La chaîne pyrénéenne présente des structures de déformation bien exposées et des roches sédimentaires syntectoniquesbien conservées qui en font un objet idéal pour étudier les failles. En effet, les textures, structures, compositions chimiques etisotopiques enregistrées par le coeur de la faille chevauchante peuvent renseigner sur les conditions et mécanismes de ladéformation et aussi contraindre dans le temps l’activité de la faille étudiée. Dans la présente thèse, trois chevauchements duversant sud Pyrénéen ont été étudiés pour mieux appréhender le comportement mécanique, chimique et isotopique desphyllosilicates dans des roches sédimentaires déformées. Ces roches sont d'âge éocène à triasique et sont impliquées dans degrand chevauchements (zone cisaillantes) à vergence sud. Ce travail combine observation pétrographique, analyse chimique,modélisation thermodynamique et technique de datation radiométrique 40Ar/39Ar sur des minéraux de moscovite/illite et dechlorite. La première faille étudiée est le chevauchement du Pic de Port Vieux (PPV), chevauchement de second ordre lié auchevauchement majeur de Gavarnie dans le sud-ouest de la Zone Axiale Pyrénéenne. Des mécanismes de pression-dissolutionet recristallisation, accompagnés d’interactions avec un fluide très réducteur sont les principaux paramètres responsables deschangements minéralogiques/chimiques observés dans la zone centrale de la faille. L'indice Kübler de la moscovite et lesdonnées thermométrique sur chlorite suggèrent des températures de 285°C ± 28°C pour l'activité de PPV. De plus, la datation40Ar/39Ar de la moscovite syn-cinématique indique que la faille a fonctionné il y a 36.9 ± 0.2 Ma, ce qui coïncide avec l’âge del'activité du chevauchement de Gavarnie. Les deux autres failles étudiées sont le chevauchement de Lakora qui est situé sur lebord sud de la zone Nord Pyrénéenne et celui de Monte Perdido (au niveau de Torla) situé dans la partie ouest de la zone Sud-Pyrénéenne. Ces deux chevauchements ont été affectés (déformés) par la mise en place de chevauchement de Gavarnie. Lesobservations pétrographiques et les analyses microstructurales ont démontré que la déformation est marquée par du plissement,du boudinage, par le développement d'une schistosité intense, de surfaces de cisaillement, de veines et par un enrichissement enphyllosilicates au coeur de la zone de faille des deux chevauchements. De manière similaire au chevauchement du Pic de PPV,les mécanismes de pression-dissolution et recristallisation sont les principaux mécanismes qui contrôlent la déformation et ilssont à l’origine de l'enrichissement en phyllosilicates néoformés dans les zones de failles des deux chevauchements. En se basantsur les mesures de l'indice de Kübler, il apparait que la déformation de Lakora et Torla s'est produite dans des conditions detempérature plus basse que celles enregistrées pour le chevauchement du PPV. Par ailleurs, es âges les plus jeunes obtenus parla technique 40Ar/39Ar ne peuvent être rattachés à l'âge de la déformation car ils sont plus vieux que les âges des sédimentsimpliqués dans les zones de faille. D'autres hypothèses sont proposées à la fin de cette thèse afin de comprendre les raisons decette incohérence dans les âges et afin de dater la déformation de Lakora et Torla. Ainsi l'ensemble des résultats de cette thèsemontrent que les minéraux phyllosilicatés peuvent être des outils thermochronologiques fiables permettant de dater avecprécision l'activité des failles lorsqu'ils ont été combinés avec des préparations d'échantillons précises et caractérisation détailléedes échantillons. / The Pyrenees belt features well-exposed deformation structures and well preserved syntectonic sedimentary rocksthat make it ideally suited to study thrust faults. The texture, structure and chemical-isotopic compositions of synkinematicphyllosilicates are widely used to estimate the deformation conditions-mechanisms and timing of fault activities. Therefore, inthe present thesis, three thrusts from the Pyrenean orogen have been studied to better understand the mechanical, chemical andisotopic behavior of phyllosilicates from deformed sediments of Eocene-Triassic age that have been involved in large southvergingshear zones. This work combined petrographic observation, chemical analyses, and thermodynamic modeling with40Ar/39Ar geochronology on muscovite/illite and chlorite. The first studied fault is the Pic de Port Vieux thrust (PPVT), a secondorderthrust related to the major Gavarnie thrust (GT) in the south-western part of the Pyrenees Axial Zone. The dissolutionrecrystallization,pressure solution mechanisms, and interaction with highly reductive fluids are the main parameters responsiblefor the mineralogical and chemical changes in the fault core zone. The Kübler index and chlorite thermometry suggest upperanchizoneto epizone conditions with a temperature of 285°C ± 28°C for the PPVT activity. Moreover, the 40Ar/39Ar step-heatingdating of synkinematic muscovite indicates that the fault activity occurred at 36.9 ± 0.2 Ma which coincides