Thesis (doctoral)--Johann Wolfgang Goethe Universität, 2004. / Includes bibliographical references (p. [270]-299).

No description available.

A large portion of South west Africa/Namibia is underlain by 2 great orogens. They are the Irumide (Sinclair/Rehoboth) and Damara Orogenies. The L-shaped Irumide Province forms part of a belt which extends over the subcontinent from Namaqualand to as far as Zambia. The volcano-sedimentary sequences of the Irumide are believed to have formed in intracratonic rifts and pull-apart basins during the period 1400 to 900 Ma. The evolution of the NW trending Sinclair Group proceeded by means of 3 major cycles each beginning with the emplacement of basic to intermediate magmas followed by felsic ones. The cycle ended off with subsidence, deposition of immature clastic debris and final tilting of the volcano-clastic sequence. It was suggested that the extensive calc-alkaline lavas present, developed within a magmatic arc above a subduction zone, but this proposal has not been generally accepted. The NE trending Klein Aub-Witvlei Basins consist essentially of red bed alluvial fans and lacustrine sediments with minor volcanics near the base. The red beds and aeolian sediments were deposited in an arid climatic condition. The regional greenschist facies metamorphism and deformation is attributed to a major tectono-thermal event at 1100 Ma. The Damara Orogen (900 - 550 Ma) forms part of the Pan-African mobile belt system of global proportions. The NE trending intracontinental branch (aulacogen) and 2 coastal branches constitute a triple junction with its focal point near Swakopmund. The NE extension of the intracontinental belt has been linked with the Lufilian Arc hosting the renown Zambian Copper Belt deposits. In South West Africa/Namibia this belt hosts many different mineral occurrences which can be grouped into rift and collision related deposits. The tectonic history of the Damara Orogen supports a geodynamic-evolution-with-time hypothesis and represents a transitional phase in which limited Wilson Cycle Tectonics was active. The Theory of Mantle Advection is invoked to explain rifting, thinning and subsidence. Extensive ensialic rifting resulted in a relatively stable Northern Carbonate Platform and several deep troughs hosting turbiditic sequences. Crustal rupture in the Khomas Trough allowed for the emplacement of ocean floor tholeiites known as the Matchless Amphibolite Belt. Subsequent ocean closure and collision resulted in deformation, metamorphism and generation of predominantly S-type granites. The southern continental plate was partially overridden by the northern plate during final collision at 550 Ma. These low angle thrust faults allowed for the emplacement of the Naukluft Nappe Complex on top of younger Nama sediments. The break up of Gondwanaland during the Mesozoic with the splitting of the Atlantic Ocean was responsible for the intrusion of anorogenic alkaline ring complexes along the extension of the NE trending transform faults within the intracontinental branch of the Damara Orogen. A close relationship between the tectonic setting and mineral deposits has been recognized in both the Irumide and Damara Orogenies. In the Irumide, stratiform syngenetic copper deposits are hosted by alluvial fan, playa and lacustrine sediments. The uninterrupted sedimentation from the Irumide to Damara Orogen resulted in similar stratiform copper deposits during the early stages of rifting. In the Damara Orogen the rifting (extensional) phase is characterized by 4 main mineralizing systems: diagenetic/syngenetic (Kupferschiefer-type), epigenetic/hydrothermal Cu-Pb-Zn (Mississippi Valley-type), volcanogenic cupriferous pyrite (Besshi-type) and volcano-exhalative Pb-Zn (Red Sea-type). The collision (compressional) phase was accompanied by 4 main mineralizing processes: epigenetic/hydrothermal Cu-Pb-Zn, hydrotheral/metasomatic Sn-W-rare earth, metamorphogenic Au and U-bearing anatectic melts. The key to the selection of viable exploration targets lies in the understanding of the field evidence and the geodynamics modelling to explain the evolution of the orogen and its associated mineral deposits.

