Thesis (M.S.)--Brigham Young University. Dept. of Geological Sciences, 2006. / Includes bibliographical references (p. 25-34).

Thesis (Ph. D.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (Ph. D.)--University of Canterbury, 2009. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2008. / Newman, Andrew, Committee Member ; Lowell, Robert, Committee Chair ; Germanovich, Leonid, Committee Member.

Explosive volcanic eruptions are propelled to the surface by the exsolution of vapour bubbles from magma due to decompression. A long-held view is that the amount of H₂O dissolved in the magma at depth controls the intensity of an explosive eruption. Growing evidence from studies reporting H₂O concentrations of melt inclusions (MIs) do not support this view. Instead, the rate at which magma ascends to the surface may play an important role in modulating the eruption style. Slow magma ascent allows the vapour bubbles to rise ahead of the magma, thereby diffusing the driving force for an explosive eruption, whereas for fast magma ascent, the bubbles remain essentially trapped within the magma, causing acceleration and the potential for an explosive eruption. Chapter 1 presents a new modelling approach to constrain magma decompression rate based on the incomplete diffusive re-equilibration of H₂O in olivine-hosted melt inclusions. We apply this chronometer to two contrasting eruptions at Cerro Negro volcano in Nicaragua: the 1992 VEI 3 and 1995 VEI 2 eruptions. Both eruptions have the same basaltic composition (SiO₂ ∼ 50 wt%) and maximum volatile concentrations (H₂O ∼ 4.7 wt%). However, MIs from the less explosive 1995 eruption appear to have experienced more water loss compared to those from the 1992 eruption, which is consistent with slower magma ascent. We present a parameterization of the numerical diffusion model in chapter 2, which significantly reduces the calculation time, facilitating the use of Monte Carlo simulations to evaluate uncertainties. We use this parameterization to create a regime diagram that can be used to guide when melt inclusions may be used as magma hygrometers and when they are better suited to act as magma speedometers. We develop diagnostic tools to recognize where and when water loss has occurred in a magma’s ascent history, and we outline quantitative tools that may be used to restore the primary and/or pre-eruptive water content. We find that one of the largest sources of uncertainty in modelling diffusive re-equilibration of H₂O in MIs and olivines is the diffusivity of H+ in olivine. We present new experimental constraints on H+ diffusivity in olivines from Cerro Negro (1992 eruption) and Etna (3930 BP ‘Fall Stratified’ eruption) (chapters 1 and 3, respectively). Our results show that H+ diffusion is highly anisotropic with the diffusivity along the [100] direction more than an order of magnitude faster than along [010] or [001], implying a large role for the ‘proton-polaron’ diffusion mechanism, which shares this anisotropy. We also find that the lower forsterite (Fo ~ 80) olivines from Cerro Negro have significantly faster H+ diffusivity than higher forsterite (Fo ~ 90) olivines from Etna. The results for Etna agree well with other estimates on high forsterite olivines from San Carlos and Kilauea, suggesting that the Fe content of the olivine strongly affects the H+ diffusivity. In chapter 4, we apply the methods from the first three chapters to an unusually explosive eruption of picritic magma at Etna, Sicily in 3930 BP (termed the ‘Fall Stratified’ eruption). MIs from this eruption show limited evidence for water loss and so cannot be modelled to determine decompression rate. Instead, we model H+ diffusion profiles within the olivine crystals themselves and determine rapid ascent rates of ~15 m/s. We perform rehomogenization experiments on the MIs to accurately assess their pre-eruptive CO₂ concentrations, and find nearly 1 wt.% CO₂. Solubility modelling indicates that these MIs must have been trapped at near Moho depths (24–30 km). The magma’s high CO₂ concentration and deep initial pressures may have been responsible for the magma’s rapid ascent, which ultimately led to its great eruption intensity.

