>Magister Scientiae - MSc / The Platreef, is a contact-type pyroxenitic reef in the Northern Limb of the Bushveld Complex, enriched in platinum group elements (PGE) and base metal sulfides (BMS). Relatively subdued mining in the Platreef, compared to RLS, has been attributed to limited knowledge regarding irregular distribution, complex style and genesis of PGE mineralisation in the Platreef. This study was, therefore, aimed at investigating the petrogenesis of the Platreef, particularly to evaluate whether the formation of the ore reefs resulted from a single or multiple sill-like magma intrusions. The study also sought to unveil the interplay of fractional crystallisation, hydrothermal fluid activities, floor rock and crustal contamination on the formation of Platreef types, PGE mineralisation and the magma source.

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<p>St. Joseph peninsula is situated on the panhandle of Florida west coast in the northeastern Gulf of Mexico at N29°50‘ and W85°20‘ and is located at the west edge of the westernmost portion of the Apalachicola Barrier Island Complex (ABIC) on the Gulf of Mexico shoreline. Three vibra-cores were collected on Saint Joseph Bay side of Cape San Blas which is part of St. Joseph peninsula to determine its evolution in context of previous work by Rink and Lopez (2010). The study uses detailed textural analysis (PSD - Particle Size Distribution plots), multivariate statistics on the PSDs (Q-mode cluster analysis) and organic matter geochemistry (C/N and δ13C). In addition, Ground Penetrating Radar (GPR) profiles are used to provide broader stratigraphic context.</p> <p>The stratigraphic analysis found that CSB has an older nucleus of strandplain deposits dating to >12 Ka that were subsequently flooded and modified through Holocene sea-level rise at ≈ 2.2 Ka. Actual barrier formation began sometime between 2.2. Ka and 0.6 Ka which is the oldest beach ridge measured by Rink and Lopez (2010). Progradation of the barrier on the St Joseph Bay side began at least by 0.3 Ka and likely earlier. There is no evidence to indicate a higher than present sea-level in our core data and our data follows that of other sea-level studies using submerged offshore samples</p> / Master of Science (MSc)

