Mapping the basement architecture using magnetotelluric data across a coastal part of the Borborema structural province, Cear ́a – Brazil

Abstract

The Borborema Province (BP) constitutes part of the west Gondwana supercontinent formed by several tectonic collisions during Neoproterozoic, widely known as Brasiliano - Pan-African orogeny. It consists of a complex tectonic mosaic composed mainly by Archean to Paleoproterozoic migmatite-gneiss basement complexes, Pro- terozoic metasedimentary belts, a large volume of Neoproterozoic granitic intrusions, and Phanerozoic covers that represent ca. 25 % of the total area of BP. This work presents the results from 21 Magnetotelluric (MT), and electromagnetic time-domain (TDEM) soundings interpretations carried out along a 120 km profile in a coastal area of the northeast Borborema Province covered by Phanerozoic sedimentary rocks and sediments. The final geoelectric model allows delineating the architectural geometry of the subsurface and variations in physical properties of different crustal blocks bounded by major electrical discontinuities. The interpretation was based on a 2D and 3D model from the inversion of the MT data. The 2D model has a visually satisfactory agreement with the region’s geological framework and a reasonable resolution of the upper crust compared to the 3D model. The geoelectric section allows delineating the variation in physical properties of different upper crust blocks bounded by major electrical discontinuities. The result enables the characterization of 1) the uppermost struc- tures correlated to the Mesozoic to mid-Cenozoic sedimentary formations; 2) covered lithotectonic framework represented by lithotypes and main shear zones related to Ceara Central and Rio Grande do Norte crustal tectonic domains; 3) distinctive anomalies corresponding to the Senador Pompeu, Or ́os, and Jaguaribe Neoproterozoic main shear zones. Our interpretations agree with the results and interpretation presented by previous MT works in the Borborema Province, which reveals the existence of an important conductive zone, interpreted as a suture zone, spatially related to the Senador Pompeu shear zone and in smaller proportion to the Orós shear zone. The results presented here are a starting point to further MT long-period investigation to understand this complex part of the Borborema Province