| Summary: | The Manaíra-Princesa Isabel dike swarm forms one of the most expressive examples of Neoproterozoic (c. 600 Ma)peralkaline magmatism in the Borborema Province (NE Brazil). It consists of about a hundred NE-trending bodies intrusivein older, Neoproterozoic porphyritic granites (Princesa Isabel and Tavares plutons), and orthogneisses and low-grademetasediments of the Eo-neoproterozoic Riacho Gravatá complex. The dike swarm includes mostly silica-saturated syenites,with potassic to ultrapotassic, peralkaline affinity, containing microcline and sodic amphibole ± pyroxene as the mainmineral assemblage. Amphibole is dominantly Mg-riebeckite (Manaíra, Princesa Isabel and Tavares sub-swarms), whereaspyroxene is mainly aegirine-augite (Manaíra and Tavares sub-swarms). A minor set of dikes from this swarm is slightlymetaluminous with Mg-biotite as the major mafic phase. Geochemical and isotopic signatures indicate strong enrichmentin incompatible elements (Rb, Ba, K, Th, U), in association with a negative Nb anomaly, and strongly radiogenic 87Sr/86Srand 143Nd/144Nd (= negative εNd values) initial ratios. These features suggest a common source, which was probably an enriched lithospheric mantle reservoir, chemically modifi ed by an ancient subduction component inferred to be Paleoproterozoic fromTDM model ages. Conversely, Pb isotopic ratios lower than average crustal values indicate the influence of a non-radiogenic componentinteracting with the enriched mantle source. A SHRIMP U-Pb age of c. 600 Ma obtained for the Manaíra-Princesa Isabel dike swarmdefi nes an important crustal exhumation period which was relatively synchronous with intensive tectonomagmatic activity related tothe Brasiliano orogeny, which occurred in distinct structural domains within the Transverse Zone of the Borborema Province.
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