Intraplate volcanism is a worldwide phenomenon producing volcanoes away from active plate boundaries, a process that cannot yet be sufficiently explained by plate tectonic processes, and thus is still a missing piece in the understanding of the dynamics and evolution of our planet. Models for the formation of intraplate volcanism are dominated by mantle plumes, but alternative explanations, such as adiabatic decompression triggered by lithospheric delamination, and edge driven convection (EDC), could be responsible for magmatism. This dissertation explores intraplate volcanic locations that do not fit the mantle plume model, and presents geochemical evidence for lithospheric delamination and edge driven convection for the cause of volcanism. I studied an Eocene volcanic swarm exposed in the Appalachian Valley and Ridge Province of Virginia and West Virginia, which are the youngest known igneous rocks along the Eastern North American Margin (ENAM). These magmas provide the only window into the most recent deep processes contributing to the post-rift evolution of this margin. This study presents the first high precision 40Ar/39Ar ages along with new geochemical data, and radiogenic isotopes that constrain the melting conditions and the timing of emplacement. Modeling of the melting conditions suggests that melting occurred under conditions slightly higher than average mantle beneath mid-ocean ridges. Asthenosphere upwelling related to localized lithospheric delamination is a possible process that can explain the intraplate signature of these magmas that lack evidence of a thermal anomaly. The Virginia-West Virginia region of the ENAM also preserves a second post-rift magmatic event in the Late Jurassic. By studying both the Late Jurassic and Eocene magmatic events we can better understand the post-rift evolution of passive margins. This study presents a comprehensive set of geochemical data that includes new 40Ar/39Ar ages, major and trace-element compositions, and analysis of radiogenic isotopes to further constrain their magmatic history. Modeling suggests that the felsic volcanics from both the Late Jurassic and Eocene events are consistent with fractional crystallization. Lithospheric delamination is the best hypothesis for magmatism in Virginia/West Virginia, due to tectonic instabilities that are remnant from the long-term evolution of this margin, resulting in a 'passive-aggressive' margin that records multiple magmatic events long after rifting ended. Finally, Bermuda is an intraplate volcano that has been historically classified as mantle plume related but evidence to support the plume model is lacking. Instead, geophysics have argued that EDC is the best model to explain Bermuda volcanism. This study presents the first geochemical analysis of Bermuda volcanism, and found that Bermuda was built by two different magmatic processes: melting of carbonated peridotite to produce silica under-saturated, trace element enriched volcanics and melting of an enriched upper mantle component that produced silica saturated volcanics. We attribute the cyclicity of silica under-saturated and silica saturated volcanics to EDC melting. / Ph. D. / Intraplate volcanoes are found away from active plate boundaries and cannot be explained by plate tectonics. Most introductory geology textbooks attribute intraplate volcanism to the mantle plume model, where hot material rises buoyantly through the Earth’s mantle from depths near the core-mantle boundary. The associated volcanoes are then found in a linear track, due to plate motion over the stationary mantle plume. The mantle plume model is valid for some locations, such as Hawaii, but cannot explain all intraplate volcanoes. Other localized models such as lithospheric delamination and edge driven convection are needed to explain intraplate volcanism. Lithospheric delamination is a process where the base of the lithosphere (crust and upper mantle) pulls away from the top of the lithosphere due to density contrasts. The delamination of the base of the lithosphere allows for the warmer asthenosphere (mantle beneath the lithosphere) to upwell and produce melts by decompression. Edge driven convection is a process where temperature differences in thick, cold continental crust and thin, warm oceanic crust creates a localized convecting cell in the mantle. This convecting cell is associated with down-welling beneath the continental crust and upwelling beneath the oceanic crust, and associated volcanism would be found on the oceanic crust. In Virginia-West Virginia there are two pulses of intraplate volcanic activity. Chapter 2 of this dissertation explores the geochemistry of the youngest volcanoes of Eastern North America, which are 48 million years old. Combining the geochemistry with the regional geophysics I proposed that lithospheric delamination is a plausible mechanism for these volcanic rocks. Chapter 3 further examines these volcanoes and adds a second pulse of magmatism that occurred 152 million years ago. Lithospheric delamination can also explain the 152 million year old volcanics. Bermuda is an extinct volcanic island found in the Atlantic Ocean, and has been historically explain by the mantle plume model. However, there has been no geochemical data to support the mantle plume model and the geophysical evidence supports edge driven convection. I present the first geochemical analysis of Bermuda’s volcanic pedestal and find that edge driven convection is a more plausible mechanism to account for volcanism.

Climate change is predicted to be the most pronounced in high latitude ecosystems, however very little is known about their vulnerability to the projected warmer temperatures. In particular, natural organic matter (NOM) in the high latitude cryosphere which includes dissolved organic matter (DOM) and cryoconite organic matter (COM) from glaciers and soil organic matter (SOM) in permafrost, is highly susceptible to climate change which may lead to severe consequences on both local and global carbon biogeochemical cycles. Examination of DOM in glacier ice by a novel 1H nuclear magnetic resonance (NMR) water suppression pulse sequence at its natural abundance revealed and quantified the composition and the organic constituents in ice samples from Antarctica. 1H NMR spectra of samples from several glaciers were acquired and compared to the dominant fluorescent DOM fraction. This comprehensive approach showed that glacier ice DOM was mainly composed of small, labile biomolecules associated with microbes. Examination of the organic debris found on glacier surfaces (COM) from both Arctic and Antarctic glaciers were determined to be derived from microbes. Samples from Arctic glaciers were more chemically heterogeneous with small inputs of plant-derived material detected after targeted extractions. Therefore the COM carbon composition was determined to be dependent on the local glacier environment, suggesting a site specific contribution to the carbon cycle. Finally, the distribution of extracted branched glycerol dialkyl glycerol tetraether (GDGT)microbial membrane lipids and the deuterium incorporation of plant-wax n-alkane biomarkers extracted from dated permafrost SOM (paleosols) were independently applied for Canadian Arctic climate reconstruction during the last glacial maximum. Overall, the branched GDGT based temperature reconstructions from the Arctic paleosols reconstruct higher temperatures, likely when bacterial activity was optimal. The deuterium composition of the C29 n-alkane plant lipids appears to integrate an average annual signal. Further analysis by both non-selective NMR spectroscopic and targeted biomarker techniques on these paleosol samples revealed that the major vegetative sources from this paleoecosystem originated from woody and non-woody angiosperms. This thesis demonstrates several novel analytical characterization techniques, along with the major sources and composition of NOM in the cryosphere while demonstrating its use in paleoclimate applications.

