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New U-Pb SHRIMP zircon ages for pre-variscan orthogneisses from Portugal and their bearing on the evolution of the Ossa-Morena tectonic zone

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Author(s): Cordani Umberto G. | Nutman Allen P. | Andrade Antonio S. | Santos José F. | Azevedo Maria do Rosário | Mendes Maria Helena | Pinto Manuel S.

Journal: Anais da Academia Brasileira de Ciências
ISSN 0001-3765

Volume: 78;
Issue: 1;
Start page: 133;
Date: 2006;
Original page

Keywords: Cadomian orogeny | U-Pb geochronology | Iberian Massif | Ossa-Morena Zone

ABSTRACT
New SHRIMP U-Pb zircon ages for the Portalegre and Alcáçovas orthogneisses document a complex pre- Variscan history for the Iberian basement in Portugal. The available geochemical and geochronological data for the Alcáçovas orthogneiss (ca. 540 Ma) tend to favor its involvement in a Cadomian orogenic event. This is consistent with the development of an active continental margin setting at the end of the Proterozoic and supports a Gondwanan provenance for the Iberian crust. On the other hand, the Ordovician emplacement age obtained for the magmatic precursors of the Portalegre orthogneisses (497?10 Ma) provides additional evidence for the occurrence of rift-related magmatic activity during the Lower Paleozoic.
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