Tectonostratigraphic models of the Alpine terranes and subduction history of the Hellenides

Abstract

The tectonostratigraphy of the Hellenic terranes is related to their paleogeodynamic and paleogeographic evolution, which comprises three major stages: (i) Continental rifting in the northern margin of Gondwana, characterised by volcanosedimentary complexes of Late Paleozoic–Triassic. (ii) Continental drifting and contemporaneous oceanic opening of Tethyan basins in between the continental terranes during Triassic–Paleogene with shallow-water carbonate platforms on the continental terranes and ophiolite suites interlayered with pelagic sediments within the Tethyan basins. (iii) Accretion of the tectonostratigraphic terranes with docking along the active European margin, characterised by flysch/melange sedimentation along the trenches from ?early Jurassic to Neogene. Two tectonostratigraphic models can be distinguished: one for the continental terranes/carbonate platforms and another for the oceanic basins. The duration of each geodynamic stage for each terrane is obtained from the chronology of the tectonostratigraphic facies change. The general trend is younger ages observed in the southern terranes and older ages towards the northern terranes. The two alternative tectonostratigraphic models are applied in the two groups of terranes and the chronology of the geodynamic–paleogeographic stages is estimated. The Hellenic subducted slab as shown in the seismic tomographic images is correlated to the terrane paleogeography using the estimated widths and the average subduction rates. The upper 1700km of the slab correspond to the three southern more external terranes whereas the remainingpart of the slab may represent the other more internal terranes. A palinspastic model of the Hellenides is presented taking into account the chronology of each stage for every terrane. Obduction of ophiolites over the southern platforms, is observed in all four oceanic basins. Blueschist exhumation, formation of core complexes and tectonic windows through extensional detachments occur after micro-collision of continental terranes/platforms and their isostatic uplift within the upper plate after their detachment from the subducting slab.