Le Delta de l'Okavango est un système endorhéique formant un cône alluvial dans la dépression du Kalahari. L'écosystème y est rythmé par une crue annuelle en provenance de l'Angola et entravée par l'escarpement des failles normales du graben de l'Okavango. Ce régime annuel est très variable, car la répartition de la crue annuelle diffère tous les ans. À plus grande échelle temporelle, du millénaire au Ma, l'endorhéisme du Delta peut varier entre des marais (actuel), un mega-lac ou perdre son caractère endorhéique (rivière). Les processus pouvant contrôler ces variations de régime sont 1) l'hydrologie du système, 2) l'activité des failles du graben, 3) l'apport sédimentaire et 4) l'écosystème. Cette étude apporte des contraintes quantifiées éclairant deux de ces processus à travers l'observation de la déformation de la surface terrestre par l'enregistrement de stations GPS permanentes. Le signal observé est annuellement impacté par la charge hydraulique résultant de la saison des pluies, et inter-annuellement par les variations de cette charge, ainsi que l'activité tectonique du graben. Les satellites GRACE fournissent un enregistrement quasi-continu de la variation du stock d'eau continentale, rendant possible la modélisation de la déformation élastique de la surface terrestre sous l'effet de cette charge. Le signal de déformation ainsi modélisé est comparable au signal saisonnier enregistré, validant les données satellitaires GRACE et révélant un important aquifère dans le bassin de l'Okavango. GRACE fournit ainsi un nouveau proxy permettant de suivre l'évolution de l'aquifère, et de valider le modèle hydrologique calibré précédemment pour le bassin. Les variations inter-annuelles d'eau souterraine dans le bassin validées par GRACE confirment le rôle de tampon des variations climatiques joué par l'aquifère sur la modulation des variations climatiques. La phase des variations du stock d'eau met de plus en évidence un effet de seuil dans la recharge de ce stock, en fonction de l'intensité des premières pluies. La faible résolution spatiale des variations du stock d'eau continental fournie par GRACE peut finalement être mieux contrainte par un examen plus détaillé des signaux GPS dans le bassin. Les vitesses de déformation horizontales de part et d'autre du graben révèlent une déformation tectonique faible sur l'ensemble du graben, de 1 mm/an exclusivement décrochante dextre. Une si faible déformation exclut une influence significative de l'activité tectonique et sismique du graben sur la variabilité de la distribution de la crue. Cette déformation observée remet en question le modèle géodynamique admis dans la région, soit une phase précoce de rifting liée à la propagation d'une branche SW du Rift Est-Africain. Un recensement des nombreuses études géophysiques réalisées dans la région dans la dernière décennie et un réexamen de la sismicité de l'Afrique australe n'amène aucune preuve significative de rifting dans le graben de l'Okavango. Un autre modèle géodynamique pour l'Afrique australe est proposé, basé sur l'accommodation lointaine de la déformation associée à l'ouverture à taux différentiels du Rift Est-Africain et le déplacement du craton du Kalahari par rapport au reste de la plaque nubienne. / The Okavango Delta is an endorheic system forming an alluvial fan in the Kalahari depression. The local ecosystem is paced by the annual flood coming from the Angolan highlands, blocked downstream by the normal faults scarps of the Okavango graben. This annual regime is highly variable, with the spatial distribution of the flood differing every year. At the geological time scale, from millenary to mega-annual, the Delta's endorheism can also vary between wetlands (current regime), mega-lake or loose its endorhism to turn into a river. Processes driving these regime variations are 1) the hydrological system, 2) the faulting of the graben, 3) the sedimentary input and 4) the ecosystem. This study brings quantitative constraints regarding two of these processes through the deformation of the Earth's ground surface monitored by permanent GPS stations. The observed signal is impacted seasonally by the hydrological loading resulting from the rainy season, and inter-annually by the variations of the terrestrial water storage, as well as the tectonic activity of the graben. GRACE satellites provide a quasi-continuous record of the variations of the Earth's continental water storage, allowing the modelling of the elastic deformation imposed on the Earth's crust by loading. The resulting modelled deformation signal is well correlated to the observed seasonal signal, hence validating the GRACE data products and revealing a large aquifer in the Okavango basin. GRACE thus provides a new proxy to monitor the evolution of water storage, and to validate more robustly the hydrological model calibrated for the basin. The variations in terrestrial water storage (TWS) in the basin validated by GRACE confirm the buffer effect of the aquifer in the modulation of climatic variations. The phase of the TWS variations moreover highlights a threshold in the recharge of TWS during the rainy season, depending on the intensity of the first rains. Finally, the poor spatial resolution of TWS variations provided by GRACE can be further constrained by a detail examination of the GPS signals in the basin. Horizontal displacements rates across the graben reveal a low tectonic deformation rate, of 1 mm/yr, exclusively along a dextral strike-slip component. Such a low deformation rate excludes a significant influence of the graben faulting on the variability of the flood distribution. The observed deformation calls into question the current geodynamic model for the area, i.e. incipient rifitng due to the propagation of a southwestern branch of the East African Rift System. A review of the numerous geophysical studies in the study area over the last decade, as well as a re-examination of the seismic data in southern Africa does not provide significant evidence for rifting in the Okavango graben. An alternative geodynamic model is proposed, based on the far-field accommodation of the deformation resulting from the differential extension rates in the Rift Valley, and the displacement of the Kalahari craton relative to the Nubian plate.

