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Cratonic basins cover more than 10% of Earth's continental surface area, yet their origin remains enigmatic. In this thesis a suite of new and legacy geophysical and geological data are integrated to constrain the origin of the Parnaíba basin, a cratonic basin in Northeast Brazil. These data include a 1400 km long, deep (20 s two-way travel time) seismic reflection profile, five +/- 110 km offset wide-angle split-spread receiver gathers, gravity anomaly, and well data. In the centre of the basin, the depth to pre-Paleozoic basement is ~ 3.3 km, a zone of midcrustal reflectivity (MCR) can be traced laterally for ~ 250 km at depths between 17-25 km and Moho depth is ~ 42 +/- 2 km. Gravity and P-wave modelling suggests that the MCR represents the upper surface of a high density (2985 kg m³) and V_p (6.7 - 7.0 km s^-1) lower crustal body, likely of magmatic origin. Backstripping of well data shows a concave up decreasing tectonic subsidence, similar in form to that commonly observed in rift-type basins. It is shown, however, that the seismic and gravity data are inconsistent with an extensional origin. It is shown that an intrusive body in the lower crust that has loaded and flexed the surface of the crust, combined with sediment loading, provides a satisfactory fit to the observed gravity anomaly, sediment thickness and basin shape. A buried load model is also consistent with seismic data, which suggest that the Moho is as deep or deeper beneath the basin centre than its flanks and accounts for at least part of the tectonic subsidence through a viscoelastic stress relaxation that occurs in the lithosphere following load emplacement. Comparative analysis of the Michigan and Congo basins shows gravity data from these basins is also consistent with a lower crustal mass excess, while subsidence analysis shows viscoelastic stress relaxation may also contribute to their early subsidence histories. However, unlike Parnaíba, both of these basins appear to have been subjected to secondary tectonic processes that obscure the primary 'cratonic basin' subsidence signals. Parnaíba basin, therefore, offers an excellent record for the investigation of cratonic basin formation.

It is recognised that some proportion of South American large-scale topography has been generated by convection within the Earth's mantle. Yet, spatial and temporal patterns of dynamic topography remain poorly understood. Variation of present-day dynamic topography can be mapped in the oceans by calculating residual depths with respect to the well-known age-depth relationship. Along the margins abutting South America, anomalies with amplitudes of $\pm1$ km and wavelengths of $\sim10^{3}$ km are observed. Onshore, dynamic topography is investigated by analysing a range of disparate datasets. Positive long-wavelength free-air gravity anomalies and slow shear-wave mantle velocities correlate with high plateaux of the Borborema Province and the Central Andean Altiplano. Admittance analyses of these regions are used to gauge dynamic support. Admittance of $ > 20$ mGal km$^{-1}$ at wavelengths $ > $ 500 km suggests partial dynamic support. In this context, inverse modelling of longitudinal river profiles is applied to retrieve a continental-scale uplift history. Erosional parameters are calibrated against an independently derived uplift history of the Borborema Province that reveals uplift in the last 30 Ma. Results suggest that the bulk of South American regional topography grew during Cenozoic times. In the Central Andean Altiplano and Southern Patagonia, most uplift occurred in the last 20 Ma. In both areas, widespread Cenozoic magmatism suggests that youthful uplift might be related to asthenospheric upwelling. Uplift histories are used to predict sediment flux to the Amazon Fan, which reveals that onset of the delta is a direct consequence of intensified Andean uplift. Analysis of the Parna\'iba cratonic basin of northeast Brazil is carried out to evaluate long-term evolution of vertical motions and to understand the mechanisms driving this basin's subsidence. Joint interpretation of a deep seismic reflection profile that traverses the basin and receiver function analyses reveal a 3 km thick basin underlain by three crustal blocks. Moho depths of 38--43 km are observed beneath the Amazon craton west of the basin, whereas depths of 35 km are found underneath the Borborema Province to the east. The Moho is located at 38--42 km depth beneath the basin. Stratigraphic architecture from shallow seismic reflection profiles reveals undisturbed deposition between Palaeozoic and Mesozoic times. Rift-type structures are locally imaged. Subsidence analysis reveals thermally-driven subsidence with thermal time constants of $\sim$ 70--80 Ma. Assessment of crustal thickness variations indicates that minimal extension of up to 80 km, with small stretching factors (up to 1.15), is plausible beneath Parna\'iba. One- and two-dimensional strain rate histories suggest that pre-Silurian rifting followed by thermal subsidence is possible if a minimum of 1 km of syn-rift deposition occurred. Basin-wide erosional unconformities are observed throughout the sedimentary section and correlate with departures from long-term subsidence trends. These steps are interpreted as transient uplift events that led to development of ephemeral landscapes, suggesting that dynamic topography could have played a role in the evolution of this Phanerozoic basin.

