Orientador: Elson Paiva de Oliveira / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Geociências / Made available in DSpace on 2018-08-19T05:31:18Z (GMT). No. of bitstreams: 1 DonattiFilho_JosePaulo_D.pdf: 4183333 bytes, checksum: fdab4641a69f3e0cb09bddeb14a2dedf (MD5) Previous issue date: 2011 / Resumo: A presente tese concentrou-se na classificação do magmatismo kimberlítico do Campo Kimberlítico Brauna no nordeste do Craton do São Francisco, e sua relação com as rochas encaixantes, xenólitos (e.g. crustais e mantélicos), mineralizações diamantíferas e contexto tectônico regional associado ao Greenstone Belt do Rio Itapicuru e Bloco Serrinha. O escopo do estudo refere-se à utilização de técnicas analíticas convencionais como microscopia, microscopia eletrônica de varredura, microssonda eletrônica e difratometria de raios-X para a classificação da mineralogia e da química mineral dos kimberlitos e xenólitos associados. Somado a isto, utilizou-se técnicas analíticas mais avançadas aplicadas ao estudo de kimberlitos, como a obtenção de dados geoquímicos de alto poder interpretativo (e.g. HFSE e REE) por ICPMS e XRF, com a finalidade de se entender a petrogênese dessas rochas. Além de análises isotópicas de Sr-Nd em rocha total e perovskita da matriz kimberlítica, e U-Pb em grãos de zircão e perovskita por SHRIMP e TIMS respectivamente, para definir e determinar fontes geradoras do magmatismo do campo kimberlítico. Este volume foi organizado sob forma de dois artigos completos, onde a grande maioria dos resultados desta tese foram apresentados. O primeiro artigo intitulado ?Age and Origin of the Neoproterozoic Brauna Kimberlites: magma generation within the metasomatized base of the São Francisco craton, Brazil?, teve como principal objetivo a classificação petrogenética dos kimberlitos e xenólitos associados do Campo Kimberlítica Brauna, desde então superficialmente explorada por empresas de exploração de diamantes na década de 80 e 90. Neste artigo foram utilizadas técnicas convencionais de classificação de rocha bem como: descrições petrográficas, relações de campo, microscopia eletrônica de varredura, microssonda RAMAM, difratometria de Raio-X e geoquímica de elementos maiores e traços. O artigo contempla também a utilização de técnicas mais avançadas até então inexistentes na literatura sobre kimberlitos no Brasil, são elas: datação radiométrica U-Pb em fenocristais de perovskita por Termal Ionization Mass Spectrometry (TIMS), dados isotópicos de Sr-Nd em rocha total e isótopos de Nd em fenocristal de perovskita. Além disso, o artigo contribui de forma representativa para uma discussão freqüente entre a comunidade internacional de kimberlitólogos sobre tipos de magmas kimberlíticos heterogêneos. O segundo artigo intitulado ?Zircon xenocrysts U-Pb dating from the Neoproterozoic Brauna Kimberlite Field, São Francisco Craton, Brazil: geodynamic implications for kimberlitic intrusion?, foi contemplado com dados isotópicos precisos de U-Pb em xenocristais de zircão do kimberlito e fenocristais de zircão do granodiorite encaixante por Sensitive High Resolution Ion Microprobe (SHRIMP II). Este artigo teve como principal objetivo a identificação das diferentes idades registradas nos xenocristais de zircão trazidos à superfície da Terra pelo magmatismo kimberlítico com o intuito de se entender a constituição da litosfera sob o Bloco Serrinha, onde o campo kimberlítico Brauna encontra-se intrudido. Além disso, o estudo isotópico detalhado do granodiorito encaixante também se fez importante para o entendimento da mecânica de colocação e forma de contaminação crustal desse tipo de magmatismo tão peculiar, tornando este artigo o segundo no mundo com esse tipo de abordagem / Abstract: The present thesis deals with the classification of the Brauna Kimberlite Field magmatism, northeast São Francisco Craton, and its relationship with the host-rock, xenoliths (e.g. crustal and mantelic), diamondiferous mineralization and the regional tectonic context associated to the Rio Itapicuru greenstone belt and Serrinha Block. The scope of this study refers to conventional methodologies such as scanning electron microscope, electronic microprobe and X-ray difratometry for the mineralogy classification of the Brauna kimberlites and the related xenoliths. Additionally, we have used more robust analytical techniques applied to the kimberlite study, such as ICPMS and XRF and also isotopic analysis of whole rock and perovskite Sr-Nd isotope, and also zircon U-Pb geochronology, using TIMS and SHRIMP respectively, to understand the kimberlitic source and magma generation process. This volume was organized under paper form where the results, discussions and conclusions are reported. The first manuscript entitle -Age and Origin of the Neoproterozoic Brauna Kimberlites: magma generation within the metasomatized base of the São Francisco craton, Brazil, had the main subject the Brauna kimberlites and xenoliths petrogenetic classifications, since then superficially explored by the exploration Companies during the 80's and 90's decades. In this article we have utilized conventional techniques for rock classification such as petrographic descriptions, field relationships i.e. SEM, RAMAM and X-Ray difratometry for major and trace elements geochemistry. Also we have analysed the samples by most advanced techniques inexistent in the Brazilian literature so far, for example: trace elements using ICPMS, U-Pb perovskite dating and whole rock Sr-Nd and perovskite Nd isotope by TIMS. Furthermore, this manuscript has contributed for the international kimberlite community discussion about the heterogeneous kimberlitic magma types. The second manuscript entitled -Zircon xenocrysts U-Pb dating from the Neoproterozoic Brauna Kimberlite Field, São Francisco Craton, Brazil: geodynamic implications for kimberlitic intrusion, was awarded with U-Pb isotopic data in zircon xenocrysts in Brauna kimberlites and its host rock Nordestina granodiorite batholith using the SHRIMP. This article had the principal objective, to place constraints on the lithosphere beneath the Archean Serrinha Block. Furthermore, the detailed isotopic study on the host-rock was important to improve our understanding about the form and dynamic of the kimberlitic intrusion. It is important to note that this paper is the second published paper with this subject in the world / Doutorado / Geologia e Recursos Naturais / Doutor em Ciências

