EVOLUTION OF EARLY MESOZOIC BACK-ARC BASINS IN THE BLACK SEA - CAUCASUS SEGMENT OF A TETHYAN ACTIVE MARGIN

Abstract

Six new reconstructions illustrate the evolution of back-arc basins in the Black Sea-Caucasus region from the Mid-Triassic to the end of the Mid-Jurassic. The c. 2000 km long Tauric (Küre) basin opened in the Late Permian-Early Triassic as the Pontides-Transcaucasus and Rhodope microcontinents rifted from the Eurasian margin. The oceanic floor of the Tauric basin in the Mid-Triassic was at least 300 km wide. In the east the basin closed near the present-day Caspian Sea and to the west of the West Crimea transform it split into two branches to the south and north of the Moesian platform. The Tauric basin was partly inverted in the Carnian, when several Gondwanian terranes (Iran, South Armenia) collided with the Palaeotethyan subduction zone. Following the initiation of a new subduction zone, the back-arc extension resumed in the Norian-Early Jurassic. Opening of the Izmir-Ankara-Sevan back-arc basin commenced south of the Pontides-Transcaucasus. Simultaneously, rifting began in the Greater Caucasus and continued until the Early Pliensbachian. This was followed by the continental break-up in the Late Pliensbachian-Toarcian. A narrow (100-150 km) strip of oceanic crust had formed by the beginning of the Aalenian. In the Late Aalenian a southward-migrating subduction zone at the southern margin of the Izmir-Ankara-Sevan basin had reached the central part of Neo-Tethys and presumably collided with a mid-oceanic ridge. Subduction was blocked and Africa-Eurasia convergence was compensated by inversion in the Tauric and Greater Caucasus basins. The basins were closed by the end of the Bathonian. © The Geological Society of London 2006.