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• Electrical structure of the northern São Francisco Craton derived from MT soundings. • Resistive and conductive crustal blocks indicate a Paleoproterozoic accretion system. • Mesoproterozoic to Neoproterozoic fluids and melts reworked the craton lithosphere. Broadband and long period magnetotelluric (MT) data were collected along an east-west oriented, 580-km-long profile across the northern São Francisco Craton where extensive Proterozoic and Phanerozoic sedimentary cover and lack of deep-probing geophysical surveys have prevented to establish unequivocally the cratonic character of the Archean-Paleoproterozoic lithosphere. Following dimensionality analyses, the MT dataset was interpreted using both 2-D and 3-D inversion procedures. The near-surface structure is better resolved in the 2-D model due to its finer resolution. A huge upper crustal conductor is found all along the shallow early Neoproterozoic Irecê Basin in the central domain of the craton, extending laterally for approximately 150 km and restricting signal propagation below the basin. Its high conductance is explained by a combination of high porosity and high fluid salinity in the sedimentary package. Another upper crustal conductor is observed on the west side of the profile, interpreted as fractured metasedimentary rocks of the Rio Preto belt thrusted on top of the craton basement during Neoproterozoic marginal collision. The 3-D model explains significantly better the measured data related to deep structure. Contrary to what is expected for a stable cratonic block, the geoelectric model shows pronounced electrical complexity and heterogeneity, an indication that the cratonic lithosphere was multiply reworked in the past by tectonothermal events. Different lithospheric resistive blocks bounded by major conductive zones are identified. Constrained by geochemical and isotopic data, these vertical conductive interfaces are interpreted as cryptic suture zones due to large-scale amalgamation of continents and microcontinents leading to the assembly of the São Francisco Craton in the Paleoproterozoic. The conductivity enhancement is more likely explained by emplacement of sulfides along previous suture zones during mafic magmatism. At upper mantle depths, high conductivity observed below most of the profile indicates that metasomatism or refertilization processes with incompatible elements caused by the Paleoproterozoic subducting slabs and Mesoproterozoic to Neoproterozoic upwelling of deep fluids and melts reworked this portion of the craton mantle. [ABSTRACT FROM AUTHOR]

Magnetotelluric data were collected at 25 stations along a NNW–SSE linear profile deployed perpendicularly to the main structures in the southeastern portion of the Borborema province, northeast Brazil. The geotectonic scenario is characterized by a broad range of tectomagmatic events including periods of compressive tectonism associated with amalgamation of lithospheric blocks during the Brasiliano orogeny in the Late Neoproterozoic, superimposed by extensional events related to the continental break-up and plate drift that led to the formation of the southern Atlantic Ocean in the Early Cretaceous. Strike analysis and distortion decomposition show that most of the data are two-dimensional (2D) but sensitive to distant off-profile structures. Data fit an ENE regional geoelectric strike direction, consistent with the geological and tectonic setup. A joint 2D inversion of the TE and TM modes defined by this strike direction was undertaken and the obtained model exhibits signatures of the different tectonic events in the area. The model suggests that the SE Borborema province is electrically separated into two parts. The first, comprising the southern domain of the province (Sergipano belt and Pernambuco–Alagoas block), has a highly heterogeneous crust and an anomalously conductive upper mantle. The second, comprising the transversal domain of the province (Alto Moxotó terrain), displays crust and upper mantle predominantly homogeneous and resistive. A deep Neoproterozoic lithospheric shear zone (Pernambuco lineament) marks the limit between the two contrasting domains. Also, the region where the Jatobá basin is located in the southern domain presents a striking conductor at upper- to mid-crustal depths beneath the basin. These results correlate well with seismic refraction data that indicate thicker crust for the transversal domain than for the southern domain, with the thinnest crust coinciding with the location of the Jatobá basin. The data support the conclusion that the lithosphere of the southern domain of the Borborema province was significantly stretched in the Cretaceous during the opening of the South Atlantic Ocean, allowing refertilization of depleted upper mantle with incompatible elements from enriched deeper mantle material and reactivation of older crustal fabrics. The conductivity increase below the Jatobá basin is associated with ionic conduction in a currently reactivated fracture zone filled with high salinity fluid. Apparently, the Alto Moxotó terrain worked as a region of higher resistance to stretching, causing the crustal thinning and geoelectric effects to be concentrated to the south of the Pernambuco lineament. [ABSTRACT FROM AUTHOR]

Abstract: The deep structure of the northern part of the Paraná Basin has been investigated through the analysis of a SW–NE magnetotelluric (MT) profile composed of 24 broadband stations with periods from 0.001 to ∼1000 s that are regularly spaced ∼10 km apart. The SW portion of the profile crosses a negative Bouguer anomaly with amplitudes of ∼20 mGal. Our analyses show that there are two lithospheric domains with different gravity and electric conductivity properties. In the regularized two-dimensional MT inversion model the mid-to-lower crust in the SW part of the profile is almost two orders in magnitude more conductive compared to the NE portion. This difference in conductivity extends to the uppermost mantle depths, suggesting the existence of a major lithospheric discontinuity in the north-central Paraná Basin, locally coincident with the position of the Aporé River. We interpret this discontinuity as a juxtaposition of terranes with distinct natures and ages, possibly as result of tectonic accretion during the formation of Western Gondwana. [Copyright &y& Elsevier]