Presence of palaeoproterozoic and archean components in the granulite-facies rocks of central Iberia : the Hf isotopic evidence

Hf-isotope analyses in previously dated zircon crystals from four Variscan granulite-facies rocks from central Iberia have been studied to examine crustal evolution processes. Two samples are from exposed migmatite terranes, the other two are granulite xenoliths from lower crustal levels. Hf model ages show that lower crustal granulites display a bigger contribution of Archean components than exposed high-grade rocks (14% of the zircon population instead of 6%), reinforcing ideas of preservation of ancient crustal material in the lower crust. The distribution of age-Hf isotope data from zircon suggests two juvenile crust formation events in central Iberia: the main one during the Neoproterozoic (540-620. Ma) and a possible second Mesoproterozoic event around 1.0-1.2. Ga. Magmatism appears in the Central Iberian Zone exclusively related to that younger juvenile addition. Hf data of granulite zircons agrees with recent palaeogeographical reconstruction models which present central Iberia as a peri-Gondwanan terrane located between the West African craton and the Arabian shield, far from the Amazonia microplate.12 page(s