L'objectif de cette thèse est d'étudier le rôle joué par les zones de cisaillement sur la localisation de la déformation et de l'exhumation de la croûte inférieure grâce à une série de modèles numériques thermomécaniques 2D et 3D que nous avons appliqué à deux cas d'étude: le craton ouest-africain (WAC) et les zones de failles alpines en Nouvelle Zélande. En ce qui concerne la localisation de la déformation dans la croûte supérieure, différentes orientations pour un système de décrochement en ramification ont été testées. Sous un régime compressif, les résultats montrent que les zones de failles internes, ainsi que les unités de roches présentes entre ces failles réagissent de façon plus fragile que les unités rocheuses présentes à l'extérieur de ces domaines. Pour le cas d'un régime de déformation en cisaillement simple, nous avons exploré le processus de réorganisation qui s'est produit aux limites de deux plaques (i.e. Australie et Pacifique) au sud de la Nouvelle-Zélande. Les modèles montrent que la déformation se concentre le long des zones de cisaillement étroites, situées au centre du modèle, lorsque les coefficients d'amollissement sont élevés. Inversement, la contrainte cisaillante ressort de façon plus diffuse à travers le modèle lorsque les coefficients d'amollissement sont faibles. Les cisaillements s'expriment alors sur l'ensemble du modèle bien que les taux de cisaillement restent les plus élevés sur les bordures du modèle. Afin de tester l'impact de failles héritées et de bassins préexistants sur l'exhumation de la croûte inférieure, des modèles 2D et 3D ont été testés avec différentes conditions aux limites (traduisant extension, transtension et compression). * En contexte extensif, dans les portions Est et Ouest des corridors fortement métamorphisés du Nord-Ouest Ghana, des roches partiellement fondues, issues de la croûte inférieure, ont pu être exhumées au sein des croûtes moyenne à supérieure. Dans la partie centrale du domaine de Bolé-Bulenga, des roches très métamorphisées ont été exhumées grâce au couplage de deux mécanismes: (1) la concentration de roches partiellement fondues entre les failles de Jirapa et de Bolé-Nangodi; ces failles convergent vers le sud, induisant un rétrécissement de l'espace disponible pour accueillir ce matériel fondu; (2) la concentration de roches partiellement fondues dans la partie centrale, induite par un jeu de failles héritées d'orientation Est-Ouest. * En contexte de transtension, dans le terrane de Sefwi au Sud-Ouest Ghana, le domaine de Kukuom-Juaboso (KJD), composé majoritairement par des roches à faciès de type amphibolite à migmatitique, semble s'être mis en place sous forme d'intrusions au sein d'une zone relais située entre les zones de cisaillements de Kenyase et de Ketésso. Ces deux zones de cisaillement sont marquées par un stade de croissance puis de maturation qui semblent être reliés aux phases de déformation D1 puis D2 reconnues régionalement. L'exhumation régionale des roches très métamorphisées dans le terrane de Sefwi s'est probablement produite en moins de 5 Ma. * En régime compressif, l'impact joué par les bassins volcano-sédimentaires sur le processus d'exhumation de la croûte inférieure a été testé numériquement. Les modèles suggèrent que de multiples injections de magmas granitoïdiques, dérivant soit de matériaux subductés, soit d'une fusion de produits crustaux ou de matériel mantellique accumulés en profondeur, ont pu être canalisées au sein de diapirs avant de venir nourrir la croûte supérieure. Ce modèle suggère également une asymétrie des structures entre la croûte supérieure d'une part, et la croûte inférieure à moyenne d'autre part: i.e. (i) les bassins de roches vertes faiblement métamorphisés de la croûte supérieure reposent sur les diapirs métamorphisés et (ii) les bassins de roches vertes très métamorphisés constituent le soubassement des dômes granitoïdiques de la croûte supérieure. / The objective of this thesis is to explore the role shear zones play in localization of deformation and exhumation of the lower crust by using a series of 2D and 3D thermo-mechanical numerical models using the West African Craton (WAC) and the Alpine Fault zones as study areas. With respect to the localization of deformation in the upper crust, different orientations of a system of branched strike-slip faults were studied. Under compression boundary conditions, the results show that the internal fault zones as well as the host rocks in between the faults behave as relatively weaker domains than the external regions. Under simple shear boundary conditions, we explored the process of self-organization of the Australian-Pacific plate boundary fault in southern New Zealand. The models show that deformation is focused along narrow high-strain shear zones in the centre of the model when the softening coefficients are high, whereas the strain is more diffuse with many shear zones spread over the model and possibly some high-strain shear zones focused near one border at lower softening coefficients. Regarding the role pre-existing faults and basins play in exhumation of the partially molten lower crust, 2D and 3D models with different boundary conditions were tested (including extension, transtension and compression). * Under extension, in the Eastern and Western parts of the high grade rock corridors in NW Ghana, partially molten rocks exhumed from the lower into middle-upper crustal levels are interpreted to have been dominantly facilitated by the km-scale high-strain corridors. In the central part of the Bole-Bulenga domain, the high grade rocks are interpreted to have been exhumed as a result of a coupling between two mechanisms: (1) the concentration of partially molten rocks between the Jirapa and Bole-Nangodi faults increases due to the reduction in space from north to south; (2) the concentration of lower partially molten rocks in the central part, as a result of inherited orthogonal (E-W) faults. * Under transtension, in the Sefwi terrane of SW Ghana, the Kukuom-Juaboso domain (KJD) composed of up to amphibolite-migmatite facies could result from the concentration of upwelling partially molten rocks in the relay zone between the Ketesso and Kenyase shear zones during transtension. The two shear zones probably underwent two main stages for growth and maturation from the D1 to D2 deformation phases. The regional exhumation of the high grade rocks in the Sefwi terrane probably occurred within a duration of less than 5 Ma. * Under compression, the role of volcano-sedimentary basin on spatial-temporal evolution of the lower crust exhumation was tested. The models suggest that a series of sheet-like granitoids possibly derived from either subducted mélanges, lower crust and/or mantle melting accumulated at depths of the subcontinental mantle would channel along diapirs before feeding the upper crust. When the granitoids arrive at the solidified lids of the diapirs, they would favour migrating horizontally and intruding into the upper crust through weakening zones between the diapirs. This model also suggests an asymmetry of structures between the upper and middle-lower crust, with the dome-like granitoids overlying high-grade sedimentary synforms and high-grade diapirs underlying low-grade greenstone belts.