PEDROSA, Adriana Albuquerque. A geodinâmica e morfogênese das dunas eólicas com base nas suas taxas de migração no município de Canoa Quebrada, Aracati, Ceará, Brasil. 2016. 110 f. Tese (Doutorado em geologia)- Universidade Federal do Ceará, Fortaleza-CE, 2016. / Submitted by Elineudson Ribeiro (elineudsonr@gmail.com) on 2016-06-07T19:19:29Z No. of bitstreams: 1 2016_tese_aapedrosa.pdf: 7551151 bytes, checksum: 76af8c4bd62d1d01a7ca5bef085b91c2 (MD5) / Approved for entry into archive by José Jairo Viana de Sousa (jairo@ufc.br) on 2016-06-07T23:19:17Z (GMT) No. of bitstreams: 1 2016_tese_aapedrosa.pdf: 7551151 bytes, checksum: 76af8c4bd62d1d01a7ca5bef085b91c2 (MD5) / Approved for entry into archive by José Jairo Viana de Sousa (jairo@ufc.br) on 2016-06-07T23:24:35Z (GMT) No. of bitstreams: 1 2016_tese_aapedrosa.pdf: 7551151 bytes, checksum: 76af8c4bd62d1d01a7ca5bef085b91c2 (MD5) / Made available in DSpace on 2016-06-07T23:24:35Z (GMT). No. of bitstreams: 1 2016_tese_aapedrosa.pdf: 7551151 bytes, checksum: 76af8c4bd62d1d01a7ca5bef085b91c2 (MD5) Previous issue date: 2016 / This thesis presents an analysis of geodynamic and morphogenesis of the dune field in the Canoa Quebrada region located in the municipality of Aracati inserted in the state of Ceará. It covers the area formed by fluvial-marine plain, the strip of beach and dune field located on the right bank of the mouth of the river Jaguaribe. The estimated time frame corresponds to the dynamic analysis of the dune field based on migration rates from 1988 to 2013. The objectives of this study are to analyze the environmental dynamics of the mobile dune field towards the mangrove ecosystem located at the mouth of the river Jaguaribe. Associated with the methodological approach, we used a set of techniques necessary for the completion of this research. From then analyzed through GIS aerial photographs of the 80 on the scale of 1: 25,000 and 2004 Quickbird the years of satellite images, 2010 and 2013 associated with the study of wind dynamics based on the variation of records their migration rates. In the study area, we find the moving dunes of the longitudinal type, small occurrence barcanoids, expressive occurrence and prevalence of sand sheets. The vegetation point of view, semi-fixed dunes were identified in contact with the mangrove ecosystem. These dunes can be classified as semi-fixed shapeless. There is no occurrence of fixed dunes or cemented dunes in the region. As for dune generations in Canoa Quebrada, dominates the generation D1, characterized by the occurrence of current dunes, furniture. In contact with the mangrove ecosystem, the semi-fixed dunes combine with the previous generation of dunes to the current, the current sub-type, defining the existence of D2 generation dunes. The average migration of the dune field during that period of 40 years was 7m / year. In the years 2010-2013 virtually no migration occurred, but the dunes continue to migrate towards the mangrove ecosystem. / Esta Tese apresenta uma análise da geodinâmica e morfogênese do campo de dunas na região de Canoa Quebrada localizada no município do Aracati inserido no estado do Ceará. Abrange a área formada pela planície fluvio-marinha, a faixa de praia e o campo de dunas localizados na margem direita da foz do rio Jaguaribe. O recorte temporal avaliado corresponde à análise da dinâmica do campo de dunas com base nas taxas de migração no período de 1988 a 2013. Os objetivos dessa pesquisa foram analisar a dinâmica ambiental do campo de dunas móveis em direção ao ecossistema manguezal localizado na foz do rio Jaguaribe. Associado à abordagem metodológica, utilizou-se um conjunto de técnicas necessárias à realização da presente pesquisa. A partir de então, analisou-se através do geoprocessamento de fotografias aéreas da década de 80 na escala de 1:25.000 e imagens de satélites Quickbird dos anos de 2004, 2010 e 2013 associados ao estudo da dinâmica eólica com base nos registros da variação de suas taxas de migração. Na área de estudo, encontramos dunas móveis do tipo longitudinais, de pequena ocorrência, barcanóides, de expressiva ocorrência e a predominância dos lençóis de areias. Do ponto de vista de cobertura vegetal, foram identificadas dunas semi-fixas no contato com o ecossistema manguezal. Essas dunas podem ser classificadas como semi- fixas sem forma definida. Não há ocorrência de dunas fixas ou de dunas cimentadas na região. Quanto às gerações dunares, em Canoa Quebrada, domina a geração D1, caracterizada pela ocorrência de dunas atuais, móveis. No contato com o ecossistema manguezal, as dunas semi-fixas se combinam com a geração de dunas anteriores às atuais, do tipo sub-atuais, definindo a existência de dunas de geração D2. A taxa média de migração no campo de dunas durante todo esse período de 40 anos foi de 7m/ano. Nos anos de 2010 a 2013 praticamente não ocorreu migração, mas as dunas continuam migrando em direção ao ecossistema manguezal.

