by high contents of divalent cations like Mg2+, Fe2+ and Ca2+ and relatively fast dissolution rates. The acidic CO2-loaded water will dissolve the basalt thereby releasing cations, which can react with the aqueous carbonate ions to form carbonate minerals (magnesite, siderite, calcite, ankerite and Ca-Mg-Fe solid solutions). The rate-limiting step of this carbon sequestration process is thought to be the dissolution of basaltic rocks, thus any effect that could potentially limit basalt dissolution would be detrimental to the overall CO2 sequestration process. My part of the CarbFix project has been to look at the effects the formation of calcium carbonate coatings would have on the dissolution of the primary phase, in this case basaltic glass and the clinopyroxene diopside, so there would be a glass phase to compare with the results of a mineral phase. Furthermore, a series of experiments were conducted where we tested the primary mineral structure's affect on calcite nucleation. This was done in order to test if different silicate structures would lead to different extent of calcite nucleation and growth. Finally, extensive series were conducted on the dissolution of basaltic glass in the presence of dead and live heterotrophic bacteria, Pseudomonas reactans in order to determine the potential effect of bacteria on the carbon storage effort at the Hellisheiði site. The basaltic glass and diopside dissolution experiments were run at 25 and 70 ºC and pH 7-8 in mixed-flow reactors connected to solutions containing CaCl2±NaHCO3 with ionic strengths > 0. 03 mol/kg. Two sets of experimental series were run simultaneously, one series called the "precipitation" experiments in which the solution inside the reactor was supersaturated with respect to calcite, and the other series called the "control" experiments, where PHREEQC modeling foretold no major secondary mineral formation. By this, it was possible to compare dissolution rates of basaltic glass and diopside at 25 ºC with and without calcium carbonate and other secondary mineral formation in order to deduce the effect on their dissolution rates. Scanning electron microscope images showed substantial amounts of calcium carbonate had precipitated in the "precipitation" experiments, but in the case of basaltic glass the primary growth appeared as big, discrete cluster of calcite and aragonite with no growth on the glass itself. Opposed to this, several of the diopside crystals were extensively overgrown by calcite coatings and no aragonite was found. In neither cases did the presence of calcite/aragonite have an effect on the dissolution rates of basaltic glass and diopside when compared to the "control' dissolution rates. It appears the discontinuous cover of the carbonate allows the ions of the primary phases to continue to diffuse through the secondary layer unhindered. To further assess the effect of silicate surface on the nucleation of calcite, the dissolution rates of six selected silicate minerals and rocks were measured in mixed-flow reactors in solutions supersaturated with respect to calcite at 25 ºC and pH ~9. 1. The silicate phases were: Mg-rich olivine, enstatite, augite, labradorite, basaltic glass and peridotite. The results show different onset time of calcite nucleation and thus different extent of carbonate coverage with elapsed time depending on silicate phase. Within the same timeframe olivine, enstatite and peridotite (mainly composed of Mg-rich olivine) were the most covered by calcite precipitations, followed by augite, labradorite and finally basaltic glass. All calcite growth took place on the silicate surface including on the basaltic glass. Kinetics favor calcite nucleation growth on the orthorhombic minerals (enstatite and olivine) over the monoclinic and triclinic minerals. Least calcite was found on the glass, which has no ordered silicate structure. Heterotrophic bacteria, Pseudomonas reactans was extracted from one of the monitoring wells at Hellisheiði, and then separated, purified and cultured in the laboratory. Its optimal growth conditions were found to be 5-37 ºC and pH 7. 0-8. 2 on Brain Heart Broth nutrient. Being a common water- and soil bacteria it offered a good candidacy to test what could be expected of heterotrophic bacteria in general when storing CO2 in a natural aquifers like the one at the Hellisheiði site, in Iceland. Basaltic glass dissolution rates were measured at 25 ºC in newly developed Bacterial Mixed-Flow reactors (BMFR) in buffer solutions carrying 0. 1-0. 4 g/L of dead bacteria and 0. 9-19 g/L of live bacteria at 4 = pH =10. The results show that the presence had either no or a slightly rate-limiting effect. The overall conclusion is that neither the carbonate coatings nor the bacteria had major impact on the measured dissolution rates of the primary silicate phases, thus their effect are expected to be negligible on the CO2 sequestration process in basalt. Crystalline basalt might be faster covered by calcium carbonate, but also basaltic glass can act as a nucleation platform for calcite nucleation

Laboratory experiments were conducted on vesicular basalt cores to estimate hydraulic properties. Properties included dry bulk density, effective porosity, skeletal density, saturated hydraulic conductivity and determination of moisture characteristic curves. Unsaturated hydraulic properties estimated included hydraulic conductivity and diffusivity as a function of matrix suction. Infiltration tests were run on a larger block of the same basalt. Infiltration curves were developed and saturated hydraulic conductivity estimated.

Seismic imaging of sub-basalt sedimentary layers is difficult due to high impedance of the basalt layer, the roughness of the top and bottom of the basalt layer and sometimes the heterogeneities within the basalt layer. In this thesis we identify specific problems within the modern imaging technology which limit sub-basalt imaging. The basic framework for the identification of this limitation is that we are able to group most basalt layers into the following four categories: A basalt layer having smooth top and bottom surfaces. A basalt layer having rough top and bottom surfaces. Small-scale heterogeneities within the basalt layer. Intra-basalt velocity variation due to different basalt flows. All the above models of basalt layers obviously have high impedance with respect to the surrounding sedimentary layers. These four models encapsulate all the possible heterogeneities of basalt layers seen in areas like the Voring and More basins off mid- Norway, basins in the Faroes, W. Greenland, Angola and Brazil margins, and the Deccan Traps of India. In this work, problems in seismic processing and imaging specific to these models have been presented. For instance, we have found that the application of the multiple attenuation technique, which first predicts the multiples and then subtracts them from the data, using least-squares criteria, can be effective for all the models except for the model, which has intra-bedded layers within the basalt. The failure in the second case is due to the destructive interference of multiple scattering from the intra-bedded layers within the basalt and the multiples located below the primary associated with the top of the basalt layer. This interference degrades the signal-to-noise (S/N) ratio of the multiples contained in the data, whereas the predicted multiples, which are constructed from the reflectors above the basalt, have a much higher signal-to-noise ratio. Our recommendation is to subtract the predicted multiples from the data using either leastabsolute- value criteria or any other higher-order-statistics-based criteria.

