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La présente étude porte sur les caractéristiques structurales de la zone de cisaillement de Kandi dans la région Savalou-Dassa au Centre-Bénin et ses relations avec le magmatisme spatialement associé. Elle vise à comprendre l’évolution tardi- à post-collision de la chaîne panafricaine des Dahoméyides. Les études structurales, pétrologiques et géochronologiques indiquent que la zone de cisaillement de Kandi au Centre-Bénin correspond à un décrochement ductile dextre, large d’au moins 50 Km, et dans laquelle l’évolution de la déformation jusqu’à plus basse température a entraîné l’apparition des bandes de tectonites d’épaisseur kilométrique. Le décrochement ductile de Kandi a fonctionné dans la chaîne des Dahoméyides à partir de c. 606 Ma et il a affecté des granulites d’âge paléoprotérozoïque et des gneiss, migmatites et granitoïdes néoprotérozoïques. Les magmatites spatialement associés à la zone de cisaillement de Kandi sont anté- et syn-décrochements ductiles. Le magmatisme anté-décrochement ductile est sub-alcalin et comporte une composante crustale et une composante mantellique appauvrie. Le magmatisme sub-alcalin s’est poursuivi au cours du décrochement ductile et cette période se caractérise par un cogénétisme plutonisme-volcanisme. De même, on observe une transition de magmas sub-alcalins-alcalins, qui traduit un changement de sources mantelliques-manteau appauvri manteau enrichi. Nous montrons également que le bassin volcano-sédimentaire de Idaho-Mahou est ouvert par le jeu de décrochements. Les volcanites du bassin, présentant des analogies de composition chimique et de chronologie de mise en place avec le pluton syn-cisaillement de Fita, indiquent que ce bassin est syn-orogénique, intramontagneux. La présence de magmas d’origine mantellique remontant dans la zone de cisaillement implique l’ampleur lithosphérique de la zone de cisaillement de Kandi. La synthèse des données indique que le fonctionnement du décrochement ductile de Kandi est contemporain de l’édifice de nappes et chevauchements dans les unités externes des Dahoméyides et démontre ainsi une partition de la déformation à l’échelle de la chaîne pendant la période post-collision. Elle indique également que le fonctionnement du décrochement ductile de Kandi à l’Ouest de la chaîne des Dahoméyides est synchrone de la période d’activité des zones de cisaillement à l’Est de la chaîne et du Hoggar et du Brésil / The present study focuses on the structural characteristics of the Kandi shear zone (KSZ) and the time and space relationships between deformation and magmatic events in the central region of Bénin. This tectonic structure is a segment of a lithospheric-scale shear zone that extends from the Hoggar massif (Algeria) to the Atlantic Coast in Bénin and continues down to western Brazil. The present work aims at better understanding the late to post-collision geodynamic evolution of the pan African Dahomeyide fold beltIn summary, this study reveals that the Kandi shear zone in the Central-Bénin is a large (more than 50 km width) dextral transcurrent shear zone, where the latest increments of deformation occur as more localized (kilometric-scale width) shear bands at low temperature. The KSZ activity started at c. 610 Ma and affected the rock basement, including Paleoproterozoic granulites and Neoproterozoic gneisses, migmatites and granitoids. The granitoids intrusions that are spatially associated to the KSZ display ante- to syn-shearing structural features. The earliest intrusion, ante-tectonic Dassa has sub-alkaline affinity deriving from crustal and depleted mantle magmas. This sub-alkaline series carry on during the transcurrent shearing with the Gobada, Tré, Tchetti intrusions. The latest magmatic event of Fita intrusion suggests the transition from sub-alkaline to alkaline magmas, probably reflecting mantle source evolution, from depleted to enriched mantle. We also showed that the Idaho-Mahou volcano-sedimentary basin opened during the transcurrent shearing and the volcanic mafic and felsic rocks are probably related to the successive sub-alkaline to alkaline intrusions. The occurrence of mantle-derived magmas in the shear zone confirms the lithospheric scale of the Kandi shear zone. According to the available radiometric data from the Dahomeyides fold belt, the Kandi shear zone activity seems to contemporaneous with the nappes stacking and thrusting stages in the external orogenic zone (Atacora and western Benin plain) orogen-scale. It also indicates that the KSZ was coeval with the major shear zones from the easternmost region of the Dahomeyides fold belt (NE Nigeria), of the Hoggar and Braziliano belts.

Le Cabinda qui est intégré à l’Angola depuis 1975, revendique son autonomie. En rappelant des données historiques, on comprend que ce territoire a toujours bénéficié d’un statut de Protectorat sous la domination portugaise. Ceci a contribué à l’épanouissement des spécificités culturelles et sociales du peuple cabindais. Ce statut a été supprimé à l’indépendance de l’Angola qui a absorbé Cabinda, fortement convoité pour ses richesses naturelles, pétrolières et minières. De 1970 à 1980, le Cabinda est impliqué dans une guerre meurtrière. Nous avons retenu cette période pour examiner la manière dont deux magazines de la presse panafricaine, Jeune Afrique et Afrique-Asie, en ont rendu compte. A travers des corpus d’articles publiés, nous voyons la manière dont les journalistes ont produit de l’information à propos du Cabinda. Cette thèse met en lumière le manque d’intérêt de la presse panafricaine francophone, pour la situation sociopolitique au Cabinda. / The province of Cabinda, included to Angola since 1975, claims for autonomy. The history tells us about its status as a Portuguese protectorate; what contributed to the blossoming of the cultural and social specifities of the Cabinda people. This status was ignored at the Angolan independence with as consequence the absorption of Cabinda, highly coveted because its kerosene and other mineral resources. In the 1970s, the province of Cabinda was involved into a civil war extremely deadly. We have kept this temporal setting to see the way two magazines of the African Press, Jeune Afrique and Afrique-Asie, reported about the war andwe have simultaneously analyzed through a set of published articles the way journalists have reported about Cabinda. This dissertation throws light on the disinterest of the French-speaking Pan African Press about the sociopolitical situation of Cabinda.