>Magister Scientiae - MSc / The group of granites on the eastern margin of the Mesoproterozoic Namaqua sector of the polydeformed and highly metamorphosed Namaqua-Natal Province of southern Africa is known as the Keimoes Suite. The suite includes mixtures of diverse rock types not belonging to a single intrusive series and so it should be subdivided into more than one intrusive suite. The exact definition, extent, distribution and petrogenesis of these granites have been poorly defined in the past, with various authors defining the suite differently due to the lack of proper geochronology and geochemical data. The exact contact between the Namaqua sector and Kaapvaal Craton together with the role of the suite to the Namaqua tectonic evolution is still unclear. The granites of the Keimoes Suite are thought to mark the contact between the Namaqua sector and the Kaapvaal Craton. This study seeks to address the above mentioned problems by making use of new geochronology, isotope, major and trace element geochemistry together with petrography. The granites of the Keimoes Suite were previously grouped based on their degree of deformation. The geochronology, undertaken as part of this study, has proven that this classification is unfounded. The degree of foliation in these granites appears to be largely controlled by the abundance of platy minerals, such as biotite and muscovite, together with the intrusion mechanism, with deformational processes, such as shearing, playing a secondary role. The geochronology, together with geochemistry has helped to redefine the previously defined Keimoes Suite so that two well defined separate suites are recognized and the third is poorly defined due to lack of more samples of that age group. The new classification or grouping of the granites of the eastern Namaqua sector allows a more detailed examination of the tectonic evolution of this region. A member of the 1225 to 1200 Ma early syn-tectonic granites, the Josling Granite, shows a strongly developed foliation and was derived from a depleted source with a relatively low continental crustal component. This granite intruded during the time of arc accretion, and is associated with, and partly responsible for the D₁ deformation and M₁ metamorphism recognized in most of the rocks of the eastern terranes of the Namaqua sector. In terms of age, the syn-tectonic granites of the Augrabies Suite extend from 1200 to 1120 Ma and were largely derived from depleted sources with variable but more substantial amounts of continental crustal components as compared to the early syn-tectonic granite. The granites of this suite intruded during the period of peak D₂ deformation with peak magmatism between 1180 - 1135 Ma, and particularly around 1150 Ma, during the peak of metamorphism (M₂) caused by, and associated with these voluminous intrusions. The Keimoes Suite can now be defined as comprising granites of late- to post-tectonic age relative to the 1.2 - 1.08 Ga Namaquan Orogeny with magmatism occurring on the western side of the Kaapvaal Craton. The 1116 to 1066 Ma Keimoes Suite intruded during the stage of the Namaquan Orogeny in which there was continued indentation of the Kaapvaal Craton into the Namaqua sector with wrenching and shearing causing the development of rifting into which the granites intruded. The Keimoes Suite granites were derived from continental crustal sources and incorporated varying degrees of depleted source components. The intrusives and extrusives of this age occured after the main collisional event between the Namaqua Sector and the Kaapvaal Craton and are associated with the D₃ deformational event, imparting the thermal conditions leading to the M₃ metamorphic event of the rocks within both the Kakamas and Areachap Terranes. The suites mark the suture between the Archean Kaapvaal Craton and the Proterozoic Namaqua sector. The compositions of the granites of the individual suites were mainly controlled by the source with the degree of partial melting exerting a major control. The proportion of entrained peritectic assemblages and accessory minerals played a major role in controlling the compositions of the granites, particularly those of the trace elements. Variations within the compositions of the same suite are due to source heterogeneities. Generally, fractionation processes played a secondary role in influencing the composition of the granites. / Council for Geoscience and National Research Foundation

M.Sc. / The Kaapvaal craton is one of few regions on earth with an almost continuous record of wellpreserved supracrustal rocks ranging in age from ~3.5 Ga to the late Paleoproterozoic at ~1.75 Ga. In this study diagenetic carbonates from the Paleoarchean Buck Reef Chert and Joe’s Luck Formation of the Swaziland Supergroup, the Mesoarchean Thalu and Promise Formations of the Mozaan/Witwatersrand Supergroups and the Paleoproterozoic Timeball Hill and Silverton Formations of the Transvaal Supergroup were sampled and analyzed. The aim of the study was to determine possible variations in the composition of the carbonates through time and their significance especially with regards to microbial activity in diagenetic systems in early Earth history. Results indicate similar petrographic observations and geochemical signatures in diagenetic carbonates of iron formations in the Buck Reef Chert, Joe’s Luck and Griquatown Iron Formation. The carbonates all tend to be siderites with iron derived from hydrothermal input and all are depleted in 13C relative to Peedee Belemnite standard. It suggested that siderite formed as a result of microbial respiration. Microbes degrade organic matter and reduce iron in this process. This resulted in the depletion in 13C and in the precipitation of siderite. However in order for iron reduction to have occurred the