LATE PALEOZOIC MARGINAL BASIN AND SUBDUCTION-ACCRETION - THE PALAEOTETHYAN KURE COMPLEX, CENTRAL PONTIDES, NORTHERN TURKEY

The Kure Complex, located in the Central Pontides of northern Turkey, is a c. 20 km thick pile of thrust-imbricated deep-sea sediments, inte rcalated with a dismembered ophiolite. The ophiolitic rocks include se rpentinized harzburgite, massive gabbro (cumulate and isotropic), shee ted dykes and basic volcanic rocks. The extrusive rocks are mainly pil low lavas, sheet flows and lava breccias. Geochemical evidence of immo bile major- and trace-elements and pyroxene chemistry indicate mid-oce an ridge (MOR) and volcanic arc basalt (VAB) compositions, and suggest that the Kure Ophiolite was generated above a subduction zone. Chrome spinel analysis also supports this interpretation. In some thrust she ets the extrusives are depositionally overlain by hemi-pelagic shales, passing up into terrigenous turbidites and shales, which are up to se veral 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, u p to several kilometres thick within the Kure Complex are separated by narrow (up to 10 m wide) zones of intense shearing, layer-parallel ex tension and melange formation. Asymmetrical folds, reverse faults, thr usts and duplex structures throughout the Kure Complex indicate mainly northwards emplacement. The Kure Complex is thought to have opened in the late Palaeozoic, as a marginal basin above a northward-dipping Pa laeotethyan subduction zone, located along the southern margin of Eura sia. The Kure marginal basin later closed, in response to inferred sou thward subduction, leading to development of an accretionary prism, pr ior to late Jurassic time. The Kure Complex is unlikely to represent t he main Palaeotethyan suture, as has been suggested in some earlier te ctonic reconstructions. Regional comparisons with Dobrogea, Crimea and Caucasus suggest the Kure basin opened, then closed, along a south Eu rasia active margin.