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This work describes rare accessory minerals in volcanic and subvolcanic silica-undersaturated peralkaline and agpaitic rocks from the Permo-Triassic Cerro Boggiani complex (Eastern Paraguay) in the Alto Paraguay Alkaline Province. These accessory phases consist of various minerals including Th-U oxides/silicates, Nb-oxide, REE-Sr-Ba bearing carbonates-fluorcarbonates-phosphates-silicates and Zr-Na rich silicates. They form a late-stage magmatic to deuteric/metasomatic assemblage in agpaitic nepheline syenites and phonolite dykes/lava flows made of sodalite, analcime, albite, fluorite, calcite, ilmenite-pyrophanite, titanite and zircon. It is inferred that carbonatitic fluids rich in F, Na and REE percolated into the subvolcanic system and metasomatically interacted with the Cerro Boggiani peralkaline and agpaitic silicate melts at the thermal boundary layers of the magma chamber, during and shortly after their late-stage magmatic crystallization and hydrothermal deuteric alteration.

The eastern border of the Sao Francisco craton is characterized by widespread Mesoproterozoic (∼1.0 Ga) tholeiitic dykes and minor analogues of Early Cretaceous age (∼130 Ma). The Mesoproterozoic dykes (Salvador, Olivenca, Espinhaco, Diamantina) show large elemental and Sr–Nd isotopic variations that suggest different parental melts related to a small-scale heterogeneous mantle of depleted residua and enriched components (Statistical Upper Mantle Assemblage, SUMA), responsible for plume- and crust-type signatures. The Mesoproterozoic intrusions, compatible with early stages of Rodinia breakup, may represent the initial breakup of the Sao Francisco–Congo junction. Early Cretaceous dykes (Espinhaco) reveal normal and reversed polarities, indicating two distinct intrusive periods. These intrusions have elemental and Sr–Nd isotopic compositions similar to those of the coeval (∼132 Ma) high-TiO2 tholeiites from southern Parana Basin (Urubici-type, Brazil) and northern Etendeka (Khumib-type, Namibia). The genesis of these tholeiites requires lithospheric mantle components, as represented by K-alkaline (and carbonatitic) rocks from the Asuncion-Sapucai graben (Paraguay), that highlight the intriguing Pb-isotope relationships involving the Urubici-Khumib tholeiites. The essential role of the Tristan plume is difficult to determine. The spatial distribution of such uncommon high-TiO2 tholeiites reveals that similar lithospheric components may exist in different cratonic blocks and associated mobile belts.