The basement of Calabria (southern Italy) within the context of the Southern European Variscides: LA-ICPMS and SIMS U–Pb zircon study

Abstract

U–Pb spot zircon ages from metagabbros and metasediments of the Variscan lower crust in the Serre massif (southern Calabria) have been determined using LA-ICPMS and SIMS. The results, together with the literature data deriving from conventional and spot zircon ages and from Rb–Sr whole-rock isochrons, allow the geological history of the crustal block to be more tightly constrained from the Late Neoproterozoic to the Triassic, with particular emphasis on Variscan evolution. In a peri-Gondwana Pan-African/Cadomian basement, preserving memory of recycled older terrains with West African Craton affinities, mafic and felsic magmas emplaced at ca. 584 Ma (protoliths of metagabbros) and in the range 575–537 Ma (protoliths of felsic orthogneisses). Partially or completely recrystallized domains of zircons from metaigneous rocks yield ages ranging from 500 to 440 Ma. These ages (consistent with those of recrystallized cores of magmatic zircon from felsic orthogneisses and with Rb–Sr isochron data for the lower crust metasediments) suggest tectonothermal Ordovician activity, which is likely to be connected to the opening of Palaeozoic basin(s) separating the future Variscan blocks from Gondwana. Most zircon ages in the metasediments cluster in the 340–260 Ma range, which probably corresponds to two major events: (i) crustal thickening between 340 and 300 Ma (Barrowian metamorphic event) and (ii) lower-P/high-T metamorphism, Bt-dehydration melting, crustal extension between 300 and 260 Ma. Triassic ages ranging from 249 ± 4 Ma to 231 ± 5 Ma, together with whole-rock Rb–Sr isochron age at 234 Ma for the lowermost metapelites of the section, suggest tectonothermal activity, which prepared the opening of the Jurassic Neotethys. Similarities and differences relative to some circum-Mediterranean Variscan lower crust sections are also discussed, which contribute to the knowledge of south European Variscides evolution.