Estruturação de derrames e interações lava-sedimento na porção central da província basáltica continental do Paraná

A Província Basáltica Continental do Paraná (PBCP) ocupa uma área de cerca 1,2 x 106 km2 na América do Sul e tem sua origem vinculada a fragmentação do Gondwana e a abertura do Oceano Atlântico Sul durante o Cretáceo Inferior. Estudos enfocando a morfologia e origem das estruturas nos basaltos na PBCP, realizados na porção oeste do estado do Paraná, determinaram a identificação de derrames do tipo pahoehoe e ‘a‘a , com o predomínio de pahoehoe simples e compostos. Em alguns locais constatou-se o processo de interação entre lavas e sedimentos e a ocorrência de peperitos fluidais. Na área estudada verificou-se que os derrames pahoehoe compostos são formados por lobos do tipo P (pipe) e do tipo S (spongy), com o predomínio dos primeiros. A predominância de lobos do tipo P pode ser relacionada com o rompimento e geração de pequenos lobos na porção distal de espessos derrames inflados. As características destes lobos indicam um longo tempo de residência das lavas, em um sistema de distribuição antes da extrusão. As feições de superfície originadas em derrames pahoehoe e ‘a‘a estão bem preservadas e são de fácil reconhecimento. Os derrames possuem extensão lateral de até 50 km e podem ser divididos em três porções em relação ao conduto: proximal, mediana e distal. Na porção proximal os derrames pahoehoe são espessos (40-70 m) e possuem a crosta superior e o núcleo maciço bem delimitado. Na porção mediana predominam derrames pahoehoe simples com espessura entre 20 e 30 m, localmente ocorrem derrames compostos. Na porção distal predominam derrames compostos de até 5 m de espessura, formados por lobos. A geração de derrames tipo pahoehoe inflados sugerem baixas taxas de erupção na geração dos basaltos do oeste do Paraná. Estimativas baseadas na espessura da crosta superior indicam um período de 33 meses para a geração de fluxos inflados com 25 m de espessura total. Os peperitos foram gerados pela interação entre derrames e sedimentos úmidos, predominantemente silte e argila, depositados em um ambiente lacustre. A presença destes sedimentos indica uma mudança climática, que ocorreu entre a erupção da porção basal da PBCP, associada com ambiente desértico (Formação Botucatu) e a porção superior associada com ambiente lacustre. Nesta fase interrupções no vulcanismo possibilitaram a deposição de sedimentos em pequenos lagos estabelecidos sobre os derrames. A presença de sedimento vesiculado preenchendo vesículas e fraturas e a deformação de estruturas sedimentares indicam que a fração sedimentar estava inconsolidada ou pouco consolidada e úmida, quando da geração dos peperitos. As texturas presentes nos peperitos fluidais indicam que os principais fatores que influenciaram no mingling entre lava e sedimentos foram: 1- as propriedades da lava (baixa viscosidade), 2- a presença de sedimentos inconsolidados a pouco consolidados e úmidos e 3- um evento único na interação entre lava e sedimento. Neste ambiente os peperitos eram formados na base do derrame e processos posteriores, como a inflação do derrame e a extrusão de outros derrames, não causaram perturbações nos domínios de peperito gerados previamente. Os trabalhos realizados na porção oeste do Paraná indicam que os derrames da PBCP são dominantemente do tipo pahoehoe, tanto simples como compostos, associados com fluxos inflados. Estas evidências contrariam a estruturação convencionalmente estabelecida para a Formação Serra Geral onde os derrames são espessos, maciços e com geometria tabular. Esta aparente organização pode ser também gerada pela amalgamação de sucessivos e simultâneos lobos de lavas.

Escravidão na Vila do Príncipe, província do Rio Grande do Norte (1850/1888)

This dissertation presents a study on the slave population of Vila do Príncipe, from 1850 to 1888, based on the judicial and notarial collection of hand written documents as well as on the Reports of Presidents of the Province of Rio Grande do Norte. The issue that drives the research relates to the reproduction of slavery in a region of cattle breeding colonization. Therefore, the research aims to understand how in a peripheral socio-economic place (in Vila do Príncipe, cattle breeding Seridó) after the prohibition of the African slave trade, the slave relationships subsisted and structured themselves. In the sense, the research analyzed the dynamics of socio-economic slave units and their relationship with space, ownership structure and the slave family.

Escravos em ação na Comarca do Príncipe - Província do Rio Grande do Norte (1870-1888)

The aim of this research is to study the actions of slaves in Comarca do Príncipe, Rio Grande do Norte (1870/1888). Considering the space as a relevant category in the subservient relationship, we investigate how negotiations about the captivity conditions and freedom took place in the domain of this province. The slaves are considered as subjects, who fought for better living conditions in the captivity and who sometimes practiced criminal offenses to achieve freedom. To analyze their actions in the socio-economic environment of the province, we resort to different types of sources. They are: civil and criminal processes, reports from the president of Rio Grande do Norte, the census of 1872, a newspaper called O Assuente, the Livro do Fundo de Emancipação do Município de Príncipe (1873-1886) (The Emancipation Book of Príncipe city) and Imperial Laws. We used the following steps to analyze the data obtained from these sources: the compilation, reading, paleographic transcription, classification of the data according to the thematic, analysis and comparison of information and statistic quantification, submitting empirical data to the discussion built according to the historiographies debates about this subject

Dinâmicas centrípetas e centrífugas na formação do Estado monárquico no Brasil: o papel do Conselho Geral da Província de São Paulo

O presente artigo avalia a formação e o funcionamento do Conselho Geral da Província de São Paulo durante o Primeiro Império. Organismo previsto na Constituição de 1824, com funções que podem ser consideradas um embrião do Poder Legislativo provincial, organizou-se efetivamente na província de São Paulo em 1828, quando o governo de D. Pedro I já se desgastava. O significado de sua existência no contexto das dinâmicas centrífugas e centrípetas atuantes na primeira construção do Estado no Brasil independente constituem o principal objetivo da presente análise.

Arcabouço geofísico, isostasia e causas do magmatismo cenozóico da província Borborema e de sua margem continental (Nordeste do Brasil)

The Borborema Province (BP) is a geologic domain located in Northeastern Brazil. The BP is limited at the south by the São Francisco craton, at the west by the Parnaíba basin, and both at the north and east by coastal sedimentary basins. Nonetheless the BP surface geology is well known, several key aspects of its evolution are still open, notably: i)its tectonic compartmentalization established after the Brasiliano orogenesis, ii) the architecture of its cretaceous continental margin, iii) the elastic properties of its lithosphere, and iv) the causes of magmatism and uplifting which occurred in the Cenozoic. In this thesis, a regional coverage of geophysical data (elevation, gravity, magnetic, geoid height, and surface wave global tomography) were integrated with surface geologic information aiming to attain a better understanding of the above questions. In the Riacho do Pontal belt and in the western sector of the Sergipano belt, the neoproterozoic suture of the collision of the Sul domain of the BP with the Sanfranciscana plate (SFP) is correlated with an expressive dipolar gravity anomaly. The positive lobule of this anomaly is due to the BP lower continental crust uplifting whilst the negative lobule is due to the supracrustal nappes overthrusting the SFP. In the eastern sector of the Sergipano belt, this dipolar gravity anomaly does not exist. However the suture still can be identified at the southern sector of the Marancó complex arc, alongside of the Porto da Folha shear zone, where the SFP N-S geophysical alignments are truncated. The boundary associated to the collision of the Ceará domain of the BP with the West African craton is also correlated with a dipolar gravity anomaly. The positive lobule of this anomaly coincides with the Sobral-Pedro II shear zone whilst the negative lobule is associated with the Santa Quitéria magmatic arc. Judging by their geophysical signatures, the major BP internal boundaries are: i)the western sector of the Pernambuco shear zone and the eastern continuation of this shear zone as the Congo shear zone, ii) the Patos shear zone, and iii) the Jaguaribe shear zone and its southwestern continuation as the Tatajuba shear zone. These boundaries divide the BP in five tectonic domains in the geophysical criteria: Sul, Transversal, Rio Grande do Norte, Ceará, and Médio Coreaú. The Sul domain is characterized by geophysical signatures associated with the BP and SFP collision. The fact that Congo shear zone is now proposed as part of the Transversal domain boundary implies an important change in the original definition of this domain. The Rio Grande do Norte domain presents a highly magnetized crust resulted from the superposition of precambrian and phanerozoic events. The Ceará domain is divided by the Senador Pompeu shear zone in two subdomains: the eastern one corresponds to the Orós-Jaguaribe belt and the western one to the Ceará-Central subdomain. The latter subdomain exhibits a positive ENE-W SW gravity anomaly which was associated to a crustal discontinuity. This discontinuity would have acted as a rampart against to the N-S Brasiliano orogenic nappes. The Médio Coreaú domain also presents a dipolar gravity anomaly. Its positive lobule is due to granulitic rocks whereas the negative one is caused by supracrustal rocks. The boundary between Médio Coreaú and Ceará domains can be traced below the Parnaíba basin sediments by its geophysical signature. The joint analysis of free air anomalies, free air admittances, and effective elastic thickness estimates (Te) revealed that the Brazilian East and Equatorial continental margins have quite different elastic properties. In the first one 10 km < Te < 20 km whereas in the second one Te ≤ 10 km. The weakness of the Equatorial margin lithosphere was caused by the cenozoic magmatism. The BP continental margin presents segmentations; some of them have inheritance from precambrian structures and domains. The segmentations conform markedly with some sedimentary basin features which are below described from south to north. The limit between Sergipe and Alagoas subbasins coincides with the suture between BP and SFP. Te estimates indicates concordantly that in Sergipe subbasin Te is around 20 km while Alagoas subbasin has Te around 10 km, thus revealing that the lithosphere in the Sergipe subbasin has a greater rigidity than the lithosphere in the Alagoas subbasin. Additionally inside the crust beneath Sergipe subbasin occurs a very dense body (underplating or crustal heritage?) which is not present in the crust beneath Alagoas subbasin. The continental margin of the Pernambuco basin (15 < Te < 25 km) presents a very distinct free air edge effect displaying two anomalies. This fact indicates the existence in the Pernambuco plateau of a relatively thick crust. In the Paraíba basin the free air edge effect is quite uniform, Te ≈ 15 km, and the lower crust is abnormally dense probably due to its alteration by a magmatic underplating in the Cenozoic. The Potiguar basin segmentation in three parts was corroborated by the Te estimates: in the Potiguar rift Te ≅ 5 km, in the Aracati platform Te ≅ 25 km, and in the Touros platform Te ≅ 10 km. The observed weakness of the lithosphere in the Potiguar rift segment is due to the high heat flux while the relatively high strength of the lithosphere in the Touros platform may be due to the existence of an archaean crust. The Ceará basin, in the region of Mundaú and Icaraí subbasins, presents a quite uniform free air edge effect and Te ranges from 10 to 15 km. The analysis of the Bouguer admittance revealed that isostasy in BP can be explained with an isostatic model where combined surface and buried loadings are present. The estimated ratio of the buried loading relative to the surface loading is equal to 15. In addition, the lower crust in BP is abnormally dense. These affirmations are particularly adequate to the northern portion of BP where adherence of the observed data to the isostatic model is quite good. Using the same above described isostatic model to calculate the coherence function, it was obtained that a single Te estimate for the entire BP must be lower than 60 km; in addition, the BP north portion has Te around 20 km. Using the conventional elastic flexural model to isostasy, an inversion of crust thickness was performed. It was identified two regions in BP where the crust is thickened: one below the Borborema plateau (associated to an uplifting in the Cenozoic) and the other one in the Ceará domain beneath the Santa Quitéria magmatic arc (a residue associated to the Brasiliano orogenesis). On the other hand, along the Cariri-Potiguar trend, the crust is thinned due to an aborted rifting in the Cretaceous. Based on the interpretation of free air anomalies, it was inferred the existence of a large magmatism in the oceanic crust surrounding the BP, in contrast with the incipient magmatism in the continent as shown by surface geology. In BP a quite important positive geoid anomaly exists. This anomaly is spatially correlated with the Borborema plateau and the Macaú-Queimadas volcanic lineament. The integrated interpretation of geoid height anomaly data, global shear velocity model, and geologic data allow to propose that and Edge Driven Convection (EDC) may have caused the Cenozoic magmatism. The EDC is an instability that presumably occurs at the boundary between thick stable lithosphere and oceanic thin lithosphere. In the BP lithosphere, the EDC mechanism would have dragged the cold lithospheric mantle into the hot asthenospheric mantle thus causing a positive density contrast that would have generated the main component of the geoid height anomaly. In addition, the compatibility of the gravity data with the isostatic model, where combined surface and buried loadings are present, together with the temporal correlation between the Cenozoic magmatism and the Borborema plateau uplifting allow to propose that this uplifting would have been caused by the buoyancy effect of a crustal root generated by a magmatic underplating in the Cenozoic