Turkish Journal of Earth Sciences Turkish J Earth Sci (2016) 25: 341-366 http://journals.tubitak.gov.tr/earth/ © TÜBİTAK Research Article doi:10.3906/yer-1507-9 Assimilation and fractional crystallization of foid-bearing alkaline rocks: Buzlukdağ intrusives, Central Anatolia, Turkey 1, 1,2 Kıymet DENİZ *, Yusuf Kağan KADIOĞLU 1 Department of Geological Engineering, Faculty of Engineering, Ankara University, Ankara, Turkey 2 Earth Sciences Application and Research Center, Ankara University, Ankara, Turkey Received: 15.07.2015 Accepted/Published Online: 06.04.2016 Final Version: 09.06.2016 Abstract: Felsic intrusive rocks within the Central Anatolian Crystalline Complex provide a window into the geodynamic processes in operation during the final closure of the Neotethys Ocean. Previous studies were largely restricted to the calc-alkaline granitoids, and the structural and petrogenetic relations of syenitoids are poorly studied. The Buzlukdağ Intrusive Complex is a silica-undersaturated alkaline syenite that is differentiated into three concentric subgroups according to texture and grain size. Mineral compositions do not vary between the subgroups but differentiation has resulted in different mineral proportions. Mafic microgranular enclaves are present throughout the suite, indicating mingling and mixing between the coeval felsic and mafic magmas. Major element concentrations are consistent with fractional crystallization of nepheline + K feldspar ± Na rich plagioclase + Na amphibole + pyroxene ± melanite ± cancrinite. Mineral chemistry reveals that the syenites are crystallized under a wide range of pressures (1.5–3.7 kbar), at varying temperatures (732–808 °C), and are likely emplaced at depths of 6–14 km. Large-ion lithophile element and light rare earth element enrichments with respect to high field-strength elements and heavy rare earth elements are consistent with their derivation from an incompatible element-enriched magma source. Incompatible trace element concentrations (e.g., Sr, Ba, Th, Ta, Pb, La, Ce, and Yb) revealed that the magma has a subduction fluid component, which can be distinguished from crustal assimilation. The Buzlukdağ alkaline intrusive rocks are likely to be derived from decompressional melting of the lithospheric mantle above asthenospheric upwelling as a result of crustal thinning of Central Anatolia during the Late Mesozoic–Early Cenozoic. Key words: Buzlukdağ syenite, alkaline rocks, assimilation and fractional crystallization, subduction zone metasomatism, lithospheric mantle, enclave 1. Introduction Africa, America, Europe, Asia, the Hawaiian Islands, and Silica-undersaturated alkaline rocks are formed in nearly Russia. Even though the products of alkaline magmatism all tectonic environments with the exception of mid- in Turkey are observed in all areas (northern, western, ocean ridges (Fitton and Upton, 1987). They are formed eastern, and central parts of Anatolia), cropping out in during oceanic and continental intraplate magmatism small areas, the alkaline igneous rocks of the northeastern and subduction magmatism. Despite this, these rocks part of Anatolia are located near Ordu (Yenisayaca, comprise volumetrically less amounts of all igneous rocks İkizce), Trabzon, and Artvin (Pırnallı) (Temizel and (Fitton and Upton, 1987). Silica-undersaturated alkaline Arslan, 2008, 2009; Karsli et al., 2012; Temizel et al., 2012). rocks also point out the areas where crustal thinning The alkaline igneous rocks of western Anatolia are mostly is observed in association with continental intraplate located around Kütahya (Seyitgazi, Kırka), Afyon (Şuhut, magmatism and the partial melting of the deepest and Sandıklı), Isparta (Gölcük, Bucak), and Manisa (Kula). phlogopite-rich part of the subducted plate. However, Adıyaman (Nemrut) and Van (Tendürek) are the areas they attract attention because of their characteristic high where alkaline igneous rocks are observed in the eastern concentrations of incompatible, large-ion lithophile part of the Anatolia (Keskin, 2003; Özdemir et al., 2006; elements (LILEs) and rare earth elements (REEs) and Ersoy and Helvacı, 2007; Ersoy et al., 2008, 2010a, 2010b, their important ore deposits of fluorite, barite, apatite, 2011, 2012; Dilek and Altunkaynak, 2009, 2010). Kırşehir and diamond (Fitton and Upton, 1987). As a result of a (Akçakent, Bayındır, Buzlukdağ), Kayseri (Hayriye), wide range of tectonic occurrences, alkaline igneous rocks Nevşehir (Devepınarı, İdişdağ), and Yozgat (Ömerli) are are noticed in northwestern Ontario, Greenland, Iceland, the main locations for central Anatolia (Kadıoğlu et al., * Correspondence: [email protected] 341 DENİZ and KADIOĞLU / Turkish J Earth Sci 2006). The alkaline volcanic rocks are mostly observed Otlu and Boztuğ, 1998; Tatar, 2003; İlbeyli, 1999, 2005; in northeastern, western, and eastern parts, whereas İlbeyli et al., 2004, 2009; Köksal et al., 2004; Köksal and the plutonic equivalents are seen in central parts in the Göncüoğlu, 2008) and little emphasis on their importance composition of syenites (Figure 1). Buzlukdağ is the for the tectonic evolution of the region and ore deposition. best area where these rocks are observed in the Central The Buzlukdağ Intrusive Complex, which is located in the Anatolia Crystalline Complex (CACC) and the only area northwestern part of the CACC, is one of largest silica- where syenites have contact with metamorphic rocks. undersaturated alkaline bodies and includes syenite, The Late Cretaceous igneous rocks of Central felsic and mafic dykes, and enclaves (Tolluoğlu, 1986, Anatolia, Turkey, recorded the magmatic and tectonic 1993; Kadıoğlu et al., 2006; Deniz, 2010) (Figure 1). The evolution of the region during closure of the İzmir- compositional range of rocks present in the complex makes Ankara-Erzincan (İAE) and Inner Tauride (IT) oceans, it a good place to study the formation and evolution of the which constituted the northern branches of the Neotethys CACC syenitic rocks. The aim of this study is to present Ocean (Şengör and Yılmaz, 1981; Bozkurt and Mittwede, a detailed geology map, petrographic investigation of the 2001). Syenites are important indicator for reflecting the main lithologies, the relationship between the syenite and changes of the tectonic regime from compressional to dykes, and the mineral and whole-rock major and trace extensional and the type of tectonic settings (Channel, element geochemical characteristics of the Buzlukdağ 1986). Their petrographic and geochemical characteristics Intrusive Complex (Deniz, 2010) in order to understand have significant importance in understanding mantle the petrogenesis of the complex, and the comparison with activities in the subduction zones and also mantle–crust the other alkaline syenitic rocks (İdişdağ, Hayriye, Ömerli, interactions. Previous geochemical and geochronological Akçakent, Dumluca, Murmana, Karakeban, Kösedağ, studies largely concentrated on the calc-alkaline plutonic Hasançelebi, Karaçayır, Davulalan, Baranadağ, Bayındır rocks (Aydın et al., 1998; Tatar and Boztuğ, 1998, 2005; (Hamit), Durmuşlu, Çamsarı) within the CACC. Boztuğ and Arehart, 2007; Boztuğ and Harlavan, 2008; Boztuğ et al., 2009; Köksal et al., 2012; Elitok et al., 2014). 2. Geological background In contrast, there are few comparative studies of the calc- The CACC is the microcontinent that is bounded by the alkaline, transitional, and alkaline igneous rocks with İAE Suture Zone dipping northward beneath the Pontides very poor data from alkaline rocks (Boztuğ, 1998, 2000; at the north and the IT Suture Zone with NE-dipping ANKARA . N ZONE KOSEDAĞ . KARAÇAYIR KARAKEBAN KIRIKKALE YOZGAT DAVULALAN MURMANA AKÇAKENT SİVAS DUMLUCA ÖMERLİ HASANÇELEBİ DURMUSLU BAYINDIR AKDAĞMADENİ CAMSARI Syen te Supersu te Monzon te Supersu te BUZLUKDAG Study Area Gran Supersu te BARANADAĞ Gabbro c plutons Tethyan oph ol tes STUDY AREA STRIKE-SLIP Munzur l mestone C HAYRİYE FAULTS Paleozo c-Mesozo c KIRŞEHİR THURST FAULTS metamorph cs TGF CITY/ TOWN Metamorph un te GÜMÜŞDAĞ Black Sea IDISDAĞI Pont de Belt İSTANBUL SALT NAF IAESZ LAKE Ankara CACC EAF Aeagean NEVŞEHİR Sea Taur de Belt 20 km 0 100 Arab an Plate Med terranean Sea Km Figure 1. Geological sketch map of the Central Anatolia Crystalline Complex (CACC) modified from Kadıoğlu et al. (2006) with inset map from Bozkurt (2001). 342 DENİZ and KADIOĞLU / Turkish J Earth Sci subduction beneath the CACC at the south (Kadıoğlu et anatexis was suggested for the formation of syenites al., 2006). The magmatism within the CACC is related to in the Nevşehir region (Göncüoğlu et al., 1997), while the closure of the IT Ocean, which is the southern strand of others considered the lower crust–upper mantle origin the northern branch of the Neotethys between the Tauride for derivation of these rocks (Boztuğ et al., 1994; Boztuğ, Anatolide Platform (TAP) and CACC. These magmatisms 1998; Otlu and Boztuğ, 1998). Most authors suggest a produce several distinct suites of felsic and mafic igneous postcollisional geodynamic setting for the syenitic rocks rocks, which intruded into the metamorphic basement (Boztuğ, 1998, 2000; İlbeyli, 1998, 2005; İlbeyli et al., 2004, during the Middle to Late Cretaceous after the obduction 2009; Köksal et al., 2004; Köksal and Göncüoğlu, 2008), of the suprasubduction zone Tethyan ophiolite emplaced whereas Kadıoğlu et al. (2006) prefer a syncollision model. southward along the northern edge of the CACC in Turonian–Santonian times (90–85 Ma) and before the 3. Field description and petrography final