D.Phil. (Geology) / A specific geological event has been characterized with the aid of an integrated metamorphic and fluid inclusion study of data obtained from syn-tectonic vein-quartz associated with thrusting and bedding-parallel shear along the northern margin of the Witwatersrand Basin. The vein-quartz associated with this event occurs as boudin-shaped bodies with their long and intermediate axes orientated within the foliation-, bedding- or fault-planes. The length of the quartz lenses which are spatially confined to shear zones often exceeds the thickness of the shear zones. These phenomena and the fact that quartz-fibres are orientated parallel to and not at right angles to the foliation confirms the syn-tectonic nature of the quartz veins. Heterogeneous P-T condition is indicative of imbrication, i.e. crustal thickening which is also substantiated by the random growth of pyrophylite and kyanite in shear zone assemblages, indicating that metamorphism outlasted deformation. Metamorphic studies of aluminous schists and vein-quartz with pyrophylliteand pyrophyllite - kyanite selvages established the development of two critical mineral assemblages: 1 Kaolinite + 2 Quartz = 1 Pyrophyllite + 1 H20 ... (1) and at higher P-T conditions 1 Pyrophyllite = 1 Kyanite + 3 Quartz + 1 H20 ... (2). The schists and quartz vein assemblages are quartz-oversaturated in contrast to the study material of Wallmach and Meyer (1990) which is quartz-undersaturated. Peak metamorphic conditions, therefore, are closely constrained by the position of the reaction curve (2) in P-T space, as is also substantiated by the presence of coexisting kyanite and pyrophyllite which are closely associated with syn-tectonic vein-quartz at the Florida Lake, Monarch Shaft and Krugersdorp localities. The nature of and circumstances under which the equilibrium aSsemblage pyrophyllite + kyanite + quartz has formed support an univariant situation, i.e. this assemblage can only coexist along the pyrophyllite kyanite isograd. The mineral assemblages that equilibrated during peak metamorphism are still present in the rocks of the shear zones, and show only incipient rehydration. The quartz-oversaturated nature of the rocks in the shear zones and the fact that kyanite formation is ascribed to reaction (2), cannot explain the abundance of quartz veins. Accordingly it is concluded that there must have been an external source from which Si02 was imported into shear zone to give rise to the formation of the large quantities of vein-quartz.

Fluid inclusions of pegmatites from two localities in the Moldanubina Zone were studied in order to constrain PT conditions of their crystallization and establish composition and properties of fluids associated with pegmatite formation. The first locality is Vepice near Tábor, second locality is Vlastějovice near Zruč nad Sázavou. Pegmatit of Vepice consists of irregular pockets in amphibole- biotic granite dark type to a porphyric syenodioritot Čertova břemene. Fluid inclusions have been studied in several cm large quartz crystals of miarolic cavities from the central zone pegmatites pockets within the central zone of the pegmatite pockets. The collected fluids are aqueous- type with a low salt content (usually in the range of 4-6 hm% NaClekv. Pegmatites in Vepice among the complex Y-REE-Nb-Ta-Ti pegmatites. In terms of PT conditions pegmatites belong to the classification of rare element pegmatite or miarolitic's pegmatites. The studied sample of Vlastějovice (skarn's body) represented a transition from quartz-feldspar pegmatite lithium zone to zone with predominance of quartz (quartz core). Only one sample was studied, which originated from the historical collections F. Čech (Čech, 1985). The sample is an exceptional presence of large quantities of the solid phase (up to 4-5 stages). Using Raman...

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Les réseaux hydrographiques sont les principaux vecteurs de l'érosion des reliefs et de transport des sédiments jusqu'aux bassins. Leur développement, contraint par la tectonique et le climat, est au coeur des recherches sur l'évolution des chaînes de montagnes. Or, la dynamique et la stabilité des réseaux de drainage dans les bassins d'avant-pays, soumis à la subsidence flexurale et à la tectonique locale, restent mal connus. Cette étude s'intéresse à la formation et la dynamique érosive du réseau de drainage du bassin d'avant-pays du SE de la France en lien avec l'exhumation des Alpes occidentales à l'Eocène-Miocène basal (45-20 Ma). Les résultats sédimentologiques et structuraux montrent que ce réseau a été formé précocement au cours de la subsidence du bassin à la faveur de la tectonique compressive régionale. Les sédiments Eocènes déposés dans les paléo-vallées reflètent d'abord un réseau local. A l'Oligocène, l'exhumation des Alpes induit l'extension du réseau jusqu'aux massifs internes alors en érosion. Les galets exotiques déposés dans le bassin contiennent des fractures dévoilant une circulation complexe d'eau (probablement météorique) dans les Alpes. L'étude géochimique des inclusions fluides indique que cette eau a été piégée dans ces veines sous environ 2 km de roches, suggérant l'altitude des reliefs alpins à l'Oligocène. Aujourd'hui, le réseau hydrographique réemprunte en partie les vallées Miocènes, indiquant une relative stabilité de sa géométrie depuis 25 Ma, malgré une activité tectonique constante. Ces résultats peuvent servir de contrainte aux modèles d'évolution des réseaux hydrographiques dans les bassins à différentes échelles spatio-temporelles / Drainage networks represent the main vectors of erosion of topographies and transport of sediments toward the basins. Their development is constrained by both tectonics and climate, and thus represents the focus of research of mountain belt evolution. However, in foreland basins, the drainage network dynamics and stability are still not well understood due to the overlapping effect of local tectonic activity on the flexural subsidence. This study focus on the formation and on the erosive dynamics of the drainage network in the French South Alpine Foreland Basin that is related to the Western Alps exhumation during the Eocene-early Miocene (45-20 Ma). Combined sedimentological and structural results show that the drainage network has been tectonically-formed during the early stage of subsidence of the basin due to the regional compressional stress. Primarily, the Eocene sediments deposited in the palaeovalleys highlight a local network. During the Oligocene, the Alps exhumation induces the development of the network to the internal massifs that are then eroded. Some exotic pebbles deposited in the basin contain veins that evidence for a complex water circulation (probably meteoric water) within the Alps. The geochemical study of fluid inclusions indicates that the water has been trapped under about 2 km of rocks suggesting the altitude of the alpine reliefs at the Oligocene. Despite a constant tectonic activity, the modern drainage network partially uses the Miocene palaeovalleys that suggest a geometrical stability since about 25 Ma. These results can serve to constrain the various models of drainage network evolution in basins at different space and time scales

Les circulations de fluides aux interfaces entres les socles cristallins et leur couvertures sédimentaires sont des événements majeurs de transferts élémentaires dans la croûte. Dans de nombreux contextes, des fluides de bassins peuvent pénétrer dans les socles de faible perméabilité, interagir avec eux, y lessiver des métaux, et donner lieu à des concentrations métalliques, notamment en Pb, Zn, Cu, Ag et U. Les gisements d’uranium de type discordance du bassin d’âge protérozoïque de l’Athabasca (Canada), sont des témoins essentiels de ce type de circulations de fluides, et sont des objets modèles pour comprendre les mécanismes et les conséquences de tels événements. Les inclusions fluides permettent d’échantillonner et d’analyser directement les paléofluides. Malgré les difficultés d’analyse, ces objets de taille micrométriques apportent des informations importantes sur les propriétés des fluides. Les techniques d’analyse disponibles (microthermométrie, LA-ICP-MS, écrasement-lessivage, écrasement sous vide) permettent de reconstituer la température, la pression, la composition chimique détaillée des fluides, dont les teneurs en métaux, ainsi que la composition isotopique de l’hydrogène de l’eau, du chlore et du carbone du CO2 dissous. De plus, l’analyse de la composition isotopique de l’oxygène et du carbone des minéraux dans lesquels sont piégées les inclusions fluides apporte des informations complémentaires sur la température des fluides et les interactions fluides-roches. Cette approche a été utilisée sur six gisements d’uranium du Bassin de l’Athabasca, et a permis d’apporter les résultats suivants, potentiellement généralisables à l’ensemble du bassin. (1) Deux saumures, une calcique et une sodique ont circulé et se sont mélangées à la base du bassin et dans le socle au cours de la formation des gisements à environ 150 ± 30°C. (2) Ces deux saumures ont transporté de l’uranium, dont les concentrations exceptionnelles et très hétérogènes (entre 0.2 et 600 ppm) indiquent qu’il a été lessivé dans le socle. (3) Ces saumures ont une origine commune et se sont formées essentiellement par évaporation en surface de l’eau de mer, et mélange avec des fluides issus de la dissolution de minéraux évaporitiques. (4) La saumure calcique s’est formée par interaction entre la saumure sodique et les roches du socle. (5) Les interactions des saumures avec les minéraux et le graphite du socle, la radiolyse de l’eau, et la synthèse de bitumes ont contrôlé la composition isotopique en oxygène, hydrogène et carbone de ces saumures. / Fluid circulations between crystalline basements and their sedimentary covers are major events for element transfer in the crust. In numerous settings, basinal fluids penetrate the low-permeability basement, interact with basement lithologies, leach metals, leading to metal concentrations, notably Pb, Zn, Cu, Ag and U. Unconformity-related uranium deposits from the Proterozoic Athabasca Basin (Canada) are crucial witnesses and useful tools for the understanding of mechanisms and consequences of such fluid events. Fluid inclusions allow us to directly sample and analyze paleofluids. Despite analytical difficulties, these micrometer size objects provide key information on fluid properties. Available analytical techniques (microthermometry, LA-ICP-MS, crush-leach, in-vacuo crushing) provide reconstruction of temperature, pressure, detailed fluid chemistry, including metal concentrations, as well as isotopic composition of water hydrogen, chlorine and of dissolved CO2 carbon. In addition, analysis of isotopic composition of oxygen and carbon from minerals in which fluid inclusions are trapped provide supplementary information on fluid temperatures and fluid-rock interactions. This approach was used on six uranium deposits from the Athabasca Basin and provided the following results, which can be potentially generalized to the entire basin. (1) Two brines, a calcium-rich brine and a sodium-rich brine have circulated and mixed at the base of the basin and in the basement at the time of formation of uranium deposits, at temperature close to 150 ± 30°C. (2) Both brines have transported uranium, whose exceptional and highly heterogeneous concentrations (0.2 to 600 ppm) indicate that it was leached in the basement. (3) Both brines share a common origin and were formed mainly by surface evaporation of seawater and mixing with fluids originating from dissolution of evaporitic minerals. (4) The calcium-rich brine was formed by interaction between the sodium-rich brine and basement lithologies. (5) Interaction with basement minerals and graphite, water radiolysis, and bitumen synthesis were the main controls on the oxygen, hydrogen and carbon isotopic composition of brines.

