The Late Paleogene Çankırı Basin of Türkiye: The geologic record of lithospheric foundering beneath the Central Anatolian Plateau

We hypothesized that the Çankırı Basin of Türkiye records lithospheric foundering beneath the Central Anatolian Plateau in Late Paleogene time. Geologic mapping and stratigraphic sections supplemented by detrital zircon U-Pb and Hf isotopic analyses demonstrate that a 7500 km2 saline lake developed within a 125 × 75 km box-fold along the İzmir-Ankara-Erzincan Suture Zone at ca. 37.5 Ma. Lacustrine environments mark the transition from polymodal to bimodal detrital zircon age spectra during the onset of a trend toward crustal εHf(t) values. Such geologic and geochemical changes are consistent with subsidence above thickening lithosphere. At ca. 32.5 Ma deposition transitioned to volcanogenic-alluvial, fluvial, and lacustrine environments along the northern margin of the Çankırı Basin. Detrital zircon from such deposits return to polymodal age spectra and record a 15-unit εHf(t) mixing array. Such changes are consistent with unroofing and multi-source melting during isostatic rebound above foundering lithosphere. Today, the Çankırı Basin resides within an elliptical ∼750-m-high topographic depression that is bisected by the north-northeast flowing Kızılırmak River and surrounded by rugged landscapes reaching elevations of ∼1500 m. Such radial physiographic symmetry exhibits a wavelength of ∼250 km (50,000 km2) and further defines the Sarıcakaya-Kızılırmak and Yeşilırmak-Kızılırmak river drainage divides. Indeed, both drainage divides are underlain by a slow shear wave velocity geophysical anomaly. Thus, the geomorphological expression of drip tectonics endures today. Our results, therefore, demonstrate that upper plate lithospheric removal along the İzmir-Ankara-Erzincan Suture Zone began in Late Paleogene time and is tied to the ongoing development of the Central Anatolia Plateau.