reduced iron first had to be oxidized. This most probably occurred through iron oxidizing chemolithoautotrophs under microaerophilic conditions. Diagenetic carbonate concretions of the Thalu and Promise Formations are manganiferous and are highly depleted in 13C relative to PDB. There is also strong evidence for hydrothermal input of manganese and iron into the system because of positive europium anomalies. The carbonates from both of the formations strongly suggest the presence of some free oxygen. The reasoning behind this conclusion is as follows: The depletion of 13C in the carbonates points to microbial decomposition of organic matter and manganese respiration (the decomposition of organic matter by microbial MnO2 reduction) is shown to be the most reasonable process that led to the formation of the carbonate concretions. The implication is that MnO2 must first have been precipitated and that can only be achieved in the presence of free oxygen with the oxidation reaction often catalyzed by manganese oxidizing chemolithoautotrophs. The carbonates of the Timeball Hill and Silverton Formationsare calcites ad contain little no iron. There is also little or no evidence for hydrothermal input and the basin appears to be a clastic dominated. It is generally accepted that a major rise in oxygen in the oceans and the atmosphere occurred at about 2.32 Ga. This rise in oxygen levels is reflected in the diagenetic calcite concretions of the Silverton Formation. Both iron and manganese reduction where not very effective because of the depletion in the basin water of these two elements, organic carbon taken up in the calcite concretions, indicated by negative δ13CPDB carbonate values, was most probably derived from aerobic and/or nitrate respiration. The most important conclusion from this study is that sufficient free oxygen and hence oxygenic photosynthesis were present to oxidize both Fe and Mn at least as far back as the Paleo-Mesoarchean.

L'objectif de ce travail de thèse était de réaliser une étude structurale détaillée des minéralisations et des zones d'altération associées, de trois gisements d'or situés au Nord-Ouest du Ghana, sur la marge orientale du Craton Ouest Africain: Kunche et Bepkong, situés dans la ceinture de Wa-Lawra, et Julie situé dans la ceinture de Julie. Ces trois gisements présentent de multiples différences d'ordre géologique, structural, tectonique et géochimique, mais leur caractéristique commune est que leur minéralisation est associée à un métamorphisme de faciès schiste vert. A Julie, la minéralisation aurifère est encaissée dans des granitoïdes de composition tonalite-trondhjemite-granodiorite (TTG) alors qu'à Kunche et Bepkong elle est localisée au sein de formations sédimentaires volcanoclastiques et de schistes graphiteux fortement silicifiés. Cette minéralisation est associée à un réseau de veines souvent boudinées de quartz formées en relation avec une zone de cisaillement orientée Est-Ouest à Julie, mais N à NNO à Kunche et Bepkong, constituant un couloir de déformation de 0.5 à 3,5 km de longueur et de 20 à 300 m de puissance suivant les gisements. La paragenèse d'altération dominante de la zone minéralisée est à séricite, quartz, carbonate et sulfures, et suivant la nature de la roche hôte se rajouteront par exemple la tourmaline dans les granitoïdes et la chlorite dans les schistes ou les métavolcanites. A Julie, l'or est étroitement associé à la pyrite alors qu'à Kunche et Bepkong l'or est associé à l'arsénopyrite. Deux générations d'or sont distinguées ; la première correspond à de l'or invisible associé aux zones de croissance primaire des cristaux de pyrite à Julie et d'arsénopyrite à Bepkong, et de l'or visible tardif en inclusion et plus fréquemment en remplissage de fractures. / The objective of this thesis was to perform a detailed structural, mineralization and associated alteration studies of three gold deposits located in northwest Ghana, on the eastern margin of the West African Craton. Thus, the Kunche and Bepkong deposits, located in the Wa-Lawra belt and Julie deposit located in the Julie belt. These three deposits have multiple differences interms of geological, structural, tectonic and geochemical characteristics but gold mineralization in these deposits are all associated with a green schist facies metamorphism. In Julie, the gold mineralization is hosted in granitoids with its composition akin to tonalite-granodiorite-trondhjemite (TTG) where as in the Kunche and Bepkong deposits, the gold mineralization are localized within volcaniclastic sedimentary formations and strongly silicified graphitic schists. The gold mineralization is associated with a network of quartz veins often boudinaged and formed in connection with a shear zones, oriented E-W in the Julie deposit and N to NNW at Kunche and Bepkong deposits. The dominant alteration in the mineralized zone is sericite, quartz, carbonate and sulfides with influences from the host rock. For example, the granitoid is influenced by tourmaline and chlorite in the schists or in themetavolcanic rocks. At Julie, gold is closely associated with pyrite whereas Kunche and Bepkong gold is associated with arsenopyrite. Two generations of gold are distinguished; the first corresponds to the invisible gold associated with primary growth areas in the pyrite crystals in Julie and arsenopyrite in Kunche and Bepkong, and late visible gold inclusions which are frequently found in fracture fillings. In Julie, the mineralizing fluid is rich in CO2, and has low to moderate salinity (NaCl-H2O-CO2 system), trapped in P / T conditions around 220 ° C and <1 kbar; whilst in Bepkong, the mineralizing fluid is associated with quartz are rich in CH4, with a low salinity (CH4-CO2-SO2-H2O system) which indicates that the visible trapping temperatures is around 320°C.

