Alpine and Pre-Alpine Formations of the Hellenides

Abstract

The research history of the Hellenides is described from the early 19Th century to present. The history of the continental fragment of India which was rifted and detached from Eastern Africa within the Gondwana dispersion in the early Mesozoic, drifted within the Tethys Ocean and accreted to the sourthern margin of Eurasia, creating the collisional mountain range of the Himalayas since Oligocene – Miocene is used as an example for the Tethyan tectono-stratigraphic terranes. The Tethyan paleogeography comprised shallow water carbonate platforms developed on top of continental terranes and abyssopelagic sediments deposited on top of the ophiolites inside the opening intermediate oceanic basins. The general drift movement of the Hellenic terranes was constantly occurring from south to north, with a gradual rifting from Africa during the Triassic and a gradual arrival and accretion to Europe from the Jurassic to present. Two types of stratigraphic columns arise from the overall terrane development and evolution of the tectono-stratigraphic terranes of the Hellenides along with the three stages of rifting, drifting and docking. Pre-Alpine non-crystalline rocks are traced only in the islands of the Eastern Aegean, Chios and Kos. In Northwestern Chios the lower Paleozoic fossils are restricted in blocks – olistholiths, together with blocks of mafic volcanic rocks within a Permian wild flysch formation. Kos Island is the only case where a Paleozoic slightly metamorphic sedimentary sequence crops out with some preserved fossils of Ordovician and Carboniferous age. The Permian- is the base of the Alpine sequences and not their pre-Alpine basement and there is no evidence of a Triassic unconformity. The geochronologic data on metamorphism and magmatism of the pre-Alpine basement in the Hellenides point to a Carboniferous age around 300 Ma. The Internal Hellenides are characterized by two orogenic periods separated by the Cenomanian unconformity. In contrast, the External Hellenides are characterized by continuous stratigraphic columns, tectonised only once, during Eocene – Miocene. Large displacements of the tectonic nappes have created tectonic windows and tectonic klippen both within the internal and the external Hellenides. Three parallel tectono-metamorphic belts are distinguished in the Hellenic arc with different history. Tectonic zonation, either isopic or geotectonic, is currently avoided because it implies the notion of cylindrism. The term tectonic unit preserves all the common pre- and syn- orogenic characteristics and simultaneously allows a non-cylindrical geological interpretation.