SHRIMP U Pb zircon dating of Neoproterozoic granitic magmatism and collision in the Pelotas Batholith, southernmost Brazil

The introduction of robust geochronological methods for age determinations of the southernmost segment of the Neoproterozoic terranes of Brazil, namel y the Dom Feliciano Belt, provides important clues for unraveling the compl ex evolution of the Brasiliano/Pan-African orogeny in this southwestern por tion of the Gondwana supercontinent. Except for associated small schist bel ts and postorogenic foreland basins, the belt is represented in this region of southeastern South America by the Pelotas Batholith. Precise SHRIMP U/P b zircon geochronological techniques based on the study of 95 individual sp ots on 74 zircon crystals (three samples) and on Nd-isotopic determinations (three samples) are used to assess the late Neoproterozoic history of the belt, especially the orthogneisses interleaved with the batholithic plutons . Three petrotectonic associations were selected for detailed isotopic inve stigations-the Pinheiro Machado syncollisional monzogranites, the widesprea d Piratini gneiss tonalitic xenoliths, and the Arroio dos Rates (now Encant adas) gneiss. The results allow the establishment of the timing and ages of the metamorphic peak and early magmatism. We demonstrate that evolution of Neoproterozoic magmatism within the Pelotas Batholith occurred through a l ong-lived crustal recycling process from the Paleoproterozoic Rio de la Pla ta craton. Three major events are recognized, two corresponding to crustal granite generation by partial melting of Paleoproterozoic protoliths at sim ilar to 780 and similar to 610 Ma, and one related to the high-grade syncol lisional meta morphic peak at similar to 630 Ma. The data also yield precis e criteria to distinguish between thrust-related granitoids of the Dom Feli ciano belt and older orthogneisses, both previously interpreted as a unique , pre-collisional, Brasiliano Cycle magmatic-arc association.