Pre-Cenozoic tectono-stratigraphic components of the Western Pontides and their geological evolution

The Western Pontides of northern Turkey are a tectonic mosaic formed as a r esult of progressive welding of continental and oceanic fragments during th e Palaeozoic and Mesozoic. In this region, three approximately east-west tr ending zones can be distinguished: the Pontide Zone representing the Pontid es sensu stricto; the Sakarya Zone which is regarded as the southerly conti nental fragment; and the Armutlu-Ovacik Zone which is viewed as a tectonic mixture of the two zones. The Pontide Zone records development of an ensimatic island are which are e mplaced upon a continental fragment of Laurasian origin prior to the develo pment of the Ordovician sediments. On top of this amalgamated basement, ass ociation thick sediments were deposited during the Palaeozoic and Early Mes ozoic. During the Dogger, Palaeotethyan ophiolites were obducted onto the P ontides. The thick pile of cover sediments and the ophiolite slab were exhu med along a detachment surface while the underlying rocks were elevated to form a metamorphic core complex during the Early Cretaceous. The metamorphi c rocks are exposed along the Ballidag, Sunnice? Almacik and Armutlu mounta in ranges, This east-west trending structural high separated two coeval bas ins, the Ulus Basin and the Boyali Basin: which are located to the north an d south respectively. During the Late Cretaceous, collision occurred betwee n the Sakarya continent and the Pontide Zone. The continental convergence a ffected the region until the late Early Eocene. The present tectonic style of the region was established during this phase. From the Middle Eocene onw ards only; structural rearrangements have occurred. Copyright (C) 1999 John Wiley & Sons, Ltd.