The Sabie River Basalt Formation is a group of tholeiitic basaltic rocks erupted ca 190 Ma ago in the eastern zone of the Karoo Igneous Province of southern Africa. It is traceable over a distance of 700 km from Zululand, northwards along the Lebombo monocline into the Transvaal and south-east Zimbabwe. An abrupt compositional change in this formation occurs about halfway down its length in the vicinity of the Sabie and Komati Rivers: basalts to the north are known to be enriched in certain incompatible elements relative to basalts in the south, which are comparable in geochemistry to most basaltic rocks in the southern part of the Karoo Igneous Province. New data obtained in this work include 134 major and trace element whole-rock analyses, some 400 analyses of constituent minerals, 38 ⁸⁷Sr/⁸⁶Sr ratio determinations, 19 ¹⁴³Nd/¹⁴⁴Nd ratio determinations, 16 common Pb determinations and 12 oxygen isotope analyses. The "normal" (N) and "enriched" basaltic rocks are distinguished by differences in the concentrations of Ti, P, Zr, Nb, Y, La, Ce and Nd (high field strength elements). Broadly these differences are substantiated by K, Rb, Ba and Sr, but with much more overlap. The "enriched" group of basaltic rocks has been further subdivided into a low-Fe "enriched" (LFE) group and a high-Fe "enriched" group (HFE). The LFE-group basalts, which predominate at the base of the stratigraphic sections, are considered to be equivalent to basalts occurring in the N. Lebombo. In the central Lebombo N-group basalts predominate in the mid- and upper portions of the sections and HFE-group basalt occurs near the top of each section. Interbedding of all basalt groups occurs in the Sabie River section at the northern end of the study area, while the N- and HFE-group basalts are interbedded in the Crocodile and Komati River sections further to the south. The decrease in LFE-group basalt abundance southwards is accompanied by an increase in N-group basalt abundance. HFE-group basalts appear to be unique to the central Lebombo area of the Karoo Igneous Province and are volumetrically less significant than N- or LFE-group basalts. Petrogenetic models involving closed-system fractional crystallization; coupled assimilation (of granitic crust) fractional crystallization; replenished, tapped and fractionated magma chambers and partial melting are examined. Granitic crustal contamination appears to have been significant only in some samples of the N group where assimilation of granitic material has proceeded in a bulk fashion described by an AFC model. RTF models are dynamically more realistic than closed-system fractional crystallization models and explain increases in incompatible elements with decreasing MgO in the LFE and HFE groups. Variations in the N group, however, require varying degrees of partial melting of a N-type source to be explained fully. RTF models may explain the absence of any stratigraphic correlations of element abundances in the three groups. The HFE group may be related to an uncontaminated N-type parent composition by a combination of continued fractional crystallization from an N-group parent composition and varying degrees of partial melting of an N-type source. The only petrogenetic process by which the N and LFE groups may be related is different degrees of partial melting. However, this demands a source composition which has no resemblance on trace element and isotopic grounds, to observed mantle xenolith compositions. The preferred model is one in which the LFE group is derived from old sub-cratonic mantle similar to garnet-bearing "cold" peridotite xenoliths and the N group from a source similar in composition to estimates of primitive mantle. The existence of two types of mantle derived continental flood basalt magmas occurs in other Mesozoic basalt provinces in "southern" Gondwanaland (e.g. Kirwanveggan of Antarctica, Etendeka of Namibia and the Parana Basin of South America). It is suggested that there is a geographical association of LFE-type basalts with Archaean crust (or Archaean crust re-worked in low temperature - high pressure events) and N-type basalts with post-Archaean crust (or Archaean crust re-worked in high temperature - low pressure events). This model suggests the derivation of the LFE group, from old sub-cratonic lithospheric mantle relatively enriched in incompatible elements and the N group being derived from more recently accreted and less enriched lithospheric mantle underlying younger crustal terraines.

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.

A Sucessão Magmática do Arquipélago de Abrolhos é composta por quatro unidades, quais sejam: Olivina-Plagioclásio Basalto (b1), Piroxênio-Plagioclásio-Olivina Basalto (b2), Piroxênio-Plagioclásio Basalto (b3) e Cumulado (b4). As unidades não são correlacionáveis litoestratigraficamente e estão empilhadas da base para o topo em unidade b1, b2, b3 e b4. As unidades da sucessão magmática são diferentes quanto à textura, estrutura e mineralogia. A análise litogeoquímica de vinte e três amostras de rochas basálticas das unidades da sucessão magmática discriminou uma série transicional de afinidade alcalina para as rochas estudadas. As razões Nb/Y > 1 das rochas estudadas corroboraram a afinidade alcalina da série. As rochas foram classificadas como basaltos e traqui-basaltos (unidades b1 e b2), basaltos, traqui-basaltos, basanitos e tefritos (unidades b3 e b4). A análise de diagramas de variação para elementos maiores e traços e das razões de elementos traços da amostra representativa do líquido parental e do líquido mais evoluído indicaram cristalização fracionada sem mudança de assembléia francionante como possível processo evolutivo da série transicional estudada. A incongruência entre a assembléia fracionante e a assembléia de fenocristais (identificada na petrografia), além de feições indicativas de desequilíbrio cristal-líquido mostraram que a cristalização fracionada foi o único processo evolutivo na geração dos basaltos do Arquipélago de Abrolhos. Modelos evolutivos mais complexos devem ser considerados, como, por exemplo, um modelo de reabastecimento de câmaras crustais com subseqüentes pulsos de magmas basálticos. As razões La/Yb (N) >1 e La/Nb (N) <1 indicaram que as unidades mapeadas no Arquipélago de Abrolhos estão associadas a uma mesma fonte mantélica fértil (tipo pluma).
The Magmatic Succession of Abrolhoss Archipelago is composed by four units: Olivine-Plagioclase Basalt (b1), Pyroxene-Plagioclase-Olivine Basalt (b2), Pyroxene-Plagioclase Basalt (b3) and Cumulado (b4). The units are not stratigraphically correlated. They are stacked from the basis to the top in units: b1, b2, b3 and b4. The units of the magmatic succession are different in terms of texture, structure and mineralogy. The litogeochemical analyses of twenty three samples of basaltic rocks discriminated a transitional series of alkaline affinity to the studied rocks. The values of Nb/Y ratios higher than unity of the studied rocks corroborate the alkaline affinity of the series. The rocks were classified as basalts, tracky-basalts, basanites and tephrites (units b3 and b4), basalts and tracky-basalts (units b1 and b2). The interpretation of variation diagrams to major and trace elements together with the trace elements ratios of the representative sample of the parental and the more evaluated liquids indicated fractional crystallization without changing of fractionated assemblage as the evolutionary process of the studied transitional series. The incongruity between the fractionated assemblage and porphyries assemblage (recognized by the petrography) in addition to the indicative features of crystal-liquid disequilibrium discard fractional crystallization as the evolutionary process in the generation of the basaltic rocks of Abrolhoss Archipelago. More complex evaluative models should be considered as, for example, a refueling model of crustal chambers with subsequent pulses of basaltic magmas. The La/Yb (N) ratio >1 and La/Nb (N) ratio <1 indicated that the mapped units of Abrolhoss Archipelago are associated to a fertile mantellic source (plume-like type).

The objective of this research is to determine if the deflection equations currently adopted in ACI 440.1r-15 and previously ACI 440.1r-06 accurately reflect the flexural behavior of an over-reinforced Basalt Fiber Reinforced Polymer (BFRP) concrete beam. This was accomplished with experimental, analytical and numerical models. The experiment consisted of two beams doubly-reinforced with BFRP rebar. A three-point flexural test on beams with a 30 in. clear span was performed and the deflections were recorded with a dial gauge and LVDT system. This data was compared to the equations from ACI 440.1r-06, ACI 440.1r-15, Branson’s equation and a numerical model created in ANSYS Mechanical APDL.

Experimental results show a stiffer beam than expected when compared to the four predictive models for deflection. This can be due to the level of over-reinforcement and the small clear-span to depth ratio. Further research should be conducted to determine the cause for the additional stiffness.

