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

• Main Author: Cordani,Umberto G.
• Publication Date: 2006
• Other Authors: Nutman,Allen P., Andrade,Antonio S., Santos,José F., Azevedo,Maria do Rosário, Mendes,Maria Helena, Pinto,Manuel S.
• Format: Article
• Language: eng
• Source: Anais da Academia Brasileira de Ciências (Online)
• Download full: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652006000100013
• topic: Cadomian orogeny; U-Pb geochronology; Iberian Massif; Ossa-Morena Zone

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.