The Arkot Dağ Mélange in Araç area, central Turkey: Evidence of its origin within the geodynamic evolution of the Intra-Pontide suture zone.

In northern Turkey, the IntraPontide suture zone is represented by an east-west trending belt of deformed and/or metamorphic units located at the boundary between the Istanbul-Zonguldak Terrane to the north and the Sakarya Terrane to the south. These units can be regarded as issued from the IntraPontide domain, whose geodynamic history is still matter of debate. Along the Akpinar-Araç-Bayramoren geotraverse, located in central Turkey, an ophiolite-bearing mélange known as Arkot Dağ Mélange, is well exposed along the IntraPontide suture zone. The Arkot Dağ Mélange, that plays a key role in the interpretation of the geodynamic history of the IntraPontide domain, can be described as a Late Santonian chaotic sedimentary deposits consisting of an up to 1000 m thick succession of slide-blocks, with different size and lithology, enclosed in a sedimentary matrix consisting of shales, coarse-grained arenites, pebbly-mudstones and pebbly-sandstones. The slide-blocks, from few meters to some hectometers in size, are represented by metamorphic rocks (mainly micaschists and gneisses), by ophiolites (peridotites, gabbros, IAT and BABB basalts and cherts) and by sedimentary rocks (cherts, neritic and pelagic limestones, marly-limestones and ophiolite-bearing turbidites). The youngest age among the slide-blocks has been provided by the ophiolite-bearing turbidites where a late Coniacian nannofossil assemblage has been found. The cherts have provided a wide range of ages from Middle Trias to Late Cretaceous, whereas the fossils found in the limestones indicate Late Jurassic to Early Cretaceous ages. The matrix of the Arkot Dağ Mélange, even if unaffected by metamorphism, shows deformations represented by multiple, m-thick cataclastic shear zones, recognized at the boundaries of the mélange slices or inside them. According to its features, the source area of the Arkot Dağ Mélange was probably represented by a continental and oceanic thrust sheets emplaced in the Late Cretaceous onto a continental margin. The data collected from the different slide-blocks suggest that the IntraPontide domain was characterized by an oceanic basin opened at least in the Early Jurassic. The opening of the IntraPontide oceanic basin was followed by the development of a subduction zone with a consequent opening of suprasubduction oceanic basin in the Middle Jurassic – Early Cretaceous time span. The convergence in this suprasubduction oceanic basin started at the Early/Late Cretaceous boundary by an obduction process, whereas its final closure can be regarded as Late Paleocene in age.