spatial, temporal and geochemical evolution of - miami university

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Spatial, temporal and geochemical evolution of Oligo–Miocene granitoid magmatismin western Anatolia, Turkey

Şafak Altunkaynak a,⁎, Yıldırım Dilek b, Can Ş. Genç a, Gürsel Sunal a, Ralf Gertisser c, Harald Furnes d,Kenneth A. Foland e, Jingsui Yang f

a Department of Geology Engineering, Istanbul Technical University, Maslak 34469, Istanbul, Turkeyb Department of Geology, 116 Shideler Hall, Miami University, Oxford, OH 45056, USAc School of Physical and Geographical Sciences, Earth Sciences and Geography, Keele University, Keele, Staffordshire, ST5 5BG, United Kingdomd Department of Earth Science and Centre for Geobiology, University of Bergen, Allegt. 41, 5007 Bergen, Norwaye School of Earth Sciences, Ohio State University,125 South Oval Mall, Columbus, OH 43210, USAf State Key Laboratory of Lithosphere Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825,Beijing 100029, China

⁎ Corresponding author. Tel.: +90 212 2856272; fax:E-mail address: [email protected] (Ş. Altunkaynak).

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Please cite this article as: Altunkaynak, Ş., etAnatolia, Turkey, Gondwana Res. (2012), do

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Article history:Received 15 June 2011Received in revised form 10 October 2011Accepted 26 October 2011Available online xxxx

Handling Editor: M. Santosh

Keywords:Oligo–Miocene granitoidsWestern AnatoliaPost-collisional magmatismOpen system processesThermal weakening and synconvergentextension

Western Anatolia (Turkey) experienced widespread Cenozoic magmatism after the collision between the Sa-karya (SC) and Anatolide–Tauride continental blocks (ATP) in the pre-middle Eocene. Voluminous graniticmagmas were generated and emplaced into the crystalline basement rocks of the Rhodope (RM) and Sakaryacontinent to the north and Anatolide–Tauride Platform to the south of the ~E–W-trending Izmir–Ankara su-ture zone (IASZ) during the late Oligocene–middle Miocene. We report here a comprehensive geochronolog-ical (combined zircon U–Pb and 40Ar–39Ar dating) and geochemical (major and trace element geochemistry,and Sr–Nd isotopes) dataset from the Oligo–Miocene granitoids in order to evaluate the nature and the spa-tial–temporal distribution of the Cenozoic magmatism in the Aegean extensional province. Zircon SHRIMPU–Pb dating of these plutons yields ages between 19.48±0.29 and 23.94±0.31 Ma as the timing of their em-placement, whereas 39Ar/40Ar dating of biotite separates from these plutons reveals cooling ages of 18.9±0.1–24.8±0.1 Ma. Regardless of the lithological make-up of the collided blocks, the RMG, SCG and NATPGgranitoids that were emplaced into the RM, SC and ATP, respectively, show similar major and trace elementand Sr–Nd isotopic compositions, indicating commonmantle melt sources andmagmatic evolutionary trends.The isotopic signatures and trace element characteristics of these granitoids indicate that both lithosphericand asthenospheric mantle melts appear to have contributed to source region of the RMG, SCG and NATPGmagmas. The compositional variations observed in these granitoids are interpreted as a result of open-system processes (AFC and/or MASH) rather than a reflection of different compositions of crustal lithologiesthrough which RMG and SCG, ATPG magmas migrated. On the other hand, the SATPG with crustal signaturesstronger than the other groups may have been produced by crustal melting or significant contributions fromthe ATP crystalline basement. The isotopic compositions and cooling age relationships of western Anatoliangranitoids indicate an increasing crustal signature from 24 to 18 Ma coinciding with crustal exhumation (Kaz-dag and Menderes core complexes) and extension in western Anatolia. Asthenospheric upwelling caused bypartial delamination or convective thinning of lithosphere led to underplating of mantle-derived magmasthat provided melts and heat to induce partial melting of sub-continental lithospheric mantle. Stalling ofmantle-derived melts in the crust triggered open system processes in separate magma chambers, resultingin the production of granitic magmas. This inferred melt source and magma evolution readily explains the I-type granitoid nature of most late Oligocene to middle Miocene plutons in western Anatolia regardless oftheir temporal and spatial position. The widespread early to middle Cenozoic magmatism caused thermalweakening and played a significant role for the initiation of synconvergent extension, exhumation and thin-ning in the hinterland of a young Tethyan orogen in western Anatolia and the broader Aegean region.

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2 Ş. Altunkaynak et al. / Gondwana Research xxx (2012) xxx–xxx

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 02. Regional geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 03. Synopsis of Cenozoic plutonism in western Anatolia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 04. Analytical techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0

4.1. SHRIMP dating. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 04.2. 40Ar/39Ar dating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 04.3. Major, trace elements and Sr–Nd isotope analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0

5. Geochronology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 05.1. U–Pb zircon ages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 05.2. 40Ar/39Ar dates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0

6. Geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 06.1. Major and trace element characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 06.2. Sr and Nd isotopic signatures and Nd model ages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0

7. Petrogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 07.1. Source characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 07.2. Magma evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 07.3. Petrogenetic modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0

8. Interplay between syn-convergent extension and magmatism in western Anatolia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 09. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0

1. Introduction

Western Anatolia is one of the best natural laboratories in thebroader Alpine–Himalayan orogenic system to investigate in four-dimensions the nature and distribution of post-collisional magma-tism, the interplay between tectonic and magmatic processes, andthe crust–mantle interactions in a young mountain belt.

The consumption of a Neo-Tethyan oceanic lithosphere at a subduc-tion zonedipping northwards beneath the Sakarya continent during thelate Cretaceous resulted in a continent–continent collision between theSakarya and Anatolide–Tauride continental fragments in the easternMediterranean region (Şengör and Yılmaz, 1981). The timingof this col-lision has been well established in the literature as pre-middle Eocene(Harris et al., 1994; Okay and Tüysüz, 1999). The widespreadmagmaticactivity in NW Anatolia postdates this continental collisional event inthe region (Yılmaz, 1989, 1990; Güleç, 1991; Şengör et al., 1993;Harris et al., 1994; Seyitoğlu and Scott, 1996). The first products ofpost-collisional magmatism are the middle Eocene granitic plutonsand andesitic extrusive rocks (Harris et al., 1994; Genç and Yılmaz,1997; Delaloye and Bingöl, 2000; Köprübaşı and Aldanmaz, 2004;Altunkaynak and Dilek, 2006; Okay and Satır, 2006; Altunkaynak,2007). The following magmatic episode during the Oligocene andEarly Miocene is known to have produced the widespread granitic plu-tons (i.e., Kozak, Evciler, Cataldag, Kestanbol, Ilica-Samli, Eybek, Egrigoz,Koyunoba) and associated volcanic rocks in western Anatolia (Yılmaz,1989; Altunkaynak and Yılmaz, 1998, 1999; Genç, 1998; Yılmaz et al.,2001; Özgenç and İlbeyli, 2008; Akay, 2009).

The relationships between tectonics and magmatism and their vari-ation in time and space since the beginning of the Neogene remainsome of the most fundamental questions in the geodynamic evolutionof western Turkey and the broader Aegean extensional province. Al-though some geochemical data exist from this region (Harris et al.,1994; Genç and Yılmaz 1997; Altunkaynak and Yılmaz, 1998, 1999;Genç, 1998; Karacık and Yılmaz, 1998; Delaloye and Bingöl, 2000;Köprübaşı and Aldanmaz, 2004; Okay and Satır, 2006; Altunkaynak,2007; Altunkaynak and Genç, 2008; Özgenç and İlbeyli, 2008; Akay,2009; Altunkaynak et al., 2010; Hasözbek et al., 2010; Mackintosh andRobertson, 2011), it is not systematic and it does not contain sufficientisotopic and geochronological information to develop a regionally co-herent and viable geochemical and geodynamic model for the post-collisional magmatic evolution of NW Anatolia.

Please cite this article as: Altunkaynak, Ş., et al., Spatial, temporal and geocAnatolia, Turkey, Gondwana Res. (2012), doi:10.1016/j.gr.2011.10.010

We have investigated the geochronology, geochemistry and pet-rogenesis (magma sources, magma genesis and crust–magma inter-action) of post-collisional granitic plutons and stocks emplaced intothe Anatolide–Tauride and Sakarya continental blocks on both sidesof the Izmir–Ankara suture zone (Fig. 1). Straddling one of themajor continental collision zones in the eastern Mediterranean re-gion, the granitoids we have investigated provide us with an opportu-nity to evaluate the geochemical fingerprint and melt evolution ofpost-collisional magmatism in and across a suture zone, and to docu-ment, for the first time, the different isotopic domains beneath theearly Tertiary western Anatolia. In this paper, we present our newgeochemical data, Sr–Nd isotope compositions, 40Ar–39Ar and zirconShrimp ages from the late Oligocene to middle Miocene granitoid plu-tons, and the petrogenesis of thirteen granitoids to constrain themagmatic evolution and melt sources of the post-collisional magma-tism in the region. We then discuss the mantle dynamics and the meltevolution beneath western Anatolia as a case study of alpine-stylecollision zone magmatism.

2. Regional geology

The crustal architecture of western Anatolia and the broader Aege-an region is formed from a collage of continental blocks, separated byophiolites and suture zones that are nearly parallel to each other(IPSZ, VS_IASZ, PS in Fig. 1). The basement geology of NW Anatolia in-cludes five tectonic units. These are, from north to south, the Rhodopemassif (RM), the Intra-Pontide Suture zone (IPSZ), the Sakarya conti-nent (SC), the Izmir_Ankara suture zone (IASZ) and the Anatolide–Tauride platform (ATP) (Şengör and Yılmaz, 1981; Okay and Satır,2000 and references therein).

The Çamlıca micaschist which is a part of the Rhodope massif(Okay and Satır, 2000) is exposed around the Ezine and Karabiga(Fig. 2) in northwestern areas. The Sakarya continent (Şengör andYılmaz, 1981) consists of two types of rock associations; a) Palaeozoiccontinental metamorphic rocks (i.e. the Uludağ and Kazdağ meta-morphic massifs and the Söğüt basement) and b) Triassic metamor-phic rocks (mainly the Karakaya complex, Bingöl et al., 1975; Okayet al., 1990; Genç, 2004). The Çamlıca micaschist and the Sakarya con-tinent are separated by a high-angle fault zone, marked by ophioliticfragments of IPSZ (Okay and Satır, 2000, 2006). The Anatolide–Taur-ide platform farther south is composed of carbonates and intercalated

hemical evolution of Oligo–Miocene granitoid magmatism in western


32°N

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Fig. 1. Generalized map of the Aegean region showing the distribution of Neogene granitoids, metamorphic massifs and major structural elements (modified from Pe-Piper andPiper, 2001, 2006).

3Ş. Altunkaynak et al. / Gondwana Research xxx (2012) xxx–xxx

volcanosedimentary and epiclastic rocks ranging in age from Cambro-Ordovician (and older?) to Lower Cretaceous (Ricou et al., 1975;Demirtasli et al., 1984), and is tectonically overlain by Cretaceousophiolite nappes derived from a Tethyan seaway to the north(Juteau, 1980; Şengör and Yılmaz, 1981; Dilek and Moores, 1990;Dilek et al., 1999).

The Kazdag and Menderes metamorphic massifs representing corecomplexes of western Anatolia (Bozkurt and Park, 1994; Hetzel et al.,1995; Hetzel and Reischmann, 1996; Bozkurt and Satır, 2000) consistof high-grade lower crustal rocks that were exhumed during the post-collisional extensional tectonic evolution of the region. They are over-lain by relatively unmetamorphosed cover sequences and are intrud-ed by granitoids (Hetzel and Reischmann 1996; Bozkurt and Park,1994; Okay and Satır, 2000; Gessner et al. 2004). The Menderes meta-morphic massif (i.e. Şengör et al., 1984) was formed mainly from


continent-type metamorphic rocks (micaschists and gneisses) andseparated from the Sakarya continent by the Izmir–Ankara suturezone (Şengör and Yılmaz, 1981; Okay and Tüysüz, 1999) (Fig. 2).

