An olistostrome–mélange belt formed along a suture: Bornova Flysch zone, western Turkey

• Published in: Tectonophysics 2012-09, Vol.568-569, p.282-295
• Main Authors: Okay, Aral I., İşintek, İsmail, Altıner, Demir, Özkan-Altıner, Sevinç, Okay, Nilgün
• Format: Article
• Language: English
• Subjects: Bornova Flysch Zone; Faults; Limestone; Massifs; Mesozoic; Mélange; Northwest; Oceans; Olistostrome; Peninsulas; Radiolaria; Stratigraphy; Sutures; Tearing; Turkey
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2012.01.007

The Bornova Flysch Zone (BFZ) in western Turkey is a regional olistostrome–mélange belt located between the İzmir–Ankara Tethyan suture in northwest and the Menderes Massif in the southeast. The BFZ consists mostly of tectonized gravity mass flows. The blocks are Mesozoic limestone and ophiolite, which are enclosed in Cretaceous–Paleocene sheared sandstone and shale. The limestone blocks are of two types. The first type consists of Late Triassic to Cretaceous shallow marine carbonates. The second type has an Upper Triassic shallow marine section overlain by Jurassic to Cretaceous pelagic limestones. A semi-intact part of the platform occurs in the Karaburun peninsula and on the island of Chios. The ophiolitic blocks in the BFZ include ultramafic rock, gabbro, basalt and radiolarian chert of Middle Triassic to Cretaceous in age. The formation of the BFZ overlaps with the Cretaceous subduction and HP/LT metamorphism of the northern passive continental margin of the Anatolide–Tauride Block. This subduction zone was bounded in the west by a strike–slip tear fault. The BFZ formed in a narrow basin between this tear fault and the Tethyan ocean. The mass flows came from the southeast from the overriding ophiolite and accretionary complex, and from the northwest from the uplifted segments of the platform margin. This model provides an explanation as why the BFZ is unmetamorphosed, whereas the equivalent strata in the Menderes Massif were metamorphosed at depths of over 20km. It also explains the prominence of gravity flows and the southward younging in the BFZ, and for the apparently anomalous observation that, although the Tethyan ocean lay to the northwest, the ophiolitic blocks are more common on the southeastern part of the BFZ. Regions away from the tear fault, such as the Karaburun peninsula, were least affected by subsidence and deformation during the Cretaceous and Paleocene. ► A regional mélange–olistostrome belt in western Turkey located between the Izmir-Ankara suture and the Eocene metamorphic rocks of the Menderes Massif. ► Blocks consist of Mesozoic limestone and ophiolite. ► Limestone blocks are platform and passive margin type and Triassic to Cretaceous in age. ► The formation of the mélange belt is contemporeneous with Cretaceous–Paleocene HP/LT metamorphism in the adjoining zones. ► The mélange belt formed northwest of a major tear fault that guided the continental subduction of the Anatolide–Tauride Platform.