A geological cross-section through northern Greece from the Pindos to Rhodope Mountains: a field guide across the External and Internal Hellenides

Adamantios Kilias, Efi Thomaidou, George Falalakis, Stylianos Avgerinas, Aristides Sfeikos, Manolis Katrivanos, Agni Vamvaka, Charalampos Fassoulas, and Korina Pipera

The aim of this work is to introduce the architecture and structural evolution of the Hellenic orogen in northern Greece, during the Alpine orogeny, through observations of selected outcrops, samples and view-points, along an east-west directed traverse in northern Greece, from the Pindos Mountain range (External Hellenides) to the Rhodope Mountainous province (Internal Hellenides). For this purpose, we describe and discuss in detail, during an 8-days field trip, the most interesting tectonic and sedimentary structures in macro- and micro-scale, of the geological units, occupied along this cross-section.
From the west to the east we cross: I. The Ionian, Gavrovo and Pindos nappes, II. The Tertiary sediments of the Meso-Hellenic trough, III. The Pindos and Vourinos ophiolite nappes with their underlain and overlain Mesozoic sedimentary units and ophiolite mélanges. IV. The Pelagonian nappe, IV. The Ampelakia unit and its underlain Olympos-Ossa unit, V. The Axios zone and VI. The Serbo-Macedonian/Rhodope metamorphic province of the Internal Hellenides.
The External Hellenides zones are characterized by a continuous sedimentation from the Triassic to the Paleogene-Neogene with a flysch deposition, as the last synorogenic sediment, being progressively younger from the east to the west due to the orogeny migration. A Tertiary thin-skinned tectonics marks the structural evolution of the External Hellenides.

The geometry and kinematics of the ophiolite bodies’ emplacement on top of the Pelagonian nappe and the External Hellenides remain until today an open question. Are they obducted from one or more ocean basins?

The Pelagonian nappe constitutes a complicated, polymetamorphic, internal imbricated nappe, composed of a Paleozoic or older basement (gneisses, schists and Carboniferous granitoids) overlain by a Triassic-Jurassic clastic and carbonate cover. The Pelagonian nappe was emplaced during the Early Oligocene together with the Tertiary metamorphosed HP-LT Ampelakia unit on top of the External Hellenides. The tectonic contact between External Hellenides and the overlain Ampelakia-Pelagonian nappe pile has been reworked by an Oligocene-Miocene normal detachment fault related to the uplift and exhumation of the External Hellenides in the form of tectonic windows in the Olympos and Ossa Mountains.

The Axios zone is traditionally divided into the Almopias, Paikon and Peonias subzones, each one characterized by its own structure and deposition features.

The Serbo-Macedonian/Rhodope metamorphic province occupies the eastern most part of our section. It forms an Alpine heterogeneous nappe stack, consisting of both continental and oceanic crustal rocks. Synmetamorphic compression versus syn- to post- orogenic extension and progressively exhumation of deep crustal levels characterize the Alpine structural evolution of the Serbo-Macedonian/Rhodope massif. Tertiary granitoids intruded the whole massif during the extensional event. Ultra-high- and high-pressure metamorphic rocks occurring between the nappe stack and in the volcano-sedimentary origin Circum-Rhodope belt around the Serbo-Macedonian/Rhordope massif, indicate subduction processes during the nappe stacking.

The most important structures of the above described Hellenides geological sequences will be resented, in order to show the main structure of the Hellenic orogen and its structural evolution during the Alpine orogeny, taking also into account our views and interpretations concerning the tectonic setting and evolution history of the Hellenides.

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