Basalt and granodiorite (medium to fine sand particle size) were leached by three low molecular weight aliphatic organic acids, namely citric, oxalic and acetic acid of . 1M concentration. To evaluate the effectiveness of the organic acids in dissolving the rock samples, two control solutions, .005M HCl and distilled water were added to the number of dissolution treatments. Dissolution of ions from granodiorite, by the leaching treatment shown in parenthesis, decreased in the following order: Fe(OX) > Al(OX) ~ Si(OX) > Ca(CIT) ~ Mg(OX) ~ K(OX) > Na(OX) Dissolution of ions from basalt decreased in the following order: Fe(CIT) > Si(CIT) > Mg(CIT) > Ca(CIT) > Al(OX, ACETIC) > Na(OX) > K(HCl) Oxalic acid effectively outcompeted citric acid in the weathering of granodiorite in spite of having lower stability constants for certain elements. This was attributed to differences in pH of the solutions (affecting both concentration of H⁺ ions and anionic species), ionic competition in solution for ligand sites and geometry and oxidation state of ions in the parent mineral. There was no conclusive evidence to indicate that chelation of K⁺ or Na+ took place in any of the experiments. However, mass balance calculations revealed that oxalic acid extracted approximately 40-50% of the K from granodiorite; citric acid extracted approximately 12%. These levels were significantly higher than those extracted by non-sequestering agents. XRD analysis of granodioritic-oxalate precipitate suggested the possible formation of a K-oxalate salt. The chelating acids, citric and oxalic, greatly outcompeted acetic acid and HCl of similar pH for multivalent cations in both basalt and granodiorite. Concentrations of Fe, Al, and Si, in solution were many fold higher than calculated concentrations of those ions in equilibrium with the amorphous oxide in water. Oxalic acid and citric dissolution curves, determined from 11 weeks of leaching, showed initially increasing rates followed by declining rates which approached steady state towards the eleventh week of the experiment. Declining rates followed by steady-state rates were attributed to the presence of hyperfines the build-up of secondary precipitates, the increase of ions in solutions, and to an eroding leached surface layer. Non-chelating acids namely acetic acid, HCl and H₂O revealed dissolution curves that were approximately constant (steady-state) throughout the 11 week weathering period. XRD, XRF, SEM, and EDX analyses of weathered basalt and granodiorite as well as AA spectrophotometric solution analyses provided evidence which indicated incongruent dissolution of granodiorite and basalt by all 5 leaching treatments. SEM and XRF analyses indicated that citric acid was less effective than oxalic acid in forming precipitates from granodiorite. EDX revealed that the amorphous precipitate which did form in citric acid consisted primarily of Fe. EDX analyses of inorganic coatings indicated predominantly Si and Fe in 1:1 ratio. Although citric acid was able to extract greater amounts of Fe from basalt than granodiorite, extractable Fe, Al and Si analysis and SEM detected no organo-amorphous precipitates. Also EDX of inorganic surfaces showed no accumulation of Fe or Al. It was concluded that the Fe extracted from the basalt remained in complexed or soluble form due to the higher pH (3-5) of the basaltic solution. An amorphous precipitate formed from the leaching of granodiorite with oxalic acid. EDX analysis gave evidence that the precipitate consisted primarily of Si and Fe in a 1:1 ratio. An amorphous precipitate formed also from the leaching of basalt with oxalic acid. EDX analysis gave evidence that the precipitate consisted primarily of Mg and Fe in a 1:1 ratio. Data from molar oxide ratios and mass balance calculations as well as XRD, XRF, extractable Fe, Al and Si analyses were relied upon to determine the possible organic and inorganic components of these precipitates.
Land and Food Systems, Faculty of
Graduate

Das heutige Naturdenkmal Stolpener Basalt (Nationaler Geotop) kann auf eine lange und vielseitige kulturgeschichtliche Entwicklung verweisen. Seine schriftliche Ersterwähnung lag in der Zeit der Reformationsauseinandersetzungen und jährt sich 2020 zum 500. Mal.

The extrusive and intrusive members of the St. Helena rock suite (SHRS) are formed in an intra-oceanic plate tectonic setting as part of two shield volcanoes. The SHRS vary from picrobasalts to phonofites. The former represent mantle derived melts, whereas the remainder of the suite have undergone differing degrees of crystal fractionation. A stratigraphic framework is developed to illustrate temporal geochemical variations over 2 Ma of subaerial activity. This is accomplished in conjunction with a detailed field study of the SHRS by Baker(1968) which is shown to be largely accurate. It is demonstrated that ascending magma batches are substantially modified by crystal fractionation and subsequent alteration processes. Petrogenetic modelling shows that the genesis of the SHRS is consistent with small degree (1-10%) melting of an olivine - clinopyroxene - orthopyroxene - garnet source containing a residual K-rich phase. Combined Sr-Nd-Pb isotope and fractionation corrected trace element data for fresh rocks enable consideration of changing thermal and chemical fluxes impinging on and interacting with the base of the lithosphere over a period of at least 2 Ma. The existence of two geochemically distinct components in the source region is indicated. A H/MU (high 238U /104Pb)c omponent has extremely radiogenic Pb isotopes (206Pb/104Pb> 20.8) with 143Nd/'44Nd and 87S8r,6 Sr displaced below the mantle array. The complementary depleted component has less radio genic Pb and Sr isotopic compositions and more radio genic Nd compositions. The limited variation of geochemical compositions in the SHRS (caused by mixing of these components) is attributed to the dissimilarity of the components in terms of their trace element abundance and their similarity in terms of ratios of highly incompatible elements. Coupled trace element and isotope variations are evident during the activity of each volcano. During shield development an increase in incompatible trace element enrichment occurs. This is coupled to a decrease in 143Nd/'44Nd, whilst Sr and Pb become progressively more radiogenic. The time dependent variations are thought to be consistent with mixing and melting processes occurring at the base of, or within the lithosphere. A decrease in the signature of the depleted component at the end of activity of the NE volcano and SW volcano is the inferred result of a decreasing thermal flux acting on the base of the lithosphere. With lower heat input less fusion of the depleted component (from the asthenosphere or lithosphere) occurs resulting in an increased H/MU signature in the erupted products through time. Previous explanations for the development of the dominant HIMU component are critically reviewed by considering shared isotope and trace element characteristics for HIMU OIB. U-Th-Pb systematics suggest the HIMU component has remained discrete from other mantle components for approximately 2 Ga. The fractionation event producing the H/MU component is shown to cause an increase in U/Pb and a decrease in Rb/Sr and Th/U.. This is thought to be consistent with a model suggested by Hofmann and White(1980,1982). in which HIMU represents ancient recycled altered oceanic crust. It is demonstrated that other models are less tenable. It is thought that the HIMU characteristics necessitate modification of oceanic crust in subduction zones in addition to the geochemical changes caused by hydrothermal alteration of oceanic crust.

Altered flows that are low-MgO chemical types of the Grande Ronde Basalt crop out in the steep walls of the Grande Ronde River canyon near Troy, Wallowa County, Oregon. The alteration effects in these flows are being investigated as a natural analog system to a high level nuclear waste repository in basalt. The flows within the study are referred to as the analog flow, in which the alteration effects are the strongest, and the superjacent flow. The analog flow crops out at Grande Ronde River level and a roadcut-outcrop is developed in the flow-top breccia of this flow. The two flows have been divided into flow zones based on intraflow structures observed in the field and primary igneous textures observed in thin section. These zones include, from the base upward, the flow interior, transition, and flow-top breccia zones of the analog flow, the interflow contact zone, and the flow interior and flow-top breccia zone of the superjacent flow. The intraflow structures and textures of the transition and interflow contact zones are atypical of Grande Ronde Basalt flows. The transition zone is transitional in textures between the flow interior zone and flow-top breccia zone, and includes holocrystalline spines mantled with fused in situ breccias. The interflow contact zone reflects the dynamic interaction during the emplacement of the superjacent flow manifested as invasive basalt tongues, clasts shed from tongues, pipe vesicles and tree molds, and pockets of breccia caught up in the base of the superjacent flow.