with the activity ofthe GT. The two other faults are: Lakora thrust that is located on the southern edge of the North Pyrenean Zone, and the MontePerdido thrust (Torla location) situated on the western part of the South Pyrenean Zone. The two thrust are affected (deformed)by the emplacement of the Gavarnie thrust. The petrographic-microstructural analyses on these faults demonstrated thatdeformation is marked by folding, boudinage, intense cleavage, shear surfaces/veins and enrichment of phyllosilicates in thefault zone of both thrusts. Similar to the PPVT, pressure-solution and dissolution-recrystallization mechanisms are the mainmechanisms that control deformation and enhanced the enrichment of the newly-formed phyllosilicates in the fault zones ofboth thrusts. Based on the Kübler index measurements, the deformation in the Lakora and Torla faults occurred at relativelylower temperature compared to the PPVT. The youngest total gas ages obtained by the 40Ar/39Ar technique are very old for theactivity time of both thrusts as they are older than the depositional ages of the sediments in the fault zones. Further investigationsare proposed at the end of this dissertation in order to better understand this anomaly in age and to successfully obtain the rightage of the two thrusts activity.Based on the results of this thesis, phyllosilicate minerals proved to be reliable thermochronological tools for fault activity atlow-grade metamorphism, when such tools are combined with careful sample preparations and detailed sample characterization.

Unidades litológicas, em particular arenitos, muitas vezes, carecem de um posicionamento cronoestratigráfico preciso. Como os arenitos são importantes rochas-reservatório de hidrocarbonetos e aquíferos, a falta de exatidão nestas informações dificulta a exploração destes bens minerais. A datação relativa de rochas sedimentares pode ser obtida por análise do conteúdo fossilífero ou por correlação estratigráfica. Entretanto, em algumas rochas sedimentares, esta análise não é possível ou tem um caráter duvidoso. Este é o caso da Formação Marizal (Bacia do Recôncavo) que apresenta um histórico controverso sobre a real idade deposicional. A Formação Marizal é um arenito flúvio-eólico cuja idade é discutível e, por isso, sua posição na coluna estratigráfica (aproximadamente Albiniano/Aptiniano), ainda é questionável. Em algumas amostras são encontrados overgrowths de K-feldspatos e nos quais é possível aplicar a técnica de datação 40Ar-39Ar visando obter idades que possam ser relacionadas com processos ocorrentes nestes arenitos (em geral, deposição e/ou diagênese). Entre os minerais pesados existentes nas amostras da Formação Marizal, foram encontrados grãos de zircões. A datação U-Pb de zircões detríticos pode fornecer informações sobre a proveniência desta unidade. Assim, zircões da Formação Marizal foram analisados visando complementar as informações sobre esta unidade, permitindo uma melhor interpretação. Os overgrowths de K-feldspatos indicaram valor de 159.89 ± 23.96 Ma e, para o núcleo detrítico, 432.57 ± 11.89 Ma. O valor médio obtido em torno de 160 Ma, considerando-se que todos os cuidados analíticos e de seleção de amostra foram considerados, é mais antigo do que o esperado. Assim, este valor foi interpretado como indicativo de que o overgrowth teria sido desenvolvido numa rocha fonte sedimentar sendo posteriormente transportado. Esta idade pode ser relacionada a fase pré rifte da Bacia do Recôncavo. O valor confirma ideias existentes de remobilização do substrato da bacia durante a fase rifte. Como tem sido discutido, overgrowths de K-feldspato são estáveis e possíveis de serem transportados por pequenas distâncias, o que corrobora a interpretação acima. Já o valor obtido para o núcleo mostra a contribuição do Paleoprotrozóico adjacente à bacia, retrabalhado no Brasiliano. Em relação ao zircão, a idade do núcleo detrítico de 432,53± 6,54 Ma pode ser associada com a cobertura sedimentar do Paleoproterozóico retrabalhada no ciclo Brasiliano, também observada nos valores U-Pb definidos para os zircões. Em relação ao zircão, os dados indicam ausência aparente de fontes arqueanas. Os resultados mostram duas fontes principais para a sedimentação: uma Rhyaciana (Paleoproterozóico onde ± 53 % dos grãos são “Transamazônicos”) e outra Neoproterozóica-Cambriana (30% dos zircões são “Brasilianos”). / Sandstones represent the most important reservoir rocks and aquifers in many sedimentary basins. It is necessary to have a precise chronostratigraphic position in order to provide a better explotation of water or hydrocarbons. Traditionally, the relative dating of sedimentary units is obtained with fossil content or stratigraphic correlation. But in many sedimentary rocks these analyses are not possible and sometimes have a dubious interpretation. This is the case of the Marizal Formation (Recôncavo Basin) where many questions arise when the age of the unit is questioned. The Marizal Formation is a fluvio-eolic sandstone which has been associated with an Albian/Aptian