The tectonics of the Strandja Massif: late-Variscan and mid-Mesozoic deformation and metamorphism in the northern Aegean

The Strandja Massif is a mid-Mesozoic oro genic belt in the Balkans build o n a late-Variscan basement of gneisses, migmatites and granites. New single -zircon evaporation ages from the gneisses and granites indicate that the h igh-grade metamorphism and plutonism is Early Permian in age (similar to 27 1 Ma). The late-Variscan basement was unconformably overlain by a continent al to shallow marine sequence of Early Triassic-Mid-Jurassic age. During th e Late Jurassic-Early Cretaceous (Oxfordian-Barremian) the lower Mesozoic c over and the basement were penetratively deformed and regionally metamorpho sed in greenschist facies possibly due to a continental collision. An Rb-Sr biotite whole-rock age from a metagranite dates the regional metamorphism as Late Jurassic (155 Ma). Deformation involved north-vergent thrust imbric ation of the basement and the emplacement of allochthonous deep marine Tria ssic series over the Jurassic metasediments, The metamorphic rocks of the S trandja Massif are unconformably overlain by the Cenomanian shallow marine sand stones. During the Senonian, the northern half of the Strandja Massif formed a basement to an intra-arc basin and to a magmatic are generated abo ve the northward-subducting Tethyan oceanic lithosphere. The Srednogorie ar e closed during the early Tertiary through renewed northward thrusting of t he Strandja Massif.