Les objectifs de ce travail sont les suivants. 1- Reconstitution de la géométrie syn-rift du demi-graben de Bourg-d 'Oisans 2- Quantification des vitesses de fon ctionnement des failles normales syn-rift 3- Relation entre vitesse de fonctionnement et processus de croissance des failles normales dans la croûte continentale 4- Reconstitution de la géométrie profonde des failles normales 5- Caractérisation des facteurs de contrôle de l'étirement crustal en contexte de rift 6- Variabilité spatiale et temporelle de l'étirement sur une paléomarge. Secteur d'étude Pour répondre aux différentes problématiques évoquées ci-dessus, le choix du secteur d'étude s'est porté sur le bassin de Bourg-d'Oisans, situé dans la zone dauphinoise du domaine externe des Alpes occidentales françaises . Les raisons qui ont motivé cette décision sont les suivantes. (1) Le bassin correspond à un demi-graben d'âge Jurassique inférieur, situé sur la marge nord-téthysienne (e.g. Lemoine et al. , 1986). (2) La série sédimentaire liasique préservée au sein du demi-graben présente une forte épaisseur au regard des séries réduites situées sur les hauts-fonds voisins (têtes de blocs) (e.g. Mouterde, 1964; Barfety, 1985 ; Bas, 1985). (3) Les sédiments sont de nature essentiellement carbonatée et argilo-carbonatée et contiennent des faunes servant de marqueurs biostratigraphiques (ammonites) qui permettent de dater les séries sédimentaires (Barfety, 1985 ; Bas, 1985). (4) La faille d'Ornon n'a été que modérément inversé durant l'orogenèse alpine (e.g.. Gillchrist et al., 1987). (5) Les structures tectoniques précoces sont bien conservées et affleurent sur l'ensemble du secteur (e.g. Barfety, 1985). (6) Le secteur est connu et a déjà fait l'objet d'études cartographiques et/ou structurales sans analyse stratigraphique détaillée (e.g. Reboul, 1962; Bornuat, 1962 ; Barfety, 1985 ; Pinto-Bull, 1987 ; Grand, 1987).

La Fièvre de la Vallée du Rift (FVR) est une zoonose observée pour la première fois au Kenya en 1930 qui s'est peu à peu propagée à la plupart des pays d'Afrique. La FVR est une maladie à transmission vectorielle dont le virus appartient au genre Phlebovirus de la famille des Bunyaviridæ. En Afrique de l'Est, l'émergence de foyers est prédite par des modèles statistiques, ce qui n'est pas le cas en Afrique de l'Ouest où les facteurs et les mécanismes en jeu sont encore mal définis. L'objectif de cette thèse est d'identifier les facteurs et les processus épidémiologiques expliquant l'émergence de foyers de FVR au Sénégal, en mettant en œuvre une approche éco-épidémiologique centrée sur les principaux moustiques vecteurs du virus. Par l'étude de variables environnementales et climatiques et par leur exploitation dans des modèles mathématiques, nous avons tenté de répondre à deux questions épidémiologiques majeures : (1) quelles sont les zones potentiellement à risque, et (2) quelles sont les périodes favorables à l'apparition de foyers. L'étude a été menée à l'échelle locale, dans une zone d'environ 10 km2 autour du village de Barkedji situé dans la région sylvo-pastorale du Ferlo.Pour localiser les zones à risque de transmission du virus, nous utilisons la télédétection et l'analyse paysagère afin de caractériser l'environnement favorable aux deux principaux candidats vecteurs du virus, Aedes vexans et Culex poicilipes. Pour identifier les périodes à risque, nous avons développé un modèle d'abondance de populations de moustique des deux espèces vectrices prenant en compte la dynamique des gîtes larvaires (les mares), et dont les simulations ont été validées avec des données de terrain de capture de moustiques. Pour se faire, nous avons dû préalablement développé un modèle dynamique de hauteur d'eau des mares temporaires, modèle calibré et validé à partir de données de terrain et de données d'observation de la Terre.Les résultats de l'analyse paysagère ont confirmé que les milieux favorables aux vecteurs de la maladie pouvaient être caractérisés par télédétection. Ils ont aussi mis en évidence l'importance des mares et de la densité de végétation environnante, et ont abouti à une cartographie de l'hétérogénéité spatiale du risque de circulation de la FVR. Les résultats de l'analyse temporelle ont montré que les années de circulation active du virus coïncidaient avec les années pour lesquelles les deux espèces de moustiques étaient présentes en forte quantité. On observe ainsi deux années à très forte densité des deux moustiques vecteurs, en 1987 et en 2003, correspondant aux années d'épidémie/épizootie les plus importantes dans la région.

