Ophiolite emplacement by strike-slip tectonics between the Pontide Zone and the Sakarya Zone in northwestern Anatolia, Turkey

Northwestern Anatolia contains three main tectonic units: (a) the Pontide Z one in the north which consists mainly of the Istanbul-Zonguldak Unit in th e west and the Balhdag-Kure Unit in the east; (b) the Sakarya Zone (or Cont inent) in the south, which is juxtaposed against the Pontide Zone due to th e closure of Paleo-Tethys prior to Late Jurassic time; and. (c) the Armutlu -Ovacik Zone which appears to represent a tectonic mixture of both zones. T hese three major tectonic zones are presently bounded by the two branches o f the North Anatolian Transform Fault. The two tectonic contacts follow old er tectonic lineaments (the Western Pontide Fault) which formed during the development of the Armutlu-Ovacik Zone. Since the earliest Cretaceous, an o verall extensional regime dominated the region. A transpressional tectonic regime of Coniacian/Santonian to Campanian age caused the welding of the Is tanbul-Zonguldak Unit to the Sakarya Zone by an oblique collision. In the L ate Campanian, a transtensional tectonic regime developed, forming a new ba sin within the amalgamated tectonic mosaic. The different tectonic regimes in the region were caused by activity of the Western Pontide Fault. Most of the ophiolites within the Armutlu-Ovacik Zone belong to the Paleo-Tethyan and/or pre-Ordovician ophiolitic core of the Istanbul-Zonguldak Unit. The L ate Cretaceous ophiolites in the eastern parts of the Armutlu-Ovacik Zone w ere transported from Neo-Tethyan ophiolites farther east by left-lateral st rike-slip faults along the Western Pontide Fault. There is insufficient evi dence to indicate the presence of an ocean (Intra-Pontide Ocean) between th e Istanbul-Zonguldak Unit and the Sakarya Zone during Late Cretaceous time.