Closing the Neotethys Ocean in western Anatolia: Insights from forearc and foreland sedimentary basin records

Across the Tethyan realm, subduction zones are characterized by phases of forearc and backarc extension, and subsequent collisions are protracted and polygenetic, often resulting in significant discrepancies among proxies of collision age. The closure of the northern branch of the Neotethys Ocean along the İzmir-Ankara-Erzincan suture in Anatolia has been variously estimated from the Late Cretaceous to Eocene. It remains unclear whether this age range results from a protracted, multi-phase collision or disparities between proxies and geographic location. Near-continuous Jurassic through Eocene deposition in the forearc-to-foreland Central Sakarya Basin system in western Anatolia makes it an ideal location to integrate pre-collisional extension and multi-stage collision into a holistic reconstruction of subduction through collision. The Central Sakarya Basin system is located north of the Izmir-Ankara-Erzincan suture, where the Gondwanan-derived Anatolide and Tauride terranes to the south collided with the Laurasian-derived Pontide terrane in the north. By integrating new sandstone petrography and detrital zircon U-Pb and Hf isotopes with other geologic proxies, we demonstrate four phases of evolution of subduction and collision. (1) Magmatism began on the Pontides at 110 Ma, potentially the signal of subduction (re-)initiation, and is coincident with extension in the forearc. (2) Forearc obduction began around 94 Ma with initial subduction of lower plate continental lithosphere. Extension migrated to the backarc and opened the Black Sea. (3) The onset of intercontinental collision at 76 Ma is marked by gradual arc shutdown, basement exhumation, and uplift of the suture zone. (4) This first contractional phase is followed by thick-skinned deformation and basin partitioning starting around 54 Ma, coeval with regional syn-collisional magmatism. The 20-Myr protracted collision in western Anatolia could be explained by three non-exclusive mechanisms that produced a change in plate coupling: relict basin closure, progressive underthrusting of thicker lithosphere, and slab breakoff.