The IPSZ marks the collision zone between the RM (to the north)and SC (to the south) in northern Turkey (Okay and Tüysüz, 1999;Okay and Satır, 2006). These continental blocks collided as theIntra-Pontide ocean was consumed at a north-dipping subductionzone throughout the Cretaceous (Şengör and Yılmaz, 1981). Allthese tectonic entities juxtaposed to form a tectonic mosaic prior tothe deposition of the Upper Campanian–Maastrichtian successionsthat form the first common non-metamorphic cover (Yılmaz et al.,1995). Following this event, a new sedimentation phase accompaniedby rigorous andesitic volcanism and co-eval granitic plutonismstarted at the beginning of the middle Eocene (Lutetian, 48–39 Ma;Gulmez and Genc, 2009; Genc et al., unpublished age data). These




granitic rocks and the volcano-sedimentary succession were de-scribed as “post-collisional” magmatic activity (Genç and Yılmaz,1997; Yılmaz et al., 1997).

The Izmir–Ankara suture zone in western Anatolia representsthe collision zone between the Sakarya continent and Anatolide–Tauride platform (Şengör and Yılmaz, 1981). The Izmir–Ankara su-ture zone includes two different tectonostratigraphic units. In itsnorthwestern and western parts, it consists of a wild-flysch se-quence (Bornova flysch of Okay and Siyako, 1993), which containsabundant platform type carbonate olistholiths and olistostromestogether with the ophiolitic slices and blocks embedded in fine-grained flysch-type sediments. In the northern and eastern areas(i.e. south of Uludağ, near the Orhaneli and its east continuation)the Izmir–Ankara suture zone is represented mainly by the dis-membered and tectonically mixed ophiolitic rocks. These tectonicunits were juxtaposed with each other as a consequence of the col-lision between the Sakarya continent to the north and the Anato-lide–Tauride Platform to the south during the late Cretaceous–Paleocene (Şengör and Yılmaz, 1981; Okay and Tüysüz, 1999). Thenorthern branch of the Neo-Tethyan ocean, located between the Sa-karya continent and the Anatolide–Tauride Platform, was totallyconsumed at the beginning of the pre-middle Eocene at a subduc-tion zone dipping northwards beneath the Sakarya continent(Harris et al., 1994; Okay and Tüysüz, 1999). Following the colli-sion, the units of the Sakarya continent and the Bornova flyschwere covered unconformably by continental to shallow marine

Fig. 2. Simplified geological map of W Anatolia showing the distribution of granitoids (Mosuture zone, RM: Rhodope Massif, SC: Sakarya Continent, and ATP—Anatolide–Tauride4-Eybek, 5-Yenice, 6-Danisment, 7-Sarıoluk, 8-Kozak 9-Uludag, 10- Ilica-Samli 11-Davutlar,Data for radiometric ages: This study; Bingol et al., 1982; Hetzel et al., 1995; Delaloye andet al., 2008; Boztuğ et al., 2009.


sedimentary rocks (Baslamis Formation; Akdeniz, 1980 and Gebe-ler Formation; Akyurek and Soysal, 1983) during middle Eocene.This stratigraphic relationship indicates that the timing of the colli-sion in NW Anatolia was earlier than the middle Eocene.

After the continental collision, two major magmatic episodesoccurred in the region. The first was developed during the mid-dle–late Eocene, and produced extensive plutonic and volcanic as-sociations in different parts of NW Anatolia. The middle Eocenemagmatic associations have been studied in detail previously(Genç and Yılmaz, 1997; Köprübaşı and Aldanmaz, 2004;Altunkaynak, 2007; Dilek and Altunkaynak, 2007). The secondmagmatic phase occurred during the late Oligocene–middle Mio-cene. It is represented by granitic plutons and co-eval volcanicrocks, similar to those of the middle Eocene magmatic associations.Our study focuses mainly on the Late Oligocene–middle Miocenegranitic rocks.

We studied thirteen granitic bodies (Fig. 2), including, fromnorthwest to southeast, the Kestanbol, Evciler, Karakoy, Katrandag,Yenice, Hıdırlar, Ilica-Samlı, Kozak, Çataldag, Eybek, Çamlık, Eğrigözand Salihli granitoids. The Katrandağ, Yenice, Hıdırlar and Salihligranites are represented by stocks, whereas the others are largeplutons. The Kestanbol granite was emplaced into the Sakaryabasement rocks (Karacık and Yılmaz, 1998), which are imbricatedwith the Çamlıca micaschists of the Rhodope belt. The Kozak, Evci-ler, Ilıca-Şamlı, Eybek, Çataldağ, Hıdırlar and Katrandağ graniteswere emplaced into the metamorphic basement rocks of the

dified from Yılmaz et al., 2000; Okay and Satir, 2006). IAESZ; Izmir–Ankara–Erzincanplatform). E1 to 7: Eocene granitoids, 1-Kestanbol, 2-Evciler, 3-Hıdırlar-Katrandag12-Çataldag, 13-Egrigoz, 14-Koyunaoba, 15-Çamlik, 16-Turgutlu, 17-Salihli granitoids.Bingöl, 2000; Işık et al., 2004; Ring and Collins 2005; Glodny and Hetzel 2007; Karacik




Sakarya continent. The Çamlık, Eğrigöz and Salihli granitoids arethe representatives of the granites that were emplaced into theAnatolide–Tauride Platform (i.e. the metamorphic rocks of theMenderes Massif).

The late Oligocene–middle Miocene plutons are magmatic bodiesthat were emplaced at shallow depths in the crust. They crosscutthe metamorphic country rocks and have well developed contact au-reoles around their periphery. Along the border zone, the plutonscontain numerous metamorphic xenoliths and mafic microgranularenclaves. Many of the late Oligocene–middle Miocene granites havebeen described as caldera type, sub-volcanic plutons showing closerelationships with their co-genetic volcanic rocks in time and space(Yılmaz, 1989; Altunkaynak and Yılmaz, 1998, 1999; Genç, 1998;Yılmaz et al., 2001).

3. Synopsis of Cenozoic plutonism in western Anatolia

Cenozoic plutonism in western Anatolia has been the subjectof many studies. The models and interpretations derived fromthese studies support different and often conflicting views aboutthe nature, origin and evolution of Cenozoic magmatism in theregion.

Borsi et al. (1972), Fytikas et al. (1976) and Delaloye and Bingöl(2000) have argued that the western Anatolian plutons originatedfrom the Paleocene and younger magmatism associated with the Hel-lenic subduction zone. The Kozak, Kestanbol, Evciler and Karaköy plu-tons are post-collisional in character and are likely to have beenderived from the mantle and contaminated by thickened orogeniccrust, and may have evolved from a mixed magma source under acompressional regime (Altunkaynak and Yılmaz, 1998, 1999; Genç,1998; Karacık and Yılmaz, 1998; Yılmaz et al., 2001; Yılmaz-Şahinet al., 2010). The Ilıca, Cataldag and Kozak granitoids were derivedfrom different magma sources generated by partial melting of varioussources including metasomatized mantle and crustal material in apost-collisional extensional setting as a result of slab break-off eventfollowing the collision between the SC and the ATP (Boztuğ et al.,2009). Işık et al. (2004) reported that the syn-extensional Egrigözand Koyunoba plutons in the footwall of the Simav Detachmentwere emplaced in the early stages of continental extension in the Ae-gean province. These granitoids are hybrid in nature with dominantlyupper crustal compositions similar to the coeval Oligo–Miocene gran-itoids in the central Aegean Sea region. For the same granitoids, Akay(2009) and Hasözbek et al. (2010) argued for a hybrid magma sourceproduced under a compressional regime. Özgenç and İlbeyli (2008)proposed that the Egrigöz pluton formed by partial melting of mafic,lower crustal rocks during post-collisional extensional tectonics inthe region. Catlos et al. (2008) suggested that the trace-element geo-chemical features of the Salihli and Turgutlu granitoids are consistentwith a continental arc origin and that the magmas were generatedunder a compressional regime above the north-dipping Hellenicsubduction zone. Dilek et al. (2009) and Öner et al. (2010) proposedthat the Salihli and Turgutlu granitoids represent syn-extensionalintrusions and formed by partial melting of the subduction-metasomatized lithospheric mantle and the overlying lower–middlecrust. Altunkaynak and Dilek (2006), Altunkaynak (2007) and Dilekand Altunkaynak (2007, 2009) suggested that partial melting ofenriched, subcontinental lithospheric mantle-derived melts and sub-sequent fractional crystallization, accompanied by crustal assimila-tion, were important processes in the genesis and evolution of themagmas. They demonstrated that mantle-derived melts experienceddecreasing subduction influence and increasing crustal contamina-tion during the evolution of the Eocene and Oligo–Miocene volcano-plutonic associations. They further argued that collision-inducedslab break-off allowed an influx of asthenospheric heat that resultedin partial melting of the orogenic lithospheric mantle, which was pre-viously metasomatized by slab-derived fluids beneath the Izmir–


Ankara suture zone, producing the Eocene and Oligo–Miocene igne-ous suites.

4. Analytical techniques

4.1. SHRIMP dating

Zircons were extracted from 5 to 10 kg of rock samples by stan-dard mineral separation techniques, mainly grinding, sieving, Frantzisodynamic separator and heavy liquids. Separated zircons werehandpicked under a binocular microscope, and then a fraction withgrain sizes of 63–200 μm was selected and sorted according to theircrystal properties (i.e. euhedral morphology, lack of overgrowth andvisible inclusions). Zircons were mounted in epoxy resin and polisheddown to expose grain interiors for cathodoluminescence (CL) andSHRIMP studies. Zircons were dated on the SHRIMP II ion microprobeat the Beijing SHRIMP Centre, Institute of Geology, Chinese Academyof Geological Sciences. The analytical procedures were similar tothose described by Williams (1998). Mass resolution during the ana-lytical sessions was ~5000 (1% definition), and the intensity of theprimary ion beam was 5–8 nA. Primary beam size was 25–30 μm,and each site was rastered for 120–200 s prior to analysis. Fivescans through the mass stations were made for each age determina-tion. U abundance was calibrated using the standard SL13(U=238 ppm, Williams, 1998) and 206Pb/238U was calibrated usingthe standard TEMORA (206Pb/238U age=417 Ma; Black et al., 2003).The decay constants used for age calculation are those recommendedby the Subcommission on Geochronology of IUGS (Steiger and Jager,1977). Measured 204Pb was applied for the common lead correction,and data processing was carried out using the Squid and Isoplot pro-grams (Ludwig, 2001). The uncertainties for individual analyses arequoted at the 1 sigma confidence level, whereas errors for weightedmean ages are quoted at 95% confidence.

4.2. 40Ar/39Ar dating

Incremental step-heating 40Ar/39Ar age measurements were per-formed on amphibole and biotite mineral separates from the west-ern Anatolian Oligo–Miocene granitoids. The analyses wereperformed in the Radiogenic Isotopes Laboratory at Ohio State Uni-versity. The general procedures have been described by Foland etal. (1993) and references therein, except for the use of a newnoble-gas mass analysis system. Sized aliquots (~1–15 mg) of biotiteor amphibole were irradiated in the L-67 position of Ford NuclearReactor, Phoenix Memorial Laboratory, at the University of Michiganfor 36 h. They were subsequently heated incrementally to succes-sively higher temperatures using a custom-built, resistance-heating,high-vacuum, low-blank furnace. The step heating was continuouswith ramp times from one temperature to another of about 1 minand with dwell times of about 30 min at each temperature. Theseincremental-heating fractions were analyzed by static gas mass anal-ysis with a MAP 215-50 mass spectrometer. Corrections for interfer-ing reactions producing Ar from K, Ca, and Cl were made usingfactors determined. The monitor used was an intra-laboratory mus-covite standard (“PM-1”) with an 40Ar/39Ar age of 165.3 Ma; an un-certainty of ±1% is assigned to this age in order to allow foruncertainties in the standards against which PM-1 was calibrated.The age for this monitor was determined by simultaneous cross cal-ibration with several monitors including the Fish Canyon Tuff biotitestandard (FCT-3) with an age of 27.84 Ma.

