Simultaneous development of semigrabens orthogonal and oblique to the extension direction: physical modeling of natural analogues in Northeastern Brazil

A modelagem física é uma ferramenta cada vez mais usada na geologia para fornecer informação sobre os diversos estágios evolutivos (nucleação, desenvolvimento e geometria) de estruturas geológicas em várias escalas. No caso particular da simulação da tectônica distensional, a modelagem proporciona uma melhor compreensão da geometria e evolução de falhas e da arquitetura tectonoestratigráfica de bacias rifte. Neste trabalho foi utilizado um aparato tipo caixa de areia para estudar a nucleação e o desenvolvimento de bacias influenciadas por estruturas prévias no embasamento, com trend variável em relação à direção de distensão. Para tal, foram realizados dois tipos de experimentos para: (i) simular o desenvolvimento individual (independente) de semigrabens com abertura ortogonal ou oblíqua à direção de distensão; (ii) simular o desenvolvimento simultâneo desses semigrabens ortogonais ou oblíquos à direção de distensão. Em ambos os casos foram utilizados os mesmos materiais analógicos (areia de quartzo e uma mistura de areia e gesso, simulando o material sin e pré-tectônico, respectivamente) bem como foram mantidas as demais condições de contorno. Os resultados obtidos foram comparados com um análogo natural representado pela Bacia do Rio do Peixe (uma das bacias interiores eocretáceas do Nordeste do Brasil). Os modelos permitiram observar o desenvolvimento segmentado das falhas de borda, com geometria lístrica, frequentemente formando rampas de revezamento, além do desenvolvimento de falhas internas às bacias localizadas nas suas porções mais basais, similares àquelas observadas nas seções sísmicas do análogo natural. Os resultados confirmam a influência da herança tectônica do embasamento na geometria dos depocentros rifte.The physical modeling tool is being increasingly used in geology to provide information about the evolutionary stages (nucleation, growth and geometry) of geological structures at various scales. In the simulations of extensional tectonics, modeling provides a better understanding of fault geometry and evolution of the tectonic-stratigraphic architecture of rift basins. In this study a sandbox type apparatus was used to study the nucleation and development of basins influenced by previous structures in the basement, variably oriented as regards to the main extensional axis. Two types of experiments were conducted in order to: (i) simulate the individual (independent) development of half-grabens oriented orthogonal or oblique to the extension direction; (ii) simulate the simultaneous development of such half-grabens, orthogonal or oblique to the extension direction. In both cases the same materials (sand mixed with gypsum) were used and the same boundary conditions were maintained. The results were compared with a natural analogue represented by the Rio do Peixe Basin (one of the eocretaceous interior basins of Northeast Brazil). The obtained models allowed to observe the development of segmented border faults with listric geometry, often forming relay ramps, and the development of inner basins faults that affect only the basal strata, like the ones observed in the seismic sections of the natural analogue. The results confirm the importance of basement tectonic heritage in the geometry of rift depocenters

Simultaneous development of semigrabens orthogonal and oblique to the extension direction: physical modeling of natural analogues in Northeastern Brazil

The physical modeling tool is being increasingly used in geology to provide information about the evolutionary stages (nucleation, growth and geometry) of geological structures at various scales. In the simulations of extensional tectonics, modeling provides a better understanding of fault geometry and evolution of the tectonic-stratigraphic architecture of rift basins. In this study a sandbox type apparatus was used to study the nucleation and development of basins influenced by previous structures in the basement, variably oriented as regards to the main extensional axis. Two types of experiments were conducted in order to: (i) simulate the individual (independent) development of half-grabens oriented orthogonal or oblique to the extension direction; (ii) simulate the simultaneous development of such half-grabens, orthogonal or oblique to the extension direction. In both cases the same materials (sand mixed with gypsum) were used and the same boundary conditions were maintained. The results were compared with a natural analogue represented by the Rio do Peixe Basin (one of the eocretaceous interior basins of Northeast Brazil). The obtained models allowed to observe the development of segmented border faults with listric geometry, often forming relay ramps, and the development of inner basins faults that affect only the basal strata, like the ones observed in the seismic sections of the natural analogue. The results confirm the importance of basement tectonic heritage in the geometry of rift depocenters