Seismic characteristics of central Brazil crust and upper mantle: A deep seismic refraction study

A two-dimensional model of the Brazilian central crust and upper mantle was obtained from the traveltime interpretation of deep seismic refraction data from the Porangatu and Cavalcante lines, each approximately 300 km long. When the lines were deployed, they overlapped by 50 km, forming an E-W transect approximately 530 km long across the Tocantins Province and western Sao Francisco Craton. The Tocantins Province formed during the Neoproterozoic when the Sao Francisco, the Paranapanema, and the Amazon cratons collided, following the subduction of the former Goias ocean basin. Average crustal V-P and V-P/V-S ratios, Moho topography, and lateral discontinuities within crustal layers suggest that the crust beneath central Brazil can be associated with major geological domains recognized at the surface. The Moho is an irregular interface, between 36 and 44 km deep, that shows evidences of first-order tectonic structures. The 8.05 and 8.23 km s(-1) P wave velocities identify the upper mantle beneath the Porangatu and Cavalcante lines, respectively. The observed seismic features allow for the identification of (1) the crust has largely felsic composition in the studied region, (2) the absence of the mafic-ultramafic root beneath the Goias magmatic arc, and (3) block tectonics in the foreland fold-and-thrust belt of the northern Brasilia Belt during the Neoproterozoic. Seismic data also suggested that the Bouguer gravimetric discontinuities are mainly compensated by differences in mass distribution within the lithospheric mantle. Finally, the Goias-Tocantins seismic belt can be interpreted as a natural seismic alignment related to the Neoproterozoic mantle domain.