Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1912. / One folded map inside back cover. The entire thesis text is included in file. Typescript. Illustrated by author. Title from title screen of thesis/dissertation PDF file (viewed April 20, 2009) Includes bibliographical references.

Thesis (M.Sc.)--Memorial University of Newfoundland. / Bibliography : leaves 183-205. Also available online.

Thesis (M. Sc.)--University of Hong Kong, 2004. / Also available in print.

In many ore deposits throughout the world, brecciation often accompanies or occurs in association with mineralization (Sillitoe, 1985). Such is the case in the Tintic Mining District (Ag-Pb-Zn) of north-central Utah, where unique breccia features called pebble dikes occur alongside significant mineralization. Pebble dikes are tabular bodies of breccia, which consist of angular to rounded clasts of quartzite, shale, carbonate, and minor igneous rock cemented in a fine-grained clastic matrix. All clasts now lie above or adjacent to corresponding source rocks. Dikes are thin, typically less than 0.3 m wide to as much as 1 m, and can exceed 100 m in length. The average of the largest clast sizes is less than 3 cm but correlates positively with pebble dike width. Contacts are sharp and an envelope of fine breccia surrounds roughly half of the dikes. Pebble dikes are mostly hosted in an Eocene rhyolite lava flow, which displays argillic to silicic alteration when in contact with a pebble dike, but are also hosted in an assortment of folded Paleozoic sedimentary rocks. The dikes show a strong northeast trend in orientation, following a regional fabric of northeast-trending strike-slip and oblique-slip faults.The formation of pebble dikes has been historically attributed to the intrusion of the Silver City Stock, the Tintic District's main productive intrusion (Morris and Lovering, 1979; Hildreth and Hannah, 1996; Kim, 1997; Krahulec and Briggs, 2006). However, pebble dikes are spatially associated with a previously unrecognized porphyritic unit, informally named the porphyry of North Lily, which is texturally, mineralogically, and chemically distinct from the Silver City Stock, and like pebble dikes, is emplaced in northeast-trending plugs and dikes. Pebble dikes show a strong spatial correlation to outcrops of the porphyry of North Lily. Additionally, clasts of the porphyry of North Lily have been found in pebble dikes, while pebble dike quartzite clasts have been found as xenoliths in the porphyry of North Lily. These similarities and interactions suggest simultaneous formation. Low-grade alteration associated with pebble dikes indicates that they formed at elevated temperatures (<150°C). Stable isotope characteristics of rhyolite altered during the emplacement of pebble dikes suggests that the dikes formed in the presence of heated groundwater, with little to no magmatic water association. The overall physical, spatial, and chemical characteristics of pebble dikes of the Tintic Mining District suggest that they formed by the mobilization of breccia in the explosive escape of groundwater that had been heated by the porphyry of North Lily. This escape occurred along pre-existing northeast-trending faults and fractures. Pebble dikes then became pathways for later ore fluids, easing the creation of the district's abundant mineral resources.

