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

• Published in: Anais da Academia Brasileira de Ciências Vol. 78; no. 1; pp. 133 - 149
• Main Authors: Cordani, Umberto G, Nutman, Allen P, Andrade, Antonio S, Santos, José F, Azevedo, Maria do Rosário, Mendes, Maria Helena, Pinto, Manuel S
• Format: Journal Article
• Language: English
• Published: Brazil Academia Brasileira de Ciências 01-03-2006
• Subjects: Cadomian orogeny; Iberian Massif; MULTIDISCIPLINARY SCIENCES; Ossa-Morena Zone; U-Pb geochronology; U-Pb geochronology; Ossa-Morena Zone; orogênico Cadomiano; Maciço Ibérico; Cadomian orogeny; Zona de Ossa-Morena; Iberian Massif; geocronologia U-Pb
• ISSN: 0001-3765; 1678-2690; 0001-3765; 1678-2690
• DOI: 10.1590/S0001-37652006000100013

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.