The mode of tectonics by which early Archean proto-continents were deformed was investigated in the Pilbara Craton in Western Australia, which has not been substantially tectonically deformed since ~3.2 Ga. The craton consists of a unique dome and keel structure where vertical, low-grade metamorphism basaltic greenstone keels surround large granitic (TTG) domes. The dominant model for 3.5-3.2 Ga deformation in the Pilbara is gravity-driven vertical tectonics, or partial convective overturn in a hot crust. In this model, the granitic bodies rose upward as solid-state diapirs, and the greenstones "sagducted" downward around the granitic bodies. Australian scientists acquired deep seismic reflection data crossing a granitoid-greenstone boundary. Their processing did not image the geologically mapped steep dip of the boundary because standard methods limit the maximum dip. A 37-km section of these data were reprocessed using 2D Kirchhoff prestack depth migration to include vertical dips. The western half of the migrated section images a granitoid dome with weak to no reflectivity that extends deeper than 4 km. The eastern half images 2-3 km of layered volcanic rocks of the Fortescue Group overlying the greenstones. Seismic velocity models created using travel-time tomography suggest a thin weathering layer overlying slightly fractured crystalline rocks. These fractures close within 200-300 m depth, and velocity reaches bedrock speeds consistent with expected values of granitoids to the west and volcanic rocks of the Fortescue Group to the east. The best migrated image contains several reflections with dips (~45-55˚) cross-cutting each other from both directions at the location of the expected granitoid-greenstone boundary. This strongly suggests the presence of steep dips in the upper ~1.5 km but does not provide a definitive image. This inconclusive result is due to strong surface-wave noise, the crooked 2D seismic line, and the 3D nature of the geologic boundary at the seismic line. A very small seismic velocity gradient within the crystalline bedrock limits the maximum depth to which vertical features can be imaged. / Master of Science / The Pilbara craton is one of the few exposed and intact pieces of continents that were formed ~3.2 billion years ago. This research analyzes how these early land masses were deformed. There are two methods by which early land masses evolved—vertical tectonics (a more rudimentary, gravity-driven form of plate movement) or horizontal tectonics (which is closer to modern-day tectonics and requires many stages of deformation). This area has a unique dome-and-keel structure where greenstones (metamorphosed volcanics) are vertically wrapped around large granitic domes. Studying the vertical features of the greenstones will allow us to ascertain how tectonics evolved in the area. A seismic survey was conducted in 2018 in the area. These data were reprocessed to include steep dips to extract the exact location of the steeply dipping boundary between the dome and keel structure at depth. The resulting image contains inconclusive evidence due to the physical limitations of the geology and the sharp bend in the seismic line. Further studies need to be done to determine if the Pilbara Craton was formed by vertical tectonics.

Pour mieux comprendre le processus géodynamique qui a permis la destruction du craton Nord Chinois (NCC), le rôle des fluides mantelliques a été examiné. Pour cela, les distributions des teneurs en eau et des compositions isotopiques du Lithium dans le manteau lithosphérique NCC ont été déterminées à partir des xénolites de péridotite entrainés par les basaltes mésozoïques et cénozoïques. Une variation temporelle des teneurs en eau est observée. Le manteau lithosphérique cénozoïque est appauvri en eau, sans doute suite à l'amincissement crustal et au réchauffement du manteau résiduel par un flux ascendant asthénosphérique. Le manteau lithosphérique mésozoïque montre des teneurs en eau intermédiaire entre les teneurs élevées du Crétacé et les teneurs basses cénozoïques, indiquant une déshydratation du manteau commençant dès le début de sa destruction. Cette déshydratation, facilitée par la destruction du manteau lithosphérique profond, permet de renforcer la rigidité de la lithosphère et lui permet de résister à la convection mantellique. Les distributions élémentaire et isotopique du Li montrent une grande hétérogénéité, aux échelles intra et inter-cristallines. Par simulation numérique, nous démontrons que deux enrichissements successifs ont affecté le manteau, un enrichissement limité (<5ppm) avec une signature pauvre en 7Li ([delta]7Li ~ -20 [pour mille]), suivi d'un enrichissement important (> 100 ppm) avec une signature riche ([delta]7Li ~ +20 [pour mille]), précédent de peu l'exhumation des xénolites. La formation des liquides métasomatiques responsables de ces enrichissements nécessite une distribution hétérogène dans le manteau NCC d'éléments recyclés lors de la subduction à l'est du NCC / In order to investigate the geodynamic cause for destruction of the North China Craton (NCC), the role of mantle fluids is examined. The aim of the PHD work is to clarify H2O contents and lithium isotopic compositions of the NCC lithospheric mantle by studying peridotite xenoliths hosted by Mesozoic-Cenozoic basalts across eastern NCC. A temporal variation of H2O content has been revealed, and it has deep implications for processes of craton destruction. The Cenozoic lithospheric mantle was featured by low H2O content, interpreted to be the relict mantle that survived the lithospheric thinning and has been dewatered by reheating from upwelling asthenospheric flow. The late-Mesozoic lithospheric mantle showed relatively high H2O content, a hydrous status intermediate between the Cretaceous hydration and the Cenozoic dryness, indicating the dehydration of the NCC mantle with time during NCC destruction. The dehydration, facilitated by thinning of weak mantle pieces at bottom, is one way by which the lithosphere strengthens itself to survive in the convecting mantle. Extreme Li and isotopic disequilibria were observed intra- and inter-mineral in the peridotites. With numerical simulations, we demonstrate two superimposed Li enrichment events occurring at the mantle: a limited Li enrichment (< 5 ppm) and large delta7Li depletion (-20~-10[per 1000]) of the mantle domain, followed by a recent and transient infiltration of high Li and delta7Li (up to +20 [per 1000]) melts/fluids. The anomalous Li isotopic compositions of mantle metasomatic agents call upon the same of their mantle sources, and we assume recycled components, both Li isotopically heavy and light, in the mantle beneath the eastern NCC