Zur Erweiterung der Grundlagenkenntnisse für diese beiden bisher wenig genutzten Verstärkungsfasern werden in dieser Arbeit Einzelfaserzugversuche durchgeführt, um den Einfluss der Prüfbedingungen und der Faseroberflächenbehandlungen auf die mechanischen Eigenschaften der Fasern zu charakterisieren. Durch die Analysen der unimodalen und bimodalen Weibullverteilung wird der Zusammenhang zwischen der Faserzugfestigkeit und den kritischen Oberflächendefekten untersucht. Um den Einfluss der Faseroberflächenbehandlungen auf die Oberflächenenergien und Grenzflächenhaftung zu ermitteln, werden in dieser Arbeit der Schlichteauftrag aus wässriger Phase (Silan, Filmbildner), Plasmabehandlungen in verschiedenen Medien, Excimer-UV-Bestrahlungen in Anwesenheit verschiedener Monomeren und eine Säurebehandlung durchgeführt. Zur Charakterisierung der Oberflächentopografie der oberflächenbehandelten Fasern vor und nach dem Einzelfaserauszugversuch wird die Rasterkraftmikroskopie (AFM) verwendet. Der Effekt einer Plasmabehandlung auf die freie Oberflächenenergie der PBO-Fasern und die Grenzflächenscherfestigkeit wird mittels der Kontaktwinkelmessung und der Einzelfaserauszugprüfung untersucht. Um die durch diese Oberflächenmodifizierungen hervorgerufenen Veränderungen der mechanischen Verbundeigenschaften sowie der Faser-Matrix-Haftung zu charakterisieren, werden in dieser Arbeit sowohl endlosfaserverstärkte thermoplastische und duroplastische Unidirektionalverbunde bzw. kurzfaserverstärkte thermoplastische Verbunde als Modellfälle betrachtet, bei denen sowohl die Verstärkungsfasern als auch die Matrix signifikant unterschiedlich sind. Zur Verstärkung werden zwei ausgewählte Fasermaterialien (Basalt- und PBO-Fasern) und als Matrix zwei Thermoplaste (PP und PA6) sowie ein Epoxidharz ausgewählt. Der Einsatz von Commingling-Hybridfäden zur Entwicklung der thermoplastischen Unidirektionalverbunde erfordert Voruntersuchungen zur Lufttexturierung mit verschiedenen Düsen und Auswahl der günstigsten Prozessparameter.

Large areas of the Earth are covered by intrusive and extrusive lavas, forming high velocity basalts, which are often opaque to cinventional seismicreflection surveys. On the North East Atlantic margin these basalts cover sediments in whose lateral extension away from the basalt cover proven hydrocarbon reservoirs and source rocks exist. To reveal the comparable structures that are expected to exist beneath the basalt cover novel seismic methods are required. The primary objectives of this thesis are to examine the effects of basalts on seismic wave propagation and the concequent implications for imaging sedimentary structures beneath them. From studies of basalt propertiesand borehole data in connection with foreward modelling and real data, I show that new acquisition methods, like low frequency set-ups and far-offset recordings, have to be used to image beneath basalt sequences.

Mechanical properties of concrete are most commonly determined using destructive tests including: compression, flexure, and fracture notch specimen tests. However, nondestructive tests exist for evaluating the properties of concrete such as ultrasonic pulse velocity and impact echo tests. One of major issues with concrete (which has cement as its prime ingredient) is that unlike steel it is quasi-brittle material. It tends to want to crack when tensile stresses develop. Fibres have been added to concrete for many years to reduce the amount of and size of cracks cause by temperature changes or shrinkage. In more recent years, significant research has been carried out into the effect of the addition of basalt fibres to cement has on its mechanical strength. As well, developing concrete that is more durable, flexible, stronger, and less permeable than traditional concrete has been explored. It has become important to test and verify improvements that are made to the cement by basalt fibres as well as testing the general strength of concrete to stand up to constant pressure at varied strengths.

The content of this thesis is based on original fieldwork by the candidate in the Black Desert, the basalt region of eastern Jordan. Very little is known about the prehistoric sequence of occupation in the area. The thesis attempts to outline this sequence through analysis of the survey data, and compare it to existing information from the better documented areas of Palestine and Syria. The first chapter describes the environment of the study area, both at present and in history, and sets out the survey and sampling techniques used in the study. The second chapter gives a brief description of the slender evidence for Lower and Middle Paleolithic in the region and the third chapter examines the evidence for the Epipaleolithic, comparing sites found on the survey with those from similar contexts and more contrasting ones in the fertile areas to the west. The fourth chapter covers the extensive evidence for aceramic Neolithic occupation and discusses the typelist adopted for the analysis. It describes the types of sites of this period, and includes detailed analyses of two excavated assemblages to demonstrate the special character of the sites in the survey area. The fifth chapter continues the discussion into the later Neolithic when there is a significant change in subsistance strategies in the desert. Many sites and findspots have been recorded for this period. The nature of their chipped stone industries and their distribution are examined and analysed, and contrasted with the evidence for this period from surrounding areas. The sixth chapter outlines the evidence for post-Neolithic occupation in the study area and elsewhere in the desert regions. It also presents the data for the chipped stone assemblage from Jawal an intrusive Late Chalcolithic/Early Bronze industry, the Cananean, typical of Palestine and western Syria. The final chapter sums up the results of the work and presents conclusions.

Zur Erweiterung der Grundlagenkenntnisse für diese beiden bisher wenig genutzten Verstärkungsfasern werden in dieser Arbeit Einzelfaserzugversuche durchgeführt, um den Einfluss der Prüfbedingungen und der Faseroberflächenbehandlungen auf die mechanischen Eigenschaften der Fasern zu charakterisieren. Durch die Analysen der unimodalen und bimodalen Weibullverteilung wird der Zusammenhang zwischen der Faserzugfestigkeit und den kritischen Oberflächendefekten untersucht. Um den Einfluss der Faseroberflächenbehandlungen auf die Oberflächenenergien und Grenzflächenhaftung zu ermitteln, werden in dieser Arbeit der Schlichteauftrag aus wässriger Phase (Silan, Filmbildner), Plasmabehandlungen in verschiedenen Medien, Excimer-UV-Bestrahlungen in Anwesenheit verschiedener Monomeren und eine Säurebehandlung durchgeführt. Zur Charakterisierung der Oberflächentopografie der oberflächenbehandelten Fasern vor und nach dem Einzelfaserauszugversuch wird die Rasterkraftmikroskopie (AFM) verwendet. Der Effekt einer Plasmabehandlung auf die freie Oberflächenenergie der PBO-Fasern und die Grenzflächenscherfestigkeit wird mittels der Kontaktwinkelmessung und der Einzelfaserauszugprüfung untersucht. Um die durch diese Oberflächenmodifizierungen hervorgerufenen Veränderungen der mechanischen Verbundeigenschaften sowie der Faser-Matrix-Haftung zu charakterisieren, werden in dieser Arbeit sowohl endlosfaserverstärkte thermoplastische und duroplastische Unidirektionalverbunde bzw. kurzfaserverstärkte thermoplastische Verbunde als Modellfälle betrachtet, bei denen sowohl die Verstärkungsfasern als auch die Matrix signifikant unterschiedlich sind. Zur Verstärkung werden zwei ausgewählte Fasermaterialien (Basalt- und PBO-Fasern) und als Matrix zwei Thermoplaste (PP und PA6) sowie ein Epoxidharz ausgewählt. Der Einsatz von Commingling-Hybridfäden zur Entwicklung der thermoplastischen Unidirektionalverbunde erfordert Voruntersuchungen zur Lufttexturierung mit verschiedenen Düsen und Auswahl der günstigsten Prozessparameter.

