Regional geology and correlation of the Eastern Circum-Rhodope Belt, Bulgaria-Greece

We review on a regional-scale the distinct units of the eastern Circum-Rhodope Belt (CRB) in Bulgaria and Greece aiming to provide an up-to-date synthesis and correlation. The eastern CRB consists of Early-Middle Jurassic supra-subduction zone Evros ophiolite, the MORB related Late Jurassic Samorthaki ophiolite and Middle Triassic-Jurassic clastic, pelitic, carbonate and Cretaceous (?) flysch sedimentary successions. The Lower Cretaceous shallow-water Aliki Limestone seals part of these sedimentary successions already metamorphosed in greenschist-facies. Bulk stratigraphy in ascending order comprises a metasedimentary series overlain by a metavolcanic series. The metamorphic grade increases towards the high-grade basement northwards reaching upper greenschist to epidoteamphibolite facies, and decreases to very low-grade (prehnite-pumpellyite facies) and nonmetamorphic stratigraphically upwards in the section. Trace element and REE comparison of the ophiolite basalts and underlying greenschist-facies metavolcanics of same composition reveals similar geochemistry within the distinct units, implying a regional-scale chemical continuity. The allochthonous eastern CRB units show N-directed internal shear deformation and thrust emplacement, obviously along rarely preserved thrust contacts, and record tectonic overprint by Tertiary collision and extensional tectonics in the region. Collectively, the onshore eastern CRB is a region-wide (180 km long along strike ×80 km wide along meridian) tectonic zone including correlative units with regard to their coherent and comparable stratigraphy, tectonics and geochemistry. These units testify for three paleogeographic domains that include Triassic-Jurassic near Rhodope continental margin shallow-water environment, adjacent to this margin Early-Middle Jurassic intra-oceanic arc system responsible for the generation of the supra-subduction zone Evros ophiolite and related to the ophiolite Middle-Late Jurassic trench-slope environment. Another MORB-related paleogeographic domain is indicated by the Samothraki back-arc ophiolite offshore.