The Alpine Geological History of the Hellenides from the Triassic to the Present—Compression vs. Extension, a Dynamic Pair for Orogen Structural Configuration: A Synthesis

Abstract

In this paper, the Hellenic orogenic belt’s main geological structure and architecture of deformation are presented in an attempt to achive a better interpretation of its geotectonic evolution during Alpine orogeny. This study was based not only on recent research that I and my collaborators conducted on the deformational history of the Hellenides but also on more modern views published by other colleagues concerning the Alpine geotectonic reconstruction of the Hellenides. The structural evolution started during the Permo–Triassic time with the continental breaking of the supercontinent Pangea and the birth of the Neotethyan ocean realm. Bimodal magmatism and A-type granitoid intrusions accompanied the initial stages of continental rifting, followed by Triassic–Jurassic multiphase shallow- and deep-water sediment deposition on both formed continental margins. These margins were the Apulian margin, containing Pelagonia in the western part of the Neotethyan Ocean, and the European margin, containing continental parts of the Serbo-Macedonian and Rhodope massifs in the eastern part of the Neotethyan ocean. Deformation and metamorphism are recorded in six main deformational stages from the Early–Middle Jurassic to the present day, beginning with Early–Middle Jurassic Neotethyan intra-oceanic subduction and ensimatic island arc magmatism, as well as the formation of a suprasubduction oceanic lithosphere. Compression, nappe stacking, calc-alkaline magmatism, and high-pressure metamorphic events related to subduction processes alternated successively over time with extension, orogenic collapse, medium- to high-temperature metamorphism, adakitic and calc-alkaline magmatism, and partial migmatization related to the uplift and exhumation of deep crustal levels as tectonic windows or metamorphic core complexes. A S- to SW-ward migration of dynamic peer compression vs. extension is recognized during the Tertiary Alpine orogenic stages in the Hellenides. It is suggested that all ophiolite belts in the Hellenides originated from a single source, and this was the Neotethyan Meliata/Maliac-Axios/Vardar ocean basin, parts of which obducted during the Mid–Late Jurassic on both continental margins, Apulian (containing Pelagonia) and European (containing units of the Serbo-Macedonian/Rhodope nappe stack), W-SW-ward and E-NE-ward, respectively. In this case, the ophiolite nappes should be considered far-traveled nappes on the continental parts of the Hellenides associated with the deposition of Middle–Late Jurassic ophiolitic mélanges in basins at the front of the adjacent ophiolite thrust sheets. The upper limit of the ophiolite emplacement are the Mid–Upper Jurassic time(Callovian–Oxfordian), as shown by the deposition of the Kimmeridgian–Tithonian Upper Jurassic sedimentary carbonate series on the top of the obducted ophiolite nappes. The lowermost Rhodope Pangaion unit is regarded as a continuation of the marginal part of the Apulian Plate (External Hellenides) which was underthrust during the Paleocene–Eocene time below the unified Sidironero–Kerdylia unit and the Pelagonian nappe, following the Paleocene–Eocene subduction and closure of a small ocean basin in the west of Pelagonia (the Pindos–Cyclades ocean basin). It preceded the Late Cretaceous subduction of the Axios/Vardar ocean remnants below the European continental margin and the final closure of the Axios/Vardar ocean during the Paleocene–Eocene time, which was associated with the overthrusting of the European origins Vertiskos–Kimi nappe on the Sidironero–Kerdylia nappe and, subsequently, the final collision of the European margin and the Pelagonian fragment. Subsequently, during a synorogenic Oligocene–Miocene extension associated with compression and new subduction processes at the more external orogenic parts, the Olympos–Ossa widow and the Cyclades, together with the lower-most Rhodope Pangaion unit, were exhumed as metamorphic core complexes.