Climate change is predicted to be the most pronounced in high latitude ecosystems, however very little is known about their vulnerability to the projected warmer temperatures. In particular, natural organic matter (NOM) in the high latitude cryosphere which includes dissolved organic matter (DOM) and cryoconite organic matter (COM) from glaciers and soil organic matter (SOM) in permafrost, is highly susceptible to climate change which may lead to severe consequences on both local and global carbon biogeochemical cycles. Examination of DOM in glacier ice by a novel 1H nuclear magnetic resonance (NMR) water suppression pulse sequence at its natural abundance revealed and quantified the composition and the organic constituents in ice samples from Antarctica. 1H NMR spectra of samples from several glaciers were acquired and compared to the dominant fluorescent DOM fraction. This comprehensive approach showed that glacier ice DOM was mainly composed of small, labile biomolecules associated with microbes. Examination of the organic debris found on glacier surfaces (COM) from both Arctic and Antarctic glaciers were determined to be derived from microbes. Samples from Arctic glaciers were more chemically heterogeneous with small inputs of plant-derived material detected after targeted extractions. Therefore the COM carbon composition was determined to be dependent on the local glacier environment, suggesting a site specific contribution to the carbon cycle. Finally, the distribution of extracted branched glycerol dialkyl glycerol tetraether (GDGT)microbial membrane lipids and the deuterium incorporation of plant-wax n-alkane biomarkers extracted from dated permafrost SOM (paleosols) were independently applied for Canadian Arctic climate reconstruction during the last glacial maximum. Overall, the branched GDGT based temperature reconstructions from the Arctic paleosols reconstruct higher temperatures, likely when bacterial activity was optimal. The deuterium composition of the C29 n-alkane plant lipids appears to integrate an average annual signal. Further analysis by both non-selective NMR spectroscopic and targeted biomarker techniques on these paleosol samples revealed that the major vegetative sources from this paleoecosystem originated from woody and non-woody angiosperms. This thesis demonstrates several novel analytical characterization techniques, along with the major sources and composition of NOM in the cryosphere while demonstrating its use in paleoclimate applications.

New and existing U–Pb and 40Ar/39Ar geochronological data, and oxygen and hydrogen stable isotope data, are combined with structural and metamorphic data from Thor–Odin, the southern culmination of the Monashee Complex. This leads to a new interpretation of the timing of deformation and metamorphism. Amphibolites in Thor–Odin with hornblende 40Ar/39Ar dates between ~75–70 and ~51 Ma experienced more 18O- and D-depletion than amphibolites with older dates. The younger dates that were previously interpreted as cooling ages, may have resulted from complete or partial Ar loss in the presence of meteoric fluids that were introduced into the rock during extension. <br><br> Monazite crystals in pelitic schist, quartzite and orthogneiss, which have U–Pb ages younger than 40Ar/39Ar hornblende ages in amphibolite in northwest Thor–Odin, may have grown during tension in the presence of fluids. Titanite, xenotime and zircon dates may be interpreted in the same way. Thus, the U–Pb dates that were previously interpreted as representing peak of metamorphism and the hornblende 40Ar/39Ar dates that were previously interpreted as representing cooling ages, may be interpreted as reflecting meteoric fluid penetration of the crust during regional extension. This implies that the age of the thermal peak of metamorphism is older than ~75–70 Ma. Migmatisation in a basement orthogneiss in Thor–Odin occurred at ~1.8 Ga. Dissolution rims are preserved in zircon between ~1.8 Ga domains and 52 Ma overgrowths. Because growth of new zircon (and possibly other U–Pb accessory phases) did not take place, any geological event that occurred during the ~1.8 Ga to 52 Ma time interval is not recorded. Cordilleran deformation and metamorphism may have taken place within that time interval, e.g. in the Middle Jurassic and/or mid- to Late Cretaceous, the time of Cordilleran deformation and metamorphism in the rocks overlying the Monashee Complex. <br><br> The Joss Mountain orthogneiss, west of the Monashee Complex in the Selkirk Allochthon, is dated at 362 +/– 13 Ma. F3 folding in pelitic schist at Joss Mountain is constrained between ~73 and ~70 Ma. Existing structural, metamorphic and geochronological data in, and close to, the Shuswap Metamorphic Complex in the southern Canadian Cordillera are shown to be consistent with a channel flow model.

