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

The Late Cretaceous accretionary complexes along the İzmir-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 Tekelidağ mélange (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 (2σ, Early Jurassic), and those from a non-metamorphic plagiogranite crosscutting the non-metamorphic ophiolitic rocks gave an age value of 168 ± 2 Ma (2σ, 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, 2σ) 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.