Nós usamos tomografia sísmica de tempo de percurso para estudar o manto superior sob as regiões Sudeste e Centro-Oeste do Brasil. Este método baseia-se na inversão de resíduos relativos de tempo para as ondas P e S (VanDecar, 1991), que foram obtidos para mais de 80 estações em uma área de 20 x 20 graus. Mais de 11000 e 8000 resíduos de tempo foram obtidos para as ondas P (P direta e PKPdf) e S (S direta, ScS, SKS e SKKS), respectivamente, utilizando correlação cruzada de forma de ondas para até 12 estações operando simultaneamente. Para avaliar a robustez dos resultados com respeito aos dados, nós utilizamos o método estatístico de re-amostragem Jackknife, o qual inerentemente leva em conta a altamente variável cobertura dos raios e os erros das medidas, e pode fornecer limites de confiança para as anomalias. Inversões regionais foram realizadas para estudar a influência da parametrização nas anomalias sísmicas. Nossos resultados mostraram boa correlação das anomalias sísmicas com as principais estruturas tectônicas e revelaram novas anomalias que ainda não haviam sido observadas nos trabalhos anteriores. Anomalias de alta velocidade na porção oeste do Cráton do São Francisco apóiam a hipótese de que este cráton foi parte de uma placa Neoproterozóica maior. Anomalias de baixa velocidade sob a Província Tocantins (principalmente nas faixas móveis entre os Crátons Amazônico e do São Francisco) foram interpretadas como causadas por afinamento litosférico, consistente com a boa correlação entre a sismicidade intraplaca e as anomalias de baixa velocidade nesta região (Assumpção et al., 2004b). A melhora na resolução da anomalia de alta velocidade sob a Bacia do Paraná (~200 km) permitiu uma discussão sobre a geometria do núcleo cratônico desta Bacia. A subducção da Placa de Nazca foi observada como uma anomalia de alta velocidade sob a Bacia do Paraná (profundidades entre 700 e 1200 km). Nestas profundidades, uma grande anomalia de baixa velocidade aparece próxima da Placa de Nazca. Testes sintéticos mostraram que esta anomalia é um artefato da inversão gerado pela presença da Placa de Nazca. / We used travel time seismic tomography to study the upper mantle beneath SE and Central Brazil. This method is based on the inversion of P- and S-wave relative travel time residuals (VanDecar, 1991) obtained from more than 80 stations in an area of 20 x 20 degrees. More than 11000 P and PKP residuals, and more than 8000 S, ScS, SKS, and SKKS residuals were obtained from waveform cross-correlations for up to 12 simultaneous stations. To evaluate the robustness of the tomographic results with respect to the data, we use the Jackknife re-sampling method, which inherently take into account the highly variable ray coverage and measurement errors, and can provide confidence limits for the anomalies. Regional inversions were carried out to study influence of the parameterization on the seismic anomalies. Our results show correlations of seismic anomalies with the main tectonic structures and reveal new anomalies not yet observed in previous works. High velocity anomalies in the western portion of the São Francisco Craton support the hypothesis that this craton was part of a major Neoproterozoic plate. Low velocity anomalies beneath the Tocantins Province (mainly fold belts between the Amazon and São Francisco cratons) are interpreted as due to lithospheric thinning, consistent with a good correlation between intraplate seismicity and low velocity anomalies in this region (Assumpção et al., 2004b). The resolution improvement of the high velocity anomalies beneath the Parana Basin (at ~200 km) allows a discussion about the geometry of the cratonic nucleous of this Basin. The slab of the Nazca Plate is observed as a high velocity anomaly beneath the Parana basin (at 700-1200 km depth). At these depths, large low velocity anomaly appears next to the slab. Synthetic tests show that these anomalies are an artifact of the inversion generated by the presence of the slab.