Les thérapsides se diversifient au cours du Permien et du Trias partout à la surface de la Pangée mais sans être épargné par la crise de la fin du Permien, extinction de masse la plus meurtrière de tous les temps. Ils représentent un groupe de transition entre les reptiles permiens et les premiers mammifères et sont le centre de plusieurs questions lié aux différences entre ces deux grands groupes. Cette thèse s'intéresse à la question de l'apparition et du développement de l'endothermie dans ce groupe, ainsi que les conditions environnementales présentes à cette époque. Pour répondre à ces questions, plusieurs espèces, provenant des grands groupes de vertébrés de l'époque (thérapsides, diapsides, parareptiles, stéréospondyles et dipneustes) ont été analysés pour leurs compositions en isotopes de l'oxygène et du carbone.Ces données ont permis de montrer que l'endothermie serait apparu au moins dans le groupe des Kannemeyeriiformes + Lystrosauridae ainsi que dans le groupe des Eucynodontia, deux lignés de thérapsides, la seconde ayant donnée les mammifères actuels. Temporellement, ces deux mises en place de l'endothermie se sont produites dans un intervalle de temps autour de la limite Permo-Trias, certainement avant celle-ci pour le groupe Kannemeyeriiformes + Lystrosauridae. Ce qu'il se passe climatiquement à cette période a été déterminé avec des espèces provenant exclusivement du bassin du Karoo en Afrique du Sud. D'après les résultats, à la fois les variations des isotopes de l'oxygène et du carbone se corrèlent avec celles observées dans le milieu marin et les valeurs obtenues à partir de matériel continental est tout autant pertinent à utiliser que celles provenant de matériel marin.Ces données appuient l'hypothèse d'un intense réchauffement et le quantifient à environ +16 °C au moment de la crise puis continua d'augmenter pendant le Trias Inférieur.Bien que les données ne permettent pas de le prouver, il est possible que l'endothermie ait permis à ces groupes de survivre ces variations de températures et de pouvoir se rediversifier par la suite / Therapsids diversified during the Permian and the Triassic all around the world on the supercontinent, Pangea, where they were not spared by the end-Permian crisis, the most destructive mass extinction of all time. The represent a transitional group between the Permian reptiles and the first mammals, and therefore are in the middle of several questions link to the difference between those two groups. This thesis focuses on the question of the emergence and development of the endothermy within this group, and the climate conditions of this period. To answer those questions, several species from the different groups of vertebrates (therapsids, diapsids, parareptiles, stereosponyls and lungfish) have been analyzed for their oxygen and carbon isotopes compositions.Such data showed that the endothermy seemed to appear within the group of Kannemeyeriiformes + Lystrosauridae as well as the Eucynodontia group, two therapsids groups with the latter being the ancestors of the extant mammals. Those two emergences of the endothermy occurred within a small timespan around the Permo-Triassic boundary, much more certainly before for the Kannemeyeriiformes + Lystrosauridae. What happened during this short period has been estimated with species from the Karoo Basin in South Africa only.According to the results, both variations in oxygen and carbon isotopes fit with those observed in marine data and therefore, values from continental material can be used, same as marine material.Those data support the hypothesis of an intense warming and quantify it to +16 °C during the end-Permian crisis and continue to increase during the Lower Permian.Even if the data don’t allow proving it, it is possible that the endothermy made those groups able to survive through such temperature variations and to diversify after

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