Mid-Ordovician U–Pb ages of porphyroids in the Peloritan Mountains (NE Sicily): palaeogeographical implications for the evolution of the Alboran microplate

Abstract

Petrographic, geochemical and geochronological work on a metavolcanic suite interbedded in a metapelitic sequence of the Palaeozoic basement in the Peloritan Mountains (Sicily) is used to contribute to a better understanding of the pre-Variscan geodynamic evolution of the former Alboran microplate. Major and trace element data show that the volcanic suite consists of two main groups: an Intermediate Unit of andesites and dacites with volcanic arc affinity and a Felsic Porphyroid Unit of rhyolites with peraluminous composition. Isotope dilution thermal ionization mass spectrometry U–Pb analyses for single- and multigrain zircon fractions from four samples of the felsic porphyroids yield results that are tightly clustered on or near concordia giving Caradoc ages in the range of 456–452 Ma. The consistent morphological characteristics and oscillatory zoning of the zircons indicate single-stage magmatic crystallization. Xenocrystic zircon grains with ages of 1150 and 2015 Ma indicate that these rocks were developed upon a cratonic basement with Grenvillian and Transamazonian components, hence supporting a peri-Gondwanan origin. From the combined evidence we conclude that this portion of the Alboran microplate formed as a Mid-Ordovician volcanic arc in a sector of the peri-Gondwanan terranes that was affected by a tectonothermal Caradoc event.