Concrete is a structural composite material with excellent properties when subjected to compression. But the poor ability to resist tensile stresses forces the concrete to be used with reinforcement. Commonly, large continuous steel bars have been applied as reinforcement since mid-1800’s to carry the tensile loads. Placing the steel bars takes many man-hours, which contributes to a significant part of the total concrete costs. By eliminating the reinforcement part of the construction work, the costs can be reduced considerably. Fibers have been incorporated into building materials since ancient times to improve the properties. Today, fibers are incorporated in concretes to improve certain properties of this material. They are added to enhance the ductility of the concretes. Additionally, the tensile and the flexural strengths of the material are enhanced. The crack widths and their propagation are decreased by the insertion of fibers. Research over the years have shown that fiber reinforcement has sufficient strength and ductility to be used as a complete replacement to conventional steel bars in some types of structures; foundations, walls, slabs. Fibers are also used in beams in combination with conventional reinforcement which increase the capacity and the stiffness of the concrete. The technology that is available today has made is possible to consider fiber reinforcement without the use of conventional steel bars in load carrying structures. For this to be a reality, the fibers must be distributed and oriented as expected, which is difficult. If fibers can be used without the need of steel reinforcement bars, the reinforcement part of the construction work will be eliminated. Hence, the construction costs will be significantly reduced.In recent years, a project within COIN has set the aim to develop a high tensile strength all-round concrete which exhibits a residual flexural tensile strength in the range of 10-15 MPa and that can be applied in load carrying structures. This MSc-thesis is a part of this work and it has consisted of testing fiber-reinforced self-compacting concretes with different types and contents of fibers, namely steel fibers and basalt fibers. The different concrete mixes were tested and the corresponding fresh and hardened concrete properties were evaluated and compared.Based upon the results achieved in these experiments, the conclusion was taken of whether or not the different concrete mixes could be used for the purpose the COIN project was aiming for.

Seventy-one samples of subalkaline and alkaline basalts from British Columbia and the adjacent Pacific seafloor were analyzed for 33 major, trace and rare earth elements using X-ray flourescence (XRF) and instrumental neutron activation analysis (INAA). These basalts are all less than 22 Ma in age and come from various magmatic belts, each with a distinct, well-known, tectonic setting; (1) Convergent margin (Garibaldi and Pemberton Belts), (2) Back-arc (Chilcotin Basalts), (3) Hotspot (Anahim Volcanic Belt), (4) Incipient rift (Stikine Volcanic Belt), (5) Arc-trench gap (Alert Bay Volcanic Belt) and (6) Ocean floor (Offshore basalts of the Juan de Fuca-Explorer Ridge Systems). Element abundances and ratios were plotted on eighteen diagrams that have been proposed to discriminate between tectonic settings on the basis of magma chemistry. Although eruption through continental crust has modified the abundances of Ba, Th, U, K and Sr, in most cases this did not affect the ability of the diagrams to distinguish tectonic setting. On most diagrams basalts from back-arc, hotspot, incipient rift and arc-trench gap settings plotted in the within plate basalt (WPB) field, but distinction between these different WPB settings could not be made. Two samples from the Masset Formation on the Queen Charlotte Islands, included with the Anahim Belt hotspot suite, were consistently classified as convergent margin. Samples from the ocean floor plotted in the N-MORB or E-MORB fields. Three convergent margin samples from the Pemberton Belt always plotted in the convergent margin field, but on most diagrams all eight samples from the Garibaldi Belt plotted in the WPB field because of their depletion in LIL elements. La is the only rare earth element obtained by INAA that is essential for identifying the tectonic environment of magma genesis. The ratio La/Nb, is an effective separator of within plate basalts (WPB), including E-MORB, (La/Nb less than 1.2) from convergent margin basalts (La/Nb greater than 2.0). N-MORB lie between the ratios 1.2 and 2.0. Th, Ta and Hf also obtained by INAA, are important discriminant elements. However, Nb and Zr, obtained by XRF analysis convey much of the same information. The ratio Nb/16 as an estimate of Ta and Zr/39 as an estimate for Hf produced acceptable results on diagrams that originally incorporated Ta and Hf. Effective discrimination can therefore usually be achieved using XRF elements alone. Convergent margin, within plate and ocean floor tectonic settings were best distinguished on Th-Hf/3-Ta, Ti-Zr-Y and Ti-Zr-Sr, Ti/Y vs. Nb/Y, Th/Yb vs. Ta/Yb, (Ba/La)CH vs. (La/Sm)CH and V vs. Ti/1000. Slightly less effective plots were MnO-Ti0₂-P₂0₅, La vs. Th, La vs. Nb and K₂0/Yb vs. Ta/Yb. On the other hand Ti0₂-K₂0-P₂0₅, MgO-Fe0*-Al₂0₃ and La vs. Ba provided little information concerning the tectonic setting of individual samples. Ti/Cr vs. Ni, Sm/Ce vs. Sr/Ce, Cr vs. Ce/Sr and Cr vs. Y diagrams were useful for distinguishing unfractionated convergent margin basalts from MORB plus WPB.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

The main aim of the research is to investigate the waste by-products as a sustainable construction material by means of Alkali-activation processes. Nowadays, cement is one of the most significant factors of climate change and global warming. It accounts for 5% to 8% of total emission, which may increase due to the increase in concrete production. In this process, sustainable and eco-products have been chosen. Basalt and metakaolin were chosen as precursors. In this, basalt is the main component of our research. Basalt is an igneous rock formed by the rapid cooling of lava at the surface of a planet and it is the most common rock in the earth’s crust and metakaolin is the anhydrous calcined form of the clay mineral kaolinite also the particle size of metakaolin is smaller than cement particles. In this experimentation, there are two activators sodium silicate and sodium hydroxide. These two activators added into precursors in certain proportions and mixed using a cement rotator. After that, this mixture is distributed into cube blocks and leave for a few minutes before packing with a plastic cover. Proceeding into a curing process, these cube blocks placed in the oven at certain temperatures between 60 to 80 degrees. These types of precursors and activators are added in different ratios using this procedure to make a cube sample following by the curing process of 28 days. These were tested in compressive strength machine to obtain load resistance results. Basalt has better chemical resistance to the extended operating temperature range and environmentally friendly material. Metakaolin is eco-friendly by reducing the amount of 〖co〗_2 emission and the heat of hydration leading to shrinkage and crack control. With the obtained synthetic mixtures, some special paving blocks were produced. Following the EN 1338 standard, these were tested in different to fully characterize the final product.

Characterisation of three lava flow fields from the Columbia River Basalt Group (CRBG), USA, reveals compositional heterogeneity on all scales, from adjacent lava lobes to the intra-crystal scale. Simple flow fields can be traced from vent areas to distal reaches, but those with multiple-layered lobes present a degree of complexity that make lava pathways and eruption sequences difficult to identify. A 3-D model based on field investigation of a single flow field establishes a volcanological context for geochemical sampling. Compositional v.ariation within each flow field suggests that small-scale geochemical heterogeneity is common within and between lobes of these flood basalt lavas. Lobe cores emplaced during the latter stages of an eruption have less evolved compositions and more enriched incompatible elements, suggesting progressive variation of magma composition caused by either recharge or sequential tapping of compositionally zoned magma. Progressive crustal contamination of magma during a single eruption is indicated by Re-Os isotope ratios. Initial 1870s/1880s ratios range from 1.405 in the earlier emplaced lava crust to 0.128 in the latter emplaced lava core. These values are more radiogenic than any known enriched sources (normative mantle -0.127, HIMU -0.15) consistent with previous data that indicate that neither an enriched source nor sub-continental lithospheric mantle can be the source of CRBG magma. Os isotope signatures can be explained by different degrees' of contamination of two isotopically distinct lithologies represented by the North American craton and Jurassic accreted terranes underlying the province. Intra-crystal Sr isotope analyses within a flow field record variable histories in an open magmatic system. Results suggest crystal residences in an increasingly contaminated melt within the crust with several recharge events of less-contaminated more primitive basaltic melt. Assembly of melt and crystal cargo occurred immediately prior to eruption without significant residence times in the final host magma. The combined compositional evidence suggests that an extensive shallow-crustal network of dykes and sills supplied magma to the CRBG eruptions.