O período pós-colisional do Ciclo Brasiliano/Pan-africano é marcado no sul do Brasil pela ocorrência de granitos metaluminosos e peraluminosos, controlados por um sistema transcorrente de zonas de cisalhamento (ZC). No Rio Grande do Sul (RS), a Zona de Cisalhamento Transcorrente Dorsal de Canguçu (ZCTDC), de cinemática sinistral e direção NE, é a principal estrutura que condicionou o posicionamento desses granitos (ca. 634 – 610 Ma). Entretanto, o Granito Butiá (GB – 629 Ma), localizado a noroeste da ZCTDC, ocorre como um corpo alongado de direção NNW que intrude rochas de alto grau metamórfico do Complexo Várzea do Capivarita (ca. 650 Ma). O GB possui trama planar bem desenvolvida (S>L), cuja foliação mergulha com alto ângulo para NNW; apesar de raramente apresentar lineação, seu posicionamento é interpretado como sintectônico a uma ZC transcorrente de cinemática destral. Dessa forma, um estudo de anisotropia de susceptibilidade magnética (ASM) foi realizado no GB, com o objetivo de melhor delimitar os mecanismos de seu posicionamento e relacioná-los com o sistema regional de zonas de cisalhamento. No total, 492 espécimes (180 cilindros) foram coletadas em 16 sítios, distribuídos no corpo principal do GB. A mineralogia magnética foi investigada através de curvas termomagnéticas, curvas de histereses e de aquisição de magnetização remanente isotermal, e detalhada com microscopia eletrônica de varredura em amostras representativas. Essas análises demonstram o domínio de fases paramagnéticas e uma pequena contribuição de minerais de baixa coercividade (e.g., magnetita, titanomagnetita) e alta coercividade (e.g., hematita). Apesar disso, a trama magnética é controlada exclusivamente por cristais paramagnéticos de biotita. A susceptibilidade magnética total é baixa e varia entre 0,1 e 8x10-5 SI. O parâmetro de forma (T) varia de 0,272 a 0,908 e o grau de anisotropia (P) varia de 1,073 a 1,266, aumentando do centro em direção as margens do GB. A presença de par S-C destral de origem magmática e microestruturas de deformação em alta temperatura (~650°C) confirmam que a deformação atuava durante o processo de cristalização. Esses elementos, junto à análise da trama magnética, sugerem que a ascensão e o posicionamento do magma foram controlados por uma ZC transcorrente de direção NNW e cinemática destral. Próximo as rochas encaixantes, os elipsoides magnéticos são fortemente oblatos, a foliação mergulha com alto ângulo para W ou E, e a lineação têm alto a moderado caimento, sugerindo significante achatamento e domínio de uma componente de cisalhamento puro de deformação. Longe das margens, a lineação tem baixos caimentos, paralelos a direção da foliação (NW-NNW), sugerindo um transporte horizontal e domínio de uma componente de cisalhamento simples de deformação, que promoveu o estiramento. No nordeste do corpo, a presença de roof pendants e menores ângulos de mergulho da foliação sugerem proximidade com a cúpula. A combinanção de bouyoancy forces e da partição da deformação regional, em cisalhamento puro e simples durante o posicionamento do GB, está de acordo com um regime transpressivo. Esses resultados também sugerem uma relação no tempo-espaço entre a ZC que controlou o posicionamento do GB e a ZCTDC. Possivelmente, elas formavam um par conjugado do mesmo sistema transcorrente durante o estágio pós-colisional do Ciclo Brasiliano/Pan-africano no sul do Brasil. / The post-collisional stage of the Brasiliano/Pan-African Orogenic Cycle in Southern Brazil is marked by metaluminous and peraluminous granites controlled by a transcurrent shear zone system. In the Rio Grande do Sul State, southernmost Brazil, the sinistral, NE-trending Dorsal de Canguçu Transcurrent Shear Zone (DCTSZ) is the best known structure that conditioned these peraluminous granites (ca. 634 – 610 Ma). However, the NNW-elongate Butiá Granite (BG – 629 Ma) is emplaced to the northwest of the DCTSZ, intrusive in the high-grade Várzea do Capivarita Complex (ca. 650 Ma). The BG has a S>L fabric, which foliation steeply dips towards NNW. Despite its poorly-developed linear fabric, BG emplacement is interpreted to have been controlled by a dextral transcurrent shear zone. Thus, anisotropy of magnetic susceptibility (AMS) study was performed in the BG aiming to constrain its emplacement mechanism and the relation of the granite with the regional shear zone system. A total of 492 specimens (180 drill cores) were obtained through 16 sites distributed along the BG main body. Magnetic mineralogy was investigated by hysteresis loops, thermomagnetic and IRM acquisition curves, and a complementary SEM analysis in representative samples. These experiments show a dominant contribution of paramagnetic phases and a small content of low-coercivity (e.g., magnetite and titanomagnetite) and highcoercivity (e.g., hematite) remanence-carrying minerals. In spite of the presence of minor ferromagnetic grains, the BG magnetic anisotropy fabric is interpreted as dominantly controlled by paramagnetic biotite crystals. The bulk magnetic susceptibility ranges between 0.1 and 8.0×10−5 SI. Shape parameter (T) ranges from 0.272 to 0.908, and anisotropy degree (P) ranges from 1.073 to 1.266, increasing from the inner portion of the pluton to its margins. The presence of dextral S-C magmatic fabric and high temperature (ca. 650 °C), solid-state deformation at the margins confirms that the pluton was deformed during its cooling process. Such features, together the magnetic fabric analysis, suggest that magma ascent and emplacement were controlled by a NNW-trending dextral transcurrent shear zone. Close to the host-rocks, magnetic foliation dips steeply towards W or E, and magnetic lineation plunges steeply to moderate, displaying strongly-oblate ellipsoids. This is interpreted as a result of shortening and the significantly pure-shear component of deformation operating close to the host-rocks. Shallow-plunging lineation parallel to the NWto NNW-striking foliation is found away from the pluton margins, which is related to the horizontal displacement, where the simple-shear component of deformation was more effective, resulting stretching. Foliation becomes less steep towards the BG northeastern portion and the presence of roof pendants in this area suggests the proximity to the roof zone. The combination of buoyancy forces and the partitioning of regional strain into simple and pure shear are in accordance with a transpressive regime. These results also suggest a time-space relationship between the NNW-dextral shear zone that controlled the emplacement of the Butiá Granite and the sinistral, NE-trending DCTSZ, responsible for the emplacement of peraluminous granites. Possibly, these zones formed a conjugate pair during the transcurrent deformation of the early post-collisional stage of the Brasiliano/PanAfrican Cycle in southernmost Brazil.

Cette thèse étudie les systèmes bancaires africains et se concentre tout particulièrement sur la question de l’actionnariat bancaire et de ses impacts. Le premier chapitre étudie l’efficience de coût. Les banques étrangères sont plus efficientes que les banques domestiques et les banques panafricaines sont les banques les plus efficientes du continent. Le second chapitre étudie la cyclicité des portefeuilles de prêt. La croissance des prêts des banques africaines est sensible à l’évolution de la croissance du PIB par habitant. Les banques panafricaines ont une croissance des prêts moins cyclique. La croissance des prêts des banques étrangères est sensible à l’évolution de la croissance dans leur pays d’origine. Les chapitres trois et quatre étudient l’inclusion financière. La probabilité d’être inclus financièrement augmente lorsque l’individu est de sexe masculin, a un revenu plus élevé, une éducation plus importante, et est plus âgé jusqu’à un certain seuil. La présence des banques panafricaines augmente l’accès au crédit des entreprises. Les banques panafricaines augmenteraient aussi l’inclusion financière des ménages, mais ce résultat est moins robuste. La conclusion générale de cette thèse souligne le rôle nouveau et bénéfique que jouent les banques panafricaines sur le continent. Ces jeunes institutions financières augmentent l’efficience de coût, diminuent la cyclicité des portefeuilles de prêt, et améliorent l’inclusion financière. / This dissertation studies African financial systems with a focus on bank ownership. Chapter one studies cost efficiency. Foreign banks are more efficient than domestic banks, and Pan-African banks are the most efficient banks on the continent. Chapter two analyses lending procyclicality. Lending growth of African banks is sensitive to the GDP per capita growth. Pan-African banks have a less pro-cyclical lending behaviour. Lending growth of African foreign banks is sensitive to GDP per capita growth in their home country. Chapter three and four study financial inclusion. Being male, wealthier, more educated and older to a certain extent increases the likelihood to be financially included. Pan-African banks presence increases firms’ access to credit. Pan-African banks would also increase households’ financial inclusion, but such result is less robust.The general conclusion of this dissertation underlines the new, beneficial role Pan-African banks play on the continent. These young financial institutions increase cost efficiency, reduce cyclicality of lending and improve financial inclusion.

O período pós-colisional do Ciclo Brasiliano/Pan-africano é marcado no sul do Brasil pela ocorrência de granitos metaluminosos e peraluminosos, controlados por um sistema transcorrente de zonas de cisalhamento (ZC). No Rio Grande do Sul (RS), a Zona de Cisalhamento Transcorrente Dorsal de Canguçu (ZCTDC), de cinemática sinistral e direção NE, é a principal estrutura que condicionou o posicionamento desses granitos (ca. 634 – 610 Ma). Entretanto, o Granito Butiá (GB – 629 Ma), localizado a noroeste da ZCTDC, ocorre como um corpo alongado de direção NNW que intrude rochas de alto grau metamórfico do Complexo Várzea do Capivarita (ca. 650 Ma). O GB possui trama planar bem desenvolvida (S>L), cuja foliação mergulha com alto ângulo para NNW; apesar de raramente apresentar lineação, seu posicionamento é interpretado como sintectônico a uma ZC transcorrente de cinemática destral. Dessa forma, um estudo de anisotropia de susceptibilidade magnética (ASM) foi realizado no GB, com o objetivo de melhor delimitar os mecanismos de seu posicionamento e relacioná-los com o sistema regional de zonas de cisalhamento. No total, 492 espécimes (180 cilindros) foram coletadas em 16 sítios, distribuídos no corpo principal do GB. A mineralogia magnética foi investigada através de curvas termomagnéticas, curvas de histereses e de aquisição de magnetização remanente isotermal, e detalhada com microscopia eletrônica de varredura em amostras representativas. Essas análises demonstram o domínio de fases paramagnéticas e uma pequena contribuição de minerais de baixa coercividade (e.g., magnetita, titanomagnetita) e alta coercividade (e.g., hematita). Apesar disso, a trama magnética é controlada exclusivamente por cristais paramagnéticos de biotita. A susceptibilidade magnética total é baixa e varia entre 0,1 e 8x10-5 SI. O parâmetro de forma (T) varia de 0,272 a 0,908 e o grau de anisotropia (P) varia de 1,073 a 1,266, aumentando do centro em direção as margens do GB. A presença de par S-C destral de origem magmática e microestruturas de deformação em alta temperatura (~650°C) confirmam que a deformação atuava durante o processo de cristalização. Esses