4.3. Major, trace elements and Sr–Nd isotope analyses

Major and trace-element (V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr) ana-lyses were carried out using a Philips PW 1140 X-ray fluorescencespectrometry (XRF), and inductively-coupled plasma source mass



Fig. 3. CL images of dated zircon crystals from; a—the Çataldağ, b—the Eybek, c—the Çamlık, and d—Eğrigöz plutons. SHRIMP sites are marked by circles. The numbers refer to an-alytical data in Tables 1, 2, 3 and 4. The size of the scale bars is 100 μm.

Table 1Summary chart of Ar–Ar and U–Pb Shrimp ages obtained from Oligo–Miocene granit-oids of the western Anatolia. Ar–Ar ages are given as plateau ages.

Unit Group 40Ar/39Ar(Ma)

238U–206 Pb Shrimp(Ma)

Hornblende Biotite K-Feldspar Zircon

Evciler SCG 28.0±0.1 24.8±0.127.7±0.1 24.8±0.1

Ilıca SCG 22.3±0.1 21.9±0.1Eybek SCG 23.94±0.31Hıdırlar SCG 23.5±0.2 23.0±0.1Çataldağ SCG 20.4±0.1 20.6±0.1 21.91±0.33Kestanbol RMG 22.8±0.2 22.3±0.2Eğrigöz NATPG 19.0±0.1 18.9±0.1 19.48±0.29Çamlık NATPG 20.3±0.1 22.60±0.77


spectrometry (ICP-MS) was used for the analysis of Sc, Cs, Ba, REEs,Hf, Ta, Nb, U, Pb, Th and U at the Department of Earth Science, Univer-sity of Bergen, Norway. The glass-bead technique of Padfield and Gray(1971) was used for major elements and pressed-powder pellets fortrace elements, utilizing international standards and the recom-mended or certified concentrations of Govindaraju (1994) for calibra-tion. The USGS standards BCR2 and W2 were run regularly toestablish reproducibility. For the major elements it is generally b2%,but for Na2O, K2O and P2O5 around 4%. For the XRF-analyzed traceelements the reproducibility is generally b10%.

The ICP-MS analyses were performed on a Thermo Fisher Scientif-ic ELEMENT2 HR-ICP-MS. 100 mg of dry sample powders weredigested in a microwave sample container using a mixture of concen-trated HNO3 (4 ml), HF (1 ml) and HCL (5Ml). After digestion, thesamples were transferred to 30 ml Savillex beakers and evaporatedto dryness at 90 °C overnight. The residue was dissolved in 2 NHNO3, transferred to 50 ml volumetric flasks and diluted to volumewith pure water. Before analysis the samples were diluted furtherand Indium (In) was used as an internal standard. For Nb, Cs, Ba, Hf,Ta, Pb, Th, U, and REE the reproducibility is ~5%, and ~9–13% for Pr,Tb, Ba, Th and U.

Rb/Sr and Sm/Nd ratios were determined using a Finnegan 262mass spectrometer and isotope dilution techniques at UoB. The chem-ical processing was carried out in a clean-room environment with


reagents purified in two-bottle Teflon stills. Samples were dissolvedin a mixture of HF and HNO3. Rb–Sr and REE were separated by spe-cific extraction chromatography using the method described by Pin etal. (1994). Sm and Nd were subsequently separated using a modifiedversion of the method described by Richard et al. (1976). Sm, Nd, Rband Sr were loaded on a double filament, and Sm, Rb and Sr were an-alyzed in static mode and Nd in multi-collector dynamic mode.



Table 2Zircon U–Pb Shrimp data of the Çataldağ pluton.

Spot U(ppm)

Th(ppm)

Th/U 206Pb*(ppm)

%206

Pbc(1)206Pb*/238U

±% (1)207Pb*/235U

±% Total207Pb/206Pb

±% Total238U/206Pb

±% (1) 206Pb/238U age

(2) 206Pb/238U age

(3) 206Pb/238U age

1–1.1 567 419 0.76 1.77 6.38 0.003380 3.1 0.0223 38 0.1019 7.3 275.7 2.3 21.74 ±0.68 21.71 ±0.55 21.85 ±0.701–2.1 662 171 0.27 1.94 3.01 0.003303 2.4 0.0227 16 0.0769 5.7 292.3 2.3 21.26 ±0.52 21.17 ±0.50 21.35 ±0.551–3.1 2835 1057 0.39 8.80 1.02 0.003567 2.1 0.0217 7.5 0.0544 2.3 276.7 2.1 22.96 ±0.49 23.02 ±0.48 23.02 ±0.521–4.1 1413 353 0.26 4.21 1.51 0.003465 2.2 0.02753 3.5 0.0576 2.7 288.6 2.2 22.30 ±0.48 21.99 ±0.47 21.96 ±0.511–5.1 1912 563 0.30 5.62 2.00 0.003294 2.3 0.0133 26 0.0594 2.9 292.3 2.1 21.20 ±0.49 21.66 ±0.46 21.58 ±0.501–6.1 4276 6678 1.61 12.3 – 0.003327 2.1 0.0201 5.2 0.04879 1.8 298.7 2.1 21.41 ±0.45 21.48 ±0.45 21.58 ±0.621–7.1 2192 756 0.36 6.09 0.93 0.003219 2.2 0.02319 3.9 0.0552 2.4 309.4 2.2 20.72 ±0.45 20.57 ±0.44 20.60 ±0.481–8.1 1997 663 0.34 6.08 2.68 0.003480 2.2 0.0232 11 0.0633 2.2 282.0 2.1 22.39 ±0.49 22.34 ±0.48 22.21 ±0.521–9.1 2215 726 0.34 6.53 1.04 0.003405 2.1 0.0266 4.2 0.0623 2.2 291.5 2.1 21.91 ±0.46 21.63 ±0.46 21.84 ±0.491–10.1 3849 5887 1.58 14.2 2.36 0.004220 5.7 0.0305 9.3 0.0682 3.4 232 5.7 27.1 ±1.5 26.9 ±1.5 27.0 ±2.22–1.1 1611 374 0.24 4.39 1.60 0.003116 2.3 0.0204 13 0.0618 4.8 315.1 2.2 20.06 ±0.45 20.03 ±0.44 20.10 ±0.472–2.1 1008 771 0.79 2.79 1.60 0.003183 2.3 0.0235 6.6 0.0633 3.6 310.3 2.3 20.49 ±0.47 20.30 ±0.46 20.41 ±0.552–3.1 614 1094 1.84 1.84 1.30 0.003409 2.4 0.0195 14 0.0608 7.1 286.2 2.4 21.94 ±0.53 22.08 ±0.54 22.19 ±0.822–4.1 2809 609 0.22 8.50 0.37 0.003499 2.2 0.02278 3.4 0.0527 2.2 283.8 2.2 22.52 ±0.49 22.49 ±0.49 22.59 ±0.512–5.1 909 1046 1.19 2.59 1.39 0.003279 2.4 0.0243 12 0.0624 3.8 301.6 2.3 21.11 ±0.51 20.91 ±0.49 21.05 ±0.632–6.1 736 597 0.84 2.22 6.90 0.003337 2.5 0.0251 16 0.0935 3.3 284.7 2.3 21.48 ±0.54 21.26 ±0.50 21.05 ±0.65

Errors are 1-sigma; Pbc and Pb* indicate the common and radiogenic portions, respectively.Error in standard calibration was 0.54% (not included in above errors but required when comparing data from different mounts).(1) Common Pb corrected using measured 204Pb.(2) Common Pb corrected by assuming 206Pb/238U–207Pb/235U age-concordance.(3) Common Pb corrected by assuming 206Pb/238U–208Pb/232Th age-concordance.


Repeated measurements of the La Jolla standard (Nd-isotopes) andthe NIST SRM 987 standard (Sr-isotopes) yielded average ratios of0.511669±5 (2 SE) for 143Nd/144Nd, and 0.710254±5 (2 SE)for 87Sr/86Sr, respectively.

25 24 23 22 21 20 19

0.04

0.05

0.06

0.07

0.08

0.09

0.10

250 270 290 310 330 350

Mean = 21.91 ± 0.33 Ma [1.5%] 2s12 spots,MSWD = 1.11 spots 1.7.1, 1.10.1, 2.1.1, and 2.2.1 were excluded

a

c

28 26 24 22 20 18

0.040

0.044

0.048

0.052

0.056

0.060

0.064

220 260 300 340 380

Mean = 22.60 ± 0.77Ma [3.4%] 2s 16 spots, MSWD = 13

238U/206Pb

238U/206Pb

207 P

b/20

6 Pb

207 P

b/20

6 Pb

Fig. 4. Tera-Wasserburg 206Pb/238U versus 207Pb/206Pb diagrams with errors depicted at thUncertainties on all weighted average age calculations are 2-sigma confidence levels.


5. Geochronology

We dated seven plutons (Evciler, Ilıca, Hıdırlar, Kestanbol, Eğrigöz,Çamlık, and Çataldağ) using the 39Ar/40Ar method, and four plutons

22 21 20 19 18 170.04

0.06

0.08

0.10

0.12

280 300 320 340 360 380

Mean = 19.48 ± 0.29 Ma [1.5%] 2s16 spots, MSWD = 0.93

30 28 26 24 22 20

0.04

0.05

0.06

0.07

0.08

0.09

0.10

210 230 250 270 290 310 330

Mean = 23.94 ± 0.31 Ma [1.3%] 2s11 spots, MSWD = 1.6spots 1.4.1, 2.1.1, and 2.4.1 were excluded

b

d

238U/206Pb

238U/206Pb

207 P

b/20

6 Pb

207 P

b/20

6 Pb

e 1-sigma level. a—the Çataldağ, b—the Eybek, c—the Çamlık, and d—Eğrigöz plutons.



Table 3Zircon U–Pb Shrimp data of the Eybek pluton.

