Stratigraphy and tectonic evolution of the Kazdağı Massif (NW Anatolia) based on field studies and radiometric ages
2013-08-08

AbstractThe Kazdağı Massif was previously considered as the metamorphic basement of the Sakarya Zone, a microcontinental fragment in NW Anatolia. Our new field mapping, geochemical investigations, and radiometric dating lead to a re-evaluation of previous suggested models of the massif. The Kazdağı metamorphic succession is subdivided into two major units separated by a pronounced unconformity. The lower unit (the Tozlu metaophiolite) is a typical oceanic crust assemblage consisting of ultramafic rocks and cumulate gabbros. It is unconformably overlain by a thick platform sequence of the upper group (the Sarıkız unit). The basement ophiolites and overlying platform strata were subjected to a single stage of high-temperature metamorphism under progressive compression during the Alpine orogeny, accompanied by migmatitic metagranite emplacement. Radiometric age data obtained from the Kazdağı metamorphic succession reveal a wide range of ages. Metagranites of the Kazdağı metamorphic succession define a U–Pb discordia upper intercept age of ca. 230 Ma and a lower intercept age of 24.8 ± 4.6 Ma. This younger age agrees with 207Pb/206Pb single-zircon evaporation ages of 28.2 ± 4.1 to 26 ± 5.6 Ma. Moreover, a lower intercept age of 28 ± 10 Ma from a leucocratic metagranite supports the Alpine ages of the massif within error limits. Reconnaissance detrital zircon ages constrain a wide range of possible transport and deposition ages of the metasediments in the Sarıkız unit from ca. 120 to 420 Ma. Following high-temperature metamorphism and metagranite emplacement, the Kazdağı sequence was internally imbricated by Alpine compression, and the lowermost Tozlu ophiolite thrust southward onto the Sarıkız unit. Field mapping, internal stratigraphy, and new radiometric age data show that the Sarıkız unit is the metamorphic equivalent of the Mesozoic platform succession of the Sakarya Zone. The underlying metaophiolites are remnants of the Palaeo tethys Ocean, which closed during the early Alpine orogeny. After strong deformation attending nappe emplacement, the unmetamorphosed Miocene Evciler and Kavlaklar granites intruded the tectonic packages of the Kazdağı Massif. During Pleistocene time, the Kazdağı Massif was elevated by EW trending high-angle normal faults dipping to Edremit Gulf, and attained its present structural and topographic position. Tectonic imbrication, erosion and younger E–W-trending faulting were the main cause of the exhumation of the massif.Keywords: Kazdağı MassifU–Pb ages207Pb/206Pb-evaporation agesAlpine orogenyNW Anatolia AcknowledgementsThis study was financially supported by the Scientific and Technical Research Council of Turkey (TUBITAK) (project no: 104Y302). Dr Cosmas Shang, Gisela Bartholomä, and Elmar Reitter (University of Tübingen, Germany) are thanked for valuable help during radiogenic age determinations. Dr George Gardenier (New Brunswick Lab, United States) and Dr Lawrie Skinner (ANL, United States) are thanked for English editing. The authors thank Dr Talip Güngör and Necdet Özgül for their helpful contributions. Dr Gary Ernst, the Editor-in-Chief and Dr Yücel Yılmaz and Dr Axel Schmitt, reviewers, are specially thanked for their constructive reviews. H. Basri Avcı, the director of the Kazdağı Mountain National Park, is thanked for his kind helps through the permission processes to enter the natural park area during field studies.