age in the stratigraphic column, although very discussible. Samples of sandstones of Marizal Formation present an important diagenetic overgrowths around K-feldspar detrital cores and they are suitable to 40Ar-39Ar dating concerning the identification of processes in the sandstones (as diagenesis or depositional ages). Among the heavy mineral suite in the Marizal Formation, zircon grains are identified. The U-Pb dating of detrital zircons can provide information about the provenance of the unit allowing better interpretation to the Marizal Formation. The overgrowths of K-feldspar indicated a value of 159.89 ± 23.96 Ma and to the detrital core, 432.57 ± 11.89 Ma. The mean value obtained around 160 Ma, considering that all care and analytical sample selection were considered, is older than expected. So, this was interpreted as indicating that the overgrowth, have been developed in a sedimentary source rock being transported latter to the depositional site. This age may be related to pre-rift stage of the Recôncavo Basin. The value confirms previous ideas of remobilization of the substrate during the rift basin stage. As has been extensively discussed, overgrowths of K-feldspars are stable and can be transported by small distances, which corroborates the above interpretation. The value obtained to the detrital core can be associated with a Paleoproterozoic sedimentary cover reworked in the Brazilian cycle. For zircon U-Pb dating, the data indicate no apparent Archean sources. The results show two main sources for sedimentation: a Rhyacian (Paleoproterozoic where ± 53% of the grains are "Transamazonian") and another Neoproterozoic-Cambrian (30% of zircon are "Brazilian").

Arc–continent collision is a significant plate boundary process that results in crustal growth. Since the early stages of evolution are often obscured in mature orogens, more complete understanding of the processes involved in arc–continent collision require study of young, active collision settings. The Banda Arc presents an exceptional opportunity to study a young arc–continent collision zone. This thesis presents aspects of the geology and geochronology of Ataúro and the Aileu Complex of Timor-Leste, and the tectonics of the Banda Arc. / U–Pb dating of detrital zircons from the Aileu Complex by LA-ICPMS show major age modes at 270–440 Ma, 860–1240 Ma and 1460–1870 Ma. The youngest zircon populations indicate a maximum depositional age of 270 Ma. The detrital zircon age populations and evidence for juvenile sediments within the sequence favours a synorogenic setting of deposition of sediments sourced from an East Malaya – Indochina terrane. / Previous uncertainty in aspects of the cooling history for the Aileu Complex is resolved with 39Ar/40Ar geochronology of hornblende. Cooling ages of 6–10 Ma are established, with the highest metamorphic grade parts of the Complex yielding the older ages. Cooling ages of 10 Ma imply that metamorphism of the Aileu Complex must have commenced by at least ~12 Ma. Metamorphism at this time is attributed to an arc setting rather than the direct result of collision of the Australian continent with the Banda Arc, an interpretation consistent with the new provenance data. / Geological mapping of Ataúro, an island in the volcanic Banda Arc north of Timor, reveals a volcanic history of bi-modal subaqueous volcanism. 39Ar/40Ar geochronology of hornblende from dacitic lavas confirms that volcanism ceased by ~3 Ma. Following the cessation of volcanism, coral reef marine terraces have been uplifted to elevations of 700 m above sea level. Continuity of the terraces at constant elevations around the island reflects regional-scale uplift most likely linked to sublithospheric processes such as slab detachment. / North of Timor, the near complete absence of intermediate depth seismicity beneath the inactive segment of the arc is attributed to a slab window that has opened in the collision zone and extends to 350 km below the surface. Differences in seismic moment release around this slab window indicate asymmetric rupture, propagating to the east at a much faster rate than to the west. If the lower boundary of this seismic gap signifies the original slab rupture then the slab window represents ~4 m.y. of subsequent subduction and implies that collision preceded the end of volcanism by at least 1 m.y. / Variations in seismic moment release and stress state across the transition from subduction of oceanic crust to arc–continent collision in the Banda Arc are investigated using earthquake catalogues. It is shown that the slab under the western Savu Sea is unusual in that intermediate depth (70–300 km) events indicate that the slab is largely in down-dip compression at this depth range, beneath a region of the arc that has the closest spacing of volcanoes in the Sunda–Banda arc system. This unusual state of stress is attributed to subduction of a northern extension of the Scott Plateau. Present day deformation in the Savu Sea region may be analogous with the earliest stages of collision north of Timor.