Spot U(ppm)

Th(ppm)

Th/U 206Pb*(ppm)

%206Pbc (1)206Pb*/238U

±% (1)207Pb*/235U

±% Total207Pb/206Pb

±% Total238U/206Pb

±% (1) 206Pb/238U age

(2) 206Pb/238U age

(3) 206Pb/238U age

1–1.1 479 293 0.63 1.68 8.14 0.00369 3.2 0.018 67 0.1101 7.7 245.8 1.7 23.72 ±0.75 24.08 ±0.50 24.05 ±0.671–2.1 417 237 0.59 1.50 4.58 0.00387 3.1 0.014 76 0.084 12 239.6 2.4 24.91 ±0.78 25.56 ±0.71 25.62 ±0.771–3.1 619 386 0.64 2.16 6.59 0.003774 2.2 0.0222 43 0.097 12 246.8 1.4 24.28 ±0.53 24.40 ±0.50 24.35 ±0.571–4.1 1046 768 0.76 3.61 2.16 0.003865 1.6 0.0195 28 0.0667 5.4 249.0 1.1 24.87 ±0.40 25.18 ±0.30 25.28 ±0.341–5.1 547 351 0.66 1.86 4.56 0.003814 1.9 0.0289 23 0.0845 7.8 252.3 1.4 24.54 ±0.48 24.28 ±0.41 24.34 ±0.481–6.1 290 173 0.62 1.11 16.07 0.00353 4.8 0.173 11 225.3 1.9 22.7 ±1.1 24.00 ±0.83 24.0 ±1.01–6.2 700 448 0.66 2.37 5.01 0.003701 2.0 0.0239 29 0.0936 6.4 254.2 1.3 23.81 ±0.47 23.80 ±0.37 24.04 ±0.441–7.1 711 444 0.64 2.39 5.29 0.003579 2.7 0.011 97 0.0900 8.9 256.1 1.3 23.03 ±0.62 23.74 ±0.40 23.80 ±0.441–8.1 956 1600 1.73 3.16 1.76 0.003739 1.4 0.0214 17 0.0645 3.3 259.7 1.1 24.06 ±0.34 24.21 ±0.29 24.34 ±0.472–1.1 1775 1214 0.71 6.54 1.49 0.004199 1.4 0.0224 13 0.0555 3.0 233.1 1.3 27.01 ±0.38 27.28 ±0.35 27.18 ±0.442–2.1 539 337 0.65 1.73 1.40 0.003681 1.3 0.0224 8.5 0.0570 4.5 267.3 1.3 23.68 ±0.32 23.75 ±0.32 23.74 ±0.372–3.1 611 427 0.72 1.95 2.19 0.003490 2.4 0.0071 100 0.0639 4.0 269.4 1.6 22.46 ±0.53 23.36 ±0.37 23.36 ±0.442–4.1 811 602 0.77 2.11 – 0.002862 3.3 0.0408 9.5 330.3 2.9 18.42 ±0.60 19.63 ±0.57 20.13 ±0.662–5.1 816 563 0.71 2.44 4.13 0.00340 3.4 0.0219 23 0.0653 14 287.4 3.3 21.87 ±0.74 21.86 ±0.78 21.46 ±0.90



(Eğrigöz, Çamlık, Çataldağ and Eybek) using the Shrimp U–Pb meth-od. Cathodoluminescence (CL) images and summary of the age dataare presented in Fig. 3 and Table 1, respectively.

5.1. U–Pb zircon ages

The zircons separated from the Çataldağ pluton have mostly euhe-dral and transparent grains with aspect ratios ranging from 1:1.5 to1:3.5 (Fig. 3a). The majority of these zircons show magmatic growthzoning with patchy recrystallization zones and local cores. Somegrains are represented by faint oscillatory and sector zoning (e.g.Grains 1–6.1 and 2–1.1, Fig. 3a). Recrystallization zones in some ofthe grains truncate the previously formed oscillatory zones (Grains1–7.1, 1–8.1, 2–2.1, 2–3.1, and 2–6.1). Grains 1–3.1 and 1–8.1 havexenocrystic cores with weakly developed Cl intensity. Laser spotswere concentrated on thin oscillatory zoned parts. All of the spots(16 measurements) yielded ages between 20 and 23 Ma, exceptSpot 1–10.1 that provided an age of ~27 Ma (Table 2). A coherentgroup of 12 measurements has been used to calculate a mean age of

Table 4Zircon U–Pb Shrimp data of the Çamlık pluton.

Spot U(ppm)

Th(ppm)

Th/U 206Pb*(ppm)

%206Pbc (1) 206Pb*/238U

±% (1) 207Pb*/235U

±%

1–1.1 4458 2433 0.56 14.0 0.40 0.003650 1.5 0.02408 3.61–2.1 3151 1887 0.62 10.5 0.003870 1.5 0.02573 3.11–3.1 1497 832 0.57 4.44 1.91 0.003410 1.7 0.0204 111–4.1 3375 1584 0.48 9.47 1.85 0.003229 1.9 0.0177 9.01–5.1 4510 3232 0.74 15.0 0.71 0.003857 1.5 0.02532 2.41–6.1 997 362 0.38 2.68 1.12 0.00308 6.0 0.0195 121–7.1 5046 1621 0.33 16.5 0.24 0.003790 1.5 0.02409 3.61–8.1 2797 1729 0.64 7.85 1.15 0.003247 1.6 0.02111 4.41–9.1 2324 625 0.28 7.08 0.34 0.003516 1.6 0.02119 4.51–10.1 3484 1469 0.44 10.4 0.40 0.003461 1.5 0.02216 3.81–11.1 3130 935 0.31 9.65 0.39 0.003574 1.5 0.02191 4.12–1.1 2020 498 0.25 5.63 0.69 0.003220 1.7 0.0202 9.92–2.1 2546 638 0.26 7.85 0.33 0.003571 1.6 0.02258 3.72–3.1 3519 1364 0.40 11.1 0.21 0.003644 1.5 0.0243 5.62–4.1 1142 434 0.39 3.22 1.25 0.003221 2.0 0.0208 142–5.1 2462 799 0.34 7.44 0.71 0.003492 1.6 0.02373 3.8

Errors are 1-sigma; Pbc and Pb* indicate the common and radiogenic portions, respectivelyError in standard calibration was 0.26% (not included in above errors but required when co(1) Common Pb corrected using measured 204Pb.(2) Common Pb corrected by assuming 206Pb/238U–207Pb/235U age-concordance.(3) Common Pb corrected by assuming 206Pb/238U–208Pb/232Th age-concordance.


21.91±0.33 Ma (Fig. 4a) for the emplacement age of the Çataldağpluton.

Zircons grains from the Eybek pluton are idiomorphic and trans-parent. Their aspect ratio ranges between 1:2 and 1:4 (Fig. 3b).Most zircon grains exhibit clear oscillatory and sector zoning, indicat-ing a magmatic origin. Some of the grains such as 1–1.1, 1–2.1, 1–3.1,1–4.1, 2–2.1, and 2–3.1 have apparent inner cores. Laser spots are lo-cated on the oscillatory zoned parts (Fig. 3b). Except for one spot(2–1.1), all results from the Eybek zircons gave ages between 20and 26 Ma (Table 3; Fig. 4b). Spot 2–1.1 yielded an age of 27.18±0.44 Ma. This particular age and the age obtained from Spot 1 to4.1 were excluded from the mean age calculation because of theirhigh U and Th values (Table 3). The corrected ages obtained fromSpot 2 to 4.1 are highly discordant, and hence this measurementwas not included in the mean age calculation either. The rest of themeasurements that represent a coherent age group were used to cal-culate a mean age of 23.94±0.31 Ma for the timing of the emplace-ment of the Eybek pluton (Fig. 4b).

Zircon grains from the Çamlık pluton have long prismatic or stubby,idiomorphic crystals (Fig. 3c). The outer rims of these grains display

Total207Pb/206Pb

±% Total238U/206Pb

±% (1) 206Pb/238U age

(2) 206Pb/238U age

(3) 206Pb/238U age

0.05054 1.9 273.0 1.5 23.49 ±0.35 23.45 ±0.35 23.48 ±0.380.0499 2.1 257.8 1.5 24.90 ±0.37 24.85 ±0.37 25.16 ±0.420.0538 5.1 289.5 1.7 21.94 ±0.38 22.03 ±0.37 21.81 ±0.410.0490 4.5 306.1 1.8 20.78 ±0.39 20.96 ±0.39 20.64 ±0.430.04890 1.7 258.8 1.5 24.82 ±0.36 24.78 ±0.36 24.68 ±0.410.0592 7.1 320 6.0 19.8 ±1.2 19.8 ±1.2 19.9 ±1.30.04868 1.7 263.0 1.5 24.38 ±0.36 24.40 ±0.36 24.41 ±0.380.0516 2.8 306.3 1.6 20.89 ±0.33 20.88 ±0.33 20.77 ±0.370.0499 2.6 282.2 1.6 22.63 ±0.35 22.71 ±0.36 22.73 ±0.370.0481 2.2 288.3 1.5 22.27 ±0.34 22.27 ±0.34 22.23 ±0.360.0473 2.3 278.8 1.5 23.00 ±0.35 23.06 ±0.35 23.00 ±0.370.0510 4.5 308.4 1.7 20.72 ±0.36 20.75 ±0.35 20.72 ±0.370.0496 2.6 278.7 1.6 22.98 ±0.36 23.00 ±0.36 23.01 ±0.380.0532 4.1 272.8 1.5 23.45 ±0.36 23.39 ±0.36 23.54 ±0.390.0618 3.8 304.6 1.8 20.73 ±0.40 20.72 ±0.38 20.86 ±0.410.0545 2.7 284.5 1.6 22.47 ±0.36 22.39 ±0.36 22.46 ±0.38

.mparing data from different mounts).



Table 5Zircon U–Pb Shrimp data of the Eğrigöz pluton.

Spot U(ppm)

Th(ppm)

Th/U 206Pb*(ppm)

%206Pbc (1) 206Pb*/238U

±% (1) 207Pb*/235U

±% Total 207Pb/206Pb

±% Total 238U/206Pb

±% (1) 206Pb/238U age

(2) 206Pb/238U age

(3) 206Pb/238U age

1–1.1 608 375 0.64 1.61 4.93 0.002848 3.2 0.0779 8.1 325.0 2.3 18.33 ±0.59 19.02 ±0.47 18.83 ±0.571–2.1 1225 739 0.62 3.42 1.44 0.003201 2.0 0.0246 9.5 0.0668 3.4 307.9 1.9 20.60 ±0.41 20.36 ±0.39 20.60 ±0.451–3.1 918 448 0.50 2.46 3.55 0.002988 2.5 0.0131 40 0.0668 7.0 320.1 2.1 19.23 ±0.49 19.59 ±0.42 19.39 ±0.481–4.1 629 326 0.54 1.66 4.16 0.002973 2.5 0.0221 18 0.0807 5.4 324.9 2.3 19.14 ±0.48 18.96 ±0.44 18.99 ±0.531–5.1 459 300 0.68 1.25 5.53 0.00292 3.5 0.0105 86 0.0893 8.5 315.5 2.4 18.81 ±0.66 19.29 ±0.50 19.27 ±0.621–6.1 278 140 0.52 0.756 7.86 0.00293 3.8 0.0221 43 0.115 9.8 315.4 2.9 18.83 ±0.72 18.64 ±0.61 18.80 ±0.701–7.1 318 191 0.62 0.865 6.82 0.00286 5.9 0.1040 5.8 315.6 2.8 18.4 ±1.1 18.91 ±0.54 19.00 ±0.761–8.1 1025 489 0.49 2.71 2.81 0.002957 2.4 0.0178 25 0.0745 6.1 325.0 2.1 19.03 ±0.46 19.10 ±0.41 19.25 ±0.451–9.1 511 214 0.43 1.49 6.76 0.00310 3.9 0.017 62 0.107 11 295.6 2.9 19.95 ±0.78 20.11 ±0.66 20.30 ±0.701–10.1 951 599 0.65 2.55 3.52 0.00304 3.4 0.0202 13 0.0665 5.5 321 3.3 19.59 ±0.66 19.55 ±0.66 19.35 ±0.761–11.1 559 322 0.60 1.58 8.99 0.00292 4.7 0.118 14 303.8 3.0 18.78 ±0.89 19.26 ±0.72 19.28 ±0.841–12.1 676 294 0.45 1.84 5.25 0.00296 3.6 0.0146 68 0.0883 8.9 315.6 2.3 19.06 ±0.69 19.31 ±0.48 19.32 ±0.541–13.1 527 276 0.54 1.39 5.02 0.00297 3.8 0.0274 22 0.0914 9.5 326 3.6 19.13 ±0.73 18.63 ±0.70 18.76 ±0.791–14.1 807 350 0.45 2.19 1.50 0.003089 2.1 0.0225 11 0.0686 5.9 317.2 2.1 19.88 ±0.43 19.73 ±0.42 19.99 ±0.461–15.1 674 312 0.48 1.79 2.18 0.003017 2.4 0.0157 26 0.0587 6.3 322.8 2.1 19.42 ±0.47 19.63 ±0.43 19.50 ±0.481–16.1 940 418 0.46 2.49 0.93 0.00302 3.3 0.0173 22 0.0587 4.3 324 3.1 19.46 ±0.65 19.58 ±0.62 19.71 ±0.68



magmatic oscillatory zoning and locally developed irregular recrystalli-zation zones with low CL (Grains 1–5.1, 1–11.1, 2–3.1 and 2–4.1;Fig. 3c). The inner parts of the grains show xenocrystic cores (e.g. Grains1–6.1, 1–7.1, and 2–5.1) and some recrystallization zones (e.g. Grains1–2.1 and 2–2.1). Grains 1–10.1 and 2–1.1 exhibit convoluted andcurved zoning. The obtained ages range from 19 to 25 Ma (Table 4).The calculated mean age from the whole data set is 22.60±0.77 Ma(Fig. 4c), representing the emplacement age of the pluton.

