Within-plate magmatism in the southern Borborema Province (NE Brazil): Mantle plumes associated with the Nuna-Columbia and Rodinia breakup?

Abstract

Formation and fragmentation of landmasses, such as the Nuna/Columbia and Rodinia supercontinents, are influenced by mantle plume activity during rifting and breakup. In the Borborema Province, NE Brazil, within-plate magmatism at ca. 1.6 and at ca. 0.8 Ga is evidenced by the formation of mafic-ultramafic volcanic and plutonic rocks, mafic-ultramafic layered intrusions, and A-type granite intrusions. The Paulistana and Santa Filomena complexes, located in the Riacho do Pontal Orogen, southern Borborema Province, correspond, respectively, to metaplutonic/volcanic-sedimentary and metavolcanic-sedimentary sequences. These sequences are composed of metamorphic rocks of the greenschist to amphibolite facies whose basement corresponds to the Paleoproterozoic rocks of the Itaizinho Complex, which is located in the southern portion of the São Pedro Terrane. The combined analysis of new field, petrographic and geochemical data obtained for the metavolcanic rocks of the São Pedro Terrane and Riacho do Pontal Orogen aided the determination of their tectonic setting. Whole-rock geochemical analyses revealed the predominance of andesites, basaltic andesites and tholeiitic alkali basalts generated in a within-plate environment (E-MORB) with shallow melting of the metavolcanic rocks of the Itaizinho Complex. In the Riacho do Pontal Orogen, basaltic to alkali-basaltic tholeiites are the dominant metavolcanic rocks of the Paulistana and Santa Filomena complexes. Tectonic setting discriminant diagrams indicate within-plate (E-MORB/OIB), deep and shallow melting environments, respectively. This study, combined with data available in the literature, suggests that the metavolcanic rocks of the Itaizinho Complex and metavolcanic rocks of the Paulistana/Santa Filomena complexes were formed in an extensional setting related to Calymmian (1631 Ma) and Tonian (882 Ma) mantle plumes, respectively, precursor to the oceanic crust between the São Pedro Terrane and the São Francisco Craton, represented by the metabasalts of the Monte Orebe complex, which underwent re-accretion and reworking during the Brasiliano-Pan-African Orogeny.