Nós usamos tomografia sísmica de tempo de percurso para estudar o manto superior sob as regiões Sudeste e Centro-Oeste do Brasil. Este método baseia-se na inversão de resíduos relativos de tempo para as ondas P e S (VanDecar, 1991), que foram obtidos para mais de 80 estações em uma área de 20 x 20 graus. Mais de 11000 e 8000 resíduos de tempo foram obtidos para as ondas P (P direta e PKPdf) e S (S direta, ScS, SKS e SKKS), respectivamente, utilizando correlação cruzada de forma de ondas para até 12 estações operando simultaneamente. Para avaliar a robustez dos resultados com respeito aos dados, nós utilizamos o método estatístico de re-amostragem Jackknife, o qual inerentemente leva em conta a altamente variável cobertura dos raios e os erros das medidas, e pode fornecer limites de confiança para as anomalias. Inversões regionais foram realizadas para estudar a influência da parametrização nas anomalias sísmicas. Nossos resultados mostraram boa correlação das anomalias sísmicas com as principais estruturas tectônicas e revelaram novas anomalias que ainda não haviam sido observadas nos trabalhos anteriores. Anomalias de alta velocidade na porção oeste do Cráton do São Francisco apóiam a hipótese de que este cráton foi parte de uma placa Neoproterozóica maior. Anomalias de baixa velocidade sob a Província Tocantins (principalmente nas faixas móveis entre os Crátons Amazônico e do São Francisco) foram interpretadas como causadas por afinamento litosférico, consistente com a boa correlação entre a sismicidade intraplaca e as anomalias de baixa velocidade nesta região (Assumpção et al., 2004b). A melhora na resolução da anomalia de alta velocidade sob a Bacia do Paraná (~200 km) permitiu uma discussão sobre a geometria do núcleo cratônico desta Bacia. A subducção da Placa de Nazca foi observada como uma anomalia de alta velocidade sob a Bacia do Paraná (profundidades entre 700 e 1200 km). Nestas profundidades, uma grande anomalia de baixa velocidade aparece próxima da Placa de Nazca. Testes sintéticos mostraram que esta anomalia é um artefato da inversão gerado pela presença da Placa de Nazca. / We used travel time seismic tomography to study the upper mantle beneath SE and Central Brazil. This method is based on the inversion of P- and S-wave relative travel time residuals (VanDecar, 1991) obtained from more than 80 stations in an area of 20 x 20 degrees. More than 11000 P and PKP residuals, and more than 8000 S, ScS, SKS, and SKKS residuals were obtained from waveform cross-correlations for up to 12 simultaneous stations. To evaluate the robustness of the tomographic results with respect to the data, we use the Jackknife re-sampling method, which inherently take into account the highly variable ray coverage and measurement errors, and can provide confidence limits for the anomalies. Regional inversions were carried out to study influence of the parameterization on the seismic anomalies. Our results show correlations of seismic anomalies with the main tectonic structures and reveal new anomalies not yet observed in previous works. High velocity anomalies in the western portion of the São Francisco Craton support the hypothesis that this craton was part of a major Neoproterozoic plate. Low velocity anomalies beneath the Tocantins Province (mainly fold belts between the Amazon and São Francisco cratons) are interpreted as due to lithospheric thinning, consistent with a good correlation between intraplate seismicity and low velocity anomalies in this region (Assumpção et al., 2004b). The resolution improvement of the high velocity anomalies beneath the Parana Basin (at ~200 km) allows a discussion about the geometry of the cratonic nucleous of this Basin. The slab of the Nazca Plate is observed as a high velocity anomaly beneath the Parana basin (at 700-1200 km depth). At these depths, large low velocity anomaly appears next to the slab. Synthetic tests show that these anomalies are an artifact of the inversion generated by the presence of the slab.

