Present-day microplate kinematics in the Black Sea-South Caspian region

Due to the collision of Arabia and Eurasia, the width of the Alpian folded belt in the Caucasian segment (500-600 km) is significantly smaller than in the regions east and west of it (800-1000 km). In the Transcaucasian region, the axis of the maximum compression coincides with a triangular block limited by the Garni-Alavar and Akhurian strike-slip faults [35]. This axis extends across the region of the maximum convergence between the Adzharia-Trialet zone and the Greater Caucasus and then deviates to the east running over the Dagestan wedge. The crustal blocks are forced to move out from the axis to the east and to the west, that is, toward the Black Sea and the South Caspian depressions, respectively. One of these kinds of blocks-the East Black Sea microplate-is bounded by a compressional boundary in the north (the South Crimean overthrust front), a transpressional boundary in the northeast (the front of the Greater Caucasus overthrusts), and strike-slip dislocations in the southeast, south, and west (the Northeast Anatolian, North Anatolian, and West Crimean fracture zones, respectively). Imbricated overthrusts in the Oligocene-Quaternary sediments of the Sorokin and Tuapse foredeeps accompany the compressional and transpressional boundaries. The overthrusts abruptly terminate at the West Crimean fracture zone (sinistral shear). West of it, the northern and northwestern passive margins of the Black Sea are not subjected to present-day compressional deformations. According to the interpretation suggested, the East Black Sea microplate is forced to move in the northwestern direction and rotates anticlockwise. The boundaries of the East Black Sea microplate are marked by belts of high seismicity, while the seismic activity in the intraplate area is weak or absent. The expulsion of the blocks toward the South Caspian Basin both from the side of the Caucasus and from Kopet Dagh is approved by the structural data [5] and by the focal mechanism solutions of the earthquakes. The compression of the South Caspian basin in the latitudinal direction probably results in the subduction of the South Caspian lithosphere in the zone of the Apsheron threshold (or, at least, provides it) and in the southward displacement of the Elburz arc.