Aplicação do método de refração sísmica profunda para a obtenção de um modelo da estrutura crustal e do manto superior sob a província Borborema, Nordeste do Brasil

Abstract

Seismic methods is one of the main research tools of the Earth's internal structure. Deep seismic refraction data, for example, has revolutionized knowledge about the physical properties of the crust and upper mantle and are key elements for a better understanding of geodynamic processes and mechanisms. In this context, in the scope of the National Institute of Science and Technology in Tectonic Studies (INCT-ET), the transect N-S of deep seismic refraction was acquired in 2011, crossing Borborema Province and North of Craton São Francisco. The Borborema Province presents a long geological record, including the first remnants of continental crust in South America, vast crustal segments formed during the Paleoproterozoic and supracrustal sequences dominantly of neoproterozoic age. These different elements were deformed, metamorphosed and intruded by numerous plutons during the events associated with Brasilian Orogenia, which culminated in the formation of the supercontinent Gondwana. Despite the numerous studies conducted in the last decades, the geometric, kinematic and dynamic evolution of the Borborema Province is still poorly understood. The purpose of this work is to use the data from the northern portion of the N-S line of deep seismic refraction, in order to define a crustal model and the upper portion of the lithospheric mantle under Borborema Province. For this purpose, P and S wave models will be generated, and from these, a Vp / Vs Ratio model and a Poison Ratio model will be generated, and it is possible to analyze the composition of the crust and the upper mantle. With the results, a geological model of six layers was proposed, the first being composed by the Potiguar Basin, the second and third forming the upper crust, the fourth representing the lower crust and the fifth and sixth belonging to the lithospheric mantle. In this model, it was possible to identify the Moho discontinuity around 29 to 36 km of depth and to differentiate two crustal blocks, based on their signatures of seismic velocity and composition. The set of characteristics revealed by the data of the deep seismic refraction profile provided evidence of moments related to the evolution of the Borborema Province, such as the crustal blocks and the implementation of the South Atlantic Ocean.