REMNANT OF A JURASSIC BACKARC OCEAN BASIN (KÜRE OPHIOLITE) IN THE CENTRAL PONTIDE BELT, TURKEY

We report here on the Jurassic Küre ophiolite in the Central Pontide belt of northern Turkey. This ophiolite is a remnant of a backarc ocean that opened during the pre-Lias and closed in the early Dogger as part of the Tethyan realm. It is tectonically imbricated with the mid-Late Paleozoic Devrekani metamorphic units and the Triassic Cangaldag Complex. The Küre Ophiolite consists of harzburgite, lherzolite and dunite, layered to isotropic gabbros, sheeted dolerite and plagiogranite dikes, and pillow-massive lava flows, volcanic breccias and hyaloclastites. Basaltic lavas are the hostrock of massive sulphide deposits. The upper mantle rocks in Küre include both depleted mantle and abyssal peridotites. The SiO₂ contents (46.97-68.84 wt.%) and alkali (Na₂O+K₂O) values (3-6 wt%) of the volcanic units show basalt, basaltic andesite, trachybasalt, basaltic trachyandesite and dacite compositions with tholeiitic and calc-alkaline affinities. Their Ti/V ratios (12.08-32.12) indicate IAT- and MORB-like compositions. Plagiogranite dikes in the ophiolite have Si₂O (68-69 wt%), K₂O (0.36 wt%), Nb (1-2 ppm), Th (0.6 ppm), displaying VAG characteristics. Ophiolitic pillow lavas are overlain by the Liassic pelitic rocks (Akgöl Formation) that grade upwards into black shales. Elsewhere, the ophiolite is unconformably overlain by an Upper Jurassic-Lower Cretaceous neritic limestone starting with a basal conglomerate. The Dogger granitoids, composed of granite, granodiorite, diorite and syeno-diorite with metaluminous and peraluminous characteristics, represent a continental arc development in the Central Pontides as a result of northward subduction of the Küre marginal basin.