Modelagem da estrutura crustal sob a porção sul do perfil N-S da província Borborema e cráton São Francisco: um estudo de refração sísmica profunda

Abstract

The lithosphere is the outermost solid layer of the Earth, composed of crust and lithospheric mantle, separated by Mohorovičić (Moho) seismic discontinuity. Studies on the structure of the lithosphere allow us to better understand regional tectonic compartmentalization and its significance in terms of continental crust origin and evolution. Among the geophysical methods applied to crustal studies, stands out the deep seismic refraction method or Wide-Angle Reflection and Refraction (WARR), which uses reflected and refracted elastic waves from the critical angle at the main interfaces of the lithosphere, it is used for determination of a model of seismic velocities. In this context, the Northeastern region of Brazil has been a challenge for geoscientists,especially regarding the geometric, kinematic and dynamic evolution of their provinces. The Borborema Province, for instance, is represented by a complex association of crustal blocks, including the first remnants of the continental crust of South America. The São Francisco Craton, in turn, it consists of an amalgam of structural units generated by successive tectonic events the end of the Paleoproterozoic. In this region, rift-type basins were installed in sites affected by tectonic heritages of precambrian structures, such as the Recôncavo-Tucano-Jatobá rift basins. This work presents the 2D seismic modeling of the crustal structure and upper mantle beneath the Borborema Province and São Francisco Craton by means of deep seismic refraction data from the southern portion of the N-S profile of the project "Study of lithosphere structure of Northeast Brazil". The P and S velocity fields obtained showed that the model can be represented by six layers, defined by different velocity range; and the Moho discontinuity has irregular behavior along the profile, varying from 34.5 to 44 km in depth. In addition, the Tucano and Jatobá basins were characterized by typical seismic velocities of sedimentary rocks, with a thickness of up to 9 km for the Tucano Central basin and 2.45 km in the Jatobá basin. The Central and Southern sub-provinces have distinct velocity curves that determine the characteristic seismic signature of each crustal domain. The crustal thickening verified at the border of the Borborema Province with the São Francisco Craton, probably it results from the neoproterozoic collision.