Mesozoic–Cenozoic Structure of the Black Sea–Caucasus–Caspian Region and Its Relationships with the Upper Mantle Structure

Abstract

Abstract—Mesozoic‒Cenozoic tectonic zoning and its evolution are characterized by analysis of geological data on the Black Sea–Caucasus–Caspian region. The following tectonic zones were located in succession to the north of the Mesotethys Ocean in the Early Jurassic: the mobile zone on the Hercynian basement; the Moesian–Black Sea–Trans-Caucasus minor plate with the Precambrian–Baikalian basement, which experienced the Hercynian tectonic and magmatic reworking in the Lesser Caucasus; the relatively deep-water Crimean–Caucasus–South Caspian Trough on the continental crust that thinned in the process of its extension; and the southern margin of the Scythian Plate with a thin sedimentary cover. In the Caucasus, the southern and northern slopes of the deep-water axial trough have been identified, where thick shelf deposits accumulated. Subduction began in the northern margin of the Mesotethys in the Bajocian and island-arc volcanism occurred in the Somkheti–Karabakh zone and Eastern Pontides, the Trans-Caucasus part of the Moesian–Black Sea–Trans-Caucasus Plate, and the southern slope of the Crimean–Caucasus–South Caspian Trough. The volcanism in the Somkheti‒Karabakh zone and the Eastern Pontides lasted into the Cretaceous. The area of island-arc volcanism was inherited by the Eocene collisional volcanic belt. The Crimean part of the Crimean–Caucasus–South Caspian Trough and its northern slope in the Caucasus underwent Cimmerian deformation and shelf facies accumulated there after deformation up to the Miocene, while relatively deep-water sedimentation occurred in the Caucasus–South Caspian part of the Crimean–Caucasus–South Caspian Trough. The Western and Eastern Black Sea basins of extension originated in the Cretaceous on the continental crust of the Moesian–Black Sea–Trans-Caucasus Plate, which thinned in the basins as they were filled by Late Cretaceous, Paleogene, and Miocene marine deposits. In the Pliocene–Quaternary, total undifferentiated subsidence and sedimentation occurred in the Black Sea, and subsidence of the South Caspian, Azov‒Kuban, and Terek‒Derbent basins accelerated. Several phases of Middle and Late Miocene fault–fold deformation formed local uplifts in the mountainous parts of the region. The total uplift of mountain systems occurred in the Pliocene–Quaternary. The formed crustal structures and the velocity inhomogeneities in the upper mantle were compared, which showed that many inhomogeneities were obliterated by sublithosphere flows that spread out of the Ethiopian–Afar superplume. In mantle volumes, where the flow intensity weakened, relics of subducted slabs remained. They are slabs of the Neotethys in the Zagros and the Mesothethys in the Lower Kura Basin, and slabs of the Scythian Plate lithosphere underthrust under the Central Caucasus and more weakly under Steppe Crimea during the Hercynian subduction.