Distribution and characteristics of the north-west Turkish blueschists

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Abstract
Summary: North-west Turkey encompasses two major tectonic units, the Pontides and the Anatolides, separated by the İzmir-Erzincan suture. The Anatolides, the metamorphosed northern extension of the Taurides, consist of several zones. The more southerly Afyon Zone is an Early Palaeozoic to Maastrichtian Tauride shelf-type sequence which rests on gneisses of the Menderes Massif. The Afyon Zone underwent greenschist facies metamorphism, gradually increasing in grade with depth, and overthrust by HP/LT metamorphic rocks and peridotites. A HP/LT metamorphic belt several hundred kilometres long constitutes the second Anatolide zone. There are two tectonic units in the blueschist sequence. A lower more recrystallised blueschist unit consists of a thick basal marble series overlain by meta-cherts, metabasites and meta-shales. An upper unit, with a wider distribution, shows only incipient HP/LT metamorphism, and consists of shales, radiolarian cherts, basic volcanic rocks, pelagic limestones and greywackes. The HP/LT rocks are tectonically overlain by a peridotite nappe, without HP/LT metamorphism. Steeply dipping major faults separate blueschists from the Inner Pontide sequence, which consists of a Permian-Triassic metamorphic basement overlain by carbonates and Upper Cretaceous flysch. Especially in the Ankara region, Upper Cretaceous flysch contains abundant ophiolitic olistoliths. Post-orogenic Palaeocene sediments are transgressive over the HP/LT metamorphic belt and the peridotite nappe. The blueschist sequence may have been the north-facing Anatolide/Tauride platform margin, subducted during the Late Cretaceous. Very fast uplift in the collision zone, aided by buoyancy of subducted continental crust, generated olistostromes in the Pontides and emplaced peridotite nappes over the Anatolide/Tauride platform.

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