Please read the abstract in the thesis. / Thesis (PhD)--University of Pretoria,1969. / gm2015 / Plant Production and Soil Science / PhD / Unrestricted

Orientador: Elson Paiva de Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências / Made available in DSpace on 2018-08-18T13:34:45Z (GMT). No. of bitstreams: 1 Piaia_Patricia_M.pdf: 22497674 bytes, checksum: ca688c1a7bfc4bf7fbbbc2fe2a92815e (MD5) Previous issue date: 2011 / Resumo: Complexos máfico-ultramáficos são comuns em faixas orogênicas e podem representar diferentes ambientes tectônicos, tais como raízes de arco, restos obductados de ofiolitos, platôs oceânicos, lascas do manto litosférico ou ainda ramos abortados de riftes. Características de campo, petrográficas, de química mineral e litogeoquímicas são importantes no intuito de diferenciar o ambiente de formação desses corpos. O orógeno Itabuna-Salvador-Curaçá corresponde a uma das faixas precambrianas do Brasil consolidada durante o Paleoproterozóico. Ele hospeda diversos complexos máficos-ultramáficos cuja compreensão petrogenética é dificultada por suas rochas muitas vezes se encontrarem metamorfisadas em fácies granulito. Um desses complexos é a Suíte metamórfica gabro-anortosítica São José do Jacuípe que compreende um conjunto de rochas cumuláticas estratificadas, formado por metaanortositos, meta-leucogabros, meta-leuconoritos, meta-gabros e meta-gabronoritos, com meta-piroxenitos subordinados. As rochas da suíte possuem características litogeoquímicas e de química mineral semelhantes ao magmatismo máfico de arco e foram interpretadas como pertencentes a um remanescente de arco, podendo representar um fragmento da raiz máfica de arco magmático que, no caso do cinturão Salvador-Curaçá, seria o Complexo Caraíba. Outros complexos máfico-ultramáficos que se destacam na região são os enxames de diques máficos que ocorrem em abundância na porção norte do Orógeno Itabuna-Salvador-Curaçá. Um deles é o enxame de diques máficos Aroeira, que ocorre na porção central e mais deformada do orógeno, cujas rochas de composição gabronorítica muitas vezes são confundidas com as rochas pertencentes à Suíte São José do Jacuípe. O enxame intrudiu a crosta continental, possui caráter tholeiítico e subalcalino, sendo que suas rochas possuem afinidade com magmas basálticos. Modelagem geoquímica indica que o derrame se formou provavelmente a partir de baixas taxas de fusão de uma fonte mantélica pobre em granada e, a partir de então, evoluiu por processos de cristalização fracionada - cujos principais minerais a cristalizarem foram plagioclásio, olivina e piroxênio - seguida de contaminação crustal. No que se refere aos aspectos petrográficos e litogeoquímicos, as rochas da Suíte São José do Jacuípe e do enxame de diques máficos Aroeira são muito semelhantes e de difícil diferenciação. No entanto aspectos macroscópicos das rochas pertencentes aos diques como presença de fenocristais, falta de outros litotipos associados, diferenças de granulação e no grau metamórfico entre diques, além das próprias relações de contato com as encaixantes, permitem separá-los dos meta-gabronoritos pertencentes à Suíte São José do Jacuípe / Abstract: Mafic and ultramafic complex are commons in orogenics belts and can represent differents tectonics environments like arcs roots, obducted parts of ophiolites, oceanic plateaus, litospheric mantle wedge or an aborted rift. Field, petrographic, mineral chemistry and litogeochemistry characteristics are important to characterize the formation environment. The Itabuna-Salvador-Curaçá belt is one of the Precambrian belts consolidated during the Paleoproterozoic. This belt hosts a lot of mafic and ultramafic bodies and the petrogenesis understanding of these bodies is difficult because they are often metamorphosed in granulite facies. The São José do Jacuípe metamorphic gabbro-anorthositic suit is one of these bodies. It's a conjunct of stratified cumulatic rocks constituted by metaanorthosites, meta-leucogabbros, meta-leuconorites, meta-gabbros and meta-gabbronorites with associated metapyroxenite. These rocks have lithogeochemistry and mineral chemistry characteristics similar to arc mafic magmatism. They are being interpreted as a remaining of a mafic root of a magmatic arc and, in case of Itabuna- Salvador Curaçá belt, this arc probably is represented by the Caraíba Complex. Others complex that stand out in this region are the mafic dykes swarms. They are abundant in the north part of the Itabuna-Salvador-Curaçá belt. One of them is Aroeira swarm that occurs in the central and more deformed part of the belt. Their rocks have a gabbronoritic composition and sometimes are confounded with São José do Jacuípe's rocks. The swarm intruded a continental crust, has a tholeitic and sub-alcaline character and affinity with basaltics magmas. Geochemistry modeling shows this magma was formed from low rates of melt of a mantle font poor in garnet and then, evolved by fractional crystallization and crustal contamination. The main minerals that crystallize were plagioclase, olivine and pyroxene. São José do Jacuípe and Aroeira's rock are petrographically and lithgeochemically similar and difficult to differentiate. However, characteristics of dyke's rocks like presence of phenocrysts, absence of any other litho type associated, differences of granulation and of the metamorphic degree between dykes and the relations of contact with the other rocks allow differentiate them of the meta-gabbonorites of São José do Jacuípe suite / Mestrado / Geologia e Recursos Naturais / Mestre em Geociências