Zircons from the Eğrigöz pluton have idiomorphic and transparentcrystals with aspect ratios between 1:1.1 and 1:2.5. The CL images ofthe dated zircons commonly show magmatic oscillatory zoning withlocally developed sector zoning (Fig. 3d). The majority of the zircongrains display ordinary magmatic growth zoning, and some growthzoning around the inclusion boundaries (Grains 1.9.1 and 1.12.1;Fig. 2d). A total of 16 measurements, taken from the outer oscillatoryzones (Fig. 3d), have revealed ages ranging from 18 Ma to 21 Ma(Table 5). The calculated mean age of the Egrigöz pluton is 19.48±0.29 Ma (Fig. 4d).

5.2. 40Ar/39Ar dates

The 40Ar/39Ar ages of the plutons, obtained from hornblende, bio-tite, and K-feldspar separates, are given in Table 1, and the age spec-trum plots are shown in Fig. 5.

The two biotite separates from the Evciler granitoid display pla-teau age of 24.8±0.1 Ma (Fig. 5a and b), whereas the two hornblendeseparates yield plateau ages of 28.0±0.1 Ma and 27.7±0.1 Ma(Fig. 5c and d). The younger biotite ages likely represent the coolingages, while the slightly older amphibole ages are close to the em-placement age of the Evciler pluton.

We obtained hornblende and biotite plateau ages of 22.3±0.1 Maand 21.9±0.1 Ma (respectively, Fig. 5e–f) from the Ilıca granitoid,and of 23.5±0.2 Ma and 23.0±0.1 Ma (respectively, Fig. 5g–h)from Hıdırlar granitoid. The plateau ages of hornblende and biotiteseparates from the Kestanbol granitoid are 22.8±0.2 and 22.3±0.2 Ma, respectively (Fig. 5i–j).

The hornblende and biotite separates from the Eğrigöz plutonyielded plateau ages of 19.0±0.1 Ma and 18.9±0.1 Ma (respectively,Fig. 5k–l), and the biotite and K-feldspar separates from the Çataldağpluton gave plateau ages of 20.4±0.1 and 20.6±0.1 Ma (respectively,


Fig. 5m–n). The biotite separates from the Çamlık pluton yielded a pla-teau age of 20.3±0.1 Ma (Fig. 5o).

6. Geochemistry

We have studied a total of thirteen plutons in NW Anatolia andhave categorized them into three groups based on the nature and dis-tribution of the tectonic units into which they were intruded. Thesegroups include the granitoids of the 1—Rhodope metamorphic massif(RMG), 2—Sakarya continent (SCG) and 3—Anatolide–Tauride plat-form (ATP). The RMG group is represented by the Kestanbol pluton,while the SCG includes the Eybek, Evciler, Karakoy, Kozak, and Ilica-Samli plutons and the Hidirlar, Katrandag and Yenice stocks (Fig. 1).All these granitoids of the RMG and SCG occur north of the Izmir–An-kara–Erzincan suture zone. To the south of this suture zone, the gran-itoids of the ATPG are further subdivided into the Northern (NATPG)and Southern (SATPG) sub-groups. The Camlik and Egrigoz plutonsare part of the NATPG, whereas the Salihli and Turgutlu granitoidsin the Menderes metamorphic massif occur in the SATPG (Fig. 2).The major and trace element compositions and Sr–Nd isotopic con-centrations of representative samples from the RMG, SCG and ATPGare listed in Table 6.

We also analyzed the major and trace element compositions andSr–Nd isotopic concentrations of representative metamorphic base-ment rocks from the Sakarya continent (Kazdağ core complex andcover rocks; Altunkaynak et al., unpublished data) and the Anato-lide–Tauride platform (Menderes core complex and cover rocks;Altunkaynak et al., unpublished data) to better evaluate the natureand extent of continental crust–magma interaction. In addition, weevaluated metamorphic rocks of the Pelagonian zone in Greece (Bri-que et al., 1986; Pe-Piper et al., 2002; Anders, 2005), the central Pon-tides of northern Turkey (Nzegge et al., 2006) and the Istranca massifin northwestern Turkey (G. Sunal, unpublished data) as possible ana-logs for the rocks in which the different groups of granitoids, northand south of the IASZ were emplaced. Kula alkaline basalts represent-ing the depleted mantle-derived melts (Aldanmaz et al., 2000, Alıcı etal., 2002, Dilek and Altunkaynak 2010), dioritic enclaves and lavasrepresenting enriched mantle melts (EMM) from China and westernAnatolia (Yang et al., 2004; Altunkaynak et al., 2010) and granitoidsemplaced into other metamorphic core complexes in the northern(Rhodope massif) and central (Cyclades) Aegean province are also



4

8

12

16

20

24

28

32

0.0 0.2 0.4 0.6 0.8 1.0

Cumulative 39 Ar Fraction Cumulative 39 Ar Fraction




Evciler-Biotite-1

a

c d

e f

g h

b

Plateau age = 24.8 ± 0.1 Ma(1σ, including J-error of .25%)MSWD = 0.60, probability=0.94

Includes 99.69% of the 39Ar

Age

(M

a)

Hıdırlar-HornblendePlateau age = 23.5 ± 0.2 Ma(1σ, including J-error of .25%)MSWD = 1.19, probability=0.22

Includes 99.53% of the 39Ar0

10

20

30

40

50

0.0 0.2 0.4 0.6 0.8 1.0

Age

(M

a)

Age

(M

a)

0

10

20

30

40

50

60

0.0 0.2 0.4 0.6 0.8 1.0

Plateau age = 28.0 ± 0.1 Ma(1σ, including J-error of .25%)

MSWD = 0.80, probability=0.68

Includes 78.7% of the 39

Ar

Evciler-Hornblende-1

Age

(M

a)

0

10

20

30

40

50

0.0 0.2 0.4 0.6 0.8 1.0




Ar

Hıdırlar-Biotite

Age

(M

a)

0

10

20

30

0.0 0.2 0.4 0.6 0.8 1.0




Ar

Ilıca-Biotite

Age

(M

a)

4

8

12

16

20

24

28

32

0.0 0.2 0.4 0.6 0.8 1.0




Ar

Evciler-Biotite-2

Age

(M

a)Plateau age = 27.7 ± 0.1 Ma(1σ, including J-error of .25%)



Ar

Evciler-Hornblende-2

0

10

20

30

40

50

60

0.0 0.2 0.4 0.6 0.8 1.0

Ilıca-HornblendePlateau age = 22.3 ± 0.1 Ma(1σ, including J-error of .25%)MSWD = 0.91, probability=0.57

Includes 83.1% of the 39Ar0

10

20

30

40

50

0.0 0.2 0.4 0.6 0.8 1.0

Age

(M

a)

Fig. 5. 39Ar/40Ar plateau age spectrums of western Anatolian granitoids. Summary of the ages are listed in Table 1. Plateau steps are shown as white color whereas rejected ones areblack. Box heights are 1 sigma errors.


Please cite this article as: Altunkaynak, Ş., et al., Spatial, temporal and geochemical evolution of Oligo–Miocene granitoid magmatism in westernAnatolia, Turkey, Gondwana Res. (2012), doi:10.1016/j.gr.2011.10.010


i j

k l

m n

o

Fig. 5 (continued).




Fig. 6. a—Total alkali vs. SiO2 classification diagram (Cox et al., 1979) and b—AFM diagram of western Anatolian granitoids (Irvine and Baragar, 1971).


used for comparison (Fig. 1; Christofides et al., 1998; Pe-Piper andPiper, 2001; Pe-Piper et al., 2002).

6.1. Major and trace element characteristics

The SiO2 contents of the RMG and SCG groups vary between 52.74and 66.77 wt.%, whereas those of the ATPG group ranges from 65.78to 72.13 wt.%. The SiO2 contents of magmatic enclave from the ATPGcontains only 58.91 wt.% SiO2. The RMG and SCG plutons are hencerepresented mainly by intermediate and silicic rocks based on theirSiO2 contents, whereas the ATPG plutons are mostly silicic in compo-sition. On a TAS diagram (Fig. 6a; Cox et al., 1979), the RMG plutonsrange from granodiorite, monzonite to syenite. Samples from theSCG plutons span a wide range of rock types, extending from syeno-diorite, monzonite and diorite to granodiorite. The ATPG plutonsplot in the granodiorite and granite fields. One of the magmatic en-claves analyzed from the ATPG is classified as monzodiorite.

Fig. 7. K2O vs. SiO2 diagram of western Anatolian granitoids using the classificationscheme of Peccerillo and Taylor (1976). See Fig. 6 for the symbols.


The majority of the samples are subalkaline in nature and dis-play a calc-alkaline trend (Irvine and Baragar, 1971; Fig. 6b), exceptfor the two alkaline samples from the RMG and one sample from aSCG pluton (Katrandağ granite) (Fig. 6a). On the K2O vs. SiO2 clas-sification diagram of Peccerillo and Taylor (1976), all pluton sam-ples from the RMG, some samples from the SCG plutons (Evciler,Karakoy, and Yenice granitoids), and one sample from the ATPGpluton (Çamlik granitoid) are classified as shoshonitic, while theothers are high-K calc-alkaline in character. Two samples from theKatrandağ and Yenice granitoids (SCG) are medium-K in character(Fig. 7). The A/CNK [Al2O3/(CaO+Na2O+K2O) molecular ratio]values of the analyzed granitoids range between 0.70 and 1.0. Allsamples of the RMG and SCG plutons are metaluminous (Fig. 8;Shand 1927). The least evolved members of the ATPG plutons andtheir enclave are predominantly metaluminous, although somemore evolved samples exhibit slightly peraluminous signatureswith A/CNK ratios ranging from 1.1 to 1.2. In the same diagram,

Fig. 8. A/CNK vs. A/NK plot of western Anatolian granitoids (Shand, 1927).



Fig. 9. Major and trace element versus SiO2 variation diagrams for western Anatoliangranitoids. See Fig. 6 for the symbols.

0.1

1

10

100

1000

CsRbBa Th U NbTa K La CePb Pr Sr P Nd ZrSmEu Ti Dy Y Yb Lu

Av. Lower crust

Av. Middle crust

Av. Upper crust

Av. Kula basalt

SATPG

NATPG

RO

CK

/N-M

OR

B

0.1

1

10

100

1000

Cs RbBaTh U Nb Ta K La CePb Pr Sr P Nd Zr SmEu Ti Dy Y YbLu

SCG

Av. Lower crust

Av. Middle crust

Av. Upper crust

Av. Kula basalt

RMG

RB

RO

M-N

/KC

O

a

b

Fig. 10. N-MORB normalized multi-element patterns for the RMG and SCG (a) andATPG (b). N-MORB normalizing values are from Sun and McDonough (1989).


the metamorphic basement rocks of the Sakarya continent and theATP are predominantly peraluminous (A/CNK=1.1–1.9), with theexception of three samples from the SC basement that are metalu-minous (A/CNK=0.9–1.0) (Fig. 8). Both the basement and graniticrocks have similar A/NK (Al2O3/Na2O+K2O) ratios between 1.1 and2.5. All of the granitoid samples display I-type granite affinity, al-though two haplogranite sample of the ATPG pluton shows S-typeaffinity (Fig. 8).

