U-Pb zircon geochronology of intrusive rocks from an exotic block in the Late Cretaceous - Paleocene Tarakli Flysch (northern Turkey): Constraints on the tectonics of the Intrapontide suture zone

In the Boyali area (northern Anatolia), a thick succession of the Early Maastrichtian - Middle Paleocene Tarakli Flysch crops out. The Tarakh Flysch represents a foredeep sediment deposited during the final stage of collision between the Sakarya and Istanbul-Zonguldak continental margins, that developed as a consequence of the closure of the Intrapontide oceanic basin. The top of the Tarakli Flysch is characterized by a level of slide-block in shaly-matrix lithofacies that can be considered as the result of several fast catastrophic events predating the closure of the basin and its deformation. This level consists of slide-blocks surrounded by monomict pebbly-mudstones and pebbly-sandstones. Among the slide-blocks, the biggest one consists of quartz-monzonites and leucocratic granodiorites of Late Permian age (260.8 +/- 2.2 Ma) dated by zircon LA-ICP-MS method. By comparison with the regional data, the source area of these granitoids can be identified in the Istanbul-Zonguldak terrane. This evidence suggests a new picture for the paleogeographic setting of the ultimate stage of the continental collision between the Istanbul-Zonguldak and the Sakarya continental margins. In this scenario the coarse-grained deposits of the Tarakh Flysch are supplied by an orogenic wedge, consisting of oceanic units topped by the Istanbul-Zonguldak terrane. This orogenic wedge represented the north side of the foredeep, while the southern one was represented by the still undeformed Sakarya continental margin.