Thesis (M. Sc. (Geology))--Rhodes University, 2006.

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.

Apart from the concentrations of chromite in layers within the Great Dyke and other ultramafic complexes, chromite also occurs as interstitial grains throughout the olivine-bearing rock-types. These olivine-bearing rocks include no rites, gabbros, dunites and pyroxenites. Chromite concentration in these rocks varies from 0.48 to 3.09 per cent of the rock, usually in the form of chromite (Ahrens, 1965; Worst, 1960). A small fraction of this chromite settled to form chromitite layers whilst the remainder is retained within the rock mass as finely disseminated chromite and chromite interstitial to olivine. This retained chromite is much finer grained than layer chromite and is the primary source of eluvial chromite (Cotterill, 1981). During weathering of the serpentine rock and transportation by rainwater, the heavier chromite and magnetite grains are re-deposited along watercourses and vleis or valleys as the speed of the water is retarded sufficiently for the heavier particles to settle. The lighter serpentine material is removed and the chromite concentration in the soil is increased, thus resulting in eluvial chromite (Keech et ai, 1961; Worst, 1960; Prendergast, 1978). The concentration of chromite particles in soil can be up to 15 (or more) Cr₂O₃ %, resulting in economic and exploitable deposits, located primarily along the Great Dyke fiacks. A preliminary evaluation of the eluvials indicate that the Great Dyke could be host to up to 10 million tonnes of potential chromite concentrates which could be processed from such eluvial concentrates. These chromite-rich soils can be mined more cheaply than the traditional seams mining and processed into chromite concentrates through simple mechanical processing techniques of spirals, jigs and heavy media separators. The resultant chromite concentrates are of high quality and can be used to manufacture chromite ore briquettes, which are an alternative to lumpy chromite smelter feed. The main challenges to eluvial mining are the inevitable environmental degradation and coming up with methods that could possibly mitigate against such environmental damage. The distribution of these eluvials over vast plains as thin soil horizons, necessitate use of mobile concentrator plants and hence establishment of extensive infrastructure. These challenges, however, are not insurmountable and test mining and previous production runs have proved profitable. The eluvials are also associated with some lateritic nickel concentrations. The nickel occurs in close association with some oxide such as goethite and garnierite and is associated with iron-manganiferous soil pisolites. The analyses of these pisolites indicate high nickel grades of generally above 1.00 %Ni. Such high nickel-content of Great Dyke laterites warrant, further investigations.

Permanent brittle deformation of rocks of the upper crust is often manifested in the growth of fractures, or sliding along fractures, which may subsequently be intruded by magma and other fluids. The brittle deformation structures described here include faults, joints and dykes. Brittle deformation structures along passive continental margins result from continental fragmentation and related uplift, as is seen around the southern African margins in response to Gondwana break-up. In many cases the fragmentation is accompanied by significant magmatic events, for example the Cretaceous mafic dyke swarms that form major components of the South Atlantic Large Igneous Province (LIP) and originated during the break-up of West Gondwana (Africa and South America). The magmatic events accompanying the break-up of Gondwana resulted in crustal extension and the formation of joint systems and dyke swarms that exhibit distinct geometric features that appear to display fractal patterns. This work analyses the relationship between the Henties Bay-Outjo Dyke Swarm (HOD) on the west coast of Namibia, and the Ponta Grossa Dyke Swarm (PG) on the coast of Brazil, both of which formed ca. ~130 Ma, to test for their co-linearity and fractal geometry before and during West Gondwana break-up. This was achieved by reconstructing Gondwana‘s plates that contained the PG and HOD swarms, using ArcGIS and Gplates software. The dyke analyses was complemented with a comparative study of joints of the Table Mountain Group quartzites (TMG, ca. 400 Ma) in the Western Cape Province and Golden Valley Sill (GVS, ca. 180 Ma) in the Eastern Cape Province, to compare their fractal patterns and possible relationship. Mapping of joints was carried out in the field with the use of a compass and GPS. The HOD trend is positioned largely NNE > NE, but a NW dyke trend is also common. The dominant joints in the TMG trend NNW > WSW and the GVS joints trend WNW > NNE and others. The GVS and HOD orientations appear strongly correlated, while TMG shows no simple orientation correlation with GVS and HOD. The lack of correlation is attributed to the TMG‘s formation in different host-rocks with variable anisotropy and/or the presence of different mechanical processes acting at a different time in geological history. All mapped dykes and joints were analysed to test for fractal geometry. The fractal dimension results of about 18605 HOD dykes from microscopic to mega scale (0.1 mm – 100 km) shows fractal patterns that range between Df = 1.1 to 1.9; and the fractal dimension of about 1716 joints in the TMG and about 1026 joints in the GVS at all scales range between ca. Df = 1.6 to 1.9. The similarity of the fractal patterns indicates that joints and dykes may have formed in response to similar tectonic stress events; and similar orientations may indicate that joints pre-dated the dyke intrusions. However, the data also indicate that dykes are not always related to pre-existing joints.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1971. / Vita. / Includes bibliograpies. / Ph.D.

No description available.

<p> Samples from two granitic offshoot dikes from the Murray granite, and from the Murray granite itself were analysed for eight major elements using X-Ray Fluorescence, to determine whether or not the dikes represented remobilized parts of the Murray granite and as such could have a different chemical composition from the parent material.</p> <p> The analyses show that only very minor chemical differences exist between the two granitic dikes and the main Murray granite. However four samples of the dike rocks appear to show element exchange with the Sudbury norite surrounding them, resulting in increased Na2O and CaO contents and lower K2O contents, resulting in increased amounts of albitic plagioclase.</p> / Thesis / Bachelor of Science (BSc)

No description available.

No description available.

The East Traverse Mountains are an E-W trending mountain range dividing Utah and Salt Lake valleys in northern Utah. Geologically perplexing, the nature of the East Traverse Mountains has been under investigation for 140 years. Previously, the mountain range was proposed to be a dismembered but still coherent down-faulted block that experienced 4 km of post-thrusting extension within the Charleston-Nebo thrust sheet. However, new insight on the origin of the East Traverse Mountains indicate that it is a mega landslide, roughly ~100 km3 in size, which catastrophically slid from the upper reaches of the Little-Cottonwood stock to its present-day location. The primary evidence for this landslide includes two unusual dike swarms whose roots are in the Wasatch Range and whose upper reaches are now in the East Traverse Mountains, 16 km to the SW. A swarm of pebble dikes, indicative of porphyry mineralization is found at the center of the East Traverse Mountains and contain pebbles of Little-Cottonwood stock as well as two other intrusions found at the center of a mineralized zone. These granitic clasts have phyllic alteration, contain molybdenite grains and are sourced from a subeconomic molybdenum-copper porphyry deposit located 16 km to the NE. The other dike swarm occurs on the SE corner of the range near Alpine, Utah, which contains various andesitic and phaneritic dikes of intermediate-felsic compositions (56-69 wt.% SiO2) with localized marble on their southern margin. These dikes range in U-Pb ages from 36-29 Ma. Moreover, other evidence includes brecciation of the entire mountain range as well as along the slide path of this landslide. Breccia, as well as pseudotachylyte and cataclasite have been discovered that formed in the rapid transportation of the 1-2 km thick detached block. Devitrified pseudotachylyte veins range in thickness from 1 cm to 1 m and are present in the roof zone of the pluton. Sixteen kilometers of sliding caused 70-80% of the Oquirrh Group rocks of the East Traverse Mountains to be fractured to less than 1-inch diameter clasts in breccias and broken formations, as documented by 16 years of mining. U-bearing opal replaced significant areas of brecciated volcanic rocks when hot water seeped into highly-fractured, argillically altered rock. U-Pb ages of 6.1 ± 0.9 Ma from these opalite areas could provide a minimum age for the emplacement of the mountain block. Underlying the East Traverse Mountains slide block is a layer of fallout tuff deposited in the Jordan River Narrows member with 40Ar/39Ar ages of 6.62 ± 0.07 Ma which provides a maximum age of emplacement. Therefore, we propose that the East Traverse Mountains mega-landslide occurred between 6.1 ± 0.9 Ma and 6.62 ± 0.07 Ma. Our interpretation for the East Traverse Mountains mega-landslide model builds upon previous research and data, with the addition of these recent findings. This new interpretation is crucial for understanding the potential for large normal fault systems to create significant landslide hazards.