In the SiO2 variation diagrams (Fig. 9), the TiO2 (0.37–0.79 and0.21–0.62 wt.%, respectively), Al2O3 (15.27–17.58 and 14.35–16.66 wt.%), FeO* (3.49–7.09 and 1.86–3.83 wt.%), MgO (1.60–3.38 and0.42–1.50 wt.%), CaO (3.67–7.08 and 1.04–4.56 wt.%) and P2O5

(0.12–0.75 and 0.08–0.25 wt.%) contents of the SCG and ATPG plutonsamples decrease with increasing SiO2 (52.74–66.77and 65.20–72.13 wt.%, respectively). In these diagrams, the RMG samples display


trends that differ from those of the other groups. For example, the TiO2

(0.44–0.48 wt.%), FeO*(3.85–4.50 wt.%) and CaO (3.44–3.95 wt.%) con-tents of the RMG pluton samples remain nearly constant with increasingSiO2 (57.09–65.51 wt.%) contents, and these rocks display two separatetrends in the diagrams of K2O (5.09–6.99 wt.%), MgO (1.38–1.71 wt.%)and Al2O3 (15.42–18.55 wt.%) against SiO2. The SCG samples (Katrandagand Yenice granitoids) and the magmatic enclave from the ATPG are theleast evolved samples with the highest MgO (2.70 wt.%), TiO2

(1.19 wt.%) and FeO* (7.89 wt.%) contents. The ATPG contains the mostsilicic compositions. The Sr (695–1573 ppm and 163–671 ppm, respec-tively) and Zr (235–391 ppm and 114–224 ppm, respectively) contentsof the RMG and ATPG plutons decrease whereas the SCG samples (Sr:421–785 ppm, Zr: 95–164 ppm) stay almost constant (or slightly de-crease) with increasing SiO2 contents. The Rb contents (38–160 ppm,178–268 ppm and 75–155 ppm, respectively) of the SCG, RMG andATPG display a positive correlation with SiO2 (Fig. 9).

On N-MORB normalized spider diagrams (Fig. 10a and b), all groups(RMG, SCG and ATPG) display similar patterns with enrichment in themost incompatible elements (e.g., Rb, Ba, Th, U, K, La and Ce) and deple-tion in Nb, Ta, Ti, P and Zr. All of the granitoid groups are stronglyenriched in LILE and LREE compared to the average lower crust, and dis-play trace element compositions similar to average middle and upper



La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

110

100

1000

RO

CK

/CH

ON

DR

ITE

RO

CK

/CH

ON

DR

ITE

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

110

100

1000

Ave. Kula BasaltAve. Lower CrustAve. Middle CrustAve. Upper Crust

RMGSCG

Ave. Kula BasaltAve. Lower CrustAve. Middle CrustAve. Upper Crust

ATPG

a

b

Fig. 11. Chondrite-normalized REE patterns for the RMG and SCG (a), and ATPG(b). Chondrite normalizing values are from Boynton (1984).

0.700 0.705 0.710 0.715 0.720 0.725

-10

-50

5

Nd

(20)

SC basementCyclades Granites

Rhodope granites (N. Greece)

Kula Basalts

ATP basement

KozakEybekHidirlar

EvcilerKatrandag Karaköy

Yenice

CamlikKestanbol

EgrigozSalihli (SATPG)

SCG

NATPGATPG

RMG

Aegean Sea Sediments

Global river average

OIB

SCLM melting array

Ave.EMM

87Sr/ 86Sr(20)

Fig. 12. εNd(20) vs. 87Sr/86Sr(20) diagram for western Anatolian granitoids. Data source:ATP (Menderes core and cover rocks) and SC (Kazdağ core and cover rocks) middle–upper crustal compositions: Altunkaynak (unpub. data), Pelagonian Upper Crust : Anders(2005), Santorini UC: Briqueu et al. (1986), Rhodope granites: Christofides et al. (1998),Cyclades granitoids and Hercinian protoliths: Pe-Piper and Piper (2001, 2006), Kula ba-salts: Dilek and Altunkaynak (2010), average EMM (enriched mantle melts: Yang et al.(2004) and Altunkaynak et al. (2010)), lithospheric mantle melting array: Davis and vonBlanckenburg (1995), Aegean Sea sediments: Altherr et al. (1988) and Global River Aver-age: Goldstein and Jacobsen (1988).

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

0 0.5 1 1.5 2

Rhodope granites (Greece)

Hercynian protoliths

ATPbasement

Kula basaltsSCG

SATPGNATPG

RMG

Cyclades granitoids

SC basement

Nd

TDM (Ga)

NATPG

SATPG

Ave.EMM

Fig. 13. εNd(i) vs. TDM (Nd-model ages) diagram of the RMG, SCG and ATPG. See Fig. 12for data source.


crustal values. They also display a significant positive Pb anomaly,which is not shown by the Kula basalts. Compared to N-MORB, theATPG samples and the SCG and RMG samples show a ~300 times anda ~100 times enrichment in Pb, respectively. The granitoid groupshave variable Ce/Pb ratios ranging from 1.1 to 4.4 that are similar tothe Ce/Pb ratios of the average middle continental crust (Ce: 43 ppm,Pb: 11 ppm; Ce/Pb=3.9) and average upper crustal values (Ce:63 ppm, Pb: 17 ppm, Ce/Pb=3.7; Rudnick and Gao, 2003).

On chondrite-normalized spider diagrams (Fig. 11a and b), the REEdistributions of the SCG samples display considerable LREE enrichmentswith respect toMREE and HREE (Lan/Ybn=10.5–24.8) with someminordepletions in MREE (Gdn/Ybn=1.2–2.4; Fig. 10a). Their HREE patternsshow nearly flat trends. The overall REE concentrations of these samplesfall between those of the Kula basalts and the average middle–uppercontinental crust. The SCG group is characterized by either minor nega-tive or slightly positive Eu anomalies. (Eu/Eu*=0.80–1.25). Only threesamples from the SCG intrusions (Ilıca-Şamlı granite, one sample fromHidirlar) display pronounced negative Eu anomalies (Eu/Eu*=0.51–0.61). In contrast, the ATPG samples show REE patterns sim-ilar to those of the average upper crust with significant negative Euanomalies (Eu/Eu*=0.30–0.60). The granodioritic samples of the RMGgroup are transitional between those of the SCG and the ATPG groups


on the basis of their Eu anomalies (Fig. 11a and b), whereas the syeniticsamples show positive Eu anomalies.

6.2. Sr and Nd isotopic signatures and Nd model ages

Sr and Nd isotopic data for the analyzed samples are shown inTable 6. The initial Sr and Nd isotopic ratios (87Sr/86Sr(i); 143Nd/144Nd(i)) were calculated for the RMG, SCG and ATPG groups assum-ing a mean magma crystallization age of 20 Ma. The 87Sr/86Sr(i) ratiosvary from 0.705248 to 0.711428, and 143Nd/144Nd(i) values rangefrom 0.512619 to 0.512184. The Karakoy granitoid of the SCG groupis characterized by the lowest 87Sr/86Sr(i)=705248–0.706106 andthe highest 143Nd/144Nd(i)=0.512619–0.512548 values. The samples



20 40 60 80 100 120

010

2030

4050

KozakEybekHidirlar

EvcilerKatrandag Karaköy

IlıcaYenice

CamlikKestanbol

EgrigozSalihli (SATPG)

SCG

NATPGATPG

RMG

La (ppm)

La /Y

b(n)

FFCC

Parti

al m

eltin

g10 20 30 40

0.0

0.1

0.2

Nb (ppm)

Nb

/Zr

MMA

MMA

Kula Basalts

Kula Basalts

Partia

l mel

ting

FFCC

Fig. 14. La/Yb versus La (ppm) diagram illustrating the effects of partial melting in comparison to fractional crystallization. The inset diagram shows the variations of Nb/Zr withchanging Nb contents of the rocks. Vectors for FC and PM are from Thirlwall et al. (1994).


from the southern sub-group (SATPG) of the ATPG display higher87Sr/86Sr(i) (87Sr/86Sr(i)=0.711428–0.71080) and lower 143Nd/144Nd(i) (143Nd/144Nd(i)=0.51227–0.512184) ratios compared tothose of the RMG samples (87Sr/86Sr(i)=0.707966–0.708799, 143Nd/144Nd(i)=0.512408–0.512335) and SCG (average: 87Sr/86Sr(i)=0.707540, 143Nd/144Nd(i)=0.512450). The samples from the north-ern sub-group (NATPG) of the ATPG have initial Sr and Nd isotopic ra-tios of 0.708001–0.709039 and 0.512370–0.512348, respectively,which are similar to those of the RMG and SCG samples (Table 6).

The calculated εNd(i) values for the western Anatolian granitesrange from −0.2 to −8.35, with one sample from the SCG (Karakoypluton) showing a value of +0.12. The SATPG samples have the low-est εNd(i) values varying from −8.4 to −7.6, whereas the SCG sam-ples have the relatively highest εNd(i) values between +0.12 to−6.3. The RMG and NATPG groups have values intermediate betweenthese other two groups (Fig. 12). The Kula basalts from western Ana-tolia have εNd(i) values varying from +5.2 to +6.5 (average: 6.1).The RMG, SCG and NATPG samples lie on an array between the Kulabasalt field, representative of the partial melts of depleted Aegeanmantle (Aldanmaz et al., 2000; Alıcı et al., 2002), and the metamor-phic basement rocks occurring to the north (SC) and the south(ATP) of the Izmir–Ankara–Erzincan suture zone (Fig. 12), whichare similar to the Rhodope granites from northern Greece–Bulgaria.In contrast, the Cyclades granitoids from the Aegean Sea, as well asthe SATPG samples from our study area plot in the field of the ATPbasement rocks. The ATP crystalline basement rocks have εNd(i)values ranging from −11.5 to −6.3 (average: −7.5). The SC crystal-line basement rocks have more restricted values of εNd(i) rangingfrom −11.3 to −7.1 (average: −8.8) (Fig. 12).

The Nd depleted mantle model (TDM) and the εNd values of thelate Oligocene–middle Miocene granitoids are plotted together inFig. 13. The RMG and SCG plutons, which were emplaced into themetamorphic basement rocks to the north of the suture zone (IASZ)have younger TDM ages in comparison to those of the ATPG plutonsthat were emplaced into the basement rocks in the ATP south of thesuture zone. The TDM of RMG and SCG plutons range from 0.6 to1.2 Ga, corresponding to a Proterozoic age, similar to the Rhodope


granites from northern Greece–Bulgaria. This time constraint is con-sistent with the inferred extraction age of the K-enriched subconti-nental lithospheric mantle source of the post-collisional lavas inwestern Anatolia (0.9–1.0 Ga; Altunkaynak, 2007) and of the Rhodo-pe granites in northern Greece (Christofides et al., 1998; Pe-Piper andPiper, 2001; Pe-Piper et al., 2002). The TDM ages of the ATPG plutonsrange from 1.2 to 1.6 Ga and constrain the residence age of theirsource in the continental crust as the middle Proterozoic. Thismodel age is consistent with those of the Cyclades granitoids andthe ATP, representative of the Pan-African crust (Fig. 13) (Pe-Piperand Piper, 2001, 2006; Pe-Piper et al., 2002).

