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1 Departmento de Ciencias de la Tierra, Área de Petrología y Geoquímica, Universidad de Zaragoza, c/ Pedro Cerbuna, 12, 50.009 Zaragoza, Spain mlago{at}posta.unizar.es
2 Departamento de Ciencias de la Tierra, Área de Geodinámica Interna, Universidad de Zaragoza, c/ Pedro Cerbuna, 12, 50.009 Zaragoza, Spain
Late Variscan magmatism in the Iberian Chain (Central Spain) is recorded by the presence of both pyroclastic units and high-level intrusions (sills and dykes). This magmatism encompasses a variety of subalkaline igneous rocks, from basalt to rhyolite; andesitic rocks are, however, dominant. The pyroclastic units contain plant fossils and pollen that suggest an Autunian age, which is consistent with the available K-Ar radiometric age data (283–292 Ma) obtained for the hypabyssal intrusions. Earlier amphibole-rich andesite, rich in crustal xenoliths (metapelite, granitoid and quartzite fragments) and xenocrysts (e.g. garnet) suggest the occurrence of significant crustal assimilation in the petrogenesis of the intermediate magmas, whereas later intrusions (pyroxene-rich andesites, basalts and some rhyolites) lack any crustal xenoliths or xenocrysts. Crustal assimilation is also suggested by the radiogenic 87Sr/86Sr290 and negative
Nd290 values for all the studied rocks. The cross-cutting relationships between the different rock types provide evidence for a multi-stage magmatic evolution, coeval with the post-orogenic transtensive evolution of the southern Variscan belt in Europe. A significant hiatus, covering the Middle Permian and most of the Upper Permian, separates this Lower Permian magmatism from the subsequent Triassic and Jurassic alkaline magmatism that represents different rifting events that affected the Iberian Chain, progressively thinning the Variscan crust as the Alpine cycle began.