Made available in DSpace on 2014-06-11T19:26:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-07-01Bitstream added on 2014-06-13T20:14:59Z : No. of bitstreams: 1 machado_fb_me_rcla.pdf: 4784777 bytes, checksum: 4e32e919d841aa28e910f8e2c2df689a (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A investigação petrográfica e geoquímica das rochas intrusivas associadas à Província Magmática do Paraná (PMP), na porção leste da Bacia do Paraná, no Estado de São Paulo, mostraram que as rochas estudadas são constituídas essencialmente por plagioclásio, augita, minerais opacos e pigeonita, caracterizando diabásio com texturas predominantemente intergranular, subofítica e ofítica. Dados geoquímicos indicaram que as rochas apresentam natureza básica, afinidade toleítica e podem ser classificadas como pertencentes ao grupo de alto titânio (ATi) da PMP. Além disso, as diferenças geoquímicas também indicam que as intrusivas pertencem aos subgrupos (magmas-tipo) Paranapanema (PAR) e Pitanga (PIT), sendo que a distribuição destes magmas pela área estudada não se faz ao acaso. O tipo PAR ocorre nos sills da região de Campinas, enquanto que PIT nas regiões de Cajuru, Leme, e Iracemápolis. Para comparação geoquímica, os derrames próximos também foram investigados, onde se observou que as amostras coletadas nas regiões de Franca, Igarapava e Rifaina em São Paulo, e São Sebastião do Paraíso, em Minas Gerais, são pertencentes ao magma-tipo Urubici (URU), já aquelas da região de Brotas e Ribeirão Preto são do tipo PIT. Contudo, as concentrações de ETRs, para as amostras representativas dos três magmas-tipo, mostraram que, embora as rochas intrusivas (PAR e PIT) e derrames (URU) possam ter uma mesma fonte mantélica, foram submetidas a processos de evolução magmática distintos. / Petrographic and geochemical investigations of the intrusive rocks related to the Magmatic Paraná Province (PMP), in the east portion of Paraná Basin, São Paulo State, have showed that the studied rocks are constituted mainly by plagioclase, augite, magnetite and pigeonite. That characterize intergranular, subophitic and ophitic diabases. Geochemical data have indicated that rocks are basic, with toleiitic affinity and can be included to the high titanium (HTi) of the PMP group. Moreover, the geochemical differences point out that the intrusive rocks belong to Paranapanema (PAR) and Pitanga (PIT) sub-groups (magmas-type), and the magma type distribution is well sectioned. The Paranapanema Magma type occurs like sills, in the neighborhood of Campinas, meanwhile Pitanga Type occurs in Cajuru, Leme, and Iracemápolis neighborhood. In order to compare, the nearby flows were also investigated, and was observed that samples collected in Franca, Rifaina e Igarapava in São Paulo, and São Sebastião do Paraíso, in Minas Gerais, neighborhoods belong to the Urubici magma-type (URU). Magmas from Brotas and Ribeirão Preto are PIT type. The concentrations of ETRs to the representative samples of three magmas-type have showed that intrusivas rocks (PAR and PIT) and lavas (URU) possibly were submitted to magmatic evolution different processes.