7. Petrogenesis

7.1. Source characteristics

All pluton groups are subalkaline in nature, as revealed by theirmajor and trace element characteristics (Fig. 6a). Only two syeniticsamples from the RMG plutons and one sample from the SCG are al-kaline. All groups are also potassic in character (high K-calcalkalineto shoshonitic), resembling the compositions of those granitoidscommonly known as post-collisional in origin. The granitoids havemoderately to highly evolved compositions, as shown by their Mg-numbers (Fig. 8, average Mg#=50 and 35, respectively) and silicacontents. All of the granitoid groups are represented by metalumi-nous to slightly peraluminous, I-type granitoids, whereas two haplo-granite samples representing the most evolved members of theNATPG are slightly to moderately peraluminous, S-Type granitoid(Fig. 8). The RMG, SCG, and NATPG plutons, which were emplacedinto different tectonostratigraphic units, show similar major andtrace element characteristics and overlapping Sr–Nd isotopic ratios.These observations may be attributed to similar evolutionary trendsand/or common melt sources. The SATPG plutons show higher Srand lower Nd isotopic compositions than those of the other groups.Given the geochemical affinities among the RMG, SCG and NATPGplutons (Figs. 12 and 13) and their distinctive isotopic differences



0.705 0.710 0.715

02

46

8

0.705 0.710 0.715

1020

3040

Ave. Kula Basalt(Ce/Pb=20) Ave. Kula Basalt

Ave. SC basement

0 0.002 0.004 0.006 0.008 0.0100.70

50.

706

0.70

70.

708

0.70

90.

710

0.71

1

Ope

n S

yste

m

Closed system

b

c d

Ce/

Pb

0.1 1.0 10 100 1000

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Nb/

La

Subduction zoneenrichment

Cru

stal

con

tam

inat

ion

Kula basalts(Ave. Nb/La:2.3Ave. Ba/Rb: 12)

a

UC

Ave. EMM

87Sr/86Sr(i) 87Sr/86Sr(i)

87S

r / 86

Sr

Ba/Rb 1/Sr

Zr/

Sm

Fig. 15. a—Nb/La versus Ba/Rb diagram illustrating the effects of crustal contamination and subduction metasomatism during evolution of the MEG. CC (Average Continental Crust):McLennan (2001), EMM (average enriched mantle melts): Yang et al. (2004) and Altunkaynak et al. (2010), Kula basalts: Dilek and Altunkaynak (2010). b—87Sr/86Sr vs. 1/Sr dia-gram, c—Ce/Pb vs. 87Sr/86Sr(i) diagram and d—Zr/Sm vs. 87Sr/86Sr(i) diagram for RMG, SCG and ATPG.

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

10 12 14 16 18 20 22 24 26 28

EVCILER

KARAKOY

KOZAK

ILICA

EYBEK

YENICE

HIDIRLAR

SALIHLI (SATPG)

CAMLIK

EGRIGOZ

KESTANBOL (RMG)

Incr

easin

g cr

usta

l sign

atur

e

Initi

atio

n of

mild

ly a

lkal

ine

volc

anis

m

Calc-alkaline volcanism associated with plutonism

Initi

atio

n of

alk

alin

e vo

lcan

ism

SCG

NATPG

Exhumation of MM andKD core complexes

εNd i

Average age (Ma)

Fig. 16. εNd(i) vs. average age diagram for western Anatolian granitoids. MM: Menderes core complex, KD: Kazdağ core complex. See Fig. 2 for data source.




0.70

0.71

0.72

0.73

0.74

8060 65 70 7545 50 55

Ave. upper crust (Sunal, unpub. data)

SCG

RMG

SC basement

Ave. Kula basalt

EMM

Ave. upper crust (Nzegge et al., 2006)

Ave. gneiss; Kazdag Massif

Ave. amphibolite, Kazdag Massif

87S

r/86

Sr

(20

Ma)

87S

r/86

Sr

(20

Ma)G

H

A

I JB

0.70

0.71

0.72

0.73

0.74

8060 65 70 7545 50 55

G

H

A

I JB

(G)(H)

(I) (J)

(G)(H)

(I)

(J)

a c

b d

8060 65 70 7545 50 55 8060 65 70 7545 50 55

G

H

A

I

JB

(H)

(J) (G)

(I)

(J)

0.5118

0.5122

0.5126

0.5130

0.5134

143 N

d/14

4 Nd

(20

Ma)

143 N

d/14

4 Nd

(20

Ma)

0.5118

0.5122

0.5126

0.5130

0.5134

G

H

A

I

J

B(I)

(G)

SiO2 (wt%) SiO2 (wt%)


Fig.17. Plots of 87Sr/86Sr(i) and 143Nd/144Nd(i), calculated at 20 Ma, versus SiO2 (wt.%), showing the results of AFC and bulk mixing modeling for the SCG and RMG. For the AFCmodels (a–b), an average Kula basalt (A), representative of a depleted mantle-derived melt, and a melt derived from an enriched mantle source (EMM; B) were used as startingmagmas and different crustal compositions as contaminants: average upper crust (Nzegge et al., 2006) (G); average upper crust (Sunal, unpub. data) (H), average amphibolitefrom the Kazdag Massif (Altunkaynak, unpub. data) (I), and average gneiss from the Kazdag Massif (Altunkaynak, unpub. data) (J). AFC model input parameters were: r=0.8,DSiO2=0.9, DSr=1.1, DNd=1.2. The dots along the AFC curves represent F (fraction of melt remaining) values decreasing in steps of 0.1 from left to right. The crustal contaminantfor each AFC curve is indicated in brackets. Bulk mixing arrays between the same endmembers with the dots along the lines at 20% intervals are shown in c–d.


from the SATPG plutons, we focus the remaining discussion on thesetwo distinct magmatic groups.

The RMG–SCG–NATPG plutons are isotopically depleted (εNd(i)=+0.12 to −6.3, 87Sr/86Sr(i)=0.705248–0.709900), with respect to thesamples from the SATPG (87Sr/86Sr(i)=0.711428–0.71080, εNd(i)=−8.4 to−7.6). These isotopic features imply either different source ma-terials or different degrees of crustal contamination. The RMG, SCG andNATPG samples have low εNd values and relatively high 87Sr/86Sr(i) com-positions and display relatively high Mg-numbers and high abundancesof many incompatible elements, suggesting derivation of their meltfrom a mantle source (Figs. 12 and 13). In Fig. 12, RMG–SCG–NATPG ex-hibit systematic co-variations within the lithospheric mantle array whichlies between the Kula basalts and the metamorphic basement rocks andlook similar to those of Rhodope granites in northernGreece and enrichedlithospheric mantle melts (EMM) from China and Turkey (Yang et al.,2004, Altunkaynak et al., 2010). These features indicate that melting ofan enriched lithospheric mantle was involved in the evolution of RMG–SCG–NATPG magmas. However, some of these granitoids have lower87Sr/86Sr ratios and higher εNd(i) values (+0.12 to −1.50) compared tothe enrichedmantlemelts (EMM). Hence, they display transitional valuesbetween the depleted and enriched mantle melts. Similarly, it can be in-ferred from Fig. 13 that the RMG–SCG and someNATPG plutons have iso-topic compositions andTDMages (TDM=0.6–1.2 Ga) transitional betweenthose of the Kula basalts (TDM=0.3 Ga), EMM (TDM=0.9–1.1 Ga) and


the crystalline basement rocks (TDM=1.2 to 2 Ga). Therefore, thesemodel ages may indicate mixed model ages between the two end-members rather than crustal extraction ages for each end-member.Based on these lines of evidence, we deduce thatmelting of enriched lith-ospheric mantle and/or depleted mantle melts (at least partly) have con-tributed to the RMG–SCG–NATPG source region. The systematic co-variation between mantle and crustal components and the large rangeof the TDM ages is also consistent with the evolution of the RMG–SCG–NATPG granitoid magmas through various degrees of crustal assimilationor mixing of mantle melt with an evolved crustal component in differentproportions (McCulloch and Chappell, 1982; Arndt and Goldstein, 1987;Chappell, 1996; Jwa, 2004, Sun et al., 2010). It is also apparent fromFig. 12, for the genesis of the RMG–SCG–NATPGmagmas, a potential con-tribution of crustal materials would have been lower in comparison tothose of the SATPG magmas. On the other hand, the SATPG sampleswith crust-like geochemical signaturesmayhave beenproducedby crust-al melting or significant contributions from the ATP crystalline basement.(Figs. 12 and 13)

Both the SC and ATP metamorphic basement rocks have higher A/CNK values and lower Mg-numbers in comparison to the granitoid sam-ples from the RMG–SCG. As the SC and ATP metamorphic basementrocks are dominantly peraluminous (Fig. 8), crustalmelting or a large de-gree of crustal contamination of the magmas would further increasetheir A/CNK ratios and cause the formation of strongly peraluminous S-



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Fig. 18. Plots of (87Sr/86Sr)i and (143Nd/144Nd)i, calculated at 20 Ma, versus SiO2 (wt%), showing the results of AFC and bulk mixing modeling for the ATPG. As in Fig. 17, an averageKula basalt (A), representative of a depleted mantle-derived melt, and a melt derived from an enriched mantle source (EMM; B) were used as starting magmas in the AFC models(a–b), alongside amphibolite from the Menderes Massif (E). Chosen crustal contaminants are: average upper crust (Anders, 2005) (C), upper crustal composition (UC9 from Anders,2005) (D), average amphibolite from the Menderes Massif (Altunkaynak, unpub. data) (E), and average gneiss from theMenderes Massif (Altunkaynak, unpub. data) (F). AFC modelinput parameters and explanations as in Fig. 17. Bulk mixing arrays between the same endmembers with the dots along the lines at 20% intervals are shown in c–d.


type granitoids. Therefore, we infer that none of the analyzed granitoidscould have been produced solely by these basement units. The metalu-minous to slightly peraluminous I-type character of the RMG–SCG–NATPG plutons precludes metapelitic rocks of the RM-SC and ATP base-ment as suitable source materials. Instead, it points to an igneous proto-lith such as metabasalt, juvenile K-rich basaltic underplate magma, and/or mantle rocks (Roberts and Clemens, 1993; Tepper et al., 1993; Pearce,1996; Patiño Douce andMcCarthy, 1998; Von Blanckenburg et al., 1998;Altherr and Siebel, 2002; Ashwall et al., 2002). On the other hand, thegeochemical and isotopic compositions and TDM ages of SATPG samplesoverlap with those of the middle to upper crustal rocks of the ATP base-ment indicating a significant crustal contribution from the ATP crystal-line basement (Figs. 8, 12 and 13).

Experimental studies report that hydrous melting of amphibolitesor basalts could produce tonalitic magmas and subsequent magma–crust interaction and/or fractional crystallization of these magmasyields granodioritic to granitic compositions. (Rapp and Watson,1995Patiño Douce, 1996, 1999; Patiño Douce and McCarthy, 1998).These studies also demonstrate that, regardless of the degree of par-tial melting, partial melts of metabasalts are characterized by rela-tively high Na2O (>4 wt.%) and low Mg numbers . The low Na2Ocontents (b4) and relatively high Mg numbers of RMG–SCG–NATPGsamples eliminates metabasalts as a suitable source material. Besidesthat, some researchers have argued that metabasaltic rocks are notsuitable source rocks for the generation of high-K calc-alkaline, I-type granitoids as metabasalts contain low-K2O and insufficient


incompatible trace elements to form appreciable volumes of graniticmelts (Roberts and Clemens, 1993; Ashwall et al., 2002). Therefore,the high-K calc-alkaline, and incompatible element-enriched natureof the RMG–SCG–NATPG and SATPG suggest that a purely metabasaltsource is not suitable for their magmas.

The REE patterns of all granitoid groups are parallel to each otherand define a trend between Kula basalts and middle–upper crustalrocks. The majority of the plutons display concave-upward patternswith only minor or no negative Eu anomalies, indicating aplagioclase- and garnet-poor and amphibole-, clinopyroxene- andtitanite-rich residual source (Altherr and Siebel, 2002) (Fig. 11a, b).Although some samples from NATPG display weakly to moderatelyperaluminous S-type affinity, isotopic compositions of these samplesoverlap with those of I-type granitoid samples from NATPG and SCG(Fig. 12). The REE patterns of these samples display more pronouncednegative Eu anomalies in comparison to other granitoids groups.Using the REE patterns of the ATPG samples, we can infer that theserocks show evidence for amphibole and feldspar fractionation duringmagma evolution, rather than a garnet bearing mantle source. Partialmelting models show that steep partial melting trajectories observedin Nb/Zr vs. Nb and La/Yb vs. La plots (Fig. 14) can only be producedby partial melting of a residual garnet-bearing mantle source(Thirwall et al., 1994), and that the effect of partial melting wasmore important than the sole influence of fractional crystallizationin controlling the compositional variations in both RMG–SCG andATPG plutons.



