Paleostress analysis of Cenozoic faulting in the Kraishte area, SW Bulgaria

Abstract Paleostress calculations from fault planes in Paleogene sediments and in the underlying basement were used to determine the orientation and the chronology of the principal stresses during the Cenozoic tectonic evolution of the Kraishte area (southwest Bulgaria). The results show that middle Eocene–early Oligocene WSW–ENE extension led to the formation of grabens and half grabens filled with thick continental to marine deposits in the hanging wall of extensional detachments. The Paleogene sediments and their basement were then intruded by subvolcanic bodies and dykes during SW–NE extension between 32 and 29 Ma. These WSW–ENE and SW–NE extensional stages are related to the general rollback of the Hellenic slab. From the late Oligocene to the earliest Miocene, SSE–NNW transtension generated coal-bearing sedimentary basins. The anticlockwise rotation of the main tensile axis by almost 50° with respect to the previous tectonic stage was probably related to a switch from the Aegean back-arc extension to crustal stretching and extrusion of continental fragments around the Moesian platform. Since the middle Miocene extension in the Kraishte area, accommodated by faults with relatively small displacement, led to the formation of restricted basins filled with alluvial to lacustrine deposits.