A U-Pb Study of Zircons from a Lower Crustal Granulite Xenolith of the Spanish Central System: A Record of Iberian Lithospheric Evolution from the Neoproterozoic to the Triassic

Abstract

A U-Pb laser ablation inductively coupled plasma mass spectrometry and secondary ion mass spectrometry geochronological study has been performed on zircons from a felsic granulite xenolith from the lower crust under the Variscan belt of Iberia. The ages obtained reveal zircon-forming events that span from the late Neoproterozoic (Cadomian-Avalonian orogeny) to the early stages of the opening of the Atlantic Ocean in the Mesozoic, through Cambro-Ordovician rifting, Devono-Carboniferous Variscan-Alleghenian collision, and Permian-Triassic extension and uplift. The U-Pb age groups found in zircons from this single lower crustal xenolith (ca. 220, 250, 280–310, 460–490, 525, and 550–490 Ma) record at least one complete cycle of closing and opening of oceanic basins and collision of continental masses. Zircons from the felsic granulite xenolith contain a synthesis of the geochronological information found on the surface geology and record most but not all major lithospheric events in the region in a ca. 400-m.yr. period.