The Transminas and Pirenópolis dike swarms: New evidence for the central and South Atlantic Magmatic Provinces in South America

This study reports new geochemical and geochronological data for the Transminas and Pirenópolis dike swarms in Brazil. The Transminas dikes comprise two branches in southeastern Brazil: The Az-170 swarm, trending NNW-SSE and extending for over 800 km, and the Az-125 swarm, trending NW-SE with a total length of 1100 km. The Pirenópolis dikes, in turn, encompass two NNW-SSE-oriented subswarms (~50 km) in Central Brazil. The dikes are subalkaline/tholeiitic basalts and basaltic andesites with high-Ti (TiO₂ = 4.3-3.1 wt.%) and low MgO (4.93-3.34 wt.%) compositions, except a low-Ti subswarm (TiO₂ < 2.0 wt.%) that exhibits higher MgO content (>6.5 wt.%). ⁴⁰Ar/³⁹Ar and K-Ar dating of the low-Ti Pirenópolis dikes yields Triassic dates (~210.7-205.5 Ma), linking their emplacement to the Central Atlantic Magmatic Province (CAMP). In contrast, the high-Ti dikes from both the Transminas and Pirenópolis swarms record Early Cretaceous dates (~133-131.5 Ma), coeval with the initial breakup of West Gondwana, and are therefore associated with the Paraná-Etendeka Magmatic Province (PEMP). High-Ti dikes have ⁸⁷Sr/⁸⁶Sr = 0.71157-0.70549 and ε_Nd = -0.9 to -16.2. Lead isotopes indicate a signature compatible with an enriched mantle source (EMI; ²⁰⁶Pb/²⁰⁴Pb = 18.40-18.12). The integrated datasets for the high-Ti tholeiites of the PEMP giant dike swarms and those of the Equatorial Atlantic Magmatic Province (EQUAMP) indicate derivation from compositionally similar or possibly shared mantle source reservoirs. Such a connection further supports the integration of these Early Cretaceous provinces into the South Atlantic Magmatic Province (SAMP). When assessing the spatial distribution of the magmatic remnants of the CAMP and SAMP, we conclude that the Transbrasiliano Lineament acted as a tectonic boundary, modulating the emplacement realm of the two LIPs during the Mesozoic.