The problems of the post-Cenomanian tectonic evolution of the central parts of the Sredna Gora Zone. The wrench tectonics - how real is real?

The Sredna Gora Zone holds a unique place in the tectonic subdivisions of the Balkanide orogen and its evolution is still a subject of debate. In the last twenty years, the idea of strike-slip-related evolution of the zone has been invoked. However, for the moment, the number of thorough studies where such a scenario is envisaged is limited, and substantial evidence based on detailed fieldwork is still missing. In this article, we discuss some of the major problems of the suggested wrench tectonic concept in the evolution of the central part of the Sredna Gora Zone. These are the character of some major shear zones in the area, to which strike-slip movements are attributed, and the transtension-transpression evolution scenario for the Chelopech and Panagyurishte basins. Despite refuting completely their wrench tectonic-related evolution, we confirm the presence of strike-slip and oblique slip structures cutting the sediments, whereas the time of their activity and role in the deformation of the basin fill are yet to be revealed. Finally, we present a model based on natural examples and analogue modeling, in which the long-lived dextral Maritsa shear zone represents a zone of localized strain partitioning, separating the opposite vergent thrust belts of the Rhodope to the south and the Sredna Gora and Balkan fold-thrust belt to the north, during oblique or possibly orthogonal convergence.