Brittle deformation, palaeostress field reconstruction and tectonic evolution of the Eastern Balkanides (Bulgaria) during Mesozoic and Cenozoic times

Brittle tectonics analysis and stress tensor reconstructions allow us to better depict the Mesozoic and Cenozoic geodynamical evolution of the Eastern Balkanides which is characterized by a series of overimposed basin-systems. The Late Permian–Triassic corresponds to a wide carbonate platform with local embryonic troughs. During the Jurassic–Early Cretaceous period, the area, limited by regional unconformities, was at first dominated by the existence of a deep basin until the latest middle Jurassic, then by its gradual closure during the Late Jurassic–Early Cretaceous. Traces of these tectonic events are found as a result of brittle tectonic data analysis, especially in the Strandja Zone where NE–SW extension and ENE–WSW compression may be related to the Early Alpine phases of rifting and shortening, respectively. The Late Cretaceous–middle Eocene period was governed by the back-arc basin/island-arc system of East Balkan/Srednogorie zones. The inversion of these extensional zones occurred after the Maastrichtian, then important shearing and thrusting developed during the major shortening in the latest Middle Eocene. These Late Alpine tectonic phases were well characterized by brittle tectonics and the analysis of faulting in terms of stress tensors allows us to identify the main directions of extension of the rifting stage which is north–south to NNE–SSW, and the directions of compression of the Laramian and Illyrian phases, which are NE–SW and north–south, respectively. The relationships between folding and reverse and strike–slip faults are established as well as the occurrence of post-folding normal faults assigned to collapse process following the shortening.