Made available in DSpace on 2014-12-17T14:20:21Z (GMT). No. of bitstreams: 1 AntonioAA.pdf: 1300916 bytes, checksum: c1879cd68345a955c5a6196670e5a5ff (MD5) Previous issue date: 2007-04-26 / This work has as objective approaches the relationship among journalism, literature and society in Lima Barreto, especially in fiction book Recorda??es do escriv?o Isa?as Caminha and in several of their chronicles, detecting the superficiality notion that author sees in the journalistic activity and to point that the literature brings the particularity of presenting as an alive laboratory for the social sciences. The used theoretical-methodological elements draw a corpus through an interactive process in which additional layers of the author's texts are submitted to the analysis. As theoretical support is worked the notion of magmas of social significances, idealized by Cornelius Castoriadis / Este trabalho tem como objetivo abordar a rela??o entre jornalismo, literatura e sociedade em Lima Barreto, notadamente no romance Recorda??es do escriv?o Isa?as Caminha e em v?rias de suas cr?nicas, detectando a no??o de superficialidade que esse autor v? na atividade jornal?stica, apesar de tamb?m dela retirar o seu sustento, e apontar que a literatura traz a particularidade de se apresentar como um laborat?rio vivo para as ci?ncias sociais. Os elementos te?rico-metodol?gicos utilizados tra?am um corpus atrav?s de um processo interativo no qual camadas adicionais de textos do autor s?o submetidas ? an?lise. Como suporte te?rico ? trabalhada a no??o de magmas de significa??es sociais, idealizada por Cornelius Castoriadis

Les intrusions magmatiques au sein d’une lithosphère soumise aux contraintes tectoniques sont souvent considérées comme des instabilités thermomécaniques à même de stimuler transitoirement et localement la localisation de la déformation. Dans le but de tester ce modèle et de déterminer les possibles mécanismes gouvernant l’initiation d’une déformation localisée au contact et au sein de corps magmatiques en cours de consolidation, ce travail de thèse se propose de coupler une étude de terrain à une approche expérimentale. Les Cyclades (Mer Égée, Grèce) constituent un domaine de croûte continentale en extension dans lequel se sont mises en place au cœur de cinq dômes métamorphiques extensifs (MCCs) des intrusions magmatiques, elles-mêmes coiffées par des systèmes de détachements. Les diverses campagnes de terrain, combinées aux données de la bibliographie, ont permis de proposer un modèle d’interaction régional dans lequel ces corps magmatiques impactent l’évolution tardive de MCCs cycladiques. Au vu des âges de mise en place des intrusions (15-9 Ma), soit plusieurs millions d’années après le début de l’extension et les premiers stades d’exhumation de roches métamorphiques, le magmatisme dans les Cyclades ne peut être considéré comme un candidat réel pour la genèse de MCCs. Néanmoins, les continuums de la déformation enregistrés en bordure des intrusions (depuis l’état magmatique jusqu’aux conditions ductile/cassant) et les relations géométriques avec les détachements laissent supposer un rôle majeur des complexes magmatiques dans les processus de redistribution et de localisation de la déformation, notamment sur le développement séquentiel de détachements. Les vecteurs de localisation de la déformation au sein de magmas partiellement cristallisés ont été en parallèle recherchés par la voie expérimentale. L’étude du comportement structural de magmas, chimiquement et texturalement proches de systèmes naturels, a permis d’une part de confirmer que la déformation se localise préférentiellement le long d’interfaces à rhéologie contrastée tels aux abords de filons syn-plutoniques. Il est d’autre part montré que la présence initiale d’inhomogénéités texturales (e.g. concentration de cristaux en amas) au sein de magmas moyennement cristallisés peut de manière drastique influencer le degré de localisation de la déformation au cours des stades de refroidissement ultérieurs. / Magma intrusions within the lithosphere are often considered as thermomechanical instabilities capable to locally and transiently stimulate strain localization. With the aim of testing this model and determining possible mechanisms that govern the initiation of localized deformation at the contact and within magmatic bodies, this thesis combine a fieldwork with an experimental approach. The Cyclades (Aegean Sea, Greece) form a highly extended continental domain in which five metamorphic core complexes (MCCs) were intruded by magmatic complexes, themselves capped by detachment systems. All collected structural and kinematic data, combined with previous investigations, converge toward a regional scheme in which magmatic bodies dynamically impacted the late evolution of the Cycladic MCCs. Granitoids were emplaced in relatively short time period (15-9 Ma) while metamorphic domes were largely exhumed after more than 10 Myrs of extension. None of those intrusions thereby proves to be a real candidate for the genesis of MCCs. However, continuums of deformation recorded within granitoids (magmatic to ductile/brittle states) as well as geometrical relationships with detachments suggest a pivotal role of magmatic complexes in redistribution and localization processes of the deformation, with in particular the sequential development of detachments. Precursors of strain localization within partially cristallized magmas have been concurrently deciphered by an experimental study. The investigation of the structural behavior of magmas, chemically and texturally similar to natural systems, corroborates that strain localization is efficiently activated along interfaces with contrasting rheology such as in the vicinity of synplutonic dikes. It has been also shown that the initial presence of textural inhomogeneities (e.g. like clusters) in medium-crystallized magmas can drastically influence the degree of strain localization during subsequent cooling stages.