L'ouverture de l'Atlantique Sud s'est initiée par une phase de rifting au Crétacé inférieur. Pendant cette période, une épaisse série salifère s'est développée dans tout le segment Central. La présence contemporaine d'évaporites, communément associées à un climat aride, suggère donc la possibilité d'avoir eu, au Crétacé inférieur, des zones arides à proximité de l'Equateur. Cette observation soulève alors des questions majeures: quelle a été l'incidence du rifting sur le climat? Et quels rôles ont pu jouer ces deux processus, climat et tectonique, dans la dynamique sédimentaire et entre autre sur la dynamique des dépôts du sel? Dans ce but, une approche par modélisation numérique a été choisie et trois grandes étapes ont été suivies, (1) une synthèse paléogéographique, (2), une modélisation climatique, et (3) une modélisation stratigraphique. La synthèse paléogéographique a permis, dans un premier temps, de mettre en évidence une évolution diachrone de l'activité du rift, précoce au Nord du segment Central avant de se propager dans la partie Sud, et d'autre part de préciser la chronologie des deux phases d'extension, rift et sag. Les modélisations climatiques ont montré l'existence d'une ceinture climatique humide au Nord de la zone d'étude, ainsi qu'une forte saisonnalité. Enfin, les modélisations stratigraphiques ont révélé l'importance de la prise en compte (1) de cette saisonnalité dans les modèles et (2) de la paléogéographie du segment Central. L'interaction entre les trois thématiques a permis de préciser l'importance des paramètres de contrôle pour la formation des évaporites. Ainsi, (1) le climat a joué un rôle majeur en offrant des conditions climatiques favorables grâce à la saisonnalité du climat dans la mise en place des évaporites, mais (2) le rift a éxercé un contrôle primordial puisqu'il a généré un régime de subsidence permettant la connexion marine et l'apport de sel nécéssaire au dépôt des évaporites dans un bassin encore protégé.

Most basaltic volcanoes are affected by recurrent lateral instabilities during their evolution. Numerous factors have been shown to be involved in the process of flank destabilization occurring over long periods of time or by instantaneous failures. However, the role of these factors on the mechanical behaviour and stability of volcanic edifices is poorly-constrained as lateral failure usually results from the combined effects of several parameters. Our study focuses on the morphological and structural comparison of two end-member basaltic systems, La Reunion (Indian ocean, France) and Stromboli (southern Tyrrhenian sea, Italy). We showed that despite major differences on their volumes and geodynamic settings, both systems present some similarities as they are characterized by an intense intrusive activity along well-developed rift zones and recurrent phenomena of flank collapse during their evolution. Among the factors of instability, the examples of la Reunion and Stromboli evidence the major contribution of intrusive complexes to volcano growth and destruction as attested by field observations and the monitoring of these active volcanoes. Classical models consider the relationship between vertical intrusions of magma and flank movements along a preexisting sliding surface. A set of published and new field data from Piton des Neiges volcano (La Reunion) allowed us to recognize the role of subhorizontal intrusions in the process of flank instability and to characterize the geometry of both subvertical and subhorizontal intrusions within basaltic edifices. This study compares the results of numerical modelling of the displacements associated with high-angle and low-angle intrusions within basaltic volcanoes. We use a Mixed Boundary Element Method to investigate the mechanical response of an edifice to the injection of magmatic intrusions in different stress fields. Our results indicate that the anisotropy of the stress field favours the slip along the intrusions due to cointrusive shear stress, generating flank-scale displacements of the edifice, especially in the case of subhorizontal intrusions, capable of triggering large-scale flank collapses on basaltic volcanoes. Applications of our theoretical results to real cases of flank displacements on basaltic volcanoes (such as the 2007 eruptive crisis at La Reunion and Stromboli) revealed that the previous model of subvertical intrusions-related collapse is a likely mechanism affecting small-scale steeply-sloping basaltic volcanoes like Stromboli. Furthermore, our field study combined to modelling results confirms the importance of shallow-dipping intrusions in the morpho-structural evolution of large gently-sloping basaltic volcanoes like Piton de la Fournaise, Etna and Kilauea, with particular regards to flank instability, which can cause catastrophic tsunamis.

A evolução da margem continental do sudeste do Brasil tem sido discutida por diversos autores desde meados do século passado até os dias atuais, especialmente no contexto da origem e evolução dos escarpamentos e das bacias tafrogênicas. Buscou-se contribuir com novos dados sobre a evolução da área a partir da aplicação da termocronologia de baixa temperatura (U-Th)/He em apatita, que oferece uma sensibilidade significativa para registrar movimentações tectônicas na crosta superior. Foi possível obter idades em 107 cristais de apatita de 18 amostras do embasamento coletadas no perfil com orientação NW-SE, numa seção entre a Serra da Mantiqueira e o Gráben da Guanabara. As idades corrigidas variam entre 250,1 8,7 Ma e 43,5 1,9 Ma (2 σ) e as não corrigidas entre 174,13 3,03 Ma e 27,07 0,60 Ma (1 σ). O Neocretáceo, o Eocretáceo e o Paleoceno são os principais registros no conjunto de dados, em ordem de importância. No Neocretáceo, o intervalo entre 83,6 e 72,1 Ma (Campaniano) representa o maior destaque nos registros termocronológicos, embora os outros registros (Maastrichtiano e Santoniano) também estejam presentes e sejam importantes. As idades do Neocretáceo destacam a importância dos eventos tectonomagmáticos e soerguimento regional na história térmica dessa área, inclusive com idades (~86 Ma) atribuídas ao contexto de soerguimento da Serra do Mar. As idades do Eocretáceo indicam o registro de eventos térmicos mais antigos, vinculados à evolução pré-rifte. Já os dados do Paleoceno estariam associados ao evento de reativação responsável pela implantação do sistema de riftes continentais (~65 Ma) e as idades do Eoceno, restritas à borda de falha da bacia de Resende (49,7 Ma e 43,5 Ma), à reativação do sistema de riftes nessa área. A dispersão de idades foi interpretada como efeito dos danos de radiação já que muitos grãos apresentam correlação entre idade e concentração de urânio (eU). Os padrões de tempo-temperatura (t-T), definidos a partir dos modelos HeFTy calibrados para o modelo de difusão que considera os efeitos de danos de radiação nos cristais, registraram eventos de resfriamento rápido, os quais mostram correlação direta com episódios de reativação e soerguimento na margem continental e com registros nas bacias continentais e marginais. O padrão de aumento das idades com a elevação, assim como da costa em direção ao interior é observado, mas mostra-se alterado pela ocorrência de idades mais jovens associadas à complexa evolução dessa margem continental com desnivelamentos de blocos vinculados à tectônica pós-rift, numa situação que ressalta a influência dos episódios de reativação. As estimativas de denudação total variam entre 1,2 e 2,8 km. As taxas de erosão variam entre 15,2 e 35,3 m/Ma. A evolução da área indica não apenas a influência de um evento específico mas, possivelmente, uma combinação de episódios que se alternaram e/ou atuaram em conjunto em determinados períodos. Os eventos de reativação mais antigos, combinados com os mais recentes, exibem os seus remanescentes na paisagem (serras da Mantiqueira e do Mar e os grábens e bacias sedimentares) e assumem papel fundamental na evolução da área. Os registros de tais episódios podem ser observados nas histórias térmicas das rochas e nos depósitos correlativos nas bacias sedimentares marginais e intracontinentais. / This doctoral dissertation involves low-temperature thermochronologic investigations to constrain the Mesozoic and Cenozoic tectonic reactivation of the continental margin of southeast Brazil. The study area is located in a segment of the Neoproterozoic Ribeira belt in southeastern Brazil, which occupied a central position in Western Gondwana. Lately, during the Mesozoic and Cenozoic, fault zones related to the development of the continental rifts in southeast Brazil reactivated. Using apatite (U-Th)/He thermochronology (AHe), we have presented the results of analysis on 107 apatite crystals of basement samples collected from a NWSE transect in the Mantiqueira Mountains to the Guanabara Graben, as well as from the NESE transverse faults. The data range from 27.07 0.60 Ma to 174.13 3.03 Ma (1 σ) for uncorrected ages, and from 43.5 1.9 Ma to 250.1 8.7 Ma (2 σ) for corrected ages. The Neo-Cretaceous, Eo-Cretaceous, and Paleocene are the main recorded AHe ages, in order of importance. The Eo-Cretaceous ages indicate the occurrence of older thermal events related to a pre-rifting phase (~121 Ma). The Neo-Cretaceous ages signify the importance of tectonic and magmatic events, and regional uplifting for the thermal history of the study area, including ages related to the Serra do Mar Mountains uplift (~86 Ma). Paleocene ages seem to be related to the reactivation (~65 Ma), which was responsible for the continental rifts in the southeastern Brazil. Finally, the Eocene ages (49.7 Ma and 43.5 Ma), which are from samples restricted to the Resende Basin border faults, indicate a continental rift reactivation. We investigated the age dispersion data, which were interpreted as an effect of radiation damage. Several samples show correlations between apatite (U-Th)/He age and effective U concentration (eU). We have applied HeFTy thermal modeling to obtain timetemperature (t T) paths using a radiation damage diffusion model. Inverse modeling of (U-Th)/He age data suggests rapid cooling episodes for all samples. The main thermal events recorded by the HeFTy models show a direct correlation with the timing of regional tectonic events: reactivation phases, continental margin uplift, and the sedimentary record. Apatite (U-Th)/He ages increase with distance from the coast and with elevation. However, these patterns are discontinued by samples of younger ages as a result of the reactivation process of pre-existing structures in the Brazilian continental margin. The total estimated denudation range from 1.2 to 2.8 km. The erosion rates range from 15.2 to 35.3 m/My. Thus, the multi-episodic thermal events, which led to the formation of important regional tectonic and geomorphological features (Mantiqueira Mountains, Serra do Mar Mountains, grabens, and sedimentary basins), seem to play a fundamental role in the evolution of the Brazilian continental margin. The records can be found in the thermal history of rocks and its correlated deposits in the continental margin.

Three-fifths of the Earth’s crust has been built at oceanic spreading centres in the last 160 million years. To explore crustal extension processes and the architecture of these constructive plate boundaries I have studied the oceanic rift in Iceland. Here the Mid Atlantic Ridge is anomalously elevated above sea level and thus easier to instrument. I have deployed and operated a dense network of seismometers in the remote volcanic highlands in central Iceland, and used the passive seismic data collected from this network to explore crustal structure and volcanic processes in the extensional rift zones. My analysis of persistent seismicity located in an intervening region between individual spreading segments, uniquely records the segmentation of plate spreading on the scale of individual volcanic systems. Precise location and characterisation of micro-earthquakes identifies a series of faults subparallel to the rift fabric, and source mechanisms define left-lateral strike-slip motion on these faults. This extremely high quality microseismic data reveals transform motion being accommodated by bookshelf faulting in a concentrated region between two such volcanic systems, providing evidence for the localisation of spreading in the discrete volcanic systems. While transform motion between spreading centres appears to be accommodated on a continuous basis, the extension of the brittle upper crust within the spreading centres occurs episodically during rifting events. Our local seismic network fortuitously recorded such a rifting episode in August 2014, during which the opening of a 5 metre wide dyke triggered a huge increase in seismicity across large areas of the rift zone. Stress-seismicity-rate modelling of this triggered seismicity, along with geodetic constraints on the deformation, provided a remarkable opportunity with which it was possible to prove the existence of stress-shadowing, a challenge which has eluded earthquake seismologists for decades. Using the excellent coverage of our extended seismic network I have also generated a new high resolution image of the regional crustal seismic structure using surface waves extracted from ambient seismic noise. The structure reveals low seismic velocities which are closely correlated with the volcanic rift zones, and faster wavespeeds in the older and non-volcanically active Tertiary crust. The strongest anomalies are seen in the north-west of the Vatnajökull icecap, at the location of thickest crust and inferred centre of the underlying mantle plume. Inversion for shear wave velocity structure shows high velocity-gradients in the top 10 km, defining a thickened extrusive upper crust in Iceland compared to standard oceanic crust, where it is normally 2–3 km thick. Below this, the shear wave velocity structure reveals a distinct low-velocity zone in the mid crust between 14–20 km depth, which is widespread across Iceland and shallows into the active volcanic rifts. This extensive feature suggests high mid-crustal temperatures and a high temperature-gradient between the extrusives of the upper crust and the intrusive mid-to-lower crust in Iceland.

xiii, 182 p. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / Representing a distinct contribution to the tradition of comparative international research in the environment, this dissertation studies the effects of national economic restructuring programs, implemented under the administration of multilateral development institutions, on the fertilizer intensity, energy intensity, and value efficiency of national commodity agriculture for the period 1980 to 2002. Known as structural adjustment, these conditional loan agreements have been thoroughly studied with respect to various social outcomes but in terms of environment impact, sociological investigation has been limited to case studies and to preliminary quantitative analyses of deforestation. Examining the consequences of structural adjustment on soil fertility management is a unique contribution to the field. Combining empirical work with theoretical explication, I frame the object of study using agrarian systems theory and the concept of societal metabolism, examining how the problem of soil fertility in the modern era has become subsumed into industrial processes that are fossil-energy intensive. Relating this historical development to the ongoing dialectic between the forces, relations, and conditions of production, I investigate how the international division of labor, manifested in the uneven and combined development of national economies, facilitates an international division of nature and thereby reproduces the hierarchical system of appropriation that drives the ongoing global expansion of the metabolic rift. Laying out competing theoretical perspectives on the potential for rational management of agricultural modernization, in the empirical component of this project I employ cross-sectional time-series panel regression analysis of secondary data on national development indicators in order to evaluate the relative merits of these contrasting theories for the sustainable development possibilities of Third World nations. The cumulative effects of structural adjustment significantly and independently increase the negative externalities of agricultural modernization while at the same time diminishing the potential economic efficiency of intensive nutrient management. / Committee in charge: Richard York, Chairperson, Sociology; John Foster, Member, Sociology; Robert 0 Brien, Member, Sociology; Joseph Fracchia, Outside Member, Honors College

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Apesar da grande quantidade de estudos geoquímicos e geocronológicos que têm sido executados no enxame de diques de Ponta Grossa (EDPG), pouco se sabe a respeito da tectônica associada ao seu sin e pós emplacement. O objetivo desse estudo é identificar nos diques possíveis indicadores cinemáticos a fim de compreender essa dinâmica, além de caracterizar a tectônica rúptil Meso-cenozóica associada à área, afetando todas as rochas. A área de estudo está situada no entorno da Baía de Paranaguá, estado do Paraná, onde os diques do EDPG afloram intrudindo domínios pré-cambrianos, compostos por gnaisses, sequências metassedimentares e suítes graníticas pertencentes ao Terreno Paranaguá e uma pequena parte às Microplacas Curitiba e Luís Alves, ambos em contato através de Zonas de cisalhamento (SIGA JR, 1995). Essas rochas possuem direção de foliação marcante NE-SW. Os diques estudados foram divididos em dois grupos com base em estudos petrográficos, com forte predomínio dos básicos toleíticos e subordinadamente, os básicos alcalinos. Alguns diques compostos também foram encontrados, o que demonstra ao menos dois pulsos magmáticos possivelmente associados ao mesmo evento. São diques verticais a subverticais e possuem direção principal NW-SE. Com frequência apresentam fraturamento interno de direção NE-SW, provavelmente associados ao seu processo de resfriamento. Possuem formato tabular, porém não é raro que ocorram irregulares. As principais feições indicativas de movimentação oblíqua na intrusão desses diques são as estruturas de borda em degraus, tocos e zigue-zague, que demonstram em geral uma componente distensional destral de deslocamento. Agregando dados dos demais enxames de diques toleíticos principais, chegou-se a um valor médio de N80E para o tensor σ3 da abertura do Atlântico Sul, coerente com o esperado também para EDPG, visto que foram intrudidos em um ambiente transtensivo (CORREA GOMES, 1996). Falhas e fraturas são observadas cortando tanto as rochas encaixantes quanto os diques, caracterizando uma tectônica posterior à intrusão. As principais famílias de fraturas são N20-30E, N30-40W, N80W e N60-70E, formando zonas preferenciais de erosão no cruzamento entre elas. As falhas podem apresentar plano de falha bem definido com estrias e ressaltos, ocorrendo preenchidas ou não, tendo sido observados preenchimento de sílica e material carbonático. Predomina nas falhas observadas, cinemática sinistral demonstrando mudança no campo de esforços com relação ao emplacement dos diques. O estudo da tectônica rúptil assim como do emplacement dos diques da área vem a contribuir para o melhor entendimento dos processos de abertura do Oceano Atlântico Sul, além de abranger a região emersa do que constitui o embasamento da bacia de Santos, foco de extensivos estudos atualmente, podendo-se inferir que os mesmos processos tenham afetado a região offshore. / Despite the large amount of geochemical and geochronological studies that have been performed in the Ponta Grossa dyke swarm (EDPG), little is known about the associated tectonics with their sin and post emplacement. The objective of this study is to identify at the dykes, possibles kinematic indicators to understand this dynamic and characterize the Meso-Cenozoic brittle tectonic associated with the area, affecting all rocks. The study area is located in the vicinity of Paranagua bay, Parana state, where the EDPG dykes arise intruding Precambrian domains, composed of gneisses, metasedimentary sequences and granite suites that belongs to the Paranaguá terrane and a small part to Curitiba and Luis Alves microplates, both in touch by a shear zone (SIGA JR, 1995). These rocks have an outstanding NE-SW foliation direction. The studied dykes were divided into two groups based on petrographic studies with a strong predominance of tholeiitic basics and subordinate, alkali basic. Some compounds dykes were found, what demonstrates that at least two magmatic pulses possibly associated with the same event. Dykes are vertical to subvertical and have a NW-SE main direction. Often have a NE-SW direction to internal fracturing, probably associated with its cooling process. The dykes have a tabular format, but is not uncommon occurring irregular. The main indicative features of oblique movement in these dyke intrusions are stepped edge structures, branchs and zigzag shapes, which demonstrate in general a extensional dextral component of displacement. Aggregating data from other major tholeiitic dykes swarms, was found an average value of N80E for the σ3 tensor for th opening of South Atlantic, consistent with the expected for the EDPG also, since they were intruded into a transtensive regime (CORREA GOMES, 1996). Faults and fractures are observed cutting both the host rocks as dikes, featuring a later intrusion tectonics. The main fracture sets are N20-30E, N30-40W, N80W and N60-70E, forming preferencial areas of erosion at the intersection between them. Faults can display well-defined fault planes with striation and steps, occurring fulfilled or not, by silica and carbonatic material. In the observed faults predominates sinistral kinematic, indicating change in the stress field in comparison to the emplacement dykes one. The study of th brittle tectonics as the dykes emplacement in the area contribute to a better understanding of the process of South Atlantic ocean opening, besides covering the submerged region of the Santos Basin basement, the focus of extensive studies currently, assuming that the same processes have affected the offshore region.

A evolução da margem continental do sudeste do Brasil tem sido discutida por diversos autores desde meados do século passado até os dias atuais, especialmente no contexto da origem e evolução dos escarpamentos e das bacias tafrogênicas. Buscou-se contribuir com novos dados sobre a evolução da área a partir da aplicação da termocronologia de baixa temperatura (U-Th)/He em apatita, que oferece uma sensibilidade significativa para registrar movimentações tectônicas na crosta superior. Foi possível obter idades em 107 cristais de apatita de 18 amostras do embasamento coletadas no perfil com orientação NW-SE, numa seção entre a Serra da Mantiqueira e o Gráben da Guanabara. As idades corrigidas variam entre 250,1 8,7 Ma e 43,5 1,9 Ma (2 σ) e as não corrigidas entre 174,13 3,03 Ma e 27,07 0,60 Ma (1 σ). O Neocretáceo, o Eocretáceo e o Paleoceno são os principais registros no conjunto de dados, em ordem de importância. No Neocretáceo, o intervalo entre 83,6 e 72,1 Ma (Campaniano) representa o maior destaque nos registros termocronológicos, embora os outros registros (Maastrichtiano e Santoniano) também estejam presentes e sejam importantes. As idades do Neocretáceo destacam a importância dos eventos tectonomagmáticos e soerguimento regional na história térmica dessa área, inclusive com idades (~86 Ma) atribuídas ao contexto de soerguimento da Serra do Mar. As idades do Eocretáceo indicam o registro de eventos térmicos mais antigos, vinculados à evolução pré-rifte. Já os dados do Paleoceno estariam associados ao evento de reativação responsável pela implantação do sistema de riftes continentais (~65 Ma) e as idades do Eoceno, restritas à borda de falha da bacia de Resende (49,7 Ma e 43,5 Ma), à reativação do sistema de riftes nessa área. A dispersão de idades foi interpretada como efeito dos danos de radiação já que muitos grãos apresentam correlação entre idade e concentração de urânio (eU). Os padrões de tempo-temperatura (t-T), definidos a partir dos modelos HeFTy calibrados para o modelo de difusão que considera os efeitos de danos de radiação nos cristais, registraram eventos de resfriamento rápido, os quais mostram correlação direta com episódios de reativação e soerguimento na margem continental e com registros nas bacias continentais e marginais. O padrão de aumento das idades com a elevação, assim como da costa em direção ao interior é observado, mas mostra-se alterado pela ocorrência de idades mais jovens associadas à complexa evolução dessa margem continental com desnivelamentos de blocos vinculados à tectônica pós-rift, numa situação que ressalta a influência dos episódios de reativação. As estimativas de denudação total variam entre 1,2 e 2,8 km. As taxas de erosão variam entre 15,2 e 35,3 m/Ma. A evolução da área indica não apenas a influência de um evento específico mas, possivelmente, uma combinação de episódios que se alternaram e/ou atuaram em conjunto em determinados períodos. Os eventos de reativação mais antigos, combinados com os mais recentes, exibem os seus remanescentes na paisagem (serras da Mantiqueira e do Mar e os grábens e bacias sedimentares) e assumem papel fundamental na evolução da área. Os registros de tais episódios podem ser observados nas histórias térmicas das rochas e nos depósitos correlativos nas bacias sedimentares marginais e intracontinentais. / This doctoral dissertation involves low-temperature thermochronologic investigations to constrain the Mesozoic and Cenozoic tectonic reactivation of the continental margin of southeast Brazil. The study area is located in a segment of the Neoproterozoic Ribeira belt in southeastern Brazil, which occupied a central position in Western Gondwana. Lately, during the Mesozoic and Cenozoic, fault zones related to the development of the continental rifts in southeast Brazil reactivated. Using apatite (U-Th)/He thermochronology (AHe), we have presented the results of analysis on 107 apatite crystals of basement samples collected from a NWSE transect in the Mantiqueira Mountains to the Guanabara Graben, as well as from the NESE transverse faults. The data range from 27.07 0.60 Ma to 174.13 3.03 Ma (1 σ) for uncorrected ages, and from 43.5 1.9 Ma to 250.1 8.7 Ma (2 σ) for corrected ages. The Neo-Cretaceous, Eo-Cretaceous, and Paleocene are the main recorded AHe ages, in order of importance. The Eo-Cretaceous ages indicate the occurrence of older thermal events related to a pre-rifting phase (~121 Ma). The Neo-Cretaceous ages signify the importance of tectonic and magmatic events, and regional uplifting for the thermal history of the study area, including ages related to the Serra do Mar Mountains uplift (~86 Ma). Paleocene ages seem to be related to the reactivation (~65 Ma), which was responsible for the continental rifts in the southeastern Brazil. Finally, the Eocene ages (49.7 Ma and 43.5 Ma), which are from samples restricted to the Resende Basin border faults, indicate a continental rift reactivation. We investigated the age dispersion data, which were interpreted as an effect of radiation damage. Several samples show correlations between apatite (U-Th)/He age and effective U concentration (eU). We have applied HeFTy thermal modeling to obtain timetemperature (t T) paths using a radiation damage diffusion model. Inverse modeling of (U-Th)/He age data suggests rapid cooling episodes for all samples. The main thermal events recorded by the HeFTy models show a direct correlation with the timing of regional tectonic events: reactivation phases, continental margin uplift, and the sedimentary record. Apatite (U-Th)/He ages increase with distance from the coast and with elevation. However, these patterns are discontinued by samples of younger ages as a result of the reactivation process of pre-existing structures in the Brazilian continental margin. The total estimated denudation range from 1.2 to 2.8 km. The erosion rates range from 15.2 to 35.3 m/My. Thus, the multi-episodic thermal events, which led to the formation of important regional tectonic and geomorphological features (Mantiqueira Mountains, Serra do Mar Mountains, grabens, and sedimentary basins), seem to play a fundamental role in the evolution of the Brazilian continental margin. The records can be found in the thermal history of rocks and its correlated deposits in the continental margin.

Made available in DSpace on 2015-03-13T17:08:36Z (GMT). No. of bitstreams: 1 RafaelSR_DISSERT_.pdf: 4378179 bytes, checksum: dc5658a221c8891102c9990af4393c19 (MD5) Previous issue date: 2013-04-13 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The 3D gravity modeling of the Potiguar rift basin consisted of a digital processing of gravity and aeromagnetic data, subsidized by the results of Euler deconvolution of gravity and magnetic data and the interpretation of seismic lines and wells descriptions. The gravity database is a compilation of independent geophysical surveys conducted by several universities, research institutions and governmental agencies. The aeromagnetic data are from the Bacia Potiguar and Plataforma Continental do Nordeste projects, obtained from the Brazilian Petroleum Agency (ANP). The solutions of the Euler Deconvolution allowed the analysis of the behavior of the rift main limits. While the integrated interpretation of seismic lines provided the delimitating horizons of the sedimentary formations and the basement top. The integration of these data allowed a 3D gravity modeling of basement topography, allowing the identification of a series of internal structures of the Potiguar rift, as well intra-basement structures without the gravity effect of the rift. The proposed inversion procedure of the gravity data allowed to identify the main structural features of the Potiguar rift, elongated in the NE-SW direction, and its southern and eastern faulted edges, where the sedimentary infill reachs thicknesses up to 5500 m. The southern boundary is marked by the Apodi and Baixa Grande faults. These faults seem to be a single NW-SE oriented fault with a strong bend to NE-SW direction. In addition, the eastern boundary of the rift is conditioned by the NE-SW trending Carnaubais fault system. It was also observed NW-SE oriented faults, which acted as transfer faults to the extensional efforts during the basin formation. In the central part of the residual anomaly map without the gravity effect of the rift stands out a NW-SE trending gravity high, corresponding to the Or?s-Jaguaribe belt lithotypes. We also observe a gravity maximum parallel to the Carnaubais fault system. This anomaly is aligned to the eastern limit of the rift and reflects the contact of different crustal blocks, limited by the eastern ward counterpart of the Portalegre Shear Zone / A modelagem gravim?trica 3D do rifte da Bacia Potiguar, apresentada neste trabalho, constituiu de um processamento digital de dados gravim?tricos e aeromagn?ticos, subsidiados pelos resultados da Deconvolu??o de Euler de dados gravim?tricos e magn?ticos e pela interpreta??o de linhas s?smicas e descri??es de po?os. O banco de dados gravim?trico ? proveniente de um trabalho de compila??o de levantamentos geof?sicos independentes realizados por diversas universidades, institui??es de pesquisa e ?rg?os governamentais. Os dados aeromagn?ticos s?o proveniente dos projetos Bacia Potiguar e Plataforma Continental do Nordeste, obtidos junto ? Ag?ncia Nacional do Petr?leo, G?s Natural e Biocombust?veis (ANP). As solu??es da Deconvolu??o de Euler possibilitaram a an?lise do comportamento dos principais limites do rifte, enquanto que a interpreta??o integrada das linhas s?smicas propiciou a delimita??o dos relevos dos horizontes da base das forma??es sedimentares e do topo do embasamento do Rifte Potiguar. A integra??o desses dados permitiu uma modelagem gravim?trica 3D do relevo do embasamento da bacia, possibilitando a identifica??o de uma s?rie de estruturas do arcabou?o estrutural do Rifte Potiguar e do embasamento cristalino sem o efeito gravim?trico do rifte. Com o procedimento de invers?o dos dados gravim?tricos, foi poss?vel identificar as principais fei??es estruturais do rifte da Bacia Potiguar, alongadas na dire??o NE-SW, bem como suas bordas falhadas nos limites Sul e Leste do rifte, onde o pacote sedimentar atinge espessuras superiores a 5500 m. O limite Sul ? marcado pelas falhas de Apodi e Baixa Grande, aparentando tratar-se de uma ?nica falha de dire??o NW-SE, com forte inflex?o para NE-SW. Observa-se ainda o limite Leste do rifte condicionado pelo Sistema de Falha Carnaubais de dire??o preferencial NE-SW. Observa-se ainda falhas de dire??o NW-SE, que atuaram como falhas de transfer?ncia aos esfor?os distensionais de forma??o da bacia. No mapa de anomalias residuais do embasamento cristalino sem o efeito gravim?trico do rifte destaca-se, na sua parte central, um alto gravim?trico de dire??o NW-SE, correspondendo a litotipos da Faixa Or?s-Jaguaribe. Observa-se ainda um m?ximo gravim?trico paralelo ao Sistema de Falhas de Carnaubais. Tal anomalia encontra-se alinhada ao limite Leste do rifte e reflete o contato de blocos crustais distintos, limitados pela continua??o Nordeste da Zona de Cisalhamento Portalegre