La dynamique des cratons reste, encore actuellement, énigmatique dans la mesure où ceux-ci sont souvent considérés comme des domaines stables à l’échelle des temps géologiques. Dans ce travail, nous avons reconstitué l’évolution d’un des plus grands cratons, le Craton Ouest Africain. Nous nous sommes également penchés sur l’étude de ses bordures nord et ouest (Anti-Atlas et marge atlantique respectivement). Cette étude utilise les méthodes de thermochronologie basse-température (traces de fission et (U-Th-Sm)/He sur apatite) ainsi que la géologie structurale. Le choix de ce craton est justifié par les multiples contextes géologiques dont témoignent ses bordures au cours du Phanérozoïque (plateforme, avant-pays distal, marge passive). Ces contextes variés au cours du temps en font donc une cible idéale pour évaluer l’influence des diverses forces susceptibles d’affecter le craton.Tout d’abord, suite à une subsidence importante au cours du Paléozoïque, le craton enregistre un refroidissement important entre le Jurassique supérieur et le Crétacé inférieur, postérieurement à l’ouverture de l’Atlantique Central. Cet événement n’est pas directement lié aux seuls processus affectant les marges passives puisque non seulement la marge est affectée, mais aussi l’intérieur du craton (jusque 800 km à l’intérieur des terres) et le domaine mobile non-cratonique au Nord. Ce refroidissement traduit une phase d’exhumation kilométrique qui permet alors le dépôt d’une épaisse séquence détritique sur la plateforme saharienne. L’hypothèse d’un raccourcissement comme explication n’est pas valide et l’hypothèse d’une anomalie thermique mantellique à cette époque rend mieux compte de cet événement d’érosion majeur. L’hypothèse thermique possède un autre avantage : celui de rendre compte du réchauffement qui suivit à l’Apto-Albien et au début du Crétacé supérieur, à la fois par le craton mais aussi par ses bordures, par le biais de la subsidence thermique.Deuxièmement, à partir du Crétacé supérieur, la tendance générale est au refroidissement dans toute la région étudiée, synchrone avec l’initiation de la convergence Afrique/Europe. La chaîne du Haut Atlas au Maroc représente à ce moment un témoin privilégié des déformations se produisant pendant le Cénozoïque. Nous avons déterminé un calendrier tectonique précis dans l’avant-pays méridional de la chaîne, afin d’avoir un point de comparaison avec l’enregistrement cratonique. Ainsi, une première phase tectonique se déroule à l’Eocène supérieur. Celle-ci fait écho à un événement de déformation de plus grande échelle qui affecte toute le craton, résultant sans doute d’une réorganisation de grande ampleur dans la dynamique de la convergence. La phase récente Plio-Quaternaire est bien décrite à l’échelle de l’Afrique du Nord dans la chaîne Atlasique, mais pourrait s’avérer trop récente pour pouvoir être décelée par nos thermochronomètres à l’intérieur du domaine cratonique. Enfin, une phase de soulèvement spécifique au domaine atlasique marocain est enregistrée pendant le Miocène inférieur-moyen et met en place des nappes dans la chaîne. Les thermochronomètres basse-température ne la détectent pas à l’intérieur du craton, et elle pourrait donc être géographiquement restreinte au domaine atlasique.Ce travail a démontré que l’absence de sédiments au cours du Méso-Cénozoïque, qui en première approche font de ce craton une zone dite « stable », occulte une réalité géologique autre, faite de la succession de plusieurs phases épeirogéniques. Une évaluation des processus à l’œuvre permet de proposer que les phénomènes mantelliques ainsi que les transferts de contraintes sont des acteurs majeurs à l’origine de ces mouvements. Néanmoins, la juste contribution de chacun de ces processus nécessite encore un travail approfondi. / The dynamic evolution of cratonic domains remains enigmatic as they are usually considered as stable through geological times. In this work, we unraveled the evolution of one of the largest cratonic area, the West African Craton (WAC), and its north and west boundaries (Anti-Atlas and Atlantic passive margin, respectively), through low-temperature thermochronology (apatite fission-track and (U-Th)/He thermochronology) and structural geology. The WAC was studied since its boundaries witnessed many different geological settings (platform, distal foreland, passive margin) during the Phanerozoic, making it a good candidate to evaluate the various driving forces acting on the craton.First, after a continuous Paleozoic subsidence, the craton records the most important cooling event between Late Jurassic and Early Cretaceous, postdating the onset of the Central Atlantic Ocean spreading. This event is unrelated to the sole passive margin in itself and affected both the craton (up to 800 km inland) and the mobile boundary in the north (Anti-Atlas and High Atlas). It represents kilometer-scale erosion that led to the deposition of thick detrital formations, the red beds, across the whole Saharan platform. This event is not characterized by shortening and is better explained through a mantle-related thermal anomaly during this exhumation. The thermal hypothesis explains the subsequent thermal subsidence undergone by the craton and its north boundary during the Aptian-Albian and the early stages of the Late Cretaceous.Second, from Late Cretaceous onward, dominant cooling trend has imprinted the thermal histories of the studied region, coevally with the onset of the Africa/Europe convergence.The High Atlas belt in Morocco is an accurate witness of the deformations occurring during Cenozoic times. We determined the precise tectonic schedule in the southern foreland of the belt and compared this evolution with the cratonic one. We show that the first Eocene tectonic event echoes to a major craton-scale deformation and results probably from a significant geodynamic change in the convergence zone. The Pliocene-Quaternary phase, well known at the North African scale, is only recorded in the Atlas belt, but might be too recent to have significantly imprinted the thermochronological record inside the craton. Finally, another uplift specific to the Moroccan Atlas Belt during Early to Middle Miocene led to the emplacement of tectonic nappes. This event is not recorded by LTT on the craton and may be restricted to its mobile boundary.This work demonstrates that, despite the lack of Mesozoic-Cenozoic sediment record that may advocate for a stable geological history, the West African Craton suffered significant epeirogenies during this period. Deep seated processes as well as stress transmission prove to be good candidates to account for these cratonic motions, although further work is needed to unravel the exact contribution of these various processes.

