Deep conductivity structure beneath the northern Brasيlia belt, central Brazil: Evidence for a Neoproterozoic arc-continent collision

The Brasيlia belt, in central Brazil, experienced a broad range of tectonic events, including several periods of compressional and extensional deformations during the Proterozoic. Magnetotelluric data were collected at 27 sites along a profile crossing the northern part of the belt. Strike analysis and distortion decomposition indicated that most of the data are two-dimensional (2D) and fit a regional geoelectric strike angle of N20E, parallel to the tectonic grain. 2D conductivity model is constrained by available gravity and seismic refraction data and reveals the cumulative effects of the multiple tectonomagmatic episodes that affected the area in the past on current crustal and upper mantle structure. The results show that the resistive lithospheric root of the Sمo Francisco cratonic plate is restricted to the easternmost part of the profile and does not extend westward beneath the Brasيlia belt. The external zone of the fold belt, composed of slightly metamorphosed rocks at the surface, presents crustal conductors that can be tentatively interpreted as regions with fossil fluid flows at mid-crust depth beneath a gold mineralization zone and as a very shallow mineralized zone within the metamorphic rocks. The external zone is separated to the west from the Goiلs massif by a strong conductivity contrast, indicative of a suture zone along the Rio Maranhمo fault system. Crustal conductivity structure under the Niquelândia complex is distinct from what is observed in other parts of the Goiلs massif, in agreement with the proposal of the complex being an allochthonous block. In spite of the large tectonothermal events that affected the Goiلs magmatic arc there are no significant conductive anomalies at crustal depths in its eastern side. The most prominent feature detected in the geoelectric model is a huge high conductivity anomaly below the entire Goiلs massif in the central part of the belt, mainly concentrated at the uppermost mantle but also affecting mid to lower crustal depths. It can be interpreted as associated with thermal events either related to Mesoproterozoic and/or Neoproterozoic continental rifting processes or to delamination and detachment processes at the end of the evolution of the belt, in the Neoproterozoic. Effects related to oceanic lithosphere subduction during the collision and accretion of the Goiلs massif and Goiلs magmatic arc to the western passive margin of the Sمo Francisco cratonic plate in the Neoproterozoic may alternatively explain the anomaly.