Late Cretaceous-Early Eocene tectonic development of the Tethyan suture zone in the Erzincan area, Eastern Pontides, Turkey

Six individual tectonostratigraphic units are identified within the ?Izmir–Ankara–Erzincan Suture Zone in the critical Erzincan area of the Eastern Pontides. The Ayikayasi Formation of Campanian–Maastrichtian age is composed of bedded pelagic limestones intercalated with polymict, massive conglomerates. The Ayikayasi Formation conformably overlies the Tauride passive margin sequence in the Munzur Mountains to the south and is interpreted as an underfilled foredeep basin. The Refahiye Complex, of possible Late Cretaceous age, is a partial ophiolite composed of ~ 75 % (by volume) serpentinized peridotite (mainly harzburgite), ~ 20 % diabase and minor amounts of gabbro and plagiogranite. The complex is interpreted as oceanic lithosphere that formed by spreading above a subduction zone. Unusual screens of metamorphic rocks (e.g. marble and schist) locally occur between sheeted diabase dykes. The Upper Cretaceous Karayaprak M´elange exhibits two lithological associations: (1) the basalt + radiolarite + serpentinite association, including depleted arc-type basalts; (2) the massive neritic limestone + lava + volcaniclastic association that includes fractionated, intermediate-composition lavas, and is interpreted as accreted Neotethyan seamount(s). The several-kilometre-thick Karada?g Formation, of Campanian–Maastrichtian age, is composed of greenschist-facies volcanogenic rocks of mainly basaltic to andesitic composition, and is interpreted as an emplaced Upper Cretaceous volcanic arc. The Campanian–Early Eocene S¨utpinar Formation (~ 1500 m thick) is a coarsening-upward succession of turbiditic calcarenite, sandstone, laminated mudrock, volcaniclastic sedimentary rocks that includes rare andesitic lava, and is interpreted as a regressive forearc basin. The Late Paleocene–Eocene Sipik¨or Formation is a laterally varied succession of shallow-marine carbonate and siliciclastic lithofacies that overlies deformed Upper Cretaceous units with an angular unconformity. Structural study indicates that the assembled accretionary prism, suprasubduction zone-type oceanic lithosphere and volcanic arc units were emplaced northwards onto the Eurasian margin and also southwards onto the Tauride (Gondwana-related) margin during Campanian– Maastrichtian time. Further, mainly southward thrusting took place during the Eocene in this area, related to final closure of Tethys. Our preferred tectonic model involves northward subduction, suprasubduction zone ophiolite genesis and arc magmatism near the northerly, Eurasian margin of the Mesozoic Tethys.