Magíster en Ciencias, Mención Geología / Este estudio evalúa el uso de la química de la apatita magmática (Ap) (incluida en fases anhidras (IAp) y como microfenocristales (MAp)) como monitor del comportamiento de H2O, Cl, F y S en los magmas que generaron los pórfidos dacíticos del Mioceno Superior del área La Huifa-La Negra (LH-LN), aledaña al depósito de Cu-Mo El Teniente. La cristalización temprana de hornblenda (Hb) en estas rocas indica que el magma fue hidratado. El geobarómetro de Al en Hb indica una presión de ~2 Kb para la formación de los fenocristales, mientras que la masa fundamental sugiere una despresurización posterior del sistema. Las rocas presentan grados variables de alteración hidrotermal potásica, fílica, argílica y propilítica regional. Los resultados sugieren que: 1) las Ap que interactúan con fluidos en condiciones de no equilibrio son susceptibles a alterarse. 2) Su alteración, total o parcial, se produce in situ, vía un proceso metasomático de reemplazo seudomórfico, que genera rasgos texturales y composicionales característicos: a) porosidad, que le otorga turbidez bajo el microscopio; b) inclusiones de monacita; c) límites netos entre sectores alterados y preservados; y d) pérdida de elementos traza (Cl, S, Na, REE). 3) La fácil identificación en Ap de áreas no modificadas por fluidos (límite neto entre partes alteradas y preservadas), permite usar estos sectores para evaluar condiciones magmáticas. 4) Las Ap de estos pórfidos se caracterizan por: a) altos contenidos de Cl (max. 4.52 %) y de SO3 (max. 0.98 %), mayores en IAp que en MAp; b) fuerte disminución de las relaciones Cl/OH y Cl/F desde las IAp a las MAp, controlada por un marcado descenso del Cl y un aumento del F; el OH se mantiene casi constante; c) un fuerte descenso de la relación Cl/OH con el aumento del F; y d) una correlación Cl-S positiva, con contenidos mayores en IAp que en MAp. 5) Altos contenidos de S en las IAp, sugiriendo un magma rico en SO4= y por lo tanto oxidado (>NNO +1); 6) Estas variaciones indican una exsolución temprana, a alta presión, de una fase volátil acuosa rica en Cl y S que evoluciona hacia composiciones menos salinas. Condiciones hidratadas y oxidantes, junto a la presencia de Cl y S debieron favorecer la concentración de Cu en el fundido residual y su posterior liberación hacia la fase volátil. La baja carga de cristales, al momento de la exsolución de fluidos, habría facilitado la migración de los volátiles y el Cu hacia las partes apicales del este sistema magmático. Por lo tanto, el sistema magmático de LH-LN habría tenido, desde el punto de vista de los procesos concentradores de Cu, el potencial para producir alteración hidrotermal y mineralización de tipo pórfido de cobre asociada.

