NEO-TETHYAN AND PALEO-TETHYAN MÉLANGES IN ANATOLIA

Anatolian mélanges can be grouped broadly in two types based on age, lithology and structure. The Neo-Tethyan mélanges consist predominantly of oceanic crustal lithologies of basalt, radiolarian chert, pelagic shale with minor serpentinite and greywacke. They show locally an incipient high-pressure metamorphism with the formation of lawsonite, sodic pyroxene and aragonite. A matrix is hard to define in the Neo-Tethyan “mélanges”; they rather consist of chaotic thrust stacks. The age of the cherts in the Neo-Tethyan mélanges range from Middle Triassic to Cretaceous. With these features the Neo-Tethyan mélanges represent sediment starved subduction-accretion complexes; they were formed during the Cretaceous subduction of a Triassic to Cretaceous oceanic lithosphere.

The Paleo-Tethyan mélanges are made up mainly of greywacke and shale with exotic blocks of Permo-Carboniferous limestone, basalt and Devonian, Carboniferous and Permian radiolarian chert. A clastic matrix is well defined in the Paleo-Tethyan mélanges, which are associated with Late Triassic eclogites and blueschists. They were formed during the Triassic subduction of a Devonian to Triassic Tethyan oceanic crust. The lithological differences between these mélange types are related to the prevalent paleogeography; during the Late Cretaceous subduction, the magmatic arcs and the active margin of Eurasia were below sea-level and there was little influx of clastic material to the trenches, whereas during the Triassic subduction the active margin of Eurasia was uplifted probably through a collision with an oceanic plateau.