A presente dissertação estuda os enxames de diques clásticos presentes na porção superior da Formação Corumbataí, Permotriássico da Bacia do Paraná, no interior do Estado de São Paulo. Foram analisadas três seções estratigráficas, levantadas em cortes de rodovias e ferrovia nos municípios de Limeira, Batovi e Santa Luzia. No total foram obtidas 273 medidas de atitudes de diques, distribuídos em quatro níveis estratigráficos em Santa Luzia e Limeira, e três em Batovi. Os diques estão intrudidos em siltitos, são compostos por arenito muito fino a siltoso, em sua maioria são subverticais, e possuem geometrias tabulares e ptigmáticas, essas devido a efeitos de compactação posterior. O processo de formação dos diques foi injeção forçada ascendente de sedimento fluidificado. As feições observadas que sustentam essa conclusão são: ramificações rumo ao topo, deformação na laminação da camada encaixante, diques alimentadores de extrusão de sedimento, intraclastos da encaixante, e orientação vertical da petrotrama paralela à parede dos diques. A fluidificação foi induzida provavelmente por atividade sísmica, os diques clásticos estudados podem ser intepretados como sismitos. As características em favor dessa hipótese são: a associação com outras estruturas de liquefação cronocorrelatas da Formação Corumbataí e Pirambóia, ampla distribuição geográfica das ocorrências (dezenas a centenas de quilômetros), confinamento em determinados níveis estratigráficos, e relação com estruturas tectônicas do embasamento. As atitudes dos diques apresentam significativa dispersão nas orientações, porém foi possível identificar orientação preferencial, com atitudes variando principalmente entre NNW a NE, e predomínio da direção NNE. Admitindo o fraturamento hidráulico como o principal mecanismo de ruptura das camadas pelíticas para a colocação dos diques, a direção preferencial NNE marca o esforço horizontal máximo atuante durante a intrusão, associado a distensão no plano vertical na direção WNW-ESSE. A considerável dispersão das atitudes é atribuída a existência de baixos valores de stress diferencial durante o fraturamento e injeção do sedimento fluidificado, situação esperada em casos de intrusão em baixas profundidades. Os sismos indutores dos diques clásticos foram resultado de reativações de falhas pré-cambrianas do embasamento da Bacia do Paraná. Essa relação é observada pelo alinhamento geográfico dos sismitos permotriássicos que corresponde de maneira geral ao traçado ENE da Zona de Cisalhamento Jacutinga. Dentre os afloramentos estudados, os diques de Limeira, os mais próximos a esse traçado, são mais abundantes e possuem maiores espessuras, produtos de maiores volumes de sedimento remobilizados pela fluidificação, provavelmente em função da maior proximidade com a região epicentral dos antigos abalos sísmicos. O campo de esforços sugerido pelas orientações dos diques implicaria numa reativação transcorrente sinistral da Zona de Cisalhemento Jacutinga durante os eventos de sismicidade penecontemporâneos à sedimentação permotriássica da Bacia do Paraná. Essa tectônica, numa quadro mais amplo, possivelmente está relacionada à propagação continente adentro da compressão de direção geral N-S, que ocorreu ao longo da borda sul do Gondwana ao final do Paleozóico, como bem documentado na deformação das rochas sedimentares e sedimentação sin-tectônica do Cinturão do Cabo, na África do Sul, e Serra La Ventana na Argentina. / The current dissertation presents the study of clastic dike swarms of the upper part of the Corumbataí Formation, Permian-Triassic of the Paraná Basin, São Paulo State, Brazil. Three columnar sections were analyzed in road and railroad cuts in the municipalities of Limeira, Batovi and Santa Luzia. A total of 273 measurements of structural attributes of dikes were obtained, grouped by stratigraphic level. Four different stratigraphic levels with clastic dikes were recognized in both the Santa Luzia and Limeira exposures, and three in Batovi. The clastic dikes intrude siltstones and are composed of very fine to silty sandstone, being mostly subvertical and with tabular forms, sometimes with ptigmatic folds caused by latter compaction. The origin of the dikes is related to upward forced injection of fluidized sediment. Observed features supporting this conclusion are upward ramification, drag folds in the host rock, sediment extrusion structures over the upper termination of feeding dikes, host rock intraclasts in the dikes and vertical fabric of the dikes grains oriented parallely to the dike walls. Fluidization of the sand was most likely caused by seismic activity, and therefore the studied dikes are considered as seismites. Other evidence support this interpretation, such as their association with other types of liquefaction features found in the coeval Corumbataí and Pirambóia formations, the broad area of occurrence of the dikes (tens to hundreds of kilometers), the confinement of the dikes to specific stratigraphic levels, and their spatial relationship with tectonic structures of the basement. Despite the great dispersion of dike directions, there are preferential orientations, with strikes varying from NNW to NE and the NNE direction being the most common.Admiting that hydraulic fracturing was the main mechanism of dike generation, the prevailing NNE direction would indicate the maximum horizontal stress during the intrusion, related to a WNW-ESE extensional. The great dispersion of attitudes can be interpreted as the consequence of low diferential stresses during the fracturing and injection of fluidized sediment, which is common in shallow intrusions. The interpreted earthquakes were the result of reactivation of Precambrian basement faults, as indicated by the geographic alignment of the Permian- Triassic seismites following the ENE direction of the Jacutinga Shear Zone. The Limeira dikes, which are the closest to the shear zone, are the most closely spaced and the thickest of all occurrences, indicating the fluidazitin of larger volumes of sediment, probably due to proximity to the epicentral zone of the earthquakes. The stress field interpreted from the dike orientations implies in a left-slip reactivation of the Jacutinga Shear Zone during the Permian-Triassic seismic events in the Paraná Basin. These events are possibly related, in a broader scene, to the far-field propagation of the compressional stresses of N-S direction originated in the southern border of Gondwana in the Late Paleozoic, recorded in the Cape Belt of South Africa and Sierra de Las Ventanas in Argentina.

published_or_final_version / Earth Sciences / Master / Master of Philosophy

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Thesis (Ph. D.)--Duke University, 2007. / Includes bibliographical references.