Fig. 19. Schematic model for the spatial, temporal and geochemical evolution of late Oligocene to middle Miocene magmatism in western Anatolia and the Aegean region.


7.2. Magma evolution

The RMG–SCG–NATPG and SATPG samples display LILE enrichmentand negative Nb, Ta, Ti, and P anomalies (Fig. 10a, b). These featuresare consistent with derivation of their magmas from an incompatible el-ement enriched source similar to those of rocks that form at convergentmargin settings (Pearce, 1982; McDonough, 1990; Pearce et al., 1990;Thirlwall et al., 1994; Pearce and Peate, 1995; Eyuboglu et al., 2011)and/or post-collisional granitoids (von Blanckenburg and Davies,1995). The subduction-related enrichment of the mantle source mayhave been a result of either arc-derivedmagmas or a subduction compo-nent inherited from earlier convergent margin events. Source enrich-ment through previous subduction events in the region has beensuggested for the western Anatolian plutons and related volcanism bysome authors (Yılmaz and Polat, 1998; Aldanmaz et al., 2000; Yılmaz etal., 2000; Dilek and Altunkaynak, 2007). Although subduction-inducedmantle metasomatism can account for enriched source characteristicsof the studied granitoids, it can be argued that the multi-element pat-terns and isotopic compositions shown by the Oligo–Miocene granitoidscould have also been inherited from crustal contamination (Figs. 10–13).The analyzed samples display similar trace-element patterns, compara-ble to those of the middle–upper continental crust (Fig. 10), whichmight have been inherited from crustal melts of variablemagma sources


and source compositions. In the Nb/La vs. Ba/Rb plot (Fig. 15a), observedin these samples cannot be explained solely by this mechanism. The ver-tical trend between continental crust andmantle derivedmelts (Kula ba-salts and EMM) suggests mixing or AFC of amantle derivedmagmawitha crustal component, rather than the sole influence of subduction gener-ated fluids (Tatsumi et al., 1986; Pecerillo, 1999; Wang et al., 1999;Marchev et al., 2004). Therefore, a critical evaluation of possible contam-ination by crustalmaterial is crucial to understandgranitoidmagmagen-eration in western Anatolia.

The relatively constant 1/Sr ratios, increasing Zr/Sm and decreas-ing Ce/Pb ratios with increasing 87Sr/86Sr(i) suggest that open-system evolutionary processes played an important role in the gener-ation of these granitoids (Fig. 15a–d). Individually, each granitoidgroup displays isotopically uniform signatures but dispersed variationpatterns in the Rb, Sr, Zr and Mg-number vs. SiO2 diagrams (Fig. 9).This may have been caused by heterogeneity in the source and/or dif-ferent compositions of the overlying crust, through which the RMG,SCG, and ATPG granitoid magmas migrated. Therefore, the observedgeochemical features of the late Oligocene–middle Miocene granit-oids may indicate that both varying degrees of crustal contaminationof mafic parental magmas and/or different compositions of the over-lying crust were in part responsible for the geochemical differencesbetween these granitoid suites. In order to test these alternative




processes, we evaluated εNd(i) vs. TDM (depletedmantle model age) re-lationships (Fig. 13).

On the εNd(i) vs. TDM diagram, the RMG and SCG granitoids plot onan array between the fields of the Kula basalts and the metamorphicbasement rocks of the SC (north of the suture zone) which overlapswith the fields of the Hercynian protoliths and the Pelagonian uppercrust and the crystalline basement of the ATP (south of the suture).The RMG and SCG granitoids have generally younger TDM values(0.6–1.2 Ga) compared to the SC basement and ATPG granitoids(1.2–1.6 Ga). The RMG and SCG granitoids with the youngest TDMvalues are characterized by a high amount of mantle-derived proto-liths in the mixed source, and the extraction age of their mantle ma-terial is younger than 1.2 Ga. Based on the patterns observed inFigs. 12 and 13, we conclude that the samples from the RMG andSCG granitoids have isotopic compositions and TDM ages similar tothose of the Rhodope granites in Bulgaria–Greece. Christofides et al.(1998), Pe-Piper and Piper (2001) and Pe-Piper et al. (2002) sug-gested that fractionation of mafic magmas and/or their mixing withfelsic crustal material, some of which was derived by crustal anatexiscould produce the granitoid plutons of the Rhodope massif. The dis-tribution of the TDM values of the NATPG samples shows a slight over-lap with those of the RMG and SCG plutons, and they generally haveolder TDM values (>1.2 Ga) that are similar to those of ATP basement.On the same diagrams, it can be inferred that the NATPG sampleshave a higher amount of crustal and a minor mantle component inthe mixed source in comparison to the RMG–SCG samples. It is alsoapparent from Fig. 13 that the SATPG samples plot in the field of themetamorphic basement rocks from the ATP and the Hercynian proto-liths, and show close similarities to the Cyclades granites from thecentral Aegean Sea. We can deduce that the extraction age of crustalsource rocks might be slightly older than 1.2 Ga, which is consistentwith the TDM model ages of the crystalline basement rocks repre-senting those occurring south of the suture zone (IASZ). This inferredage is consistent with that of the Pan-African crustal rocks and indi-cates that the both the NATPG and SATPG magmas were strongly af-fected by the ATP basement units. Alternatively, as the isotopiccompositions and TDM ages of the SATPG samples overlap withthose of middle–upper crustal rocks of ATP basement rocks an originas a middle crustal melt cannot be discarded. Some authors suggesteda metasedimentary crustal source for the generation of the I- and S-type granitoid plutons in the Cyclades, which shows similar geo-chemical and isotopic features to those of the ATPG samples(Altherr and Siebel, 2002; Stouraiti et al., 2010).

The isotopic compositions vs. average cooling ages of the RMG, SCGandNATPG granitoids as reported by previousworkers and in this study(Table 1) suggest an increasing crustal signature (crustal contamina-tion)with time (Fig. 16). The youngest granitoid group in northwesternAnatolia, SATPG (16 Ma; Catlos et al. ., 2008), displays a strong crustalsignature, and the timing of its formation corresponds to the time inter-val between the initiation of mildly alkaline and strongly alkaline volca-nism in western Anatolia (Altunkaynak and Dilek, 2006).

7.3. Petrogenetic modeling

In order to test quantitatively whether open-system processes canexplain the geochemical and isotopic variations and magmatic evolu-tion of the western Anatolian granitoids, we conducted assimilationand fractional crystallization (AFC) and simple bulk mixing modeling(Figs. 17 and 18) and evaluate these contrasting models for the SCG–RMG and the ATPG, respectively. In the AFC models (Figs. 17a–b and18a–b), calculated using the equations of DePaolo (1981), it is as-sumed that a primary magma with an isotopic composition similarto an average Kula basalt (representative of a melt derived from de-pleted mantle) and a melt derived from an enriched mantle source(EMM) evolved by crystal fractionation to give rise to a series of de-rivative magmas, which subsequently assimilated different amounts


of crustal material, thus increasing the effects of crustal contamina-tion with the degree of differentiation. To account for the variablecomposition of the crustal basement in western Turkey and for thedifferent rock types into which the granitoids were emplaced, weused different crustal lithologies and compositions as potential con-taminants in the models (Figs. 17a–b and 18a–b). For the ATPG, alower crustal amphibolite from the Menderes Massif (Altunkaynak,unpub. data) was also used as a starting composition in the AFCmodels. Bulk mixing arrays (Figs. 17c–d and 18c–d) were calculatedbetween the same endmembers.

The AFC models for the SCG–RMG presented in the 87Sr/86Sri and143Nd/144Ndi vs. SiO2 plots (Fig. 17a–b) show that the variations with-in these granitoids can be modeled successfully, using both depletedand enriched mantle melts as starting compositions, although themodels critically depend on the contaminant chosen. Suitable crustalcontaminants include the gneisses from the Kazdag Massif and themiddle and upper crustal rocks from Altunkaynak (unpub. data) andSunal (unpub. data) (Fig. 17a–b). Lower crust amphibolite can beruled out as a potential contaminant, based on the models presented.Realistic models indicate relatively high rates of assimilation to frac-tional crystallization (r; all AFC models were calculated withr=0.8). High values for r suggest a comparatively minor role for frac-tional crystallization; however, as all r values are b1.0, fractional crys-tallization still dominates over assimilation of crustal rocks. In all AFCmodels, the extent of differentiation that the parental magmas under-went to reach the values similar to those of the SCG–RMG dependslargely on the chosen contaminant. Fractions of original melt remain-ing (F) are ~0.6 for the most contaminated samples of the SCG–RMG,although higher values of “F” (or less crystallization) may be requiredfor particular potential contaminants. Bulk mixing trends betweendepleted or enriched mantle melts and most of the crustal composi-tions chosen for the AFCmodels mostly fail to reproduce the observedcompositional variations (in 87Sr/86Sr(i) and 143Nd/144Nd(i) vs. SiO2

space) of the SCG–RMG, although multi-component mixtures be-tween mantle melts (both depleted and enriched) and/or amphibo-lites and silicic crustal lithologies remain a possibility (Fig. 17c–d).

AFC and bulk mixing models for the ATPG are illustrated in 87Sr/86Sr(i) and 143Nd/144Nd(i) vs. SiO2 plots (Fig. 18a–d). Using the samedepleted and enriched mantle melts as above as well as a lower crust-al amphibolite from the Menderes Massif as starting compositionsand several crustal lithologies as potential contaminants in the AFCcalculations (Fig. 18a–b), the best-fit models for the observed compo-sitional variations of the ATPG are obtained with the same high ratesof assimilation versus fractionation (r=0.8). Models using a depletedmantle melt or lower mafic crust (amphibolites) as starting composi-tions and upper crustal values and the Menderes Massif gneisses ascontaminants reproduce best the observed compositional variationsof the ATPG (with fractions of original melt remaining (F) of ~0.6(or higher)), although derivation of the ATPG magmas from anenriched mantle source and subsequent AFC processes are also feasi-ble. As for the SCG–RMG, lower crust amphibolite can be ruled out asa potential contaminant of any mantle-derived melt, based on themodels presented. Bulk mixing models between depleted andenriched mantle-derived melts and crustal rocks (Fig. 18c–d) largelyfail to reproduce the observed compositional variations of the rela-tively silicic ATPG, although these models do not exclude the possibil-ity of mixtures of mantle-derived melts (or Menderes Massifamphibolite) with more SiO2-rich partial crustal melts.

8. Interplay between syn-convergent extension andmagmatism inwestern Anatolia

Convergence between the Eurasian and African plates played animportant role in shaping the crustal architecture of the western An-atolia and broader Aegean region during the late Mesozoic–Cenozoic(e.g., Kalvoda and Babek, 2010). This crustal architecture formed from




a collage of continental blocks, separated by suture zones (IPS, VS_IASZ,PS in Fig. 1). The continental fragments (RM, SC, ATP) were amalgamat-ed through collisional events starting in the Cretaceous (Şengör andYılmaz 1981; Dilek and Moores, 1990; Okay et al., 1996; Okay andTüysüz, 1999).

The multiple episodes of continental collision in the Aegean regioncaused orogen-wide burial metamorphism in the late Paleocene–early Eocene. This regional metamorphism was responsible for thedevelopment of high-grade metamorphic rocks in the Rhodope, Kaz-dağ and Menderes massifs. Continental collision events also producedthick orogenic crust and heterogeneous mantle that affected themode and nature of syn- to post collisional magmatism and extensionin the Aegean region (Seyitoğlu and Scott, 1996; Aldanmaz et al.,2000; Yılmaz et al., 2001; Altunkaynak and Dilek, 2006).

In western Anatