SHRIMP U-Pb age for the emplacement of the Santana Granite and reactivation of the Porto Alegre Suture, southern Brazil

Abstract SHRIMP U–Pb zircon ages are reported from a sample of the Santana Granite that represents the beginning of alkaline magmatic activity in the Neoproterozoic of the Sul-Rio-Grandense Shield, Brazil. This granite outcrops in the city of Porto Alegre and has a NE–SW elongated shape (20 km long and 5 km wide). It is a medium- to coarse-grained syenogranitic rock with subvertical magmatic foliation and subhorizontal lineation with NE–SW trends, overprinted by a weak solid-state fabric. Zircons of this rock with 206 Pb/ 238 U ages between ca. 575 and ca. 617 Ma are interpreted as having formed during magmatic crystallisation; the best fit for this age using five analyses provided a mean 206 Pb/ 238 U age of 600±10 Ma. This age is also interpreted as the age of the reactivation of the Porto Alegre Suture, a crustal discontinuity along which the Santana Granite was emplaced. Younger isotopic data (