Late Palaeozoic marginal basin and subduction-accretion: the Palaeotethyan Küre Complex, Central Pontides, northern Turkey

The Küre Complex, located in the Central Pontides of northern Turkey, is a c . 20 km thick pile of thrust-imbricated deep-sea sediments, intercalated with a dismembered ophiolite. The ophiolitic rocks include serpentinized harzburgite, massive gabbro (cumulate and isotropic), sheeted dykes and basic volcanic rocks. The extrusive rocks are mainly pillow lavas, sheet flows and lava breccias. Geochemical evidence of immobile major- and trace-elements and pyroxene chemistry indicate mid-ocean ridge (MOR) and volcanic arc basalt (VAB) compositions, and suggest that the Küre Ophiolite was generated above a subduction zone. Chrome spine1 analysis also supports this interpretation. In some thrust sheets the extrusives are depositionally overlain by hemi-pelagic shales, passing up into terrigenous turbidites and shales, which are up to several hundred metres thick in intact successions. Cyprus-type massive sulphides, interpreted as precipitates from black smokers, are located along the lava-sediment contact. Individual, intact sediment units, up to several kilometres thick within the Küre Complex are separated by narrow (up to 10 m wide) zones of intense shearing, layer-parallel extension and melange formation. Asymmetrical folds, reverse faults, thrusts and duplex structures throughout the Küre Complex indicate mainly northwards emplacement. The Küre Complex is thought to have opened in the late Palaeozoic, as a marginal basin above a northward-dipping Palaeotethyan subduction zone, located along the southern margin of Eurasia. The Küre marginal basin later closed, in response to inferred southward subduction, leading to development of an accretionary prism, prior to late Jurassic time. The Küre Complex is unlikely to represent the main Palaeotethyan suture, as has been suggested in some earlier tectonic reconstructions. Regional comparisons with Dobrogea, Crimea and Caucasus suggest the Küre basin opened, then closed, along a south Eurasia active margin.