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2014. / Intermediate-depth earthquakes occur at depths of 60 – 300 km at these depths high confining pressure inhibits brittle failure from generating earthquakes. Fault-related pseudotachylytes from Corsica are exhumed paleofaults from a high pressure, low temperature subduction zone environment, and are considered analogues of intermediate-depth earthquakes. Hence, it is important to analyse the physico-chemical processes by which these pseudotachylytes form in order to gain primary insight into the controls of their formation and how this seemingly paradoxical process takes place. Up until the recent discovery of high pressure pseudotachylytes there was no known direct method of evaluating the formation mechanisms of intermediate-depth earthquakes. High pressure pseudotachylytes found in subduction complexes are regarded as relict paleo-earthquakes. Previous research aimed at understanding the generation of these phenomena and the role of fluids on their origin has been based on seismic, experimental and numerical modelling. The principal aims of this project were to carry out detailed geochemical, petrographic and microtextural analyses of such pseudotachylytes located in the Eocene Schistes Lustres Complex, Corsica, and to determine whether the data from natural samples corroborate current models. The pseudotachylytes in this study reside in peridotitic and metagabbroic lozenges enclosed within serpentinites. Pseudotachylytes are notoriously complex and messy, with compositions that vary widely over small distances (< 1 mm). For this reason the pseudotachylytes in this study were systematically analysed from the outcropscale to the micron-scale according to their wallrock type. From these data it was observed that greenschist and blueschist facies hydrous minerals present in the peridotite and metagabbro wallrocks were entrained into pseudotachylyte fault veins. Back scatter electron (BSE) imaging shows that these hydrous minerals underwent wholesale fusion in the melt. No evidence for prograde dehydration reactions was observed in the wallrocks or in association with the pseudotachylytes. Electron microprobe analyses (EPMA) of the bulk matrix of the pseudotachylytes revealed variable H2O content, 0 – 14 wt % in peridotite-pseudotachylytes and 0 – 4 wt % in metagabbro-hosted pseudotachylytes. The principal minerals that underwent fusion are: clinopyroxene, plagioclase, glaucophane, Mg-hornblende and actinolite (metagabbro- hosted) pseudotachylyte), and olivine, orthopyroxene clinopryroxene, chlorite, serpentine and tremolite (peridotite-hosted pseudotachylyte). The bulk of H2O entering the melt remained in solution until it reached supersaturation, upon which it exsolved to form fluid-rich, vesicular veins. Cuspate and lobate rims of microlites (omphacite, clinopyroxene, olivine and orthopyroxene) along the boundaries of hydrous veins indicate that the melt was still molten when the fluids exsolved. The presence of hydrous fluids in the melt appears to have enhanced the fracturing process. Fault veins hosted by peridotite that have the greatest H2O content are the thickest, have more chaotic injection networks and exhibit more cataclastic deformation features than the anhydrous fault veins observed. With regard to the mechanism of pseudotachylyte generation, it is clear that water present in hydrous minerals or entrapped in the crystal lattices of anhydrous minerals plays a fundamental role in facilitating intermediate-depth earthquakes through hydrolytic weakening. A melt richer in hydrous fluid also has a lower viscosity, facilitating fault slip. Dissolved H2O is also a flux and may enhance further melting of the wallrock, relative to an anhydrous pseudotachylyte vein. Sheared, kinked and twinned wallrock minerals and survivor clasts associated with the pseudotachylyte fault veins indicate crystal-plastic deformation. No significant grain size reduction was observed in proximity to fault veins. The grain size of wallrock minerals at fault vein boundaries ranges from 5 – 20 mm. From this it was inferred that the mechanism of deformation is controlled by power law creep, temperature and high strain rate. The presence of metastable high temperature crystallisation products in the pseudotachylyte such as hoppers and dendrites of olivine, orthopyroxene and diopside (in peridotite) and Al-rich omphacite and Fe-rich anorthite (in metagabbro), are suggestive of a short-lived high temperature event resulting from thermal instability. These high temperature mineral assemblages are overprinted by ones indicating a return to ambient conditions (lower temperatures, but still high pressures), namely, glaucophane, albite and epidote (in metagabbro) and clinochore, fine-grained granoblastic olivine, enstatite and diopside (in peridotite). The observations from this detailed study of natural samples suggest that intermediate-depth seismicity may be generated by a thermal runaway process.

