ORIGINAL PAPER Petrogenesis of the post-collisional Eocene volcanic rocks from the Central Sakarya Zone (Northwestern Anatolia, Turkey): Implications for source characteristics, magma evolution, and tectonic setting Ahmet Yildiz 1 & Yaşar Kibici 2 & Metin Bağci 1 & İbrahim Dumlupunar 1 & Cumhur Kocabaş 3 & A. Ekrem Aritan 1 Received: 16 April 2015 /Accepted: 4 June 2015 # Saudi Society for Geosciences 2015 Abstract Eocene volcanic rocks from the Central Sakarya Zone in the north of the İzmir–Ankara suture zone (IASZ) are predominantly intermediate-acidic lava flows and pyro- clastics that crop out with a W–E orientation. The volcanic rocks include Bozaniç lavas, agglomerates, İğdir lavas, and Kapıkaya tuffs. The Bozaniç lavas contain plagioclase, horn- blende, clinopyroxene, and biotite, whereas the İğdir lavas consist of plagioclase, hornblende, biotite, and quartz. Ac- cording to the total alkali–silica (TAS) diagram, the Bozaniç lavas are mainly composed of andesite and dacite, with one sample of trachyandesite, whereas the İğdir lavas mainly con- tain dacite and minor andesite. Bozaniç and İğdir lavas exhibit moderate- to high-K calc-alkaline character. Major oxide and trace element variations suggest the effects of fractional crys- tallization in the evolution of the volcanic rocks. N-type mid- ocean ridge basalt (MORB) normalized trace element patterns of the lavas exhibit enrichment in large ion lithophile elements (LILEs; K, Rb, Ba, Th) and depletion in high field strength elements (HFSEs; Zr, Ti, Y). In addition, the chondrite- normalized rare earth element (REE) plots of the rocks show moderately enriched and nearly concave-shaped patterns (La N /Yb N = 5.4–17.6 for the Bozaniç lavas and 6.5–13.1 for the İğdir lavas), suggesting clinopyroxene (Cpx) and horn- blende dominated fractionation. Negative Eu anomalies in the acidic lavas reveal plagioclase fractionation. Some trace element ratios of the lavas demonstrate a subduction signature and crustal contamination in the generation of the parent magma(s). Multi-dimensional tectonic discrimination dia- grams suggest that the studied volcanic rocks have developed in a collisional setting. Keywords Post-collision . Volcanism . Calc-alkaline . Sakarya continent . Turkey Introduction The collision between the Arabian and Eurasian plates, sub- duction of the African plate under the Aegean-Anatolian plates, and the N–S-directed extension ensured the tectonic evolution of Anatolia (Şengör and Yılmaz 1981; Ring et al. 2010; Leroy et al. 2014; Al-Dabbagh 2014). The subduction and elimination of the northern branch of Neo-Tethyan north- ward beneath the Sakarya continent from the Late Cretaceous to the Paleocene resulted in a collision between the Sakarya and Anatolide–Tauride continental fragments along the İzmir– Ankara suture zone. The north-dipping subduction of the Neo- Tethyan Ocean caused Late Cretaceous arc volcanism in the north of the region (Fig. 1a)(Şengör and Yılmaz 1981; Koçyiğit et al. 1995; Okay and Tüysüz 1999). * Ahmet Yildiz ayildiz@aku.edu.tr Yaşar Kibici ykibici@gmail.com Metin Bağci mbagci@aku.edu.tr İbrahim Dumlupunar idumlupinar@aku.edu.tr Cumhur Kocabaş cumhurkocabas@gmail.com A. Ekrem Aritan aritan@aku.edu.tr 1 Faculty of Engineering, Afyon Kocatepe University, Afyonkarahisar, Turkey 2 Faculty of Engineering, Dumlupınar University, Kütahya, Turkey 3 Faculty of Engineering, Balıkesir University, Balıkesir, Turkey Arab J Geosci DOI 10.1007/s12517-015-1991-4