Unidades litológicas, em particular arenitos, muitas vezes, carecem de um posicionamento cronoestratigráfico preciso. Como os arenitos são importantes rochas-reservatório de hidrocarbonetos e aquíferos, a falta de exatidão nestas informações dificulta a exploração destes bens minerais. A datação relativa de rochas sedimentares pode ser obtida por análise do conteúdo fossilífero ou por correlação estratigráfica. Entretanto, em algumas rochas sedimentares, esta análise não é possível ou tem um caráter duvidoso. Este é o caso da Formação Marizal (Bacia do Recôncavo) que apresenta um histórico controverso sobre a real idade deposicional. A Formação Marizal é um arenito flúvio-eólico cuja idade é discutível e, por isso, sua posição na coluna estratigráfica (aproximadamente Albiniano/Aptiniano), ainda é questionável. Em algumas amostras são encontrados overgrowths de K-feldspatos e nos quais é possível aplicar a técnica de datação 40Ar-39Ar visando obter idades que possam ser relacionadas com processos ocorrentes nestes arenitos (em geral, deposição e/ou diagênese). Entre os minerais pesados existentes nas amostras da Formação Marizal, foram encontrados grãos de zircões. A datação U-Pb de zircões detríticos pode fornecer informações sobre a proveniência desta unidade. Assim, zircões da Formação Marizal foram analisados visando complementar as informações sobre esta unidade, permitindo uma melhor interpretação. Os overgrowths de K-feldspatos indicaram valor de 159.89 ± 23.96 Ma e, para o núcleo detrítico, 432.57 ± 11.89 Ma. O valor médio obtido em torno de 160 Ma, considerando-se que todos os cuidados analíticos e de seleção de amostra foram considerados, é mais antigo do que o esperado. Assim, este valor foi interpretado como indicativo de que o overgrowth teria sido desenvolvido numa rocha fonte sedimentar sendo posteriormente transportado. Esta idade pode ser relacionada a fase pré rifte da Bacia do Recôncavo. O valor confirma ideias existentes de remobilização do substrato da bacia durante a fase rifte. Como tem sido discutido, overgrowths de K-feldspato são estáveis e possíveis de serem transportados por pequenas distâncias, o que corrobora a interpretação acima. Já o valor obtido para o núcleo mostra a contribuição do Paleoprotrozóico adjacente à bacia, retrabalhado no Brasiliano. Em relação ao zircão, a idade do núcleo detrítico de 432,53± 6,54 Ma pode ser associada com a cobertura sedimentar do Paleoproterozóico retrabalhada no ciclo Brasiliano, também observada nos valores U-Pb definidos para os zircões. Em relação ao zircão, os dados indicam ausência aparente de fontes arqueanas. Os resultados mostram duas fontes principais para a sedimentação: uma Rhyaciana (Paleoproterozóico onde ± 53 % dos grãos são “Transamazônicos”) e outra Neoproterozóica-Cambriana (30% dos zircões são “Brasilianos”). / Sandstones represent the most important reservoir rocks and aquifers in many sedimentary basins. It is necessary to have a precise chronostratigraphic position in order to provide a better explotation of water or hydrocarbons. Traditionally, the relative dating of sedimentary units is obtained with fossil content or stratigraphic correlation. But in many sedimentary rocks these analyses are not possible and sometimes have a dubious interpretation. This is the case of the Marizal Formation (Recôncavo Basin) where many questions arise when the age of the unit is questioned. The Marizal Formation is a fluvio-eolic sandstone which has been associated with an Albian/Aptian age in the stratigraphic column, although very discussible. Samples of sandstones of Marizal Formation present an important diagenetic overgrowths around K-feldspar detrital cores and they are suitable to 40Ar-39Ar dating concerning the identification of processes in the sandstones (as diagenesis or depositional ages). Among the heavy mineral suite in the Marizal Formation, zircon grains are identified. The U-Pb dating of detrital zircons can provide information about the provenance of the unit allowing better interpretation to the Marizal Formation. The overgrowths of K-feldspar indicated a value of 159.89 ± 23.96 Ma and to the detrital core, 432.57 ± 11.89 Ma. The mean value obtained around 160 Ma, considering that all care and analytical sample selection were considered, is older than expected. So, this was interpreted as indicating that the overgrowth, have been developed in a sedimentary source rock being transported latter to the depositional site. This age may be related to pre-rift stage of the Recôncavo Basin. The value confirms previous ideas of remobilization of the substrate during the rift basin stage. As has been extensively discussed, overgrowths of K-feldspars are stable and can be transported by small distances, which corroborates the above interpretation. The value obtained to the detrital core can be associated with a Paleoproterozoic sedimentary cover reworked in the Brazilian cycle. For zircon U-Pb dating, the data indicate no apparent Archean sources. The results show two main sources for sedimentation: a Rhyacian (Paleoproterozoic where ± 53% of the grains are "Transamazonian") and another Neoproterozoic-Cambrian (30% of zircon are "Brazilian").

