Geochemical evidence used to test alternative plate tectonic models for pre‐Upper Jurassic (Palaeotethyan) units in the Central Pontides, N Turkey

East–west trending, inferred Palaeotethyan subduction–accretion complexes form much of the pre‐Upper Jurassic basement of the Central Pontides. A number of specific tectonic units are present that include variably metamorphosed basic igneous rocks, as dismembered ophiolites, coherent stratigraphical successions, ordered thrust sheets, and blocks in mélange. About 200 samples from a c . 200 km long N–S traverse were analysed by a high‐precision X‐ray fluorescence technique, supplemented by electron microprobe analysis. The basic igneous rocks have not experienced significant chemical mobility after formation and are thus useful for discrimination of tectonic settings of formation using well known binary and ternary plots and mid‐ocean ridge basalt (MORB)‐normalized ‘spidergrams’. From N to S the main results are that basalts of the Küre Complex were erupted in a subduction‐influenced tectonic setting, favouring interpretation as a dismembered ophiolite formed in a marginal basin along the S Eurasian margin. Thick, mainly volcanic, successions of the Çangaldağ Complex show a subduction‐influenced calc‐alkaline composition, above a basement varying from MORB/island arc tholeiite type to high‐Mg (boninitic) type, with an inferred origin as an oceanic arc above forearc basement. Meta‐basites from the adjacent Bayam Mélange indicate a supra‐subduction zone origin, possibly as a dismembered forearc ophiolite (possibly related to the Çangaldağ). A large overriding thrust sheet of mainly ultramafic rocks, the Elekdağ, is interpreted as a supra‐subduction zone ophiolite, based on depleted chrome spinel composition (analysed by microprobe). Eclogitic blocks in structurally underlying mélange are of mid‐ocean ridge (MOR) type. Further south, a northward‐dipping, inferred subduction–accretion complex, the Domuzdağ–Saraycıkdağ Complex, includes MOR‐type meta‐basites in the north, and more ‘enriched’ compositions in the south, of within‐plate origin. Lastly, the geochemistry of meta‐basites in the south, within the Kargı Complex, suggests a plume‐MOR to within‐plate type eruptive setting, without continental crustal influence. The geochemical data mainly support a northward rather than southward subduction model for the Palaeotethyan assembly of the Central Pontides, particularly since the Küre ophiolitic basalts in the north exhibit a subduction‐influenced chemical signature, in contrast to all the units in the south which lack any identifiable subduction component. Comparisons with published geochemical data from the Karakaya Complex in the SW Pontides reveal similar units, interpreted as accreted MORB lithosphere and oceanic seamounts, but emphasize that the Çangaldağ arc is presently the only known Palaeotethyan subduction arc‐related unit in Turkey. Copyright © 1999 John Wiley & Sons, Ltd.