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

E. Koester, E. Soliani Jr., J.A.D. Leite, L.A. Hartmann, L.A.D. Fernandes, Neal Mcnaughton, J.O.S. Santos, L.D. De Oliveira

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    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)Pp/U-238 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/U-238 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 (<575 Ma) for zircons from this sample are interpreted as due to Pb loss from metamietization. The 600-Ma age is consistent with previous results and marks a magmatic episode, probably related to an extensional tectonic episode that affected the NE of the Sul-Rio-Grandense Shield at the end of the Brasiliano Cycle. (C) 2001 Elsevier Science Ltd. All rights reserved.
    Original languageEnglish
    Pages (from-to)91-99
    JournalJournal of South American Earth Sciences
    Volume14
    DOIs
    Publication statusPublished - 2001

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