<p> The Rio Grande Rift is a major tectonomagmatic feature of the North American craton. Physiographically, the present rift is recognized as a series of grabens and half-grabens which extend for over 1000 km from south-central Colorado into Chihuahua, Mexico. Rift structures, however, are recognized as far north as the Colorado-Wyoming border. Basaltic magmatism within the rift began by 30 Ma in southern New Mexico, and by 25 Ma in northern New Mexico and Colorado. Within-rift magmatism is low in volume in comparison to rift-related activity on the rift shoulders and flanks. </p> <p> Petrologic studies of Rio Grande Rift-related volcanics are numerous, yet focus primarily on suites erupted in north-central New Mexico and Colorado. However, recently published abstracts suggest areas of southern New Mexico are receiving much needed attention. Initial attempts at characterizing the petrologic diversity and mantle sources of rift-related volcanics have concentrated on major and trace element data, as well as the application of Sr and Nd isotopes. Only minor attention has been given to Pb isotope variations. </p> <p> This thesis contains the most recent compilation of Pb isotope data for volcanic rocks erupted within the Rio Grande Rift region. The oldest rocks included in this work are· monzonite stocks erupted c. 60 Ma within the Colorado Mineral Belt. Using Pb isotope data in combination with trace element variations and Sr-Nd isotopes, a model is developed which suggests the stocks were initially derived from mantle sources with geochemical properties similar to those which produced rift-related basaltic volcanics in northwest Colorado beginning at 25 Ma. </p> <p> Two chapters of the thesis are devoted to exploring the utility of Pb isotopes as tracers of crustal influence in continental basaltic volcanism. One deals specifically with documenting Pb isotope variations in the northwest Colorado region, whereas the second focuses on variations in the Espanola Basin of north-central New Mexico. Major results of the northwest Colorado study 1) suggest that the asthenosphere contributed to early rift (25 Ma volcanism), 2) better characterize the geochemical signature of lithospheric and asthenospheric sources during periods of active volcanism, and 3) confirm earlier suspicions regarding the effects of crustal contamination in several rock suites. Work on basaltic components of volcanism in the Espanola Basin indicate that crustal contamination was also an important process in producing the observed Pb and Sr isotopic variations in both early and later rift lavas. </p> <p> The remaining chapter of the thesis is a synthesis of all available rift data, from northern Colorado to southern New Mexico. An analysis of changes in the Pb isotopic corn position of the lithosphere with latitude is presented, as well as a cross-rift transect of the central rift region. Further, a model which combines previously published ideas on the tectonomagmatic development of the Rio Grande Rift and the Basin and Range province is proposed. The most important results of the combined model are the proposition that rifting began earlier than previously thought, and that the timing of extension and magmatism in the Rio Grande Rift is very similar to that of the Basin and Range province. Additional data from the rift, particularly the southern region, will help to confirm or deny this model. </p> / Thesis / Doctor of Philosophy (PhD)

published_or_final_version / abstract / toc / Earth Sciences / Master / Master of Philosophy

No description available.

Thesis (M.S.)--University of Tennessee, Knoxville, 2010. / Title from title page screen (viewed on July 20, 2010). Thesis advisor: Robert D. Hatcher, Jr. Vita. Includes bibliographical references.

No description available.

Thesis (DSc (Geology))--Stellenbosch University, 1948. / 375 leaves printed on single pages, preliminary pages and numbered pages1-312. Includes bibliography, figures and photos. / Digitized at 330 dpi color PDF format (OCR), using KODAK i 1220 PLUS scanner.

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy