Magnetotelluric transect across the São Luís cratonic fragment, the Gurupi belt and the Parnaíba basin, N-NE Brazil

Abstract

The study area is located in the N-NE region of Brazil where Precambrian rocks of the São Luís Cratonic Fragment and the Gurupi belt are overlain by Phanerozoic sediments of the Parnaíba and São Luís basins, making the assessment of the extents of these geotectonic domains difficult. One of the main objectives of the present study was to elaborate a NNW-SSE-trending, 180-km long magnetotelluric transect, aiming to identify the geotectonic domains of the study area by means of their geoelectric characteristics. The magnetotelluric (MT) technique is a geophysical method that detects the natural variations of the terrestrial electric and magnetic fields so as to investigate the geoelectric characteristics of the subsurface. By means of a MT survey for field data acquisition, calculation of impedance tensors and 2D inversion modeling, the geophysical transect and additionally an interpretive geological model were elaborated for the study area. The combined transverse electric (TE) and transverse magnetic (TM) geophysical model revealed superficial conductive (Parnaíba and São Luís basins and sedimentary coverings), resistive (São Luís Cratonic Fragment) and very resistive (Gurupi mobile belt) portions up to depths of the order of 15 km. These results attested for correlations between the São Luís Craton (South American Plate) and the West African Craton (African Plate), especially regarding the Gurupi Belt (in Brazil) and the Rokelide Belt (in Liberia), which are considered to be the boundaries of a triple junction related to the supercontinent Rodinia taphrogenesis. Besides presenting an unprecedented geophysical investigation along the São Luís Cratonic Fragment and the Gurupi Belt, this study promotes the discussion on the correlations between the Brazilian Gurupi and the African Rokelide belts for metallogenetic purposes.