Fluids play a vital role in essentially all geologic environments and processes, and are the principal media of heat and mass transfer in the Earth. The properties of geologic fluids can be diverse, as fluids occur at conditions ranging from ambient temperatures and pressures at Earth's surface, to extreme temperatures and pressures in Earth's deep interior. Regardless the wide ranges of conditions at which geologic fluids occur, fluid properties are described and governed by the same fundamental thermodynamic relationships. Thus, application of thermodynamic principles and methods allows us to decipher the properties and roles of geologic fluids, to help understand geologic processes. Fluid inclusions in minerals provide one of the best available tools to study the compositions of geological fluids. Compositions of fluid inclusions can be determined from microthermometric measurements, based on the vapor-saturated liquidus conditions of model chemical systems, or by various microanalytical techniques. The vaporsaturated liquidus relations of the system H2O-NaCl-CaCl2 have been modeled to allow estimation of fluid inclusion compositions by either microthermometric or microanalytical methods. Carbon capture and storage (CCS) in deep saline formations represents one option for reducing anthropogenic CO2 emissions into Earth's atmosphere. Availability of storage volume in deep saline formations is a significant component of injection and storage planning. Investigation of the volumetric properties of CO2, brine and CO2-saturated brine reveals that storage volume requirements are minimized when CO2 dissolves into brine. These results suggest that a protocol involving brine extraction, CO2 dissolution and re-injection may optimize CCS in deep saline formations. Numerical modeling of quartz dissolution and precipitation in a sub-seafloor hydrothermal system was used to understand the role of fluid-phase immiscibility ("boiling") on quartz-fluid interactions, and to predict where in the system quartz could deposit and trap fluid inclusions. The spatial distribution of zones of quartz dissolution and precipitation is complex, owing to the many inter-related factors controlling quartz solubility. Immiscibility exerts a strong control over the occurrence of quartz precipitation in the deeper regions of fluid circulation. / Ph. D.

Water and other volatiles (e.g. CO2, H2, CH4, etc.) are crucial components on Earth that ensure the habitability of the planet and play an important role in many geological processes. Small aliquots of these fluids can be preserved in the geological record as fluid inclusions and can provide valuable information about the physical and chemical environment in which they formed. The ocean is the largest water reservoir on the Earth's surface, and seawater participates in important water-rock reactions such as hydrothermal alteration of the ocean floor, a process that is currently in the spotlight for hypotheses on the origin of life, as it is an environment where generation of abiotic carbohydrates occur. The ocean chemistry varied in the geologic past to reflect major changes in the intensity of weathering, rates of midocean ridge hydrothermal discharge, changes in the climate and atmospheric CO2 concentration, and also played an important part in mass extinction events. Understanding the history of Earth's ancient oceans may hold the key to answer some of the important questions about the future of the Earth. Today, oceans hold valuable resources, such as offshore basalt formations which have been considered for submarine CO2 sequestration to mitigate greenhouse gas emissions associated with global warming. In the chapters of this dissertation, the reader will be presented with studies using fluid inclusions to advance our knowledge about the chemical evolution of seawater and reaction kinetics involving CO2, seawater and olivine – an abundant mineral in the oceanic lithosphere. Chapter I "Redox conditions in Late Permian seawater based on trace element ratios in fluid inclusions in halite from the Polish Zechstein Basin" describes application of a new redox proxy for paleo-seawater that involves analysis of redox-sensitive trace elements (e.g., Fe, Mn, U, V, Mo) in ancient seawater trapped as fluid inclusions in halite. Chapter II "Partitioning behavior of trace elements during evaporation of seawater" investigates the behavior of trace elements during the evaporation of seawater. This information is required to interpret trace element data from fluid inclusions in halite. In Chapter III "In situ monitoring of the carbonation of olivine under conditions relevant to carbon capture and storage using synthetic fluid inclusion micro-reactors: Determination of reaction rates", fluid inclusions are used as micro-reactors to monitor the reaction progress of olivine carbonation in situ and in real time at elevated temperatures (50-200 °C) and pressures using non-destructive analytical techniques such as Raman spectroscopy. / Doctor of Philosophy / Many geological processes on Earth involve water and other volatiles (e.g. CO2, H2, CH4, etc.) which are crucial components that ensure the habitability of the planet. These fluids can be preserved in the geological record in the form of fluid inclusions which are small aliquots of fluids trapped in minerals that provide information about the physical and chemical environment in which they formed. The majority of water on the Earth's surface is stored in the oceans. Seawater participates in important water-rock reactions, one of which is the hydrothermal alteration of the ocean floor. This reaction is in the spotlight currently because it represents an environment where generation of abiotic carbohydrates occur, giving rise for hypotheses about the origin of life on Earth. The chemical composition of seawater varied in the geologic past reflecting major changes in the intensity of weathering, discharge rate of midocean ridge hydrothermal systems, climate, and atmospheric CO2 concentration, and affected the survival of various marine species throughout Earth's history. For example, periodic extensions of oxygen minimum zones in the oceans played an important part in mass extinction events in the last 488 million years. Understanding the history of Earth's ancient oceans may hold the key to answer some of the important questions about the future of the Earth. Today, oceans hold valuable resources, such as offshore basalt formations which have been considered for submarine CO2 sequestration to mitigate greenhouse gas emissions associated with global warming. This dissertation explores ways to use fluid inclusions to advance our knowledge about the chemical evolution of seawater in the past and present, and the reaction of seawater with CO2 and olivine – an abundant mineral in the oceanic lithosphere – to facilitate long-term storage of CO2 in minerals to decrease the rate of global warming. Chapter I describes the application of a new redox proxy for paleo-seawater that involves analysis of redox-sensitive trace elements (elements whose solubility changes significantly as the oxidation state changes, such as Fe, Mn, U, V, Mo) in ancient seawater trapped as fluid inclusions in halite. The results suggest that trace element abundances in fluid inclusions in halite vary in response to redox changes in seawater and provide a potential redox proxy. Chapter II investigates the behavior of trace elements during the evaporation of seawater. This information is required to interpret trace element data from fluid inclusions in halite. The results of this study indicate that some elements remain in the water during evaporation of seawater (e.g. Li, B, Mo, U), while others are partially removed by precipitation of various mineral phases (e.g. Ba, Sr, Cs, Rb, Mn, V) as seawater evaporates. In Chapter III, fluid inclusions are used as micro-reactors to monitor the reaction progress of olivine carbonation in situ and in real time at elevated temperatures (50-200 °C) and pressures using non-destructive analytical techniques such as Raman spectroscopy. The results highlight that this reaction occurs rapidly, which makes it an ideal candidate for safe storage of CO2 by commercial CO2 injection projects in mafic and ultramafic rocks.

The system H₂O-CH₄ is found in a variety of geological environments in the earth’s crust, from sedimentary basins to low grade metamorphic terrains. Knowledge of the PressureVolume-Temperature-Composition (PVTX) properties of the H₂O-CH₄ system is necessary to understand the role that these fluids play in different geological environments. In this study the properties of the H₂O-CH₄ fluid system at elevated temperatures and pressures has been investigated experimentally to determine the PVTX properties of H₂O-CH₄ fluids in the P-T range equivalent to late diagenetic to low grade metamorphic environments, and XCH₄≤4mol%. A study has also been conducted to determine methane hydrate stability over the temperature range of -40~20°C. Synthetic fluid inclusions were employed in both studies as miniature autoclaves. Experimental data for the PVTX properties of H₂O-CH₄ fluids under late diagenetic to low grade metamorphic conditions was used to calculate the slopes of isoTh lines (the line connecting the P-T conditions of the inclusions at formation and at homogenization) at different PTX conditions. An empirical equation to describe the slope of iso-Th line as a function of homogenization temperature and fluid composition was developed. The equation is applicable to natural H₂O-CH₄ fluid inclusions up to 500°C and 3 kilobars, for fluid compositions ≤4 mol% CH₄. The Raman peak position of CH₄ gas is a function of the pressure and temperature. This relationship was used to determine the pressure along the methane hydrate stability curve in the H₂O-CH₄ system. The combined synthetic fluid inclusion, microthermometry and Raman spectroscopy method is a novel experimental approach to determine the P-T stability conditions of methane hydrates. The method is fast compared to conventional methods, and has the potential to be applied to study other gas hydrate systems. / Ph. D.