JURASSIC OPHIOLITE FORMATION AND EMPLACEMENT AS A BACKSTOP TO A SUBDUCTION-ACCRETION COMPLEX IN THE NORTHEAST TURKEY AND POSSIBLE RELATION TO BALKAN OPHIOLITES

The eastern Mediterranean region within the Tethyan realm shows a high concentration of ophiolites with contrasting diverse times of formation and emplacement along the belt: In the Balkans, the ophiolites formed during the early to medial Jurassic, and were emplaced during late Jurassic time, whereas the known ophiolites in Turkey, Cyprus and Syria have late Cretaceous formation and emplacement ages. Here we report a previously unknown large ophiolite body of early Jurassic age from NE Turkey, the Refahiye ophiolite, located close to the suture zone between the Eastern Pontides and the Menderes-Taurus block. The ophiolite body within the studied section is made up of mantle peridotite (clinopyroxene-bearing harzburgite and minor dunite) crosscut by up to 20 cm thick veins of clinopyroxenite and later dikes/pods/stocks of gabbro ranging in size from 2 m to several hundreds of meters. The gabbro is represented by two distinct types: (i) cumulate gabbro, and (ii) non-cumulate gabbro with locally well-developed igneous foliation. Within the non-cumulate gabbro or enclosing peridotite, there are up to 5 m and 50 cm-thick veins of trondjemite and pegmatitic gabbro, respectively. Formation in a suprasubduction-zone setting is inferred from (i) wide-ranging pyroxene and spinel compositions in the peridotites as documented in most suprasubduction-zone ophiolites, and (ii) arc tholeiitic signature of the intrusive non-cumulate gabbros. LA-ICP-MS dating on zircons from two trondjemite samples yielded weighted mean ages of 182 ± 3 Ma and 175 ± 4 Ma (2σ), respectively, suggesting formation during early Jurassic time. Thus, the Refahiye ophiolite represents the first example of a non-mélanged, true Jurassic ophiolite in Turkey, thus filling the long-sought missing link between the Jurassic ophiolites in the Balkans and those in the Lesser Caucasus. Field relationships, e.g. (i) intimate association with nearly coeval metamorphosed accretionary complexes, (ii) absence of unambiguous relationship to the southern Atlantic-type continental margin, and (iii) absence of any stratigraphic indications for the ophiolite obduction in the southern Atlantic-type continental margin during the Jurassic time point to emplacement of a trapped forearc ophiolite above its own subduction-accretion complex as a backstop.