Modelagem gravimétrica 3-D de corpos graníticos e bacias sedimentares com embasamento estrutural de densidade variável

Abstract

ABSTRACT. In the present work, a computational methodology is implemented for the modeling of three-dimensional gravity sources inserted in a basement of variable density, such as granitic bodies and sedimentary basins. This procedure proceeds by separating the gravity data into two components: the component due to variations in density of underlying basement and the component caused by the basins themselves, which will be modeled. Another product of this inversion procedure is the gravitational attraction of the basement without the effects of the modeled source. It represents another important advantage of this method. Each gravity source can be isolated and modeled. Gravity synthetic data had been generated to simulate interfering sources and test the proposed methodology. The gravity effect of a sedimentary basin had been added the gravity anomalies of intrusive bodies, simulating interfering sources. The comparison between 3-D models obtained by techniques that assume the homogeneous basement and the proposed methodology demonstrates the efficiency in the isolation of the interfering sources and in the determination of its internal geometry. The application of this technique in the Guitiriz Granite (Spain) and the Rio do Peixe rift basin (Paraíba State) demonstrates an important resolution increment of the geophysical models in the regions where interfering sources are present. In the Guitiriz Granite case, its magmatic conduits are better defined without the gravity interference of others igneous bodies. In the Rio do Peixe basin, internal structures can be differentiated with more accuracy, free from gravity anomalies associated to the Paraná Granite, which outcrops in the northern portion of the basin.Keywords: 3-D gravity modeling, heterogeneous basement, interfering sources. RESUMO.No presente trabalho, uma metodologia computacionalé implementada para a modelagem de fontes gravimétricas tridimensionais, como granitos e bacias sedimentares, inseridas em um arcabouço estrutural de densidade variável. O procedimento proposto consiste em separar os efeitos gravitacionais da fonte alvo e do embasamento e, posteriormente, modelar de forma iterativa apenas a contribuição gravimétrica da fonte. Ao final do processo de inversão,é também gerado o mapa gravimétrico da região sem o efeito da fonte modelada. O que representa outra importante vantagem deste método, já que revela a assinatura gravimétrica de cada uma das fontes progressivamente, permitindo sua modelagem individual. Dados sintéticos foram gerados para testar a metodologia proposta. Os efeitos gravimétricos de uma bacia sedimentar foram adicionados a anomalias gravimétricas de corpos intrusivos, simulando fontes interferentes. A comparação entre modelos 3-D obtidos por técnicas que assumem o embasamento homogêneo e a metodologia proposta demonstra a eficiência no isolamento das fontes interferentes e na determinação de suas geometrias internas. A aplicação desta técnica no Granito de Guitiriz (Espanha) e na bacia rifte Rio do Peixe (Paraíba) revela um ...

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