The construction of coastal ports requires the use of materials that meet the demands of the marine environment, to prevent underwater concrete structures from cracking and spalling easily; basalt fiber is used to delay the expansion of concrete and prevent the formation of cracks. This research studies the behavior of concrete for prefabricated piles with Portland Cement Type I and basalt fibers added in 0.1%, 0.3% and 0.6%; the results indicate that the fiber is suitable for concrete, the slump decreases, the compressive strength increases for specimens cured in tap water and sea water, the relationship between resistances does not vary, and the depth of carbonation decreases.

This study aims to produce a type of concrete with both good thermal and mechanical properties by using environmentally friendly and low cost materials. In addition, the resistance of this concrete to fire conditions was investigated. The experimental work comprises two parts. In the first part, recycled glass was used as a partial replacement for natural sand (at proportions 20%, 40% and 60%) together with basalt fibre having different volume fractions (0.1%, 0.3%, and 0.5%). The results obtained from the experimental work showed that the optimum content is 20% glass and at 28 days, there was a 4.23% and 15% enhancement in the compressive strength and the splitting tensile strength respectively. Above 20% glass there was a slight reduction (6.6% and 22%) in the compressive strength and the splitting tensile strength when 60% glass was used. The results also showed that when glass sand and basalt fibre content increase, there is a decrease in the thermal conductivity range from 4.35% to 50% at temperature levels between 60oC to 600oC. The structural behaviour of this type of concrete was investigated in the second part of this study by carrying out small-scale slab tests at ambient and elevated temperatures. The results show that there is an increase in the load carrying capacity above the theoretical yield line load, due to membrane action, for all percentages of glass and volume fractions of basalt fibre ranging from 1.35 to 1.68 for the slab tested at ambient temperature and from 3.13 to 3.26 for the slabs tested at elevated temperature. Also the slabs with higher glass sand and basalt fibre content had a higher load enhancement and failed at a higher displacement compared to the control mix.A comparison between the simplified method and the finite element software package ABAQUS showed that the ABAQUS model gives reasonable predictions for the load-vertical displacement and the temperature-displacement relationships at both ambient and elevated temperature conditions, while the simplified method gives conservative predictions for the maximum allowable vertical displacement for the slab at elevated temperature. A parametric study showed that a 10 mm cover depth is the optimum depth as well as the reinforcement temperature predicted reduced with increasing load ratio (applied load/yield line load).

Post-extrusive hydrothermal alteration within basaltic lavas has been examined with special reference to the Lower Carboniferous Clyde Plateau Basalts of the Midland Valley of Scotland. Within this province several steep-sided, narrowly constrained zones of intense water-rock interaction have been located and examined. It is thought that these zones, or metadomains, developed where hydrothermal fluids exploited permeability contrasts within the volcanic pile and as such they represent foci for geothermal fluids which advected through the lavas. In the field metadomains are often manifest as areas of intense alteration and hydrofracting of the host basalts. Characteristic alteration mineralogies are often hydrous and typically include evolved phyllosilicate assemblages, prehnite, analcime and calcite. Petrography reveals that prehnite and analcime are always paragentetically earlier than calcite across the whole of the lavas. Also, metadomain development was accompanied by significant elemental mobility within the host basalts; Si, Ti, Fe, Mn, Mg, Ca, Na and K all exhibit varying degrees of mobility, whilst Sr, Rb, Cu and Zn display extreme mobility. Furthermore, metadomain basalts have higher volatile contents than there unaltered counterparts. Fluids present during metadomain development typically were Ca2+, Na+, Cl- dominated brines which exhibited both a wide range in salinity (approximately 0 to 25 equiv. wt. % NaCI) and temperatures (approximately 50°C to 300°C). As the development of metadomains proceeded it appears that the fluid present was a hybrid formed from the interaction and mixing of a low temperature, low salinity fluid which was ultimately of surface origin and a higher temperature brine derived from the underlying sediments. The presence of minor amounts of hydrocarbon material within the fluids testified to the involvement of organic rich sequences within the underlying Inverclyde Group sediments. These fluids also record a number of physical processes which are observed within currently active geothermal systems such as mixing and boiling indicative of near surface conditions. Such processes appeared to be largely responsible for controlling the gas content of the fluids. Combined fluid inclusion and stable isotopic analysis of alteration phases (specifically analcime and calcite) has been used to determine fluid origins and evolution during metadomain development. Fluids present during the precipitation of analcime appears to have originated as a surface derived fluid which interacted (isotopically and chemically) with reactive, carbonate rich sediments, possibly the underlying Inverclyde Group. Fluids present during calcite precipitation can be separated into two distinct groups; a low to intermediate (c. 90 to 200°C) surface derived fluid and a higher temperature fluid which also appears to have interacted with reactive sediments. Carbon isotopic results confirm that organic derived material interacted with these fluids. Uniformity in carbon isotopic compositions suggests that the carbon reservoir was active prior to calcite precipitation. As geothermal activity waned calcite precipitation still continued whilst fluid temperatures decreased due to convective cooling of the lava pile. During this stage it appears that fluids were dominantly of surficial origin.

The impact of subduction initiation on regional to global tectonics and the compositions of major Earth reservoirs are topics of vigorous ongoing research. Here, pristine glasses extracted from ~51.9 Myr old basalts and younger boninites that erupted in the Izu-Bonin Mariana forearc immediately after subduction initiation were analyzed by microbeam techniques, with goals of characterizing the mantle sources and the conditions under which melting occurred to produce nascent arc crust. Forearc basalts (FAB) have relatively differentiated major element compositions. Thus, to determine melting conditions and source compositions, primitive melt compositions were restored through an inferred crystallization history based on melt liquidus associations. Subsequent modeling indicates that they were generated at high temperatures and low pressures relative to a mid ocean ridge basalt (MORB). Incompatible trace element compositions of FAB show that they are similar to MORB in that they were generated largely by decompression melting. Differences in several trace element ratios between MORB and FAB indicate that the mantle sources for FAB were unusually depleted. Differences between FAB sub-units indicate a range of petrogenetic histories. Upper FAB sub-units are weakly enriched in fluid-mobile elements which may indicate that fluids from the subducting Pacific plate contributed to melting. Boninites are separated into high and low silica types based on preexisting whole rock analyses. Glasses separated from these boninites are highly differentiated and thus classify as high-Mg andesites rather than boninites on MgO-SiO2-TiO2 diagrams. These glasses are also enriched in a suite of fluid mobile elements indicating that they are products of flux melting of the mantle involving fluids and melts from the subducting plate. Olivine calcium concentrations are consistent with hydrous parental boninite melts. Aluminum partitioning between olivine and hosted spinel inclusions constrains the temperatures of initial crystallization between 1170 and 1330 degrees Celsius. The change from decompression melting which generated forearc basalts to flux melting which generated high silica boninites illustrates an evolution of the subduction system over the course of the initiation process. Based on trace element ratio plots, mixing relationships between upper forearc basalts and highly enriched fluids probably released by the nascent subducting slab suggest that both decompression melting and fluid fluxing operated to produce low silica boninite during subduction initiation. This melt composition progressively becomes dominated by fluid flux melts with additional components derived from the slab to make high silica boninite. These late volcanic rocks record melting of a highly depleted mantle source. The fact that heavy rare earth element concentrations become increasingly depleted from FAB to low silica boninite to high silica boninite indicates that the mantle source changed in composition over time. The progressive decrease suggests that the initial mantle source for FAB remained the mantle source for the duration of subduction initiation related magmatism.

Os materiais vitrocerâmicos de basalto representam uma importante família de vitrocerâmicos. Sendo que um dos desempenhos técnicos exigidos atualmente é o efeito anti-desgaste dos materiais, as vitrocerâmicas de basalto cobrem essa necessidade e têm uma aplicação direta por suas boas propriedades mecânicas e anti-abrasivas, além da vantagem que têm as rochas basálticas quanto à baixa temperatura de fusão e maior fluidez do fundido, o que as torna mais adequadas para o processamento cerâmico. No presente trabalho, rejeitos da mineração de rocha basáltica da região de Campinas, São Paulo, foram fundidos em escala laboratorial em forno elétrico a 1350°C, usando cadinhos de alta alumina, para a obtenção de uma primeira série de amostras de vidro. Mais uma série foi obtida, realizando a fusão da matéria-prima com adição de 0,5% em massa de Cr2O3 como agente de nucleação. Os vidros foram tratados termicamente à máxima temperatura de cristalização como sendo 880°C e 820°C durante 5, 10, 20, 30 e 60 minutos e 5, 20 e 60 minutos respectivamente. A evolução das fases cristalinas foi acompanhada por análise de densidade (método de Arquimedes) e difração de raios X (DRX). Foi realizada a medição da microdureza Vickers e resistência à micro-abrasão, e o vidro cristalizado observou-se por microscopia eletrônica de varredura (MEV). Os vidros da primeira série foram também moídos, até tamanhos de partícula ASTM 80 e ASTM 325, para avaliar sua capacidade de cristalização como pó de vidro. Eles foram caracterizados mediante DRX e MEV.
Basalt glass-ceramics represent one of the most important family of glass-ceramics. The wear resistant, is now the technical performance requirement in material, basalt glass-ceramics cover that need and have a direct application for their good mechanical and anti-abrasive properties. In addition, the basaltic rocks have the advantage of a low melt temperature and higher fluidity melt. In this paper, a mining waste of basaltic rock from the city of Campinas, São Paulo, was melted in laboratory scale, in an electric furnace at 1350°C, in high-alumina crucibles, to obtain the first series of basalt glass samples. Other series was obtained by melting of the raw material with addition of 0,5% wt. of Cr2O3 as a nucleating agent. The glasses were heat treated at the maximum crystallization temperature: 880oC during 5, 10, 20, 30, and 60 minutes and 820°C during 5, 20 and 60 minutes, respectively. The evolution of the crystalline phases was accompanied by density and X-ray diffraction (XRD) analyses. Vickers hardness and micro-abrasion resistance of the samples were also carried out, and the crystallized glasses were observed in a scanning electron microscope (SEM). The first series of glasses were also milled, until particle sizes ASTM 80 e ASTM 325, for the evaluation of their ability to crystallization as glass powder. They were characterized by XRD and SEM.

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.

Denne masteroppgaven er en eksperimentell studie av en selvkomprimerende konstruksjonsbetong (styrkeklasse B35) med antiutvaskingsegenskaper armert med enten basaltfiber (monofilament) eller stålfiber. Formålet med oppgaven har vært å undersøke fibrenes effekter på blant annet betongens ferskegenskaper, som eksempelvis synk og synkutbredelse, samt mekaniske egenskaper i herdet tilstand, hovedsakelig bøyestrekkfasthet og trykkfasthet. Motivasjonen for oppgaven har vært et ønske om å øke proporsjonalitetsgrensen for undervannsbetongen, altså bøyestrekkfastheten ved riss, samt å gi betongen duktilitet og restfastheter etter riss. Et av hovedkravene ved fremstilling av denne fiberbetongen var å opprettholde en tilfredsstillende lik reologi som referansebetongen. For bruk av fiber i konstruksjonsbetongen i jetpeler vil en slik økning av beskrevne egenskaper kunne resultere i mindre bruk av stagforankring, reduserte pelediametere og/eller redusert peleantall. Dette betyr tidsbesparelse. Basaltfibrenes effekt på bearbeidbarheten (synk og synkutbredelse) var stor allerede ved små fibermengder sammenlignet med stålfiber. For et krav til synkutbredelse på 560 mm var maksimum anvendbare innhold av basaltfiber kun 0,38 vol% (10 kg/m3). Den mest effektive endringen gjort i resepten for å fremskaffe disse verdiene, var å øke innholdet av superplastiserende tilsetningsstoff til maksimalt anbefalt. Matriksvolum og w/c-forhold ble også forsøkt øket, men med liten effekt. Det var i tillegg ønsket å beholde masseforholdet grunnet krav til bestandighetsklasse M45. Stålfibrene ble kun testet med en fibermengde på 0,7 vol% (54,6 kg/m3). Selv uten endring av resepten fra referansebetongen viste dette fiberinnholdet seg å ha liten effekt på synkutbredelsen, med unntak av litt mindre synk på grunn av tendenser til oppbygning av fiberskjelett i midten. Likevel var det god stabilitet i betongen som medførte jevn spredning av stålfiber helt ut til randen. Basaltfibrene viste ingen antydning til positiv effekt på bøyestrekkfasthet og trykkfasthet ved 28 døgn herding. Bøyestrekktesten som ble brukt var i samsvar med NS-EN 14651. Etter riss ga fibrene ingen fastning og fiberbetongen gikk til brudd på samme måte som den uarmerte referansebetongen. Basaltfibrene er derfor uegnet som fiberarmering i denne undervannsbetongen for applikasjon i jetpeler. Stålfibrene økte derimot middelverdien av proporsjonalitetsgrensen for bøyestrekkfasthet fra 4,2 MPa (for referansebetongen) til 5,6 MPa. Stålfibrene ga i tillegg umiddelbar fastning etter første riss og økte restbøyestrekkfastheten opp til ca. 7,8 MPa ved 1 til 1,5 mm rissvidde (CMOD). Betongen viste god duktilitet og stålfibrene tilfredsstilte kravet til minimumsarmering. For dimensjonering ved 0,5 mm rissvidde er den dimensjonerende restbøyestrekkfastheten = 3,6 MPa for stålfiberbetongen. Vurdering av basalt- og stålfibres effekt og mekaniske egenskaper i jetpeler Den stålfiberarmerte undervannsbetongen er en god fiberbetong sammenlignet med en ordinær selvkomprimerende konstruksjonsbetong med samme stålfibervolum og omtrentlig lik trykkfasthet. På grunn av den store mengden sement i betongen er varmeutviklingen ved herding høyere enn normalt. Dette vil resultere i overflateriss grunnet en temperaturgradient gjennom det store peletverrsnittet. Selv om dette normalt er ufarlige riss, som har en tendens til å lukke seg når konstruksjonen kjøles ned, kan de likevel fungere som svake punkt ved mekaniske laster og/eller miljømessige belastninger. Stålfiber ville kunne redusere disse rissviddene, men ikke fjerne de helt.

