Cretaceous-Paleogene Tectonics of the Pelagonian Zone: Inferences From Skopelos Island (Greece)

Abstract

We have investigated subduction-exhumation processes in the Pelagonian zone, exposed on the Northern Sporades islands (Aegean Sea) related to successive episodes of ocean continent and continent-continent convergence through integrating multiscale structural analysis, metamorphic petrology, and white mica 40Ar/39Ar dating. Two major progressive phases of ductile deformation are documented, which are related to distinct episodes of tectonic burial and exhumation of the Pelagonian continental margin, which was facing the Neotethys/Vardar ocean. Review of existing data sets from neighboring regions shows that both deformation phases can be correlated along strike up to the Dinarides. The first phase of tectonic burial and exhumation (D1) is characterized by NW-SE tectonic transport, greenschist facies metamorphism, and Early Cretaceous (~105-135Ma) 40Ar/39 Ar white mica single fusion ages. D1 is correlated with the initial closure of the Vardar ocean by top-to-the-W to NW ophiolite obduction and the underthrusting of the Pelagonian margin below the oceanic upper plate. Underthrusting was followed by exhumation and the deposition of Late Cretaceous-Paleogene sediments. The second phase of burial and exhumation (D2) is characterized by NE-SW tectonic transport, greenschist to blueschist facies metamorphism, and latest Cretaceous-Early Eocene 40Ar/39 Ar white mica ages of S2 fabrics. Top-to-the-SW shearing is correlated with the tectonic burial of the Pelagonian zone below the Eurasian continent (Rhodopia), while top-to-the-NE shearing is attributed to subsequent extensional exhumation. D2 fabrics record low-grade P-T conditions suggesting that the decoupled cover formations exposed on Skopelos were incorporated in an accretionary wedge that formed above the subducting Pelagonian basement during Paleogene times.