Late Palaeozoic-Early Cenozoic tectonic development of the Eastern Pontides (Artvin area), Turkey: stages of closure of Tethys along the southern margin of Eurasia

Abstract

Early Carboniferous-Eocene units exposed in the Arvin area document the development of the southerly, active continental margin of Eurasia. The oldest rocks exposed in the area are Early Carboniferous granites that regionally intrude schists and gneisses. The continental terrane rifted along the entire length of the Pontides (> 1000 km east-west) during the Early-Middle Jurassic. Subsidence of the rift basin in the Artvin area was accompanied by terrigenous debris flows, turbidites and deep-sea radiolarian muds, and was associated with local extrusion of chemically 'enriched' basalts. Swarms of subduction-influenced basic, intermediate, to locally silicic dykes, intruded high-grade metamorphic basement within the rift. A basement horst within the rift was covered by condensed pink ammonite-bearing pelagic facies. Large volumes of subduction-influenced basalts erupted during the later stages of extensional basin development (Mid-Jurassic), associated with volcaniclastic sedimentation. The Artvin Basin is interpreted as a supra-subduction rift associated with incipient arc magmatism. The basin was stratigraphically inverted in response to Late Middle Jurassic 'Neo-Cimmerian' deformation. It was then partially eroded and covered by Upper Jurassic continental, to shallow-marine sediments, together with localized eruption of 'enriched' (non-subduction-influenced) basalts. The margin collapsed during the Late Jurassic-Early Cretaceous, initiating deposition of pelagic carbonates and mixed terrigenous, biogenic and volcaniclastic gravity flows. Subduction during the Late Cretaceous then constructed the east Pontide magmatic arc and a thick volcaniclastic fore-arc apron to the south. Supra-subduction-type ophiolites and accretionary melange formed within Neotethys to the south during the Late Cretaceous and were emplaced regionally northwards onto the leading edge of the Pontide active continental margin during the latest Cretaceous. Continental collision during the Mid-Eocene telescoped the distal part of the active margin which was emplaced northwards onto the east Pontide continental basement. The geological evolution of Artvin area correlates with the Pontides further west and with the southern and northern Transcaucasus to the east. Our favoured tectonic model involves long-lived, episodic, northward subduction of Tethys. Finally, there is no evidence of 'Palaeotethyan' ophiolites in the eastern Pontides region.