A sedimentary basin record of multi-phase continental collision in western Anatolia

Determining the timing of intercontinental collisions can be a significant challenge in many orogens. Sedimentary, metamorphic, structural, magmatic and paleomagnetic estimates of collision can differ by 15-40 Myr. The timing of intercontinental collision along the >1,700-km long Izmir-Ankara suture zone (IAS) in Anatolia is no different: estimates span 20 Myr, from Maastrichtian to Ypresian. The collision age is debated between and within records of magmatism, deformation and exhumation, and metamorphism, and across geographical areas. To explain this range, various diachronous collision scenarios for the IAS are proposed, including a pre-collisional non-linear continental margin, an east-to-west diachronous accretion of terranes, and an initial soft collision followed by a final hard collision. It remains unclear whether IAS closure is truly multi-phased or an artifact of comparing various records.

We investigate IAS evolution in western Anatolia by focusing on the evolution of one sedimentary basin, the Central Sakarya Basin. New geochronologic and sedimentary provenance proxy results, paired with previous stratigraphic work, reveal multiple phases of IAS evolution: Albian onset of an Andean-type margin, Campanian basement exhumation, a Paleocene magmatic lull, and earliest Eocene renewed magmatism and coeval basement involved shortening. Sedimentary provenance records therefore affirm multi-phased collision models for the IAS. We suggest that the ~20 Myr delay between initial intercontinental collision and the onset of significant upper plate deformation is related to either relict basin closure, or the switch from subducting thinned, passive margin continental lithosphere to full-thickness continental lithosphere.