Izmir-Ankara Suture as a Triassic to Cretaceous Plate Boundary-Data From Central Anatolia

摘要

The Izmir-Ankara suture represents part of the boundary between Laurasia and Gondwana along which a wide Tethyan ocean was subducted. In northwest Turkey, it is associated with distinct oceanic subduction-accretion complexes of Late Triassic, Jurassic, and Late Cretaceous ages. The Late Triassic and Jurassic accretion complexes consist predominantly of basalt with lesser amounts of shale, limestone, chert, Permian (274 Ma zircon U-Pb age) metagabbro, and serpentinite, which have undergone greenschist facies metamorphism. Ar-Ar muscovite ages from the phyllites range from 210 Ma down to 145 Ma with a broad southward younging. The Late Cretaceous subduction-accretion complex, the ophiolitic melange, consists of basalt, radiolarian chert, shale, and minor amounts of recrystallized limestone, serpentinite, and greywacke, showing various degrees of blueschist facies metamorphism and penetrative deformation. Ar-Ar phengite ages from two blueschist metabasites are ca. 80 Ma (Campanian). The ophiolitic melange includes large Jurassic peridotite-gabbro bodies with plagiogranites with ca. 180 Ma U-Pb zircon ages. Geochronological and geological data show that Permian to Cretaceous oceanic lithosphere was subducted north under the Pontides from the Late Triassic to the Late Cretaceous. This period was characterized generally by subduction-accretion, except in the Early Cretaceous, when subduction-erosion took place. In the Sakarya segment all the subduction-accretion complexes, as well as the adjacent continental sequences, are unconformably overlain by Lower Eocene red beds. This, along with the stratigraphy of the Sakarya Zone, indicates that the hard collision between the Sakarya Zone and the Anatolide-Tauride Block took place in Paleocene.