Nesta tese, dados gravimétricos terrestres e de satélite foram combinados revelando que as bordas oeste e sul da Bacia do Paraná são caracterizadas por um forte gradiente que se estende por 2000 km, desde o cráton Rio Apa até a margem continental Atlântica na latitude do Sinclinal de Torres. Enquanto a Bacia do Paraná é caracterizada por anomalias Bouguer negativas (~-80 mGal), os crátons Rio de la Plata, Rio Tebicuary e Rio Apa e a Bacia do Chaco-Paraná são marcados por anomalias Bouguer positivas (~10 mGal). Dados sismológicos e de compensação isostática permitiram correlacionar a variação regional da amplitude das anomalias Bouguer à espessura crustal, de ~40 km na Bacia do Paraná para 30-35 km nos crátons. Essas observações geofísicas e a ocorrência de granitos cálcio-alcalinos de idade Neoproterozoica-Cambriana ao longo do gradiente gravimétrico indicam um ambiente tectônico de colisão e zona de subducção. A essa descontinuidade de escala litosférica denominamos Zona de Sutura do Oeste do Paraná (WPS Western Paraná Suture shear/zone). Dois perfis magnetotelúricos (MT) foram coletados para estudar a natureza e a estrutura elétrica da crosta e do manto litosférico através da WPS. O primeiro perfil se estende por 830 km desde o cráton Rio de la Plata, no Uruguai, até a parte sul da Bacia do Paraná. Modelagem inversa 2-D desses dados mostra que o manto superior no cráton Rio de la Plata é bastante resistivo (~2000 m) até 250 km de profundidade, enquanto o manto superior na Bacia do Paraná é geralmente mais condutivo e heterogêneo. Com base numa descontinuidade lateral de escala litosférica bem definida no modelo de resistividade, o limite nordeste do cráton Rio de la Plata é redefinido no norte do bloco Valentines. O segundo perfil se estende por 450 km na Argentina, entre o cráton Rio Tebicuary e a Bacia do Paraná. No modelo MT o cráton Rio Tebicuary é caracterizado por um manto superior resistivo (2000 m) até 150 km de profundidade. A litosfera na Bacia do Paraná é menos resistiva (~500 m) e provavelmente menos espessa (~80 km). Um perfil MT entre o cráton Rio Apa e a Bacia do Paraná mostra estrutura geoelétrica similar. As estruturas elétricas observadas, juntamente com dados geocronológicos, geoquímicos, sismológicos e densidade, sugerem processos de refertilização na litosfera da Bacia do Paraná. Sucessões de anomalias condutivas em antigas zonas de sutura e resistivas em blocos e terrenos juvenis nos modelos geoelétricos, integradas a dados geológicos, indicam um processo de acresção horizontal e uma progressão de subducções de placas litosféricas oceânicas, sendo a mais jovem sob a litosfera continental da Bacia do Paraná. Os resultados obtidos mostram que a WPS é uma descontinuidade litosférica de primeira ordem que marca o fechamento de um oceano durante os estágios finais da formação do Gondwana Sul-Ocidental no Neoproterozoico-Cambriano. / In this thesis, terrestrial and satellite gravity data were integrated revealing a steep gravity gradient at the western and southern borders of the Paraná Basin. This gradient extends for 2,000 km from the Rio Apa craton to the Brazilian Atlantic margin at Torres Syncline latitude. Negative Bouguer anomalies (~-80 mGal) occur over the Paraná Basin, whereas positive anomalies are observed at Rio de la Plata, Rio Tebicuary and Rio Apa cratons, as well as Chaco-Paraná Basin. Seismological data and isostasy correlate the gravity gradient with crustal thickness variation, being thicker in the Paraná Basin (~40 km) and shallower in the cratons (~35 km). These geophysical observations and the presence of Neoproterozoic calc-alkaline granites along the gravity gradient suggest a collisional and subduction tectonic setting. This lithospheric discontinuity is hereafter referred to as Western Paraná Suture/shear zone (WPS). Two magnetotelluric (MT) profiles perpendicular to WPS were set up to study the electrical structure and nature of the crust and lithospheric mantle across the suture zone. The first profile, 830 km long, extends northward from Rio de la Plata craton, in Uruguay, to Paraná Basin southern border. 2-D inversion of this MT profile shows that the Rio de la Plata craton upper mantle is highly resistive (~2000 m) down to 250 km depth, whereas the Paraná Basin lithosphere is conductive and heterogeneous. Based on a lithospheric-scale lateral discontinuity in the resistivity model, the Rio de la Plata craton northern limit is redefined to the Valentines block northern limit. The second profile is 450 km long and extends from Rio Tebicuary craton to the Paraná Basin, and all stations are in Argentina. The MT model shows that Rio Tebicuary craton is characterized by a resistive lithosphere (2000 m) down to 150 km depth. The Paraná Basin lithosphere is less resistive (~500 m) and probably thinner (~80 km). Previous MT study between the Rio Apa craton and the Paraná basin, to the north, shows a similar electrical structure. These electrical characteristics, integrated with geochronological, geochemical, seismological and density data, suggest that Paraná Basin lithosphere underwent refertilization episodes. In the geoelectrical models, a series of resistive blocks and juvenile terrains and conductive anomalies in suture zone relics, integrated with geological data, suggest a horizontal accretionary process by means of progressive oceanic lithospheres subductions, the youngest one occurring below the Paraná Basin continental lithosphere. Altogether, these results show that the WPS is a first order lithosphere discontinuity, a site of an ocean closure during the South-Western Gondwana late stages of amalgamation in Neoproterozoic/Cambrian times.

