The Rio Capim volcanic–plutonic–sedimentary belt, São Francisco Craton, Brazil: Geological, geochemical and isotopic evidence for oceanic arc accretion during Palaeoproterozoic continental collision

The collision of oceanic arcs with continents is a common plate tectonic process in the Phanerozoic, but its recognition in the Precambrian is hampered by deformation and metamorphism. The Rio Capim volcanic–plutonic–sedimentary belt lies in sharp tectonic contact with Archaean rocks of the Uauá block in the northern part of the São Francisco craton. Field relationships and high-precision geochronology indicated that the Rio Capim basalts, gabbros, diorites, and dacites were emplaced approximately at 2148–2143 Ma, and later intruded by 2128 Ma-old diorite to tonalite plutons. All rocks were metamorphosed under amphibolite to granulite facies conditions mainly between 2080 Ma and 2070 Ma, but deformation may have lasted until about 2040 Ma as estimated from syn-deformation zircon and titanite grains. The association of basalt, andesite, dacite, and their plutonic counterparts, combined with their positive εNd(t) values and incompatible trace element geochemical signatures similar to island arc magmas, support the proposition that the Rio Capim belt was a Palaeoproteorozoic intra-oceanic arc sequence that collided with a continent, of which the Mesoarchaean Uauá block is a remnant. The implications for the regional evolution and metallogenesis are also discussed.

Research Highlights
► Mafic and felsic volcanic rocks of the Precambrian Rio Capim greenstone belt (Brazil) have oceanic arc geochemical signatures.
► A Palaeoproterozoic (2148-2128 Ma) oceanic arc was accreted to an Archaean microcontinent in South America.
► Phanerozoic-style plate tectonics was already in operation in the Palaeoproterozoic.