Reconnaissance work and high-density sampling of volcanic rocks at the Quaternary Tatara-San Pedro complex (TSPC) in the Southern Volcanic Zone (SVZ) of Chile has yielded one of the most complete eruptive chrono-stratigraphies and comprehensive geochemical datasets of any arc volcano on Earth. The TSPC is a large frontal arc stratovolcano within the SVZ that exhibits a wide compositional diversity of lavas from basalt to rhyolite, covering most of the ranges in major and trace element contents across the SVZ. The TSPC occupies a pivotal position within the SVZ, where it is "intermediate" in terms of geophysical and geochemical characteristics between northern and southern SVZ volcanoes. The large TSPC dataset and stratigraphic control provides a unique opportunity to elucidate magma source heterogeneity and distinguish between contributions from upper mantle, subducted slab, and crust in a volcanic complex overlying relatively thick continental crust. Furthermore, the results of this investigation provide important constraints about the role of various recycled materials in generating the SVZ mantle and implications for along-arc magmatism and geochemical variability. TSPC magmas least impacted by crustal contamination (evolved lavas are filtered out on the basis of > 56 wt.% SiO2 and Rb/Y >1.75) have compositions bounded by three chemically and isotopically distinct mantle-derived end-members. The `prevalent TSPC mantle' end-member, which includes the largest number of analyzed lavas, is interpreted to represent melts of the upper mantle below TSPC that has been modified by long-term subduction. A second end-member shows extreme depletions in incompatible high field strength elements (HFSE) and the lowest concentrations of fluid-immobile incompatible elements, but has the highest aqueous fluid-mobile/immobile element ratios at the volcano (e.g., Sr/Nd and Pb/Ce). The source of these `low HFSE' magmas is `prevalent TSPC mantle' that experienced previous melt extraction, followed by more recent melting due to infiltration of solute-rich fluid from the subducting basaltic Nazca oceanic crust. A third end-member is enriched in incompatible elements and has the lowest Nd-Hf and highest Sr isotope ratios. This `TE enriched' end-member has common chemical characteristics with behind-the-arc basalts, indicating derivation from trace element-enriched behind-the-arc South American mantle that has been advected trenchward into the convecting mantle wedge. Determining the composition and relative input of slab-derived components to the SVZ mantle wedge has remained elusive for the last 2+ decades because of inadequate datasets and the controversial role of crustal contamination within the thick Andean continental crust. The `prevalent TSPC mantle' magmas, which best represent melts of the subduction-modified mantle wedge composition beneath the TSPC, provide important constraints on both the composition of the "pre-subduction" mantle and geochemical modifications by way of subduction. Mass-balance modeling suggests that the source of `prevalent TSPC mantle' magmas has been generated by a two-stage, three component mixing process. Isotopic and trace element evidence indicate that ~7-11% bulk subducted Chilean trench sediment has been added to an `E-MORB-like' pre-subduction mantle composition. This mantle mixture is further infiltrated by ~4% solute-rich fluid derived from the subducted Nazca basaltic oceanic crust. Trace element patterns of end-member `prevalent TSPC mantle' magmas are best fit by a two-stage partial melting model whereby the residual mantle, after a small degree melt extraction (F = 0.1%), undergoes F = 22% partial melting. The high melt fraction appears to potentially correspond with large volumes of solute-rich fluid released from the subducted Mocha Fracture Zone (MFZ). Although geochemical attributes of mafic TSPC magmas suggest that they are all derived from the same general mantle framework operating below the complex, one lava sequence appears to deviate. The mantle origins of the Upper Placeta San Pedro Sequence (UPSPS) have remained elusive since first being studied. It is a well-characterized basaltic lava series that erupted over a short interval at ~235-240 ka with highly variable incompatible element abundances and a large xenocrystic cargo. The new comprehensive chemical and radiogenic isotope (Sr-Nd-Pb-Hf) dataset, along with stratigraphic control and understanding of the larger-scale geochemical variability at the TSPC, provides fresh perspectives about the mantle sources and evolution of UPSPS magmas. While the UPSPS magmas are derived from the same sources as other TSPC magmas, they have undergone a unique petrogenetic evolution. This is evident from decoupled trace element-isotopic trends that are difficult to reconcile with other mafic TSPC magmas. Based on the Nd-Hf isotope ratios and trace element ratios, the two UPSPS unit magmas are derived from depleted-`TE enriched' and `prevalent TSPC mantle' sources. High ratios of aqueous fluid-mobile/immobile elements, such as high Pb/Ce and Sr/Nd, as well distinctive Sr and Pb isotope ratios, indicate that the UPSPS magmas were generated through fluxing of the mantle wedge, already depleted by melt removal by an solute-rich fluid derived from the subducted Pacific oceanic crust as well as the overlying trench sediment, which caused it to melt.