MULTIPLY DEFORMED LATE MESOZOIC-EARLY CENOZOIC FORELAND FOLD-THRUST BELT OF THE BALKAN OROGEN, NORTHERN BULGARIA (Invited Presentation)

The generally east-west trending Balkan orogen consists of a northern belt of folded and thrusted Mesozoic and Cenozoic strata that forms its the external fold and thrust belt of late Mesozoic and early Cenozoic age and a southern belt that consists of deformed igneous and metamorphic rocks overprinted by Cenozoic extensional basins. Unlike most foreland fold-thrust belts whose deformation commonly migrates toward its foreland, the fold thrust belt within the Balkan orogen is marginal to the Moesian platform to the north, but was deformed in at least three events related to changes in plate interactions. The earliest event of late Early to early Late Cretaceous deformed strata deposited on the Moesian continental margin and within a continental rifted belt containing deep water flysch of Late Jurassic-Early Cretaceous age, a probable eastward extension of oceanic troughs from the South Carpathians. The shortening was a consequence of S or SW synthetic subduction within Vardar zone along the southern margin of the Balkan orogen. In Late Cretaceous time a back arc or intra-arc rift zone developed along the southern margin of the fold belt terminating shortening. The back/ intra- arc basin closed in Late Cretaceous time deforming the fold-thrust belt for a second time antithetically to N or NE subduction in the Vardar zone. In Paleogene time the southern part of the Balkan orogen became extensional with abundant volcanism due to trench roll back. The final foreland fold-thrust belt deformation was Late Eocene extending into Oligocene time and was a transfer of shortening in response to clockwise rotation within the Carpathians and southward motion of the Moesian platform north of the thrust belt. During this event southern Bulgaria was in an extensional regime, the beginning of the back arc extension that dominated the south- to southwest-vergent Hellenide orogen throughout the Cenozoic.