L’origine des suites de mégacristaux des kimberlites est sujette à d’intenses débats depuis de nombreuses années. La suite complexe de mégacristaux (grenat, clinopyroxène, zircon, baddeleyite, ilménite, rutile et nodules d’intercroissances rutile-silicates) des kimberlites diamantifères de Mbuji-Mayi (Kasaï Oriental), mises en place au Crétacé dans le craton archéen du Congo-Kasaï, a été étudiée en détails dans le but d’établir les relations entre les différents minéraux de la suite, leur relation au magma kimberlitique-hôte et au manteau lithosphérique cratonique archéen. L’étude des mégacristaux de grenat des kimberlites pauvres en diamants du Kundelungu (Katanga) a permis en outre d’établir la comparaison entre les mégacristaux de deux provinces kimberlitiques en République Démocratique du Congo, qui diffèrent notamment par leur âge de mise en place et par la composition et l’âge du socle traversé. <p>L’ensemble des données minéralogiques et géochimiques acquises (éléments majeurs et en traces, géochimie isotopique de l’oxygène, du Nd et de l’Hf) est intégré dans le but de déterminer la nature du (ou des) processus qui a (ont) donné naissance à ces suites de mégacristaux. <p>En parallèle, l’origine d’un xénolite rare de clinopyroxénite à kyanite exceptionnellement riche en Cr des kimberlites de Mbuji-Mayi a été explorée.<p>Bien qu’ils partagent de nombreuses caractéristiques avec d’autres suites de mégacristaux kimberlitiques, les mégacristaux de RDC sont généralement enrichis en Cr et appauvris en Fe et Ti, et ne présentent pas de preuve d’une origine par cristallisation fractionnée à partir d’un magma, ce qui permet de suggérer une origine différente, en l’occurrence une liaison plus directe avec le manteau lithosphérique réfractaire local lors de leur formation. Une origine métasomatique par interaction entre un liquide/fluide précurseur de la kimberlite et les péridotites du manteau lithosphérique est donc favorisée. L’ensemble des espèces minérales qui forme la suite de mégacristaux peut en effet trouver un équivalent compositionnel dans les lithologies métasomatisées de la lithosphère mantélique. <p>Les mégacristaux de grenat des deux provinces partagent des similarités frappantes qui sont interprétées en termes de processus de formation similaires. En revanche, ils ont systématiquement montré un comportement géochimique singulier, suggérant un processus de formation différent des autres mégacristaux. Ils semblent en effet avoir retenu l’héritage des compositions variables d’anciens protolites de grenat affectés récemment par un métasomatisme de type kimberlitique. Ces grenats résultent de la recristallisation de grenats initialement présents dans les péridotites cratoniques de la lithosphère archéenne. Par contre, les mégacristaux de clinopyroxène, zircon, baddeleyite, ilménite, rutile et les nodules d’intercroissances rutile-silicates se sont effectivement formés récemment par l’interaction métasomatique entre le liquide/fluide proto-kimberlitique et les péridotites cratoniques. Des variations locales du rapport (fluide et/ou liquide)/roche et de l’activité en SiO2 lors de la percolation du magma proto-kimberlitique asthénosphérique dans le manteau lithosphérique cratonique, couplées à la nature propre à la kimberlite de la région, permettent d’intégrer l’ensemble des mégacristaux dans un modèle pétrogénétique commun, avec des processus de formation parfois contrastés. <p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished