Crustal structure beneath the Paleozoic Parnaiba Basin revealed by airborne gravity and magnetic data, Brazil

The Parnaiba Basin is a large Paleozoic syneclise in northeastern Brazil underlain by Precambrian crystalline basement, which comprises a complex lithostructural and tectonic framework formed during the Neoproterozoic-Eopaleozoic Brasiliano-Pan African orogenic collage. A sag basin up to 3.5 km thick and 1000 km long formed after the collage. The lithologic composition, structure, and role in the basin evolution of the underlying basement are the focus of this study. Airborne gravity and magnetic data were modeled to reveal the general crustal structure underneath the Parnaiba Basin. Results indicate that gravity and magnetic signatures delineate the main boundaries and structural trends of three cratonic areas and surrounding Neoproterozoic fold belts in the basement. Triangular-shaped basement inliers are geophysically defined in the central region of this continentalscale Neoproterozoic convergence zone. A 3-D gravity inversion constrained by seismological data reveals that basement inliers exhibit a 36-40.5 km deep crustal root, with borders defined by a high-density and thinner crust. Forward modeling of gravity and magnetic data indicates that lateral boundaries between crustal units are limited by Brasiliano shear zones, representing lithospheric sutures of the Amazonian and Sao Francisco Cratons, Tocantins Province and Parnaiba Block. In addition, coincident residual gravity, residual magnetic, and pseudo-gravity lows indicate two complex systems of Eopaleozoic rifts related to the initial phase of the sag deposition, which follow basement trends in several directions. (C) 2013 Elsevier B.V. All rights reserved.