Geodynamic evolution of ophiolites from Albania and Greece (Dinaric-Hellenic belt): one, two, or more oceanic basins?

Abstract

All the geological constraints for an exhaustive reconstruction of the Triassic to Tertiary tectonic history of the southern Dinaric-Hellenic belt can be found in Albania and Greece. This article aims to schematically reconstruct this long tectonic evolution primarily based on a detailed analysis of the tectonic setting, the stratigraphy, the geochemistry, and the age of the ophiolites. In contrast to what was previously reported in the literature, we propose a new subdivision on a regional scale of the ophiolite complexes cropping out in Albania and Greece. This new subdivision includes six types of ophiolite occurrences, each corresponding to different tectonic units derived from a single obducted sheet. These units are represented by: (1) subophiolite me ´lange, (2) Triassic ocean-floor ophiolites, (3) metamorphic soles, (4) Jurassic fore-arc ophiolites, (5) Jurassic intra-oceanic-arc ophiolites, and (6) Jurassic backarc basin ophiolites. The overall features of these ophiolites are coherent with the existence of a single, though composite, oceanic basin located east of the Adria/Pelagonian continental margin. This oceanic basin was originated during the Middle Triassic and was subsequently (Early Jurassic) affected by an east-dipping intra-oceanic subduction. This subduction was responsible for the birth of intra-oceanic-arc and back-arc oceanic basins separated by a continental volcanic arc during the Early to Middle Jurassic. From the uppermost Middle Jurassic to the Early Cretaceous, an obduction developed, during which the ophiolites were thrust westwards firstly onto the neighboring oceanic lithosphere and then onto the Adria margin.

Magmatic and tectonic history of Jurassic ophiolites and associated granitoids from the South Apuseni Mountains (Romania)

“…In contrast to this East Vardar scenario, the obduction of the West Vardar ophiolites occurred above a long-lived NE-dipping subduction zone that is associated with the formation of metamorphic soles (subduction zone in the SW; Fig. 10a) (Gaggero et al 2009;Bortolotti et al 2013;Borojević Šoštarić et al 2014). The latter have not been found in the East Vardar ophiolites (Kounov and Schmid 2013).…”

“…This probably indicates that the emplacement of the East Vardar ophiolites ultimately represents an arc-continent collision rather than a classic obduction as in the case of the West Vardar ophiolites (e.g. Bortolotti et al 2013;Borojević Šoštarić et al 2014) and the Semail ophiolite (e.g. Searle and Cox 1999).…”

“…10a). In Macedonia (FYROM) and Greece, such back arc spreading within the East Vardar ophiolites split off a continental ribbon from the originally Dacia-derived parts of the Circum-Rhodope tectonic unit (Bortolotti et al 2013) (Fig. 10a).…”

Erosion of a Jurassic ophiolitic nappe-stack as indicated by exotic components in the Lower Cretaceous Rossfeld Formation of the Northern Calcareous Alps (Austria)

“…Occurrences of Middle and Upper Triassic radiolarites on top of ocean floor basalts in the Avdella Mé-lange of the Northern Pindos Mountains of Greece (Av in Fig. 1A; Ozsvárt et al 2012), Argolis or other areas in the Hellenic belt (see Bortolotti et al 2013 for latest review) are also comparable. Therefore the proof of Middle and Upper Triassic and Middle Jurassic radiolarite pebbles together with ophiolitic material in the Lower Cretaceous Rossfeld Formation is a strong argument for the erosion of an ophiolitic nappe-stack similar to those of the DinaridicHellenic belt south of the present day Northern Calcareous Alps at that time.…”

“…For example, in the Mirdita Zone of Albania (Fi, Pe in Fig. 1A), reddish-black, red-green and red, well bedded Upper Anisian to Lower Carnian and red Upper Carnian to ?Lower Norian and Norian-Rhaetian radiolarites (Chiari et al 1996;Bortolotti et al 2006;Gawlick et al , 2008Bortolotti et al 2013) occur as primary sedimentary cover of the oceanic crust as well as single blocks of different size within the Upper Bajocian to Oxfordian Perlat Mélange (Pe in Fig. 1A; e.g.…”