Brazil's deep geology reveals how ancient continents collided and stuck

<p>The Ribeira Orogen in southeastern Brazil preserves the Neoproterozoic–Cambrian processes involved in the final assembly of West Gondwana. To investigate its largely uncharacterized deep lithospheric structure, this study integrates long-period magnetotelluric (MT) data with seismic tomography and geothermal heat-flow information. The MT dataset includes 61 stations along five NW–SE profiles spaced 15–25 km apart, with periods from 10 to 10,000 s. A 3D MT inversion produced a detailed resistivity model examined jointly with the complementary geophysical datasets. The results reveal three high-resistivity lithospheric blocks, bounded by major conductive zones, interpreted as fragments of Rodinia reassembled during the Brasiliano Orogeny. The western block represents the eastward extension of the São Francisco paleocontinent beneath the Ribeira Orogen. The central block, underlying the Paraíba do Sul Domain, corresponds to a preserved microcontinent (Paraíba do Sul–Embu), characterized by high P-wave velocities and low surface heat flow. The eastern block, beneath the Cabo Frio Terrane, is interpreted as a fragment of the Angola–Congo paleocontinent that remained attached to South America after the opening of the South Atlantic. Two main conductive anomalies correspond to distinct tectonic episodes. The older, beneath the Occidental Terrane, records eastward subduction of the São Francisco lithosphere during the Cryogenian–Ediacaran. The younger, located at the boundary with the Cabo Frio Terrane, is associated with Tonian–Cryogenian intra-oceanic magmatic arcs later accreted to the orogen during Cambrian collision. These findings provide robust geophysical evidence that southeastern Brazil evolved through subduction-related accretionary processes, rather than intracontinental deformation.</p>