Thesis (Ph. D.)--Joint Program in Marine Geology and Geophysics (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2009.
Includes bibliographical references.
To explore the ability of melting mafic lithologies to produce alkaline ocean-island basalts (OIB), an experimental study was carried out measuring clinopyroxene (Cpx)melt and garnet (Gt)-melt partition coefficients during silica-poor garnet pyroxenite melting for a suite of trace elements, including U and Th, at 2.5GPa and 1420-1450°C. Partition coefficients range from 0.0083+0.0006 to 0.020+0.002 for Th and 0.0094+0.0006 to 0.024+0.002 for U in Cpx, and are 0.0032+0.0004 for Th and 0.013+0.002 for U in Gt. Forward-melting calculations using these experimental results to model time-dependent uranium-series isotopes do not support the presence of a fixed quantity of garnet pyroxenite in the source of OIB. To use U-series isotopes to further constrain mantle heterogeneity and the timing and nature of melting and melt transport processes, U-Th-Pa-Ra disequilibria, radiogenic isotopes, and trace-element compositions were measured for the slow-spreading Arctic mid-ocean ridges (MOR). A focused case study of 33 young (<10ka) MOR basalts (MORB) from the shallow endmember of the global ridge system, the Kolbeinsey Ridge (67°05'-70°26'N) found that unaltered Kolbeinsey MORB have universally high (230Th/238U) (1.165-1.296) and relatively uniform (230Th/232Th) (1.196-1.324), ENd (8.4310.49), 87Sr/86Sr (0.70274-0.70301), EHf(16.59-19.56), and Pb isotopes (e.g. 208Pb/206Pb 2.043-2.095). This suggests a homogeneous mantle source and a long peridotite melting column produces the thick Kolbeinsey crust. Trace element ratios suggest a young, depleted mantle source. Data from the slow- to ultraslow Mohns and Knipovich Ridges north of Kolbeinsey form a sloped array, and (230Th/232Th) correlates systematically with radiogenic isotopic variations.
(cont.) These data are readily reproduced by models for heterogeneous mantle melting. MORB from 85oE on the global ultraslow-spreading endmember Gakkel Ridge are homogeneously depleted with low (230Th/238U) and high (226Ra/230Th) that lie along a global negative correlation. Arctic data support a global mantle temperature control on mean (230Th/238U).
by Lynne J. Elkins.
Ph.D.

The Cretaceous Parana-Etendeka flood basalt magmatism of South America and Africa was accompanied by intense intrusive activity. This study examines the geochemistry and petrogenesis of dykes from two regions of southern Brazil. Dykes from the Ponta Grossa region of Parana. State fed the basalt lava flows of the northern Parana. The dolerites underwent extensive crystal fractionation at pressures of less than about 5kb, but do not represent parental magmas to the associated rhyolites. The dolerites have received a contribution from a LREE enriched source with time-integrated high RblSr relative to the bulk earth, and yield model Nd and 207PbjlO6Pb ages which are similar to ages obtained from the basement rocks of southern Brazil. This suggests that the distinctive trace element and isotope signature of these dolerites was derived from a source in the subcontinental mantle. The-dolerites of Sao Paulo State are divisible into three magma types, which cannot be related either to one another, or to the flood basalts to the west by any simple petrogenetic process. The geochemical variation within dolerites of the Paraiba and Ubatuba magma types was controlled by assimilation fractional crystallisation and magma mixing processes at shallow levels in the crust In contrast, the basanites of the Sao Sebastiao magma type underwent limited crystal fractionation of olivine and clinopyroxene at pressures of >4 kb. Much of the geochemical variation within this group of rocks is related to variations in the degree of partial melting (estinlated to be 0.1-5%) of a spinel bearing source. The Sao Sebastiao basanites have very similar trace element and isotope compositions to Recent basanites erupted on the South Atlantic island of Tristan da Cunha, and are interpreted as the expression of the Tristan plume at 80 Ma. Selected whole rock samples and mineral separates have been dated by the laser ablation Ar-Ar technique. The Ponta Grossa dolerites yield isochron ages of 130.5±2.9- -134.1±1.3 Ma. The Paraiba and Ubatuba magma types were intruded at between 129.4±O.6 and 135.8±1.1 Ma. A biotite separate from a sample of the Sao Sebastiao magma type yielded a much younger age of 80.1±O.4 Ma, which suggests that these may be related to the alkalic intrusive complexes of Sao Paulo State. These ages imply that the Parana magmatism ocC1Jl'Ied within about 3 Ma at 131-134 Ma, although there is evidence that plagioclase alteration may be responsible for some of the apparent age range. The data suggest that the flood basalt magmatism occurred contemporaneously with continental rifting in the South Atlantic, and are consistent with a model in which the Parana-Etendeka flood basalts represent decompression melts generated during continental rifting above the abnormally hot mantle associated with the Tristan da Cunha mantle plume. This model can also account for the observed volume of magma. A comparison of the major element compositions of flood basalts from various CFB provinces with the predicted composition of decompression melts, suggests that many of these basalts have inherited a distinctive major element signature from the subcontinental lithospheric mantle.

Afin de parvenir à une meilleure compréhension de la dynamique d’ascension et d’éruption des magmas basaltiques, nous avons réalisé des expériences de décompression à haute pression (200–25 MPa) et haute température (1200°C) spécifiquement orientées pour documenter la nucléation des bulles de gaz ; ce processus, qui constitue la première étape du dégazage magmatique, conditionne l’évolution de la phase gazeuse (force motrice des éruptions explosives) dans le conduit volcanique. Quatre principaux ensembles d’expériences ont été menés afin de mieux comprendre le rôle des volatils majeurs (H2O, CO2, S), ainsi que les effets de la vitesse d’ascension et de la présence de cristaux sur la cinétique de vésiculation (nucléation, croissance, coalescence) des bulles dans les magmas basaltiques. L’objectif est de comprendre les mécanismes qui contrôlent les caractéristiques texturales (nombre, taille, forme des bulles) et chimiques (teneur en volatils dissous, composition des gaz) des produits naturels et de les approcher expérimentalement. Dans ce sens, les verres expérimentaux ont été analysés avant et après décompression sur le plan textural (microtomographie par rayons X, MEB) et chimique (FTIR, microsonde électronique). Nos résultats démontrent une forte influence du CO2 sur les processus ainsi que sur le mode (équilibre vs. déséquilibre) de dégazage des magmas basaltiques, en lien avec des différences de solubilité et de diffusivité entre les espèces volatiles. Nos données, obtenues dans des conditions voisines des conditions naturelles, ont des implications volcanologiques pour l’interprétation des textures de bulles et des mesures de gaz en sortie de conduit, ainsi que, plus spécifiquement, pour la dynamique des éruptions paroxysmales au Stromboli
For a better understanding of the dynamics of ascent and eruption of basaltic magmas, we have performed high pressure (200–25 MPa) and high temperature (1200°C) decompression experiments specifically oriented to document gas bubble nucleation processes. Bubble nucleation occurs first during magma degassing and, so, it is critical to understand bubble nucleation processes to constrain the evolution of the gas phase (which is the driving force of explosive eruptions) in the volcanic conduit. Four main sets of experiments were conducted to better assess the role of the major volatiles (H2O, CO2, S), as well as the effects of ascent rate and crystals, on bubble vesiculation (nucleation, growth, coalescence) kinetics in basaltic magmas. The aim of the study is to understand the mechanisms which control the textural (number, size, shape of bubbles) and the chemical (dissolved volatile concentrations, gas composition) characteristics of natural products, and also to approach them experimentally. In this way, experimental melts, before and after decompression, were analysed texturally (by X-ray microtomography and MEB) and chemically (by FTIR and electron microprobe). Our results demonstrate a strong influence of CO2 on degassing mode (equilibrium vs. disequilibrium) and mechanisms, which are shown to be controlled by differences in solubility and diffusivity between the main volatile species. Finally, our data, obtained under conditions closely approaching natural eruptions, have volcanological implications for the interpretation of bubble textures and gas measurements, as well as, more specifically, for the dynamics of Strombolian paroxysms