Nesta tese, dados gravimétricos terrestres e de satélite foram combinados revelando que as bordas oeste e sul da Bacia do Paraná são caracterizadas por um forte gradiente que se estende por 2000 km, desde o cráton Rio Apa até a margem continental Atlântica na latitude do Sinclinal de Torres. Enquanto a Bacia do Paraná é caracterizada por anomalias Bouguer negativas (~-80 mGal), os crátons Rio de la Plata, Rio Tebicuary e Rio Apa e a Bacia do Chaco-Paraná são marcados por anomalias Bouguer positivas (~10 mGal). Dados sismológicos e de compensação isostática permitiram correlacionar a variação regional da amplitude das anomalias Bouguer à espessura crustal, de ~40 km na Bacia do Paraná para 30-35 km nos crátons. Essas observações geofísicas e a ocorrência de granitos cálcio-alcalinos de idade Neoproterozoica-Cambriana ao longo do gradiente gravimétrico indicam um ambiente tectônico de colisão e zona de subducção. A essa descontinuidade de escala litosférica denominamos Zona de Sutura do Oeste do Paraná (WPS Western Paraná Suture shear/zone). Dois perfis magnetotelúricos (MT) foram coletados para estudar a natureza e a estrutura elétrica da crosta e do manto litosférico através da WPS. O primeiro perfil se estende por 830 km desde o cráton Rio de la Plata, no Uruguai, até a parte sul da Bacia do Paraná. Modelagem inversa 2-D desses dados mostra que o manto superior no cráton Rio de la Plata é bastante resistivo (~2000 m) até 250 km de profundidade, enquanto o manto superior na Bacia do Paraná é geralmente mais condutivo e heterogêneo. Com base numa descontinuidade lateral de escala litosférica bem definida no modelo de resistividade, o limite nordeste do cráton Rio de la Plata é redefinido no norte do bloco Valentines. O segundo perfil se estende por 450 km na Argentina, entre o cráton Rio Tebicuary e a Bacia do Paraná. No modelo MT o cráton Rio Tebicuary é caracterizado por um manto superior resistivo (2000 m) até 150 km de profundidade. A litosfera na Bacia do Paraná é menos resistiva (~500 m) e provavelmente menos espessa (~80 km). Um perfil MT entre o cráton Rio Apa e a Bacia do Paraná mostra estrutura geoelétrica similar. As estruturas elétricas observadas, juntamente com dados geocronológicos, geoquímicos, sismológicos e densidade, sugerem processos de refertilização na litosfera da Bacia do Paraná. Sucessões de anomalias condutivas em antigas zonas de sutura e resistivas em blocos e terrenos juvenis nos modelos geoelétricos, integradas a dados geológicos, indicam um processo de acresção horizontal e uma progressão de subducções de placas litosféricas oceânicas, sendo a mais jovem sob a litosfera continental da Bacia do Paraná. Os resultados obtidos mostram que a WPS é uma descontinuidade litosférica de primeira ordem que marca o fechamento de um oceano durante os estágios finais da formação do Gondwana Sul-Ocidental no Neoproterozoico-Cambriano. / In this thesis, terrestrial and satellite gravity data were integrated revealing a steep gravity gradient at the western and southern borders of the Paraná Basin. This gradient extends for 2,000 km from the Rio Apa craton to the Brazilian Atlantic margin at Torres Syncline latitude. Negative Bouguer anomalies (~-80 mGal) occur over the Paraná Basin, whereas positive anomalies are observed at Rio de la Plata, Rio Tebicuary and Rio Apa cratons, as well as Chaco-Paraná Basin. Seismological data and isostasy correlate the gravity gradient with crustal thickness variation, being thicker in the Paraná Basin (~40 km) and shallower in the cratons (~35 km). These geophysical observations and the presence of Neoproterozoic calc-alkaline granites along the gravity gradient suggest a collisional and subduction tectonic setting. This lithospheric discontinuity is hereafter referred to as Western Paraná Suture/shear zone (WPS). Two magnetotelluric (MT) profiles perpendicular to WPS were set up to study the electrical structure and nature of the crust and lithospheric mantle across the suture zone. The first profile, 830 km long, extends northward from Rio de la Plata craton, in Uruguay, to Paraná Basin southern border. 2-D inversion of this MT profile shows that the Rio de la Plata craton upper mantle is highly resistive (~2000 m) down to 250 km depth, whereas the Paraná Basin lithosphere is conductive and heterogeneous. Based on a lithospheric-scale lateral discontinuity in the resistivity model, the Rio de la Plata craton northern limit is redefined to the Valentines block northern limit. The second profile is 450 km long and extends from Rio Tebicuary craton to the Paraná Basin, and all stations are in Argentina. The MT model shows that Rio Tebicuary craton is characterized by a resistive lithosphere (2000 m) down to 150 km depth. The Paraná Basin lithosphere is less resistive (~500 m) and probably thinner (~80 km). Previous MT study between the Rio Apa craton and the Paraná basin, to the north, shows a similar electrical structure. These electrical characteristics, integrated with geochronological, geochemical, seismological and density data, suggest that Paraná Basin lithosphere underwent refertilization episodes. In the geoelectrical models, a series of resistive blocks and juvenile terrains and conductive anomalies in suture zone relics, integrated with geological data, suggest a horizontal accretionary process by means of progressive oceanic lithospheres subductions, the youngest one occurring below the Paraná Basin continental lithosphere. Altogether, these results show that the WPS is a first order lithosphere discontinuity, a site of an ocean closure during the South-Western Gondwana late stages of amalgamation in Neoproterozoic/Cambrian times.