Subduction, magmatism and metamorphism - case studies from Anatolia
Aral I. Okay
Istanbul Technical University, Eurasia Institute of Earth Sciences, Maslak, 34469 Istanbul
During the Late Paleozoic and Mesozoic the Pontides in northern Turkey generally formed part of the active margin of Laurasia with the Tethyan oceans subducting north under the Pontides. The Pontides had a long history of subduction-accretion, with a documented subduction history extending from Carboniferous to the Late Cretaceous, when the Pontides were separated from the mainland Laurasia with the opening of the Black Sea as a back-arc basin. The subduction was finally terminated in the early Tertiary when the Pontides collided with the Anatolide-Tauride Block. The northward subduction under the Pontides seems to have been semi-continuous with only a lull in the latest Jurassic to earliest Cretaceous (Tithonian – Berriasian).
The main lines of evidence for subduction are magmatic arcs, subduction-accretion complexes and high pressure – low temperature metamorphic rocks. Magmatic arcs of Carboniferous, Jurassic and Late Cretaceous ages are recognized in the Pontides and a major Triassic magmatic arc is most probably present north of the Black Sea under the Tertiary cover of the Scythian Platform.
Upper Triassic subduction-accretion complexes, generally called as the Karakaya complex, are widespread in the Pontides; they are made up of thick sequences of Permo-Triassic metabasites of oceanic island or oceanic plateau origin and strongly deformed Triassic greywackes with exotic blocks of Permian and Carboniferous limestone. The metabasites of the Karakaya Complex includes tectonic slices of eclogite and blueschist dated to the latest Triassic. Jurassic subduction-accretion complexes are increasingly being recognized along the southern margin of the Pontides. They consist mainly of metabasite, phyllite and recrystallized carbonates. Lower Cretaceous (Albian) accretionary complexes, including eclogites and blueschists, crop out widely in the southern parts of the Central Pontides. Upper Cretaceous subduction-accretion complexes consist mainly of oceanic crustal rocks and are commonly termed as the ophiolitic mélange.