Thirteenth International Congress of the Brazilian Geophysical Society Using airborne gravity and magnetic data to recognize crustal domains concealed un- derneath the Parnaíba basin David L. de Castro (PPGG/UFRN), Jeffrey D. Phillips (USGS – USA), Reinhardt A. Fuck (IG/UnB), Roberta M. Vidotti (IG/UnB), Francisco H. R. Bezerra (PPGG/UFRN) Copyright 2013, SBGf - Sociedade Brasileira de Geofísica This paper was prepared for presentation during the 13 th International Congress of the Brazilian Geophysical Society held in Rio de Janeiro, Brazil, August 26-29, 2013. Contents of this paper were reviewed by the Technical Committee of the 13 th Interna- tional Congress of the Brazilian Geophysical Society and do not necessarily represent any position of the SBGf, its officers or members. Electronic reproduction or storage of any part of this paper for commercial purposes without the written consent of the Brazilian Geophysical Society is prohibited. ____________________________________________________________________ Abstract This paper presents a new geophysical study to map the crustal domains beneath the Paleozoic Parnaíba basin (NE Brazil), based on airborne gravity and magnetic data. Several aeromagnetic surveys and gravity data derived from satellite altimeters were processed and merged with the Aerogeophysical Project Parnaíba Basin in order to cover an area beyond the basin boundaries. The resulting datasets are here used as a tool in the recognition and interpretation of geological structures in a large basement area occupied mainly by several Precambrian crustal blocks, amalgamated during overall collisional tectonics and later on affected by an aborted rifting process, which culminated with the Parnaíba basin formation. The hidden crustal domains have been identified based on their gravi- ty and magnetic signatures. Introduction The Parnaíba basin is a Paleozoic cratonic sag that oc- cupies a 0.6 Million km 2 nearly circular shaped area in NE Brazil (Cordani et al., 1984) (Fig. 1). This structural framework is a key region to understand the Neoprotero- zoic-Eopaleozoic Brasiliano-Pan African orogenic collage in South America (Fuck et al., 2008). The Precambrian basement comprises three cratonic areas (Amazonian, São Luís/West Africa and São Francisco/Congo) and surrounding fold belts (Gurupi belt, Tocantins and Bor- borema provinces), as well as a completely concealed basement inlier (Parnaíba block). Several tectonic rela- tions between these crustal segments remain unknown due to the lack of direct information from surface map- ping. Nunes (1993) proposed an initial tectonic subdivi- sion, which is now revised and detailed. Another aim of the present work is to map the main shear zones of the Brasiliano-Pan African orogen (0.75-0.5 Ga) and the Cambrian graben-like features in the eastern part of the Parnaíba basin (Fig. 1). Their gravity and magnetic signatures were properly recognized in the geophysical maps. This allowed correlations between the Precambrian structural framework and the graben in an attempt to show that Eopaleozoic brittle reactivation led to the gen- eration of rift basins preceding the sag formation in NE Brazil. Fig. 1. Tectonic sketch of the Parnaíba Basin basement inferred from geophysical survey (Nunes, 1993) and pre- vious geological mapping (adapted from Cordani et al., 1984, 2009; Bizzi et al., 2003). Hidden basement inlier: PNB – Parnaíba Block. Neoproterozoic tectonic provin- ces: BB – Borborema; TO – Tocantins; GU – Gurupi belt. Shear zones: TB – Transbrasiliano, SP – Senador Pom- peu, PA – Patos, PE – Pernambuco. Geophysical Datasets In this work we use new airborne gravity and magnetic data (Parnaíba Basin Project), previous magnetic air- borne surveys and gravity data derived from the geodetic satellite GRACE (Fig. 2). The aerogeophysical surveys are derived from the Brazilian Petroleum Agency (ANP) and Brazilian Geological Survey (CPRM) data banks, undertaken from 1970 until 2010 with different flight ele- vations and directions, and spacing between lines. Each magnetic data set was interpolated onto a grid, using the bi-directional method. A decorrugation filter, combined with a directional cosine filter, was applied to eliminate high frequency noise along the fly direction. Then, each project was upward continued to the same height (3000 m) and reduced to the pole, using a pseudo- inclination factor to suppress the amplitude and power in near the declination direction, over-corrected at low mag- netic latitudes (Blakely, 1996). The magnetic projects were then merged, using a grid-knitting tool to smooth the transition between adjacent grids.