Les éléments de terres rares (ÉTR) sont des métaux de grand intérêt économique et des traceurs géologiques de premier ordre mais leur cycle métallogénique reste encore méconnu. La Province de Grenville expose sa racine orogénique et présente une grande concentration d’occurrences d’ÉTR, notamment associées à des granites pegmatitiques (« PGD ») dans le Grenville central. Deux mécanismes peuvent être à l’origine de ces PGD, (i) la fusion partielle d’une croûte continentale archéenne et/ou paléoprotérozoïque de la racine orogénique, ou (ii) l’extrême différenciation de magmas mantelliques produits en contexte d’extension post-orogénique. Une approche multi-méthodes (terrain, pétrogéochimie, géochronologie et isotopie) permet de caractériser ces PGD à ÉTR et de discuter leur pétrogénèse dans le cadre de l’évolution géodynamique de la province. Ils ont intrudé à ~1005-1000 Ma (U-Pb monazite et zircon) des métaplutons (minéralisation en allanite) ou des séries métasédimentaires (minéralisation en monazite) du segment de moyenne pression de la ceinture Allochtone. La datation U-Pb sur monazite et apatite d’un leucosome de ces paragneiss migmatitiques met en évidence un pic de métamorphisme au faciès granulite à 1080-1050 Ma suivi d’un refroidissement lent à un taux de 2 à 6°C/Ma, d’abord dans les conditions suprasolidus jusqu’à l’intrusion des PGD dans des conditions proches du solidus hydraté, puis dans des conditions subsolidus jusqu’à l’isotherme 450-500°C enregistré à 970-950 Ma. L’intrusion des PGD est synchrone de l’initiation dès ~1005 Ma de la fusion partielle prolongée (> 20 Ma) des métasédiments parautochtones sous-jacents. Le caractère peralumineux des PGD, l’étude de zircons néoformés des PGD (isotopes U-Pb-Hf-O et éléments traces), et l’étude pétrogéochimique des PGD et des métapélites paléoprotérozoïques à archéennes de la ceinture Parautochtone, issues de l’érosion de la marge de Laurentia, traduisent la formation des PGD par leur fusion partielle. Au contraire, un PGD issu de la remobilisation de plutons allochtones est peu minéralisé en ÉTR, confirmant que l’extraction des ÉTR de ces occurrences du Grenville central est associée à des roches d’affinité crustale du Craton du Supérieur / The Rare Earth Elements (REE) are of great economic interest and first order geological tracers. However, their metallogenic cycle remains poorly defined. The Grenville Province exposes its orogenic root and shows numerous REE occurrences that are especially associated with pegmatitic granite dykes (“PGD”) in the central Grenville. Two hypotheses can account for the genesis of these PGD, whether (i) the partial melting of the orogenic root composed of reworked Archean and/or Proterozoic pre-existing continental crust, or (ii) the extreme differentiation of mantle melts produced during post-orogenic extension. A multi-method approach (field geology, petrogeochemistry, geochronology and isotopy) allow to characterize the PGD and discuss their petrogenesis during the geodynamic evolution of the province. They intruded at ca. 1005-1000 Ma (U-Pb on monazite and zircon) metaplutons (mineralization hosted in allanite) or metasedimentary sequences (mineralization hosted in monazite) from the mid-pressure allochthonous crustal segment. U-Pb dating on monazite and apatite from a single leucosome of these migmatitic paragneisses evidence for a peak of metamorphism at ca. 1080-1050 Ma that was followed by a slow cooling at a rate of 2 to 6°C/Ma, first under suprasolidus conditions until the close to wet-solidus intrusion of PGD, and then under subsolidus conditions down to the 450-500°C isotherm dated at ca. 970-950 Ma. The intrusion of the PGD is coeval with the initiation as early as ca. 1005 Ma of the protracted (> 20 Ma) partial melting of underlying parautochthonous paragneisses. The peraluminous character of the PGD, the investigation of pristine magmatic zircon of the PGD (U-Pb-Hf-O isotopes and trace elements), and the petrogeochemical investigations of parautochthonous Paleoproterozoic-Archean metapelites that derive from the Laurentian margin’s erosion, points to the derivation of the PGD from their partial melting. To the contrary, one PGD derived from the reworking of allochthonous plutonic units is poorly mineralized in REE, and confirms that REE from the central Grenville occurrences are issued from crustal rocks of the Superior Craton

abstract: The Jovian moon Europa's putative subsurface ocean offers one of the closest astrobiological targets for future exploration. It’s geologically young surface with a wide array of surface features aligned with distinct surface composition suggests past/present geophysical activity with implications for habitability. In this body of work, I propose a hypothesis for material transport from the ocean towards the surface via a convecting ice-shell. Geodynamical modeling is used to perform numerical experiments on a two-phase water-ice system to test the hypotheses. From these models, I conclude that it is possible for trace oceanic chemistry, entrapped into the newly forming ice at the ice-ocean phase interface, to reach near-surface. This new ice is advected across the ice-shell and towards the surface affirming a dynamical possibility for material transport across the ice-ocean system, of significance to astrobiological prospecting. Next, I use these self-consistent ice-ocean models to study the thickening of ice-shell over time. Europa is subject to the immense gravity field of Jupiter that generates tidal heating within the moon. Analysis of cases with uniform and localized internal tidal heating reveal that as the ice-shell grows from a warm initial ocean, there is an increase in the size of convection cells which causes a dramatic increase in the growth rate of the ice-shell. Addition of sufficient amount of heat also results in an ice-shell at an equilibrium thickness. Localization of tidal heating as a function of viscosity controls the equilibrium thickness. These models are then used to understand how compositional heterogeneity can be created in a growing ice-shell. Impurities (e.g. salts on the surface) that enter the ice-shell get trapped in the thickening ice-shell by freezing. I show the distribution pattern of heterogeneities that can form within the ice-shell at different times. This may be of potential application in identifying the longevity and mobility of brine pockets in Europa's ice-shell which are thought to be potential habitable niches. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2017

L’activité magmatique miocène en Petite Kabylie s’exprime par la mise en place de roches plutoniques et volcaniques de composition majoritairement riche en K ainsi que moyennement riches en K. Ces roches forment des pointements dispersés sur près de 130 km le long de la marge méditerranéenne de l’Algérie. Dans les deux secteurs d’étude : la Kabylie de Collo et l’Ouest Edough-Cap de Fer, elles recoupent les empilements de nappes de socle et de flyschs crétacés et numidiens. De nouvelles datations U-Pb sur zircons et K-Ar sur roche totale et minéraux séparés ont permis de fixer à 17 Ma le début de l’activité magmatique post-collisionnelle à affinité calco-alcaline riche en K2O. Ces âges obtenus sur le batholithe granitique de Bougaroun (200 km2) sont les plus anciens jamais obtenus dans toute la Marge Méditerranéenne du Maghreb. L’activité magmatique s’étend vers l’Est et atteint la zone ouest-Edough-Cap de Fer vers ~16 Ma puis se poursuit de façon intermittente dans les deux secteurs d’étude à ~15 Ma, 14-13 Ma jusqu’à 11 Ma avec la mise en place de corps filoniens mafiques et felsiques en Kabylie de Collo. En outre, un âge oligocène supérieur (27.0 ± 3.0 Ma et 23.3 ± 3.2 Ma) a été mesuré par la méthode Ar/Ar sur amphiboles des gabbros à caractère océanique du Cap Bougaroun s.s (Kabylie de Collo). Les nouvelles données géochimiques et isotopiques ont permis de mettre en évidence deux sources pour le magmatisme dans les deux