THE IZMIR-ANKARA-ERZINCAN SUTURE ZONE AS A PACIFIC-TYPE SUBDUCTION-ACCRETION COMPLEX IN THE TETHYAN REALM

We present new structural field observations and geochemical, biostratigraphic and geochronological data from the Izmir-Ankara-Erzincan Suture Zone (IAESZ) in northern Turkey, and introduce a regional tectonic model for its geological evolution as one of the major subduction-accretion complexes in the Tethyan realm of the eastern Mediterranean region. The IAESZ runs across the entire length of northern Anatolia and connects with the Vardar suture zone in the Hellenides to the west and the Sevan-Akera suture zone in the Lesser Caucasus to the east. It separates the Sakarya microcontinent of the Rhodope-Pontide tectonic belt in the north from the Tauride ribbon continent and the Central Anatolian Crystalline Complex (CACC) to the south. Locally well-preserved ophiolite sequences along the IAESZ include depleted harzburgite, ultramafic cumulates, layered to isotropic gabbros, doleritic to plagiogranitic dikes and lava flows, and occur in km-size blocks within a sheared serpentinite or shaly matrix as part of ophiolitic mélanges (i.e. the Ankara mélange). Both these ophiolitic blocks and the matrix rocks commonly display structural fabrics indicating south-directed shearing. Ophiolitic units range in age from Mississippian (Refahiye ophiolite) to Plienbsbachian-Toarcian (Edige-Eldivanli) and Cenomanian (Çorum), suggesting that fragments of oceanic lithosphere with the late Paleozoic, early Jurassic and early Cretaceous ages were integrated as tectonic sheets into the IAESZ during its evolution as a south-facing and southward growing accretionary prism complex. These ophiolitic fragments have MORB and IAT (island arc tholeiite) geochemical affinities, which indicate their origin as mid-ocean ridge and SSZ-generated oceanic lithosphere. Large blocks (locally >10-km-long) of tholeiitic-picritic lava flows intercalated with pelagic limestone also occur within the IAES as fragments of a large oceanic plateau (LIP), which was accreted into the subduction-accretion system in the late Cretaceous. Late Cretaceous volcanic and volcaniclastic rocks with basaltic-, basaltic-andesitic, andesitic and trachyandesitic compositions overlie the mélange units, and represent calc-alkaline to shoshonitic, island arc products. Campanian-Maastrichtian to Paleocene epiclastic and flysch-type sandstone-shale, marl-reefal limestone sequences locally overlie the mélange and island arc volcanic units, and represent forearc sediments that were deposited in local basins developed directly on the accretionary prism complex. The IAESZ, Sakarya, Tauride and CACC units are all overlain by post-collisional Ypresian-Lutetian volcanic and volcaniclastic rocks, constraining the timing of the final suturing event along the IAESZ as the latest Paleocene-early Eocene. Much of the tectonic evolution of the IAESZ involved subduction-accretion processes in intra-oceanic conditions (far from an adjacent continental margin) that are reminiscent of the subduction-accretion systems in the SW Pacific.