Unidades litológicas, em particular arenitos, muitas vezes, carecem de um posicionamento cronoestratigráfico preciso. Como os arenitos são importantes rochas-reservatório de hidrocarbonetos e aquíferos, a falta de exatidão nestas informações dificulta a exploração destes bens minerais. A datação relativa de rochas sedimentares pode ser obtida por análise do conteúdo fossilífero ou por correlação estratigráfica. Entretanto, em algumas rochas sedimentares, esta análise não é possível ou tem um caráter duvidoso. Este é o caso da Formação Marizal (Bacia do Recôncavo) que apresenta um histórico controverso sobre a real idade deposicional. A Formação Marizal é um arenito flúvio-eólico cuja idade é discutível e, por isso, sua posição na coluna estratigráfica (aproximadamente Albiniano/Aptiniano), ainda é questionável. Em algumas amostras são encontrados overgrowths de K-feldspatos e nos quais é possível aplicar a técnica de datação 40Ar-39Ar visando obter idades que possam ser relacionadas com processos ocorrentes nestes arenitos (em geral, deposição e/ou diagênese). Entre os minerais pesados existentes nas amostras da Formação Marizal, foram encontrados grãos de zircões. A datação U-Pb de zircões detríticos pode fornecer informações sobre a proveniência desta unidade. Assim, zircões da Formação Marizal foram analisados visando complementar as informações sobre esta unidade, permitindo uma melhor interpretação. Os overgrowths de K-feldspatos indicaram valor de 159.89 ± 23.96 Ma e, para o núcleo detrítico, 432.57 ± 11.89 Ma. O valor médio obtido em torno de 160 Ma, considerando-se que todos os cuidados analíticos e de seleção de amostra foram considerados, é mais antigo do que o esperado. Assim, este valor foi interpretado como indicativo de que o overgrowth teria sido desenvolvido numa rocha fonte sedimentar sendo posteriormente transportado. Esta idade pode ser relacionada a fase pré rifte da Bacia do Recôncavo. O valor confirma ideias existentes de remobilização do substrato da bacia durante a fase rifte. Como tem sido discutido, overgrowths de K-feldspato são estáveis e possíveis de serem transportados por pequenas distâncias, o que corrobora a interpretação acima. Já o valor obtido para o núcleo mostra a contribuição do Paleoprotrozóico adjacente à bacia, retrabalhado no Brasiliano. Em relação ao zircão, a idade do núcleo detrítico de 432,53± 6,54 Ma pode ser associada com a cobertura sedimentar do Paleoproterozóico retrabalhada no ciclo Brasiliano, também observada nos valores U-Pb definidos para os zircões. Em relação ao zircão, os dados indicam ausência aparente de fontes arqueanas. Os resultados mostram duas fontes principais para a sedimentação: uma Rhyaciana (Paleoproterozóico onde ± 53 % dos grãos são “Transamazônicos”) e outra Neoproterozóica-Cambriana (30% dos zircões são “Brasilianos”). / Sandstones represent the most important reservoir rocks and aquifers in many sedimentary basins. It is necessary to have a precise chronostratigraphic position in order to provide a better explotation of water or hydrocarbons. Traditionally, the relative dating of sedimentary units is obtained with fossil content or stratigraphic correlation. But in many sedimentary rocks these analyses are not possible and sometimes have a dubious interpretation. This is the case of the Marizal Formation (Recôncavo Basin) where many questions arise when the age of the unit is questioned. The Marizal Formation is a fluvio-eolic sandstone which has been associated with an Albian/Aptian age in the stratigraphic column, although very discussible. Samples of sandstones of Marizal Formation present an important diagenetic overgrowths around K-feldspar detrital cores and they are suitable to 40Ar-39Ar dating concerning the identification of processes in the sandstones (as diagenesis or depositional ages). Among the heavy mineral suite in the Marizal Formation, zircon grains are identified. The U-Pb dating of detrital zircons can provide information about the provenance of the unit allowing better interpretation to the Marizal Formation. The overgrowths of K-feldspar indicated a value of 159.89 ± 23.96 Ma and to the detrital core, 432.57 ± 11.89 Ma. The mean value obtained around 160 Ma, considering that all care and analytical sample selection were considered, is older than expected. So, this was interpreted as indicating that the overgrowth, have been developed in a sedimentary source rock being transported latter to the depositional site. This age may be related to pre-rift stage of the Recôncavo Basin. The value confirms previous ideas of remobilization of the substrate during the rift basin stage. As has been extensively discussed, overgrowths of K-feldspars are stable and can be transported by small distances, which corroborates the above interpretation. The value obtained to the detrital core can be associated with a Paleoproterozoic sedimentary cover reworked in the Brazilian cycle. For zircon U-Pb dating, the data indicate no apparent Archean sources. The results show two main sources for sedimentation: a Rhyacian (Paleoproterozoic where ± 53% of the grains are "Transamazonian") and another Neoproterozoic-Cambrian (30% of zircon are "Brazilian").

Cette étude de terrain du massif des Ecrins (Alpes Occidentales, zone externe) montre que le raccourcissement Alpin est essentiellement accommodé dans le socle par des zones de cisaillement inverse top-vers-l'ouest ductile-fragile (probablement localisé par la présence de demi-graben) ainsi que par les nappes de charriage de la Meije et du Combeynot à l'Est du massif. Les failles normales N-S ne semblent pas avoir été réactivées. Ces zones de cisaillement sont caractérisées par une phengitisation des feldspaths le long de bandes anastomosées dont la géométrie traduit un gradient de déformation qui permet d'expliquer la formation des "plis de socle" soulignée par la géométrie des téguments de Trias. Les températures maximum d'enfouissement liées au charriage des unités internes sont proches de l'isotherme 335°C pour un gradient géothermique compris entre 20 et 25°C.km-1 depuis Bourg d'Oisans au Front Pennique. Les zones de cisaillement ont été datées entre 33 et 25 Ma (40Ar/39Ar sur phengites syn-cinématiques), ce qui suggère qu'elles ont été initiées très tôt après l'enfouissement de la zone externe qui débute vers 34Ma. Les phyllonites présentent des âges plus jeunes que les mylonites, ce qui traduit une localisation de la déformation le long de ces bandes anastomosées de faible résistance entre 30 et 25Ma. Le raccourcissement NO-SE observé le long du Front Pennique semble synchrone des déformations E-O à NESO du massif des Ecrins. La présence d'une zone de cisaillement transpressive senestre diffuse entre le massif des Ecrins et les Alpes Ligures, issu de la réactivation d'une zone de transfert Liasique, permettrait d'expliquer en partie la cinématique d'édification Oligocène des Alpes Occidentales. Au Miocène, la déformation se localise le long d'un plan de chevauchement sous le massif de Belledonne, donnant naissance au Vercors, ainsi que le long du Front Pennique réactivé en faille normale. / This field-based study of the Ecrins massif (Western Alps, external zone) show that the Alpine shortening is accomodated within the basement by brittle-ductile top-to-the-west reverse shear zones (probably localized by half-graben) as well as by the thrust sheets of La Meije and Combeynot to the east of the massif. The N-S normal fault do not seems to be reactivated. These shear zones are characterized by a phengitisation of feldspars along anastomosing planes whose geometry reflect a strain gradient which explain the "basement folds" formation underlined by the geometry of Triassic teguments. The maximum temperatures reach by the cover, due to the burial under the internal nappes are close to the isotherms 335°C for a geothermal gradient close to 20-25°C.km-1 from Bourg d'Oisans to the Penninic Frontal Thrust (PFT). The shear zones were dated between 33 to 25 Ma (40Ar/39Ar on syn-kinematics phengites), suggesting that they were initiated slightly after the burial which start close to 34 Ma. The phyllonites show younger ages than mylonite; that argue a localization of the deformation along these anastomosing planes between 30 to 25Ma and traduce a weak crust. The NW-Se shortening observed alonf the PFT seems to be coeval with the E-W to NE-SW shortening of the Ecrins massif. A sinistrial transpressive diffuse shear zones between the Ecrins massif and the Ligurian Alps, which is probably a reactivated Liassic transfer zone, can explaina part of the Oligocene building kinematics of the Western Alps. During Miocence, the deformation is localized along a crustal thrust under the Belledonne massif, which has given the Vercors massif, and along the PFT, reactivated as a normal fault.

La tsavorite, grossulaire vert à V-Cr-Mn, est contenue dans des gneiss et roches calco-silicatées graphiteux, souvent associés à des marbres dolomitiques, et appartenant à la ceinture métamorphique néoprotérozoïque mozambicaine. La tsavorite se trouve soit dans des nodules ou des veines de quartz (gisements primaires), soit dans des placers (gisements secondaires). L'étude minéralogique des tsavorites propose un nouveau protocole de certification de leur origine géographique, à partir du rapport V/Cr, de la teneur en Mn et du [delta]18 O. L'étude des gisements de Lemshuku et Namalulu en Tanzanie montre que le métamorphisme des protolithes sédimentaires riches en matière organique et évaporites s'est effectué à P = 7,0 ± 0,4 kbar et T = 677 ± 14°C, à 634 ± 22 Ma (datation U-Th-Pb sur monazite). Le bâti métamorphique s'est refroidi vers 500 Ma (datation 40Ar-39Ar sur muscovite). Deux stades de métasomatose sont reliés à la formation de la tsavorite : (i) une métasomatose de diffusion formant les nodules à P = 5,0-7,4 kbar et T = 580-691°C; (ii) une métasomatose calcique d'infiltration contemporaine de la formation des veines de quartz à P = 3,6-4,9 kbar et T = 505-587°C. Ces dernières sont datées in situ par la méthode Sm-Nd à 606 ± 36 Ma. Les évaporites continentales, déposées dans une sabkha de côte marine avec des sédiments silico-calcaires, sont transformées en tsavorite dans le cas des nodules, alors que les sels fondus sont associés à la formation des veines de quartz. Les minéralisations sont contrôlées par la lithostratigraphie et la tectonique / Tsavorite, a (V, Cr, Mn)-bearing green grossular, is hosted by graphitic gneisses or calc-silicates, often asssociated with dolomitic marbles, and belonging to the Metamorphic Neoproterozoic Mozambique Belt. Tsavorite is found either as nodules or in quartz veins (primary deposits), or in placers (secondary deposits). The mineralogical study of tsavorites suggests a new protocol to certificate their geographical origin, based on the V/Cr ratio, Mn content and delta18O. The study of the Lemshuku and Namalulu deposits in Tanzania has shown that the metamorphism of organic matter-rich and evaporites-rich sedimentary protoliths occurred at P = 7.0 ± 0.4 kbar and T = 677 ± 14°C, at 634 ± 22 Ma (U-Th-Pb dating on monazite). The metamorphic series cooled down at around 500 Ma (40Ar-39Ar dating on muscovite). Two metasomatic stages are linked to the formation of tsavorite : (i) diffusion metasomatism forming nodules at P = 5.0-7.4 kbar and T = 580-691°C; (ii) calcitic infiltration metasomatism forming quartz veins at P = 3.6-4.9 kbar and T = 505-587°C. These last have been dated in situ with Sm-Nd dating at 606 ± 36 Ma. Continental evaporites, deposited in a coastal marine sabkha with (Si, Ca)-bearing sediments, transformed into tsavorite in the case of the nodules, while the molten salts are associated with the formation of the quartz veins. The mineralisations are controlled by lithostratigraphy and structure