PONTIDES - AN ACCRETIONARY OROGEN IN THE CIRCUM-MEDITERRANEAN REGION

The Alps are regarded as a typical collisional orogen with little pre-collisional deformation and metamorphism, which is compatible with the lack of Mesozoic magmatic arcs in the Alps. The Alps extend eastwards from the Balkans into Anatolia, which forms a complete orogenic belt between the Black Sea and the Mediterranean. The Anatolian orogenic belt is divided into the Pontides in the north, which was an active plate margin during most of the Late Paleozoic and Mesozoic, and the Anatolide-Tauride Block in the south, which was a passive margin. Before the Late Cretaceous opening of the Black Sea as a back-arc basin, the Pontides constituted the south-facing active margin of the Eurasia. The collision between the Pontides and the Anatolide-Tauride Block occurred in the early Tertiary, when the Anatolia was uplifted above sea level. Prior to the early Tertiary collision, the Pontides faced a wide Tethyan ocean in the south. Evidence for northward subduction under the Pontides, in terms of magmatic arcs, eclogites/blueschists, and accretionary complexes, exist for the Permo-Carboniferous, Triassic, Middle Jurassic and Cretaceous interspersed with quiet periods, especially during the Late Jurassic and earliest Cretaceous (Okay & Nikishin 2015). A result of subduction was the southward extension of the Pontide/Eurasia margin by addition of subduction-accretion complexes. This was especially important during the Late Triassic and Cretaceous. Crustal growth also occurred by arc magmatism, which was extensive during the Middle Jurassic and Late Cretaceous. Additionally a major Triassic magmatic arc, located now north of the Black Sea, is known indirectly through Triassic zircons, which form the dominant zircon population in the Late Triassic trench turbidites (Ustaömer et al., 2015).

Okay, A.I. & Nikishin, A.M., 2015, Tectonic evolution of the southern margin of Laurasia in the Black Sea region. International Geology Review, 57, 1051-1076.

Ustaömer, P.A., Ustaömer, T., Robertson, A.H.F., Gerdes, A., 2015, Implications of U–Pb and Lu–Hf isotopic analysis of detrital zircons for the depositional age, provenance and tectonic setting of the Permian–Triassic Palaeotethyan Karakaya Complex, NW Turkey. Int J Earth Sci DOI 10.1007/s00531-015-1225-8.