secteurs étudiés. Une première source mantellique appauvrie, non modifiée par un composant de subduction qui est à l’origine des gabbros à caractère océanique du Cap Bougaroun s.s et de Bou Maïza au Sud de l’Edough. Ceux-ci pourraient représenter des reliques du stade de rifting d’âge oligocène supérieur en prélude à l’ouverture en position arrière-arc du bassin algérien. Une deuxième source enrichie en terres rares légères et en éléments mobiles est représentée par le manteau lithosphérique subcontinental kabyle précédemment métasomatisé durant la subduction à vergence nord de la lithosphère océanique téthysienne au Paléogène. Les magmas mafiques enrichis en LREE issues de cette source ont ensuite évolué par cristallisation fractionnée et contamination crustale pour former les roches intermédiaires et felsiques de la marge est-algérienne. Nous proposons un modèle tectono-magmatique de rupture de slab téthysien associée à une délamination crustale au niveau des bordures des deux lithosphères continentales africaine et kabyle. A 17 Ma, le flux thermique d’origine asthénosphérique ascendant à travers la déchirure du slab téthysien induit la fusion du manteau téthysien. Les magmas mafiques calco-calcalins moyennement potassiques subissent des échanges chimiques avec le socle africain durant leur ascension à travers celui-ci, générant les magmas intermédiaires et felsiques calco-alcalins riches en K caractérisés par une importante signature crustale. / The Miocene igneous activity in Lesser Kabylia includes a ~130 km-long EW-trending lineament that extends along the eastern Algerian margin from Kabylie de Collo to Ouest-Edough-Cap de Fer area. It includes mostly medium-K to High-K calc-alkaline plutonic and volcanic rocks. In the studied area, these magmatic rocks crosscut and/or overlie the inner zones of the Maghrebides represented by basement and Kabylian cretaceous and Numidian flyschs nappes. New U-Pb dating on zircons and K-Ar ages on whole rocks and separated minerals document a 17 Ma onset for the post-collisional K-rich calc-alkaline magmatism. These Upper Burdigalian ages obtained on the Bougaroun pluton are the oldest presently identified for Krich calc-alkaline rocks in the whole 1200 km-long EW trending magmatic belt located along the Mediterranean coast of Maghreb. However, according to new K-Ar ages, magmatic activity started in Ouest Edough zone at ~16 then persisted intermittently in the two studied areas at ~15.5 Ma, 14-13 Ma and stopped at ~11 Ma, with the emplacement of mafic and felsic dykes in Kabylie de Collo. In addition, we measured older (Upper Oligocene) Ar-Ar hornblende ages of 27.0 ± 3.0 Ma and 23.3 ± 3.2 Ma on LREE-depleted gabbros outcropping at Cap Bougaroun sensu stricto. According to our new geochemical and isotopic data, we distinguish two sources for magmatic rocks in the studied area: a depleted mantle source which could represent the ambient asthenosphere still not modified by the subduction processes at the time of emplacement of the Upper Oligocene LREE-depleted gabbros. The latter could be related to the Upper-Oligocene rifting before the back-arc crust formation in Algerian basin or to dyke systems or gabbroic intrusions crosscutting the stretched Kabylian continental crust. An enriched mantle source modified by a subduction component (melt or fluid) escaping from a northward-dipping subducted Tethyan oceanic lithosphere. The enriched mafic magmas are believed to come from this metasomatized mantle and are genetically related to the differentiated rocks through crystal fractionation and assimilation of large amounts of crustal lithologies, during their ascent through the African continental crust. We propose a tectono-magmatic model involving an Early Miocene Tethyan slab breakoff combined with delamination of the edges of the African and Kabylian continental lithospheres. At 17 Ma, the asthenospheric thermal flux upwelling through the slab tear induced the thermal erosion of the Kabylian lithospheric mantle metasomatized during the previous subduction event and triggered its partial melting. We attribute the strong trace element and isotopic crustal signature of Bougaroun felsic rocks to extensive interactions between ascending mafic melts and the African crust underthrust beneath the Kabylie de Collo basement.

Le bassin canadien figure parmi les rares bassins au monde dont la nature et la géométrie du substratum, et donc le mode d'ouverture, ne sont aujourd'hui pas connus. Les modèles paléogéographiques contraints par les rares données disponibles sont sujets à des interprétations controversées avançant des mécanismes et des âges d'ouverture différents, voire contradictoires. Selon les modèles paléogéographiques proposés, les marges du bassin canadien sont tantôt extensives, tantôt transformantes. L'étude de leurs structures et de leurs histoires détaillées est un exercice préalable à la discrimination des modèles plausibles. Le modèle d'ouverture le plus couru fait appel à un changement de polarité de la subduction au sud du bassin canadien au cours de l'orogenèse brookienne polyphasée.La chaîne de Brooks se situe au nord de la péninsule alaskane et au sud du bassin canadien. Elle est un des nombreux stades d'assemblage des "terranes" de la Cordillère Nord-Américaine : celui de l'implication d' " Arctic-Alaska-Chukotka (AAC) " Son stade collisionnel est réputé synchrone de l'ouverture du bassin canadien. C'est donc là qu'il faut chercher les indices des couplages entre la tectonique du bassin au Nord, la déformation intra-cordillère en Alaska et le système de subductions au Sud. Cette orogène est un témoin actif de l'ouverture du bassin canadien, il a enregistré et modifié les conditions aux limites qui ont présidé à son ouverture. La chronologie relative du développement des deux structures est donc essentielle et toute reconstruction de la géodynamique régionale se doit de les concilier en termes de cinématique et de conditions aux limites. / The Canadian basin is among the few basins worldwide for which the nature and the geometry of the substratum, and therefore the opening mode, are still unknown. Paleogeographic models based on the few data available are subject to controversy, with different mechanisms and inception ages. According to current paleogeographic models, the margins of Canadian basin either considered as extensional or transform margins. Detailed study of their structures and chronologies is a preliminary exercise to discriminate between permissible models. The most sollicited opening model assumes a change of polarity of the overall subduction south to the canadian basin during the multiphase Brookian orogeny. The Brooks orogen is located north of the alaskan peninsula and south of the canadian basin. It constitutes one of the main assembly stage of terranes in the Northern Cordillera : docking of the Arctic-Alaska-Chukotka terrane with the peri-Pacific arcs system. Its collisional stage is deemed synchronous of the opening of the Canada Basin, which is likely to provide clues about the coupling between tectonics of the north basin and intra-Alaska Cordillera deformation. This orogen has both recorded and influenced the geodynamic history of the Canadian basin. The relative chronology of the development of the two structures is essential and any reconstruction of regional geodynamics must reconcile them in terms of kinematics and boundary conditions.

L'origine de l'atmosphère terrestre demeure énigmatique. De plus, de nombreux évènements tels que les contributions de matière extraterrestre, le dégazage de la Terre solide ou encore les fuites de l'atmosphère vers l'espace ont modifié la composition de l'atmosphère au cours du temps. Ces travaux de thèse visaient à analyser précisément la composition de l'atmosphère ancienne piégée dans des roches âgées de plusieurs milliards d'années afin de mieux contraindre son origine et son évolution. L'analyse des isotopes du xénon, un gaz rare, démontre qu'une fraction de l'atmosphère terrestre ne peut avoir été apportée par les météorites mais plutôt par des corps riches en eau et en éléments volatils tels que les comètes. De plus, la composition isotopique de l'atmosphère a évolué au cours du temps jusqu'à il y a deux milliards d'années environ. Cette évolution du fractionnement est peut-être concomitante à celle l'oxygénation progressive de l'atmosphère qui a permis le développement de la vie telle que nous la connaissons aujourd'hui. / The origin of the Earth's atmosphere remains poorly understood. Its elemental and isotopic compositions have been shaped by numerous events in the history of our planet, such as extraterrestrial contributions, mantle degassing, atmospheric escape etc. This study aimed to analyze the composition of atmospheric gases trapped in several billion years old samples in order to better understand the origin and evolution of the Earth's atmosphere. Isotope analyses of xenon, a noble gas, demonstrate that part of the atmosphere was not brought by meteorites but might have been delivered to the Earth's atmosphere by volatile-rich bodies such as comets. Furthermore, the isotopic composition of atmospheric Xe evolved over geological ages and can be linked to the progressive oxidation of the atmosphere that permitted the emergence and development of modern forms of life.