Early-Middle Jurassic metamorphic and non-metamorphic supra-subduction zone ophiolite fragments in a Late Cretaceous ophiolitic melange (northern Turkey): implications for long-lived and supra-subduction zone ophiolite formation

The Late Cretaceous accretionary complexes along the Izmir-Ankara-Erzincan (IAE) Neo-Tethyan suture zone in northern Turkey record the subduction-accretion processes of the oceanic lithosphere ranging in age from the Late Triassic to the Late Cretaceous. These accretionary complexes contain fragments of Early and Middle Jurassic metamorphic and non-metamorphic ophiolites. Here, we report new geochemical and geochronological data from the metamorphic and non-metamorphic ophiolitic rocks, which are observed in the Tekelidag melange (northern Sivas) of the IAE suture zone. Geochemical characteristics of these rocks point to formation in a subduction-related tectonic setting. Igneous zircons from meta-plagiogranite injected into the meta-ophiolitic rocks yielded zircon U-Pb age of 188 +/- 4 Ma (2 sigma, Early Jurassic), and those from a non-metamorphic plagiogranite crosscutting the non-metamorphic ophiolitic rocks gave an age value of 168 +/- 2 Ma (2 sigma, Middle Jurassic). The igneous crystallization age of the non-metamorphic plagiogranite is identical with the metamorphic age of meta-ophiolitic rocks, which has been dated as Middle Jurassic (166.7 +/- 2 Ma, 2 sigma) by the 40Ar/39Ar method. These age data indicate that (i) the supra-subduction zone ophiolite formation lasted about 20 Ma, (ii) the supra-subduction zone ophiolite and the meta-ophiolitic rocks formed simultaneously in the Middle Jurassic, and (iii) the meta-ophiolitic rocks are remnants of the metamorphosed equivalents of the Early Jurassic supra-subduction zone oceanic crust. The supra-subduction zone ophiolite formation probably occurred over an extended period of time in the Jurassic Neo-Tethys.