elementos, junto à análise da trama magnética, sugerem que a ascensão e o posicionamento do magma foram controlados por uma ZC transcorrente de direção NNW e cinemática destral. Próximo as rochas encaixantes, os elipsoides magnéticos são fortemente oblatos, a foliação mergulha com alto ângulo para W ou E, e a lineação têm alto a moderado caimento, sugerindo significante achatamento e domínio de uma componente de cisalhamento puro de deformação. Longe das margens, a lineação tem baixos caimentos, paralelos a direção da foliação (NW-NNW), sugerindo um transporte horizontal e domínio de uma componente de cisalhamento simples de deformação, que promoveu o estiramento. No nordeste do corpo, a presença de roof pendants e menores ângulos de mergulho da foliação sugerem proximidade com a cúpula. A combinanção de bouyoancy forces e da partição da deformação regional, em cisalhamento puro e simples durante o posicionamento do GB, está de acordo com um regime transpressivo. Esses resultados também sugerem uma relação no tempo-espaço entre a ZC que controlou o posicionamento do GB e a ZCTDC. Possivelmente, elas formavam um par conjugado do mesmo sistema transcorrente durante o estágio pós-colisional do Ciclo Brasiliano/Pan-africano no sul do Brasil. / The post-collisional stage of the Brasiliano/Pan-African Orogenic Cycle in Southern Brazil is marked by metaluminous and peraluminous granites controlled by a transcurrent shear zone system. In the Rio Grande do Sul State, southernmost Brazil, the sinistral, NE-trending Dorsal de Canguçu Transcurrent Shear Zone (DCTSZ) is the best known structure that conditioned these peraluminous granites (ca. 634 – 610 Ma). However, the NNW-elongate Butiá Granite (BG – 629 Ma) is emplaced to the northwest of the DCTSZ, intrusive in the high-grade Várzea do Capivarita Complex (ca. 650 Ma). The BG has a S>L fabric, which foliation steeply dips towards NNW. Despite its poorly-developed linear fabric, BG emplacement is interpreted to have been controlled by a dextral transcurrent shear zone. Thus, anisotropy of magnetic susceptibility (AMS) study was performed in the BG aiming to constrain its emplacement mechanism and the relation of the granite with the regional shear zone system. A total of 492 specimens (180 drill cores) were obtained through 16 sites distributed along the BG main body. Magnetic mineralogy was investigated by hysteresis loops, thermomagnetic and IRM acquisition curves, and a complementary SEM analysis in representative samples. These experiments show a dominant contribution of paramagnetic phases and a small content of low-coercivity (e.g., magnetite and titanomagnetite) and highcoercivity (e.g., hematite) remanence-carrying minerals. In spite of the presence of minor ferromagnetic grains, the BG magnetic anisotropy fabric is interpreted as dominantly controlled by paramagnetic biotite crystals. The bulk magnetic susceptibility ranges between 0.1 and 8.0×10−5 SI. Shape parameter (T) ranges from 0.272 to 0.908, and anisotropy degree (P) ranges from 1.073 to 1.266, increasing from the inner portion of the pluton to its margins. The presence of dextral S-C magmatic fabric and high temperature (ca. 650 °C), solid-state deformation at the margins confirms that the pluton was deformed during its cooling process. Such features, together the magnetic fabric analysis, suggest that magma ascent and emplacement were controlled by a NNW-trending dextral transcurrent shear zone. Close to the host-rocks, magnetic foliation dips steeply towards W or E, and magnetic lineation plunges steeply to moderate, displaying strongly-oblate ellipsoids. This is interpreted as a result of shortening and the significantly pure-shear component of deformation operating close to the host-rocks. Shallow-plunging lineation parallel to the NWto NNW-striking foliation is found away from the pluton margins, which is related to the horizontal displacement, where the simple-shear component of deformation was more effective, resulting stretching. Foliation becomes less steep towards the BG northeastern portion and the presence of roof pendants in this area suggests the proximity to the roof zone. The combination of buoyancy forces and the partitioning of regional strain into simple and pure shear are in accordance with a transpressive regime. These results also suggest a time-space relationship between the NNW-dextral shear zone that controlled the emplacement of the Butiá Granite and the sinistral, NE-trending DCTSZ, responsible for the emplacement of peraluminous granites. Possibly, these zones formed a conjugate pair during the transcurrent deformation of the early post-collisional stage of the Brasiliano/PanAfrican Cycle in southernmost Brazil.

O período pós-colisional do Ciclo Brasiliano/Pan-africano é marcado no sul do Brasil pela ocorrência de granitos metaluminosos e peraluminosos, controlados por um sistema transcorrente de zonas de cisalhamento (ZC). No Rio Grande do Sul (RS), a Zona de Cisalhamento Transcorrente Dorsal de Canguçu (ZCTDC), de cinemática sinistral e direção NE, é a principal estrutura que condicionou o posicionamento desses granitos (ca. 634 – 610 Ma). Entretanto, o Granito Butiá (GB – 629 Ma), localizado a noroeste da ZCTDC, ocorre como um corpo alongado de direção NNW que intrude rochas de alto grau metamórfico do Complexo Várzea do Capivarita (ca. 650 Ma). O GB possui trama planar bem desenvolvida (S>L), cuja foliação mergulha com alto ângulo para NNW; apesar de raramente apresentar lineação, seu posicionamento é interpretado como sintectônico a uma ZC transcorrente de cinemática destral. Dessa forma, um estudo de anisotropia de susceptibilidade magnética (ASM) foi realizado no GB, com o objetivo de melhor delimitar os mecanismos de seu posicionamento e relacioná-los com o sistema regional de zonas de cisalhamento. No total, 492 espécimes (180 cilindros) foram coletadas em 16 sítios, distribuídos no corpo principal do GB. A mineralogia magnética foi investigada através de curvas termomagnéticas, curvas de histereses e de aquisição de magnetização remanente isotermal, e detalhada com microscopia eletrônica de varredura em amostras representativas. Essas análises demonstram o domínio de fases paramagnéticas e uma pequena contribuição de minerais de baixa coercividade (e.g., magnetita, titanomagnetita) e alta coercividade (e.g., hematita). Apesar disso, a trama magnética é controlada exclusivamente por cristais paramagnéticos de biotita. A susceptibilidade magnética total é baixa e varia entre 0,1 e 8x10-5 SI. O parâmetro de forma (T) varia de 0,272 a 0,908 e o grau de anisotropia (P) varia de 1,073 a 1,266, aumentando do centro em direção as margens do GB. A presença de par S-C destral de origem magmática e microestruturas de deformação em alta temperatura (~650°C) confirmam que a deformação atuava durante o processo de cristalização. Esses elementos, junto à análise da trama magnética, sugerem que a ascensão e o posicionamento do magma foram controlados por uma ZC transcorrente de direção NNW e cinemática destral. Próximo as rochas encaixantes, os elipsoides magnéticos são fortemente oblatos, a foliação mergulha com alto ângulo para W ou E, e a lineação têm alto a moderado caimento, sugerindo significante achatamento e domínio de uma componente de cisalhamento puro de deformação. Longe das margens, a lineação tem baixos caimentos, paralelos a direção da foliação (NW-NNW), sugerindo um transporte horizontal e domínio de uma componente de cisalhamento simples de deformação, que promoveu o estiramento. No nordeste do corpo, a presença de roof pendants e menores ângulos de mergulho da foliação sugerem proximidade com a cúpula. A combinanção de bouyoancy forces e da partição da deformação regional, em cisalhamento puro e simples durante o posicionamento do GB, está de acordo com um regime transpressivo. Esses resultados também sugerem uma relação no tempo-espaço entre a ZC que controlou o posicionamento do GB e a ZCTDC. Possivelmente, elas formavam um par conjugado do mesmo sistema transcorrente durante o estágio pós-colisional do Ciclo Brasiliano/Pan-africano no sul do Brasil. / The post-collisional stage of the Brasiliano/Pan-African Orogenic Cycle in Southern Brazil is marked by metaluminous and peraluminous granites controlled by a transcurrent shear zone system. In the Rio Grande do Sul State, southernmost Brazil, the sinistral, NE-trending Dorsal de Canguçu Transcurrent Shear Zone (DCTSZ) is the best known structure that conditioned these peraluminous granites (ca. 634 – 610 Ma). However, the NNW-elongate Butiá Granite (BG – 629 Ma) is emplaced to the northwest of the DCTSZ, intrusive in the high-grade Várzea do Capivarita Complex (ca. 650 Ma). The BG has a S>L fabric, which foliation steeply dips towards NNW. Despite its poorly-developed linear fabric, BG emplacement is interpreted to have been controlled by a dextral transcurrent shear zone. Thus, anisotropy of magnetic susceptibility (AMS) study was performed in the BG aiming to constrain its emplacement mechanism and the relation of the granite with the regional shear zone system. A total of 492 specimens (180 drill cores) were obtained through 16 sites distributed along the BG main body. Magnetic mineralogy was investigated by hysteresis loops, thermomagnetic and IRM acquisition curves, and a complementary SEM analysis in representative samples. These experiments show a dominant contribution of paramagnetic phases and a small content of low-coercivity (e.g., magnetite and titanomagnetite) and highcoercivity (e.g., hematite) remanence-carrying minerals. In spite of the presence of minor ferromagnetic grains, the BG magnetic anisotropy fabric is interpreted as dominantly controlled by paramagnetic biotite crystals. The bulk magnetic susceptibility ranges between 0.1 and 8.0×10−5 SI. Shape parameter (T) ranges from 0.272 to 0.908, and anisotropy degree (P) ranges from 1.073 to 1.266, increasing from the inner portion of the pluton to its margins. The presence of dextral S-C magmatic fabric and high temperature (ca. 650 °C), solid-state deformation at the margins confirms that the pluton was deformed during its cooling process. Such features, together the magnetic fabric analysis, suggest that magma ascent and emplacement were controlled by a NNW-trending dextral transcurrent shear zone. Close to the host-rocks, magnetic foliation dips steeply towards W or E, and magnetic lineation plunges steeply to moderate, displaying strongly-oblate ellipsoids. This is interpreted as a result of shortening and the significantly pure-shear component of deformation operating close to the host-rocks. Shallow-plunging lineation parallel to the NWto NNW-striking foliation is found away from the pluton margins, which is related to the horizontal displacement, where the simple-shear component of deformation was more effective, resulting stretching. Foliation becomes less steep towards the BG northeastern portion and the presence of roof pendants in this area suggests the proximity to the roof zone. The combination of buoyancy forces and the partitioning of regional strain into simple and pure shear are in accordance with a transpressive regime. These results also suggest a time-space relationship between the NNW-dextral shear zone that controlled the emplacement of the Butiá Granite and the sinistral, NE-trending DCTSZ, responsible for the emplacement of peraluminous granites. Possibly, these zones formed a conjugate pair during the transcurrent deformation of the early post-collisional stage of the Brasiliano/PanAfrican Cycle in southernmost Brazil.

Le massif du Mayo Kebbi, situé au sud-ouest du Tchad entre le craton du Congo au Sud, le craton Ouest Africain à l’Ouest et le Métacraton du Sahara à l’Est, expose un segment de croûte juvenile néoprotérozoïque accrété dans la ceinture orogénique d’Afrique Centrale durant l’orogène Pan-Africaine. Il est constitué de deux ceintures de roches vertes (Zalbi et Goueygoudoum) séparées par le batholithe calco-alcalin du Mayo Kebbi et recoupées par des plutons à signature calco-alcaline hyperpotassique. Le tout est recouvert par des formations sédimentaires phanérozoïques. Les ceintures de roches vertes contiennent des zones minéralisées en sulfures encaissées par les roches métaplutoniques (granodiorites) et métavolcanosédimentaires (métabasaltes). La minéralisation est constituée d’un assemblage métallique à pyrite, pyrrhotite, arsénopyrite, chalcopyrite, pentlandite, pentlandite argentifère, pentlandite cobaltifère, sphalérite, de cobaltite. Les sulfures se trouvent à l’état disséminé ou sous forme de remplissage de fissures. Les roches vertes comprennent également des filons de quartz à calcite-chlorite et encaissant des minéralisations à pyrite, chalcopyrite, galène et or. L’analyse de l’or indique une association systématique avec l’argent. Le pluton calco-alcalin hyperpotassique de Zabili contient des indices de minéralisations en Uranium liés à la superposition de : (1) déformation ductile et altération métasomatique impliquant l'interaction entre les minéraux magmatiques avec un fluide riche en Na, d'origine magmatique, contemporain au dépôt d’oxydes d'uranium, (2) une déformation fragile et le dépôt de silicates hydratés d'uranium secondaires impliquant un fluide riche en Na-Ca. La minéralisation en uranium s’exprime sous forme d’uraninite, d’ekanite, de kasolite, de brannerite, et de silicates d’uranium tels que la coffinite. Un âge U-Th-Pb de 599 +/- 4 Ma a été obtenu sur des grains de monazite hydrothermales. Ces minéralisations d'uranium représentent l'expression extrême de la différenciation de la croûte, suite à la remobilisation de ce segment de croûte juvénile Néoprotérozoïque au cours de l’orogénèse Pan-Africaine / The Mayo Kebbi massiflocated in southwestern Chad between the Congo craton in the South, the West African craton in the west and the Sahara metacraton to the east exposes a segment of Neoproterozoic juvenile crust accreted in the Central African orogenic belt during the Pan African orogeny. It consists of two greenstone belts (Zalbi and Goueygoudoum) separated by the May Kebbi calc-alkaline batholith complexes and intruded by calc-alkaline high-K granitic plutons. The whole is covered by Phanerozoic sedimentary formations. The greenstone belts contain sulphide zones hosted mainly by metaplutonic rocks (granodiorites) and metabasalts and metavolcaniclastics. The mineralization comprises pyrite, pyrrhotite, arsenopyrite, chalcopyrite, pentlandite, pentlandite silver, pentlandite cobaltiferous, sphalerite, cobaltite. These sulphides are disseminated, aggregated in form of layers or are filling veins and cracks. The greenstones also contain quartz veins with calcite and chlorite comprising a mineralization made of pyrite, chalcopyrite, galena and gold. Gold is present both as native crystals and as electrum. The high-K calc-alkaline Zabili granitic pluton hosts uranium mineralization related to a superposition of: (1) ductile deformation and metasomatic alteration implying the interaction between magmatic minerals with a Na-rich fluid, of potential magmatic origin, coeval to the main deposition of uranium oxides, followed by (2) brittle deformation and deposition of secondary hydrated uranium silicates involving a Na-Ca-rich fluid. We propose that these uranium mineralizations represent the extreme expression of crustal differentiation as a result of Pan-African reworking of a Neoproterozoic juvenile crustal segment

Le massif du Mayo Kebbi au sud-ouest du Tchad est localisé entre le craton du Congo au Sud, le craton Ouest Africain à l'Ouest et le Métacraton du Sahara à l'Est. Formé au cours de l'orogenèse panafricaine, entre 800 et 570 Ma, il est constitué de deux ceintures de roches vertes (Zalbi et Goueygoudoum), trois complexes magmatiques (Chutes Gauthiot, Léré et Figuil) et des intrusions post-tectoniques distingués sur la base de leurs caractères structuraux, pétrologiques, géochimiques et géochronologiques. L'évolution géodynamique de ce massif comprend les phases suivantes:Phase 1: Mise en place d'un complexe mafique et intermédiaire (CMI) dont la métadiorite de Boloro datée à 748 ± 4 Ma (U-Pb sur zircon). Cette métadiorite, riche en terres rares, se caractérise par LaN/YbN ~ 12, Sr/Y > 32, teneurs en LILE, Cr, Ni élevées et des anomalies négatives en Nb-Ta. Ces caractéristiques sont attribuées à la fusion partielle de la plaque océanique plongeante et interaction des magmas produits avec le coin mantellique au cours de leur ascension.Phase 2: Mise en place des métagabbros et métabasaltes (700 ± 10 Ma: U-Pb sur zircon) de la série métavolcano-sédimentaire de Zalbi. Ces roches sont caractérisées par un découplage LILE/HFSE, des anomalies négatives en Nb-Ta et des rapports LaN/YbN indiquant un fractionnement faible à modéré des terres rares. En particulier, leurs caractères géochimiques sont similaires à ceux des bassins arrière-arcs modernes. La signature isotopique en Sr et Nd de ces roches exclut toute contamination par une croûte continentale ancienne au moment de leur mise en place. CMI et série métavolcano-sédimentaires, regroupés dans le cadre des