Late Cretaceous Tectono-Metamorphic Events in the Skyros Upper Metamorphic Unit (Olympus Mountain), Aegean Sea, Greece

Late Cretaceous metamorphic events are known in Crete and the Cyclades from klippen above the External Hellenides. This work extends their occurrence to the North Aegean area within the tectonic units of the Internal Hellenides. New 40Ar/39Ar white mica ages from garnet-bearing micaschists of the Upper Metamorphic Unit of Skyros Island, cropping out in the Skyrian Olympus Mountain, document a Late Cretaceous tectono-metamorphic evolution. Several mica generations have been distinguished using electron probe microanalyses and were dated using the 40Ar/39Ar method: a relict mica older than 96 Ma, followed by a foliation-forming mica of about 88–84 Ma and alteration phases ≤ 68 Ma were recognized. This Cretaceous tectono-metamorphic evolution falls between the closure of the internal Axios/Vardar oceanic basin in the Late Jurassic–Early Cretaceous, and the closure of the external Pindos–Cyclades oceanic basin in the Early Cenozoic. The position of the Upper Metamorphic Unit of Skyros was probably within the evolving Hellenic volcanic/magmatic arc during the continuous subduction of the African plate beneath the European plate. The present tectonic position of the units bearing the Late Cretaceous metamorphic event is the result of the Cenozoic tectonic emplacement onto the more external units across the Hellenides from the Pelagonian to the Pindos–Cyclades domain.