Opaque phases from carbonatites of the Grønnedal-Íka alkaline complex (1299±17 Ma) of Southwest Greenland were analyzed in terms of their mineralogy and microstructure. The analysis demonstrates that a later intrusion by a 55 m wide dolerite dyke of unknown age has prompted the mineralization of magnetite by activating hydrothermal fluid convection. The fluid has interacted with the carbonatite, replacing siderite and ankerite by magnetite, which at places constitutes over half of the rock volume. Magnetite is shown to have become partly replaced by hematite at a later stage. A paragenetic sequence is suggested for the opaque phases that com- prise major magnetite and hematite, accessory pyrite and trace amounts of sphalerite, chalcopyrite and galena. / Low-temperature geologic sequestration of carbon by ikaite formation

Les découvertes de systèmes hydrothermaux marins ont permis de dire qu'ils réunissaient les conditions favorables à l'apparition des premières formes de vie car des concentrations appréciables en N2, CO2, H2S, CH4, C2H6 et C3H8 ainsi que des quantités détectables (10-9 mol) de n-alcanes de poids moléculaire élevé (C16-C29) ont été mesurées dans les fluides hydrothermaux de la ride médio-Atlantique. Les premières formes de vie étaient sans doute des êtres microbiens simples et unicellulaires qui ont pu trouver dans les composés organiques l'énergie nécessaire à leur évolution. Les systèmes hydrothermaux marins peuvent avoir constitués un environnement favorable à l'apparition de la vie car ces systèmes sont caractérisés par des fumeurs noirs et des fumeurs blancs avec un écosystème indépendant de l'énergie solaire où vivent les organismes les plus primitifs trouvés dans les environnements actuels, les hyperthermophiles. Ces arguments sont très importants en ce qui concerne les conditions qui régnaient à l'Archéen. Les systèmes hydrothermaux Archéens sont les seuls environnements où la vie primitive a pu être protégée des impacts des météorites et de la vaporisation partielle de l'océan. Ces systèmes sont compatibles avec l'origine et l'évolution de la vie. Les études expérimentales, sur la synthèse et la stabilité des composés prébiotiques dans des conditions hydrothermales sont couplées aux études théoriques en thermodynamique permises par les travaux de mesure expérimentales. L'origine abiogéniques des composés organiques azotés dans les conditions hydrothermales est primordiale dans l'histoire de la Terre / Hydrothermal Systems discovery involve it gather favorable conditions to act for the appearing of the first living shape, because significant concentrations in N2, CO2, H2S, CH4, C2H6 and C3H8 and detectable quantities (10-9 mol) of heavy weights n-alcanes (C19-C29) were measured in hydrothermal fluids of the mid-Atlantic ridge. The first living shape were without no doubt simple or unicellular microbes being which finding in organic compounds the satisfying energize for their evolution. Hydrothermal systems could have constitute a favorable environment for the appearing of life because these systems are characterized by black smokers and white smokers with an ecosystems independent of solar energize where the most primitives organisms live, found in actual environments, the hyperthermophiles. These arguments are very important concerning the conditions ruling in Archean. The hydrothermal systems of Archean were the only environment where the primitive life was protect of meteoritic impact and partial vaporization of the ocean. These systems are compatible with origin and evolution of life. The experimental study, on the synthesis and stability of prebiotic compounds in hydrothermal conditions are gathered with thermodynamic studies permit by the works of experimental measures. Abiogenic origin of nitrogen organic compounds in hydrothermal conditions is primordial in the history of the Earth

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.

Os granitoides da Faixa Ribeira, sudeste do Estado de São Paulo, aparecem como complexas intrusões, aflorando em todos os \"domínios\" geológico-estruturais do embasamento paulista. Neste trabalho, foram avaliados os batólitos Cantareira, São Roque e Itaqui, os plútons Taipas e Tico-Tico, e os turmalina-granitos de Perus, no Domínio São Roque; o batólito Itu e a intrusão Terra Nova (Domínio Jundiaí); o Granito Itaquera (Domínio Embu); o granito da Ilha Anchieta e o charnockito Ubatuba (Domínio Costeiro). Este estudo observa os padrões de evoluções petrogenéticas nos granitoides, com utilização de determinações geoquímicas e isotópicas em rochas e em zircão. A espectrometria de massa (por quadrupolo) associada à ablação a laser (LAQ-ICPMS) foi aplicada para determinar elementos traço em zircão. Dados analíticos de materiais de referência (zircão 91500 e zircão GJ-1) são apresentados no capítulo sobre metodologias. Os dados lito-geoquímicos indicam que as amostras pertencem a linhagens metaluminosas a peraluminosas com elevados teores de K. Granitos metaluminosos (Cantareira, Itaqui, etc.) mostram elevados teores de Sr e da razão Sr/Y, sem anomalia de Eu, em magmas provavelmente formados em profundidade, com granada estável. Os demais granitos mostram-se compatíveis com origem a pressões menores, com plagioclásio estável (anomalia negativa de Eu, baixos teores de Sr). Os zircões, em geral, mostram teores elevados de ETR, Th e U. Os diagramas normalizados de ETR mostram anomalias positivas de Ce, geradas em ambiente oxidante. Os zircões das amostras Tico-Tico, Itu, Terra Nova, Ilha Anchieta, Itaquera, Perus e charnockito Ubatuba apresentam anomalias negativas de Eu, provavelmente determinada pela co-cristalização com plagioclásio. Os elevados teores de ETR e Y nos zircões indicam a atuação de reações acopladas tipo xenotima, com substituição de \'Si POT.4+\' por \'P POT.5+\' e de \'Zr POT.4+\' por\' ETR POT.3+\', \'Y POT.3+\'. O geotermômetro Ti-em-zircão (\'T ANTPOT.zir.\') rendeu, em geral, temperaturas de cristalização equivalentes às temperaturas de saturação de zircão e apatitas em magmas. Zircões com núcleos reabsorvidos e com reflexão escura em CL apresentaram Tzir não realistas, acima de 1000°C, devidas a incorporação exagerada de Ti junto com ETR e P, por influencia de fluidos hidrotermais, que transportam também outros elementos HFS (Nb, Ta, Mo). Os resultados de idades U-Pb em zircão destes granitóides levam a valores entre 580 a 603 Ma, 30 Ma mais jovens que os da literatura. As razões Lu-Hf mostram similaridade entre os protólitos dos granitos São Roque e Itaquera, com uma possível fonte Paleoproterozóica (~2.9 Ga) e com \'épsilon\'\'Hf de -22.8, de elevada residência crustal; as idades TDM (Sm-Nd) estão entre 2.2 e 2.5 Ga, possivelmente representando uma fonte crustal associada a Paleoplaca São Francisco. Para os demais granitoides (Domínios São Roque e Jundiaí) é necessária uma fonte mais radiogênica para os valores de \'épsilon\'Hf (-18 a -11) e \'épsilon\'\'Nd (-12 a -9). As idades TDM, e as mais antigas U-Pb obtidas em alguns núcleos herdados de zircão, indicam fonte constituída por crosta continental juvenil acrescida durante evento vulcânico (por rifteamento) em 1.75 Ga, dentro da placa tectônica, devido a abertura continental, ou mesmo durante eventos ocorridos cerca de 2.1 Ga dentro de Cráton São Francisco. / The granitoids of the Ribeira Belt, southeastern São Paulo state, southeastern Brazil, are found as complex intrusions spread out uniformly in all structural-geologic \"domains\" of the São Paulo basement area. In our work, samples were studied from the Cantareira, São Roque and Itaqui batholiths, the Taipas and Tico-Tico plutons and the Perus tourmaline granites (São Roque Domain), the Itu batholith and the Terra Nova intrusion (Jundiai Domain), the Itaquera granite (Embu Domain), the Ilha Anchieta granite and the Ubatuba charnockite (Costal Domain). This study aims to unravel the pattern of petrogenetic evolution in the granitoids, with the help of geochemical determinations in rocks and zircon crystals. Quadrupole mass spectrometry with laser ablation (LA-Q-ICPMS) was applied to determine trace elements contained in zircons. Analytical data for reference materials (zircons 911500 and GJ-1) are presented in the chapter on Methodology. The lithogeochemical data show that the granites represent meta-aluminous to peraluminous lineages, with significant potash contents. Meta-aluminous samples (Cantareira, Itaqui, etc.) are high in Sr, also with high Sr/Y ratios and no Eu anomalies, representing magmas probably formed at considerable depth, implying garnet stability. The other granites were formed from magmas at lower pressures (stable plagioclase; negative Eu anomaly; low Sr contents). Zircons from these granites contain high REE, U and Th abundances. Normalized REE diagrams present positive Ce anomalies, generated in oxidizing environments. Zircons from Tico-Tico, Itu, Terra Nova, Ilha Anchieta, Itaquera, Perus and the Ubatuba charnockite are characterized by negative Eu anomalies, probably controlled by co-crystallization with plagioclase. The high REE and Y contents in zircons are explained by coupled xenotimetype reactions, with substitution of \'Si POT.4+\' by \'P POT.5+\' and \'Zr POT.4+\' by \'REE POT.3+\', \'Y POT.3+\'. The Ti-in-zircon geothermometer (\'T ANTPOT.zir\') yields, in general, temperatures comparable to the ones obtained with the saturation temperatures of zircons and apatites in magmas. Zircons showing reabsorbed cores and dark reflection areas under CL yield unrealistic temperatures above 1000°C, explained by anomalous uptake of Ti, together with high REE and P contents, on account of hydrothermal fluid activity, also responsible for transporting other HFSE (Ta, Nb, Mo). Dating results with the U-Pb technique in zircons show values between 580 and 603 Ma, 30 Ma younger than results previously published. Lu-Hf ratios suggest similarities for the protoliths of the São Roque and Itaquera granites, with a possible Paleoproterozoic source (~2.9 Ga) and with \'épsilon\'\'Hf of - 22.8, indicating protracted crustal residence time. TDM ages (Sm-Nd) lie between 2.2 and 12.5 Ga, possibly representing a crustal source associated with the São Francisco paleoplate. For the other granitoids (São Roque and Jundiai domains), a more radiogenic source has to be considered, given the \'épsilon\'\'Hf (-18 to -11) and \'épsilon\' Nd (-12 to -9) values. TDM ages, and the older ages obtained with U-Pb on cores of some zircons, point to a source constituted by juvenile continental crust affected by a volcanic event (rifting) at 1.75 Ga, within the tectonic plate, forced by continental opening, or even during events that occurred close to 2.1 Ga within the São Francisco craton.

Os granitoides da Faixa Ribeira, sudeste do Estado de São Paulo, aparecem como complexas intrusões, aflorando em todos os \"domínios\" geológico-estruturais do embasamento paulista. Neste trabalho, foram avaliados os batólitos Cantareira, São Roque e Itaqui, os plútons Taipas e Tico-Tico, e os turmalina-granitos de Perus, no Domínio São Roque; o batólito Itu e a intrusão Terra Nova (Domínio Jundiaí); o Granito Itaquera (Domínio Embu); o granito da Ilha Anchieta e o charnockito Ubatuba (Domínio Costeiro). Este estudo observa os padrões de evoluções petrogenéticas nos granitoides, com utilização de determinações geoquímicas e isotópicas em rochas e em zircão. A espectrometria de massa (por quadrupolo) associada à ablação a laser (LAQ-ICPMS) foi aplicada para determinar elementos traço em zircão. Dados analíticos de materiais de referência (zircão 91500 e zircão GJ-1) são apresentados no capítulo sobre metodologias. Os dados lito-geoquímicos indicam que as amostras pertencem a linhagens metaluminosas a peraluminosas com elevados teores de K. Granitos metaluminosos (Cantareira, Itaqui, etc.) mostram elevados teores de Sr e da razão Sr/Y, sem anomalia de Eu, em magmas provavelmente formados em profundidade, com granada estável. Os demais granitos mostram-se compatíveis com origem a pressões menores, com plagioclásio estável (anomalia negativa de Eu, baixos teores de Sr). Os zircões, em geral, mostram teores elevados de ETR, Th e U. Os diagramas normalizados de ETR mostram anomalias positivas de Ce, geradas em ambiente oxidante. Os zircões das amostras Tico-Tico, Itu, Terra Nova, Ilha Anchieta, Itaquera, Perus e charnockito Ubatuba apresentam anomalias negativas de Eu, provavelmente determinada pela co-cristalização com plagioclásio. Os elevados teores de ETR e Y nos zircões indicam a atuação de reações acopladas tipo xenotima, com substituição de \'Si POT.4+\' por \'P POT.5+\' e de \'Zr POT.4+\' por\' ETR POT.3+\', \'Y POT.3+\'. O geotermômetro Ti-em-zircão (\'T ANTPOT.zir.\') rendeu, em geral, temperaturas de cristalização equivalentes às temperaturas de saturação de zircão e apatitas em magmas. Zircões com núcleos reabsorvidos e com reflexão escura em CL apresentaram Tzir não realistas, acima de 1000°C, devidas a incorporação exagerada de Ti junto com ETR e P, por influencia de fluidos hidrotermais, que transportam também outros elementos HFS (Nb, Ta, Mo). Os resultados de idades U-Pb em zircão destes granitóides levam a valores entre 580 a 603 Ma, 30 Ma mais jovens que os da literatura. As razões Lu-Hf mostram similaridade entre os protólitos dos granitos São Roque e Itaquera, com uma possível fonte Paleoproterozóica (~2.9 Ga) e com \'épsilon\'\'Hf de -22.8, de elevada residência crustal; as idades TDM (Sm-Nd) estão entre 2.2 e 2.5 Ga, possivelmente representando uma fonte crustal associada a Paleoplaca São Francisco. Para os demais granitoides (Domínios São Roque e Jundiaí) é necessária uma fonte mais radiogênica para os valores de \'épsilon\'Hf (-18 a -11) e \'épsilon\'\'Nd (-12 a -9). As idades TDM, e as mais antigas U-Pb obtidas em alguns núcleos herdados de zircão, indicam fonte constituída por crosta continental juvenil acrescida durante evento vulcânico (por rifteamento) em 1.75 Ga, dentro da placa tectônica, devido a abertura continental, ou mesmo durante eventos ocorridos cerca de 2.1 Ga dentro de Cráton São Francisco. / The granitoids of the Ribeira Belt, southeastern São Paulo state, southeastern Brazil, are found as complex intrusions spread out uniformly in all structural-geologic \"domains\" of the São Paulo basement area. In our work, samples were studied from the Cantareira, São Roque and Itaqui batholiths, the Taipas and Tico-Tico plutons and the Perus tourmaline granites (São Roque Domain), the Itu batholith and the Terra Nova intrusion (Jundiai Domain), the Itaquera granite (Embu Domain), the Ilha Anchieta granite and the Ubatuba charnockite (Costal Domain). This study aims to unravel the pattern of petrogenetic evolution in the granitoids, with the help of geochemical determinations in rocks and zircon crystals. Quadrupole mass spectrometry with laser ablation (LA-Q-ICPMS) was applied to determine trace elements contained in zircons. Analytical data for reference materials (zircons 911500 and GJ-1) are presented in the chapter on Methodology. The lithogeochemical data show that the granites represent meta-aluminous to peraluminous lineages, with significant potash contents. Meta-aluminous samples (Cantareira, Itaqui, etc.) are high in Sr, also with high Sr/Y ratios and no Eu anomalies, representing magmas probably formed at considerable depth, implying garnet stability. The other granites were formed from magmas at lower pressures (stable plagioclase; negative Eu anomaly; low Sr contents). Zircons from these granites contain high REE, U and Th abundances. Normalized REE diagrams present positive Ce anomalies, generated in oxidizing environments. Zircons from Tico-Tico, Itu, Terra Nova, Ilha Anchieta, Itaquera, Perus and the Ubatuba charnockite are characterized by negative Eu anomalies, probably controlled by co-crystallization with plagioclase. The high REE and Y contents in zircons are explained by coupled xenotimetype reactions, with substitution of \'Si POT.4+\' by \'P POT.5+\' and \'Zr POT.4+\' by \'REE POT.3+\', \'Y POT.3+\'. The Ti-in-zircon geothermometer (\'T ANTPOT.zir\') yields, in general, temperatures comparable to the ones obtained with the saturation temperatures of zircons and apatites in magmas. Zircons showing reabsorbed cores and dark reflection areas under CL yield unrealistic temperatures above 1000°C, explained by anomalous uptake of Ti, together with high REE and P contents, on account of hydrothermal fluid activity, also responsible for transporting other HFSE (Ta, Nb, Mo). Dating results with the U-Pb technique in zircons show values between 580 and 603 Ma, 30 Ma younger than results previously published. Lu-Hf ratios suggest similarities for the protoliths of the São Roque and Itaquera granites, with a possible Paleoproterozoic source (~2.9 Ga) and with \'épsilon\'\'Hf of - 22.8, indicating protracted crustal residence time. TDM ages (Sm-Nd) lie between 2.2 and 12.5 Ga, possibly representing a crustal source associated with the São Francisco paleoplate. For the other granitoids (São Roque and Jundiai domains), a more radiogenic source has to be considered, given the \'épsilon\'\'Hf (-18 to -11) and \'épsilon\' Nd (-12 to -9) values. TDM ages, and the older ages obtained with U-Pb on cores of some zircons, point to a source constituted by juvenile continental crust affected by a volcanic event (rifting) at 1.75 Ga, within the tectonic plate, forced by continental opening, or even during events that occurred close to 2.1 Ga within the São Francisco craton.

Les interactions entre la fracturation, les circulations fluides et la chimie des fluides au sein de marges hyper-étendues sont encore peu décrites et sont pour la plupart localisées en mer, enfouies sous des sédiments post-rift. Le bassin sud Aquitain et la partie nord des Pyrénées constituent un cas d’étude approprié pour l’investigation de ces interactions dans un modèle de marge hyper-étendue avec exhumation du manteau durant le Crétacé inférieur puis inversée. Les données de terrain ont permis de décrire trois principaux sets de fractures. Ils ont été corrélés aux principaux événements de l’évolution géodynamique du bassin correspondant au rifting triasique, à l’hyper-extension datée Aptien-Cénomanien, et à la compression pyrénéenne. Les observations pétrographiques, les analyses Raman et microthermométriques sur les inclusions fluides, les données acquises par ICP-MS, et les analyses isotopiques ont permis de déterminer les chimies, les températures, les conditions rédox, les compositions des gaz, les signatures isotopiques de l’oxygène et du carbone, et les teneurs en terres rares des fluides parents pour les ciments précipités durant chaque épisode. Ces données ont permis le calage temporel des évènements diagénétiques majeurs. En particulier, la dolomie baroque et la chlorite ont précipité dans les fractures du set 2 durant l’hyper-extension correspondant au pic thermique à des températures supérieures à 300°C. La signature isotopique, la forte teneur en CO2, l’occurrence de H2S et les fortes salinités des fluides parents suggèrent la percolation de fluides mantelliques ascendants au travers des évaporites triasiques. La phase fin et post hyper-extension est caractérisée par de la bréchification hydraulique dans les formations les plus poreuses, une baisse des températures et des salinités, une baisse de la contribution mantellique dans les fluides parents, une fermeture du système diagénétique au cours de l’enfouissement et un passage à des conditions réductrices durant la précipitation du quartz, de la pyrite et de la calcite. La phase de compression pyrénéenne associée au troisième stade de fracturation a induit une réouverture du système diagénétique et favorisé le retour à des conditions oxydantes et à des infiltrations de fluides météoriques / Interactions between fracturing, fluid circulations and fluid chemistry on hyper-extended margins is still poorly described as most of them are located offshore, buried underneath post-rift sediments. The southern Aquitaine basin and the northern Pyrenees constitute an appropriate case study to investigate these interactions since a model of hyper extended margin with mantle exhumation during the Lower Cretaceous subsequently inverted was recently proposed. From a field study, we here describe three main sets of fractures (set 1 to set 3). They are correlated with main stages of the geodynamic evolution of the basin corresponding to the Liassic rifting, the Aptian-Cenomanian hyper-extension, and the Pyrenean compression. Petrographic observations, Raman and micro-thermometry analysis on fluid inclusions, ICP-MS, and isotope analysis permitted to determine chemistries, temperatures, redox conditions, gas compositions, oxygen and carbon isotopic signatures, and REE contents of parent fluids for cements precipitated during each episode. In particular saddle dolomite and chlorite precipitated in set 2 fractures during the hyper-extension corresponding to the thermal peak at temperatures higher than 300°C. The isotopic signature, the high CO2 content, the occurrence of H2S and the high salinity of parent fluids suggest ascending mantle fluids percolating across Triassic evaporites. The late and post hyper-extensional phase is characterized by hydraulic brecciation in porous formations, a decrease in temperature and salinity, a decrease in mantle contribution in parent fluids, a closing of the diagenetic system during burial and a switch to reducing conditions during the precipitation of quartz, pyrite and calcite. The Pyrenean compressive phase associated with the third fracturing stage induced a reopening of the diagenetic system and favored a return to oxidizing conditions and infiltrations of meteoric fluids

The Siljan Ring in Dalarna, Sweden is the site of the largest meteor impact crater in Europe and has long been a topic of discussion regarding methane production. However, the source of this methane and the timing of production in relation to the impact remain unclear. An outcrop of red Ordovician limestone preserved on the edge of a downfaulted zone encircling the crater’s central plateau is crosscut by fractures surrounded by pale-coloured reduction haloes within which precipitates can be observed. These haloes suggest interaction with a reducing agent mobilised within a fluid flow, of which methane would be a prime candidate. A field study was subsequently undertaken to establish the reaction whereby these haloes were formed, as well as the timing of their formation relative to the Siljan impact based upon petrological, geochemical, and structural data obtained in the field. Results from this study show that a methane-bearing hydrothermal fluid mobilised within the fractures has preserved the original mineralogy of the limestone within the reaction haloes whilst the country rock beyond was being oxidised. Pyrite is shown to be preserved within the pale reaction haloes, whilst its oxidation within the country rock is shown to be the source of the limestone’s distinct red colouring. Fracture and bedding orientation at the study site suggest the hydrothermal event to have been simultaneous with the meteor impact, with the fractures forming part of a wider complex network of impact features. Whilst mobilisation associated with the meteor impact is a likely cause of methane release, the exact source of the methane active at the study site is unclear.

Le tungstène (W) fait partie des « ressources minérales critiques » définies par la Commission Européenne en terme d’approvisionnement pour de nombreuses applications technologiques. Le Massif Central Français (MCF), localisé dans la partie interne de la Chaîne Varisque Européenne, possède un potentiel économique significatif en W (>45 kt WO3) essentiellement sous forme de minéralisations disséminées dans des granites spécialisés ou associées à des systèmes filoniens hydrothermaux péri-granitiques à quartz-wolframite±cassiterite. Le but de cette thèse est (i) de caractériser les sources des fluides et des métaux impliquées dans la formation des minéralisations à W et (ii) de dater ces événements métallogéniques afin de les relier avec l’évolution orogénique de la Chaîne Varisque et notamment avec les événements métamorphiques et magmatiques fini-carbonifères. Ce travail est basé sur l’étude de plusieurs gisements hydrothermaux à W±Sn dans le MCF dans une approche multidisciplinaire combinant pétrographie et minéralogie détaillée, géochimie minérale et isotopique, géochimie en roche totale des granites et roches métamorphiques, géochronologie et étude des inclusions fluides. Les datations U-Pb des wolframites montrent que les minéralisations à W résultent d’événements hydrothermaux distincts sur une période d’au moins 40 Ma, correspondant à trois épisodes géodynamiques majeurs affectant la Chaine Varisque : (i) des minéralisations viséo-namuriennes (333-327 Ma) contemporaines de la compression syn-orogénique et de la mise en place des complexes leucogranitiques peralumineux à 335-325 Ma; (ii) des minéralisations namuro-westphaliennes (315-310 Ma) associées au jeu complexe de conditions compressives et extensives dans les zones internes de la Chaîne Varisque qui caractérise la fin du Carbonifère; (iii) des minéralisations stéphano-permiennes (298-274 Ma) mises en place en contexte post-collisionnel. L’analyse in situ des éléments mineurs et traces dans la wolframite a révélé l’existence de différents types de signatures géochimiques régionales, qui montrent de nombreuses similarités avec celles de granites évolués riches en métaux rares. L’étude détaillée du gisement de Puy-les-Vignes, exemple exceptionnel de minéralisation hydrothermale à W associée à un pipe bréchique, a permis de démontrer la superposition d’un stade à Nb-Ta sur la paragenèse primaire à W, interprété comme la contribution d’un fluide magmatique issu d’une coupole granitique à métaux rares. Ce résultat apparait similaire avec ceux déjà obtenus dans le cas du gisement de W d’Echassières, où le stockwerk à quartz-wolframite de La Bosse est recoupé par le granite à métaux rares de Beauvoir. De même, des aplites et pegmatites à métaux rares impactant les minéralisations à W±Sn ont été mises en évidence à Puy-les-Vignes et à St-Mélany. L’analyse par LA-ICPMS des inclusions fluides du granite de Beauvoir et du stockwerk de la Bosse a permis de caractériser la composition chimique des fluides primaires exsolvés lors de la transition magmatique-hydrothermale et de montrer leurs concentrations très élevées (102-103 ppm) en métaux rares (Sn, W, Nb) et la plus grande mobilité hydrothermale du Nb par rapport à celle du Ta. L’analyse minéralogique et géochimique de minéraux marqueurs des circulations fluides, tels que la tourmaline et les oxydes de titane, apporte de nouvelles évidences sur l’importance du rôle joué par les fluides métamorphiques régionaux précoces pour la mise en place des minéralisations à W-Sn. Enfin, cette thèse apporte des mises au point de développement méthodologique pour l’analyse multi-élémentaire des inclusions fluides et de la wolframite par LA-ICPMS. / Tungsten (W) is part of the “critical mineral resources” as defined by the European Commission in terms of supply for several technological applications. The French Massif Central (FMC), located in the internal part of the European Variscan belt, is the host for a significant economic potential in W (>45 kt WO3), mainly as disseminated mineralization in specialized granites or associated with peri-granitic quartz-wolframite±cassiterite hydrothermal vein systems. The aim of this thesis is (i) to characterize the fluids and metals sources involved in the genesis of W mineralization and (ii) to date these metallogenic events in the framework of the orogenic evolution of the Variscan belt, especially in link with the late-Carboniferous metamorphic and magmatic events. This work is based on the study of several W±Sn hydrothermal deposits in the FMC using a multidisciplinary approach combining petrography and detailed mineralogy, mineral and isotope geochemistry, whole-rock geochemistry of granites and metamorphic rocks, geochronology and fluid inclusions study. U-Pb dating of wolframite show that the W mineralization formed during several distinct hydrothermal events in a period of at least 40 Ma, corresponding to three major geodynamic episodes affecting the Variscan belt: (i) Visean-Namurian (333-327 Ma) mineralization coeval with the syn-orogenic compression and the emplacement of peraluminous leucogranitic complexes at 335-325 Ma; (ii) Namurian-Westphalian (315-310 Ma) mineralization associated with a complicated setting characterized by coeval compressive and extensive conditions in the internal zones of the Variscan belt, typical of the late-Carboniferous; (iii) Stephanian-Permian (298-274 Ma) mineralization emplaced in post-collisional context. In situ analysis of minor and trace elements in wolframite showed the existence of different types of regional geochemical signatures, which share several similarities with those from rare-metal-rich evolved granites. The detailed study of the Puy-les-Vignes deposit, an exceptional case of hydrothermal W mineralization associated with a breccia pipe, allowed to demonstrate the superposition of a Nb-Ta stage on the primary W paragenesis, which is interpreted as the contribution of a magmatic fluid derived from a rare-metal granitic cupola. This result appears similar with those already obtained in the Echassières W deposit, where the La Bosse quartz-wolframite stockwork is cut by the Beauvoir rare-metal granite. Similarly, rare-metal aplites and pegmatites overprinting W±Sn mineralization have been shown in the Puy-les-Vignes and St-Mélany deposit. LA-ICPMS analysis of fluid inclusions from the Beauvoir granite and the La Bosse stockwork allowed to characterize the chemical composition of the primary fluids exsolved during the magmatic-hydrothermal transition and to show their very high concentrations (102-103 ppm) in rare-metals (Sn, W, Nb), and the higher hydrothermal mobility of Nb compared to Ta. Mineralogical and geochemical analyses of minerals markers of fluid circulations, such as tourmaline and titanium oxides, bring new evidences of the important role played by the early regional metamorphic fluids in the emplacement of W-Sn mineralization. Finally, this thesis gives new methodological developments for the multi-element analysis of fluid inclusions and wolframite by LA-ICPMS.

L’objectif de cette thèse est d’étudier le comportement du soufre dans des fluides hydrothermaux soumis à un métamorphisme de bas grade. Elle est séparée en trois études interconnectées couplant étude naturelle et expérimentale : i) une étude du cycle du soufre dans les évaporites carniennes de la "Nappe des Gypses" des Alpes françaises comme cas d’étude naturelle a été réalisée, ii) une étude de la spéciation du soufre dans les inclusions fluides associées à ces évaporites triasiques, et iii) une étude expérimentale du rôle de la spéciation du soufre sur le mécanisme de la Thermo-Réduction des Sulfates (TSR) et l’altération des hydrocarbures associée. La première étude repose sur le couplage d’une approche pétrographique classique et d’une étude détaillée des inclusions fluides, des isotopes stable (δ34S, δ33S, δ36S, Δ33S, Δ36S, δ13C et δ18O) et de la matière organique dans la "Nappe des Gypses". Ces études couplées ont permis d’identifier le processus de TSR comme la réaction contrôlant le comportement du soufre dans cette formation en système fermé. La seconde étude repose sur une nouvelle approche analytique couplant spectroscopie Raman in-situ et platine microthermométrique permettant de réchauffer jusqu’à 300°C les échantillons (naturel et synthétique). Ainsi, à température >100°C la présence de l’ion radicalaire S3- et d’autres espèces polymériques du soufre (Snx) a été mise en évidence dans la “Nappe des Gypses”. Cette étude confirme le rôle indispensable à la TSR de l’ion S3- et des Snx dans les fluides naturels. Cette étude naturelle a été complétée par une étude expérimentale préliminaire qui a permis de mettre en place de nouveaux protocoles expérimentaux en autoclave et en capillaires de silice couplés à des analyses spectroscopiques et isotopiques. Ceci afin de mieux comprendre le rôle de la spéciation du soufre dans les interactions entre une phase aqueuse et un fluide hydrocarboné lors de la TSR. Cette thèse conduit à une meilleure compréhension du rôle de la spéciation du soufre et son lien avec des composés organiques lors de la TSR en condition métamorphique de bas grade. Cela ouvre de nouvelles perspectives de compréhension des formations géologiques basées sur le couplage d’études géologiques classiques et d’études géochimiques plus fines / The aim of this thesis is to study the sulfur behavior in hydrothermal fluids subjected to low grade metamorphism. It is separated into three interconnected studies linking natural and experimental study: i) a study of the sulfur cycle in the Carnian evaporites of the "Nappe des Gypses" from the French Alps as a natural case study is performed, ii) a study of the sulfur speciation in fluid inclusions associated to these Triassic evaporites, and iii) an experimental study of the role of sulfur speciation on the Thermochemical Sulfate Reduction (TSR) mechanisms and the associated hydrocarbons alteration. The first study is based on the coupling of a classical petrographic approach associated to a detailed study of fluid inclusions, stable isotopes (δ34S, δ33S, δ36S, Δ33S, Δ36S, δ13C and δ18O) and organic matter in the “Nappe des Gypses”. The coupling study allows to identify the TSR process as the reaction controlling the behavior of sulfur in this formation in a closed system. The second study is based on a new analytical approach coupling in-situ Raman spectroscopy and microthermometric stage. This technique allows to heat up to 300°C samples (natural and synthetic). Thus, at temperature >100°C, the presence of the radical ion S3- and other polymeric sulfur species (Snx) is demonstrated in the “Nappe des Gypses”. This study confirms the essential role in the TSR process of S3- and Snx species in natural fluids. This study natural was completed by a preliminary experimental study allowed to set up new experimental protocols in autoclave and fused silica capillaries coupled to spectroscopic and isotopic analyses. This to better understood the role of sulfur speciation in the interactions between an aqueous phase and a hydrocarbons fluid during the TSR. This thesis leads to a better understanding of the role of sulfur speciation and its link with organic compounds during TSR under low grade metamorphic conditions. This opens new perspectives to understand geological formations based on coupling of classical geological studies and finer geochemical studies

Les parties distales des marges passives pauvres en magma représentent la transition complexe entre les domaines continentaux et océaniques. Ces zones encore peu étudiées sont pourtant des endroits clefs pour comprendre les processus impliqués durant les premiers stades de l’accrétion océanique, et plus particulièrement ceux du magmatisme et du métasomatisme. Durant ces premiers stades, ces deux processus sont gouvernés par l’exhumation mantellique. L’interaction entre les liquides magmatiques, les roches du manteau et les fluides marins vont affecter le régime thermique de la marge. De par le monde, seulement deux Transitions Océan-Continent (TOC) ont pu bénéficier d’investigations scientifiques poussées et constituent naturellement les deux sites d’études de cette thèse, à savoir, les marges actuelles conjuguées d’Ibérie-Terre Neuve du sud de l’Atlantique Nord ainsi que les marges fossiles de la Platta et de Tasna, fragments de TOCs de la Téthys Alpine Jurassique. En combinant les études de terrain ainsi que les investigations minéralogiques, pétrologiques et géochimiques, nous avons pu contraindre trois processus clefs se déroulant dans les TOCs. (i) La percolation de liquide magmatique imprégnant le manteau sous-continental hérité dans les marges Ibérie-Terre Neuve permet une refertilisation de ces marges distales. (ii) La transition géochimique visible entre les basaltes des TOCs et les basaltes de dorsales océaniques peut s’appréhender par la fusion partielle du manteau sous-continental refertilisé. (iii) Le rôle des fluides hydrothermaux, ayant des températures comprises entre 60°C et 190°C, joue un rôle sur le métasomatisme de la lithosphère en produisant une intense serpentinisation et rodingitisation, respectivement du manteau sous-continental en exhumation et des dykes basaltiques. Ces températures étant cohérentes avec une exhumation mantellique au niveau du plancher océanique. / Distal parts of magma-poor rifted margins represent a complex transition between continental and oceanic domains. These areas remain poorly understood while being a key-place to unravel magmatic and metasomatic processes involved during the first stages of oceanization. At this time, these processes are enhanced by mantle exhumation, and the interaction between melts, mantle rocks and fluids affect the thermal regime of the margin. So far, only two Ocean-Continent Transitions (OCT) have been particularly investigated, namely the present-day Iberia Newfoundland conjugate margins and the fossil analog Platta-Tasna nappes, remnants of the Jurassic Alpine-Tethys OCTs. Studies presented in this Ph.D. thesis have been focused on these two margins. Here, by combining field-works, petrological, mineralogical and geochemical investigations, we have unraveled in OCTs three key-points: (i) The deep porous-flow melt percolation impregnating the long-lived inherited subcontinental mantle in Iberia-Newfoundland margins allow the refertilization of these distal domains; (ii) The geochemical transition depicted from OCT-basalts towards MOR-basalts can be explained by the partial melting of the refertilized subcontinental mantle; (iii) The role of active hydrothermal fluids, on both the exhumed mantle and basalt dikes, lead to the serpentinisation and the rodingitization respectively, at temperature ranging between 60°C and 190°C. These temperatures being consistent with the ongoing mantle exhumation towards near-seafloor conditions.