ceintures de roches vertes, représentent ainsi une accrétion juvénile en contextes d'arc insulaire/bassin arrière-arc.Phase 3: La métadiorite quartzique syntectonique du complexe magmatique des chutes Gauthiot (665 ± 1 Ma: âge U-Pb sur zircon, Penaye et al., 2006) correspond à la mise en place de magmas contemporains d'une première collision, qui implique le massif du Mayo Kebbi et le bloc rigide de l'Adamaoua-Yadé à l'Est. Cet évènement marque le début de la fermeture du bassin arrière-arc de Zalbi et d'un épaississement crustal.Phase 4 : L'épaississement est responsable de la différentiation intracrustale par fusion partielle des roches accrétées au cours des phases précédentes à la base de l'arc. Pendant cette phase se mettent en place des magmas tonalitiques, dont la tonalite à hornblende-biotite de Guegou (complexe magmatique de Léré) datée à 647 ± 5 Ma (U-Pb sur zircon). Les magmas produits ont des caractères de magmas TTG et laissent un résidu à grenat à la base de la croûte continentale.Phase 5: La tonalite syntectonique du complexe magmatique de Figuil, datée à 618 ± 6 Ma (U-Pb sur zircon), se distingue par eNd initial = -3 et 87Sr/86Sr initial = 0,7073. Les signatures isotopiques de cette tonalite démontrent l'implication dans le magmatisme d'une croûte Pré-Néoprotérozoïque. Elle est contemporaine d'une deuxième collision qui fait intervenir le massif du Mayo Kebbi et le domaine Occidental de la Ceinture Orogénique d'Afrique Centrale.Phase 6: La mise en place du granite de type A de Zabili à 567 ± 10 Ma (âge U-Pb sur zircon) est associée aux dernières manifestations magmatiques du cycle orogénique panafricain (intrusions post-tectoniques). Les caractères géochimiques (appauvrissement extrême en Sr, Eu, Ca, Mg, Ni) et isotopiques (eNd initial = +3 à +7) de ce granite indiquent une origine par cristallisation fractionnée à partir de magmas d'origine mantellique et contamination de ceux-ci au cours de leur mise en place dans la croûte supérieure par une composante crustale ancienne / The Mayo Kebbi massif (south-western Chad) is located between the Congo craton, the West African craton and the Saharan Metacraton. It consists of two greenstone belts (Zalbi and Goueygoudoum), three magmatic complexes (Gauthiot falls, Lere, Figuil) and post-tectonic intrusions distinguished on the basis of their structural, petrological, geochemical and geochronological characteristics. The geodynamic evolution of this massif includes the following phases:Phase 1: Emplacement of a Mafic to Intermediate Plutonic (MIP) complex. Boloro metadiorite, which belongs to this complex, is dated at 748 ± 4 Ma (U-Pb zircon age). This metadiorite is enriched in REE and characterized by LaN/YbN ~ 12, Sr/Y > 32, high LILE, Cr and Ni contents but negative anomalies in Nb-Ta. These features are attributed to partial melting of the slab followed by interaction of the produced magmas with the mantle wedge during their ascent.Phase 2: Emplacement of metagabbros and metabasalts (700 ± 10 Ma: U-Pb zircon age) of the Zalbi metavolcanic-sedimentary group. These rocks are characterized by a decoupling of LILE and HFSE, negative Nb-Ta anomalies, weak to moderate LREE fractionation relative to HREE. In particular, their geochemical characteristics are similar to modern back-arc basins. The isotopic compositions of Sr and Nd of these rocks preclude contamination by old continental crust of the related magmas during their emplacement. Accordingly, the MIP complex and the Zalbi metavolcanic-sedimentary group are associated to juvenile accretion in an island arc/back-arc basin tectonic setting.Phase 3: The syntectonic quartz metadiorite of Gauthiot Falls magmatic complex (665 ± 1 Ma: U-Pb zircon age, Penaye et al., 2006) is emplaced during a first collision event, which involves the Mayo Kebbi massif and the Adamaoua-Yade domain to the east. This event marks the beginning of the closure of the Zalbi back-arc basin and crustal thickening.Phase 4: The thickening is responsible of intra-crustal differentiation by partial melting of rocks accreted during the previous phases at the base of the arc. During this phase, several tonalitic intrusions are emplaced, including hornblende-biotite tonalites of Gauthiot Falls and Guegou tonalite (Lere magmatic complex). The latter is dated at 647 ± 5 Ma (U-Pb zircon age). The produced magmas have typical features of TTG magmas, leaving a garnet bearing residue at the base of the continental crust.Phase 5: The syntectonic tonalite of Figuil magmatic complex dated at 618 ± 6 Ma (U-Pb zircon age), is characterized by initial ?Nd = -3 and initial 87Sr/86Sr = 0.7073 attesting for the involvement of pre-Neoproterozoic crust on its origin. It marks a second collision event between the Mayo Kebbi massif and the Western domain of the Central African Orogenic Belt to the west.Phase 6: The Zabili A-type granite emplaced at 567 ± 10 Ma (U-Pb zircon age) and is related to the last magmatic events of the Pan-African orogenic cycle (post-tectonic intrusions). The geochemical (low Sr, Eu, Ca, Mg, Ni) and isotopic compositions (initial ?Nd = +3 à +7) of this granite point to an origin involving extreme fractionation of mantle-derived magmas which interacted with an old crustal component during their emplacement in the upper continental crust

La chaîne du Mayombe constitue la portion congolaise du système orogénique « Araçuaï-West Congo » qui se répartit entre la marge orientale du Brésil et la marge occidentale de l’Afrique centrale. Elle s’allonge parallèlement au littoral atlantique suivant la direction NW-SE. En tenant compte des données géochronologiques, elle se subdivise en deux domaines lithostratigraphiques : (i) le domaine paléoprotérozoïque et (ii) le domaine néoprotérozoïque. Le domaine paléoprotérozoique de la chaîne du Mayombe correspond à la partie interne de la chaîne et se caractérise par la co-existence des roches d’origine sédimentaire et magmatique déformées et métamorphisées à des degrés variés. Ces roches se répartissent en trois principaux groupes lithologiques : (i) le Groupe de la Loémé, (ii) le Groupe de la Loukoula et (iii) le Groupe de la Bikossi. L’analyse structurale des Groupes de la Loémé et de la Loukoula montre que ceux-ci sont plissés et fracturés. Dans le Groupe de la Loémé les plis présentent des axes qui s’orientent dans les directions NE-SW, NNE-SSW et N-S tandis que dans le Groupe de la Loukoula, le plissement se fait suivant la direction NE-SW. Le Groupe de la Bikossi se caractérise par des plis qui s’orientent dans les directions identifiées dans les précédants Groupes. L’étude géochimique réalisée sur les échantillons provenant du domaine paléoprotérozoïque de la chaîne du Mayombe montre que ce dernier est hétérogénique c’est-à-dire qu’il implique des terrains d’origine et de lithologie variées. La caractérisation pétrologique des ensembles lithologiques des groupes de la Loémé et de la Loukoula montre que ceux-ci sont affectés par au moins deux événements métamorphiques distincts qui se superposent. Le premier événement se traduit par des paragenèses à grenat-biotite-oligoclase dans les métapélites et par le développement de la hornblende brune dans les métabasites permettant ainsi de situer le contexte d’évolution dans le faciès des amphibolites. Le second événement s’enregistre de façon différente dans le Groupe de la Loémé et dans le Groupe de la Loukoula. Il se traduit respectivement par des assemblages à grenat-biotite-oligoclase dans les formtaions du Groupe de la Loémé et par une paragenèse à chlorite-albite-épidote dans le Groupe de la Loukoula. Les échantillons rattachés au Groupe de la Bikossi ne présentent que les traces d’un seul événement métamorphique marqué par les paragenèses à grenat-biotite-muscovite et grenat-chloritoïde-chlorite avec une température oscillant entre 510-568°C pour une pression d’environ 8 kbar. La datation U-Pb sur zircons a permis de : (i) définir les sources des matériaux détritiques ayant constitué les bassins évoluant de l’Archéen au Protérozoïque (3300-1500) ; (ii) de confirmer l’âge paléoprotérozoïque (2070-2040 Ma) du magmatisme éburnéen ainsi que l’âge néoprotérozoïque (925 Ma) des granites de type Mfoubou et Mont Kanda et (iii) mettre en évidence des perturbations du système isotopique U-Pb des zircons à 642 ± 36 Ma et 539 ± 18 Ma. Les analyses 40Ar-39Ar sur biotite, muscovite et amphibole des échantillons du domaine occidental de la chaîne du Mayombe ont fourni des âges qui situent l’événement tectono-thermique pan-africain entre 615 Ma et 496 Ma. / The Mayombe belt is the congolese part of the Araçuaï-West Congo belt system which extend from eastern margin of Brazil to western margin of central Africa. It runs parallel to the Atlantic coastline with NW-SE trend. Considering geochronological data, it is subdivided into two lithostratigraphic domains : (i) the Paleoproterozoic domain and (ii) the Neoproterozoic domain. The Paleoproterozoic domain of the Mayombe range corresponds to the inner part of the belt and is characterized by the coexistence of para and orthoderived rocks deformed and metamorphosed to varying degrees. These rocks are distributed among the three main lithological Groups : (i) the Loémé Group, (ii) the Loukoula Group and (iii) the Bikossi Group. Structural analysis of Loémé and Loukoula Groups shows folded and fractured stuctures. In the Loémé Group, folds trend NE-SW, NNE-SSW and N-S while in the Loukoula Group, the main shortening trends NE-SW. The Bikossi Group is characterized by folds oriented in the directions identified in the preceding Groups. The geochemical study carried out on samples from the Paleoproterozoic domain of the Mayombe belt shows that the latter is heterogeneous, by involving rocks of various origin and lithology. The petrological characterization of Loémé and Loukoula Groups shows that they are affected by at least two distinct metamorphic events that overlap. The first event is characterized by garnet-biotite-oligoclase parageneses in metapelites and by the development of brown hornblende in metabasites, thus allowing the evolution context to be situated in the amphibolite facies. The second event is recorded differently in Loémé Group and Loukoula Group. It consits respectively in garnet-biotite-oligoclase assemblages in the Loemé Group and in chlorite-albite-epidote paragenesis in the Loukoula Group. Samples from Bikossi Group present only traces of a single metamorphic event marked by garnet-biotite-muscovite and garnet-chloritoid-chlorite parageneses whose temperature is estimated at 510-568°C for 8 kbar of pressure. U-Pb dating of zircons allows to : (i) define the Archean-Paleoproterozoic (3300-1500Ma) sources of metasedimentary rocks (ii) confirm Paleoproterozoic (2070-2040 Ma) age of Eburnean magmatism and Neoproterozoic (925 Ma) Mfoubou and Mont Kanda type magmatism and (iii) to highlight the perturbations of zircons U-Pb isotopic system at 642 ± 36 Ma and 539 ± 18 Ma. The 40Ar-39Ar analyzes on biotite, muscovite and amphibole from samples of the western domain of Mayombe betl provided since the age range of Pan-African tectono-thermal event at 615-496 Ma.