121 Bull. Min. Res. Exp. (2018) 157: 121-152 Mineral chemistry, whole-rock geochemistry and petrology of Eocene I-type shoshonitic plutons in the Gölköy area (Ordu, NE Turkey) İrfan TEMİZEL a* , Emel ABDİOĞLU YAZAR b , Mehmet ARSLAN c , Abdullah KAYGUSUZ d and Zafer ASLAN e a Karadeniz Technical University, Department of Geological Engineering, 61080, Trabzon, Turkey. orcid.org/0000-0002-6293-8649 b Karadeniz Technical University, Department of Geological Engineering, 61080, Trabzon, Turkey. orcid.org/0000-0001-5196-8060 c Karadeniz Technical University, Department of Geological Engineering, 61080, Trabzon, Turkey. orcid.org/0000-0003-0816-4168 d Gümüşhane University, Department of Geological Engineering, 29000, Gümüşhane, Turkey. orcid.org/0000-0002-6277-6969 e Balıkesir University, Department of Geological Engineering, 10145, Balıkesir, Turkey. orcid.org/0000-0002-3418-4368 Research Article Keywords: Mineral chemistry, thermobarometer, geochemistry, I-type, monzonite, Eocene, Gölköy, Turkey Received Date: 21.06.2017 Accepted Date: 27.12.2017 ABSTRACT The Eocene intermediate to felsic plutons are widespread in varying sizes and compositions throughout the Eastern Pontides Orogenic Belt in NE Turkey. Of these, two monzonitic bodies (namely the Eriko Tepe and Göl Tepe Plutons) in the Gölköy (Ordu) area, extend nearly in the orientation of NW- SE and E-W and were emplaced into the Upper Cretaceous and/or Eocene volcanic and sedimentary rocks. Petrographically, the studied monzonitic plutons are compositionally fine to medium grained monzonite, monzodiorite and subordinate quartz-monzonite. They consist of plagioclase (An 35-67 ), K-feldspar (Or 61-96 ), quartz, clinopyroxene (Wo 28-49 En 35-51 Fs 10-25 ), biotite (Mg#: 0.53-0.73) ± hornblende (Mg#: 0.65-0.82), Fe-Ti oxide with monzonitic, poikilitic, perthitic, rare antirapakivi and graphic textures. Mineral thermobarometer estimations imply that the plutons were crystallized in P-T conditions of mid to shallow crustal levels. Petrochemically, these monzonitic plutons show post-collisional, I-type, metaluminous (A/CNK=0.76-0.93) and shoshonitic features. The whole- rock major oxide and trace element variations suggest that fractionational crystallization played a significant role in the evolution of these monzonitic plutons. The primitive mantle-normalized trace element patterns of the studied plutons are similar to each other with enrichment in large ion lithophile elements, Th, Ce and negative Nb and Ti anomalies. Moreover, the chondrite-normalized rare earth element plots of the plutons show moderately enriched concave-shaped patterns (La N /Lu N =9.3-12.6) with negative Eu anomalies (Eu N /Eu*=0.69-0.84), all of which imply plagioclase and clinopyroxene ± hornblende fractionations during their evolution. The geochemical data suggest that the monzonitic plutons have evolved from parental magmas derived from the melts of enriched lithospheric mantle, in a post-collisional setting. * Corresponding author: İrfan TEMİZEL, itemizel@ktu.edu.tr http://dx.doi.org/10.19111/bulletinofmre.371623 Bulletin of the Mineral Research and Exploration http://bulletin.mta.gov.tr BULLETIN OF THE MINERAL RESEARCH AND EXPLORATION CONTENTS Foreign Edition 2018 157 ISSN : 0026-4563 E-ISSN : 2651-3048 1. Introduction The plutons observed in the Eastern Pontides Orogenic Belt (EPOB) have a wide age interval from Paleozoic to Tertiary, and they are formed by mafic and felsic rocks mainly ranging from gabbro to granite. These plutons have intruded in three time periods mainly during the Permo-Carboniferous, Cretaceous and Eocene. Of these, the Permo-Carboniferous granitoids (Yılmaz, 1972; Çoğulu, 1975; Topuz et al., 2010; Dokuz, 2011; Kaygusuz et al., 2012, 2016) were emplaced into the metamorphic rocks. The Cretaceous granitoids have a contact relation with volcanic and/ or volcanoclastic rocks related to subduction (Yılmaz and Boztuğ, 1996; Karslı et al., 2010a; Kaygusuz et al., 2008, 2009, 2010, 2011, 2012; Kaygusuz and Aydınçakır, 2009, 2011; Kaygusuz and Şen, 2011; Karslı et al., 2012a; Kaygusuz et al., 2013, 2014). On the other hand, the fewer Eocene and post Eocene granitoids have cut all the series in narrow areas (Yılmaz and Boztuğ, 1996; Aslan et al., 1999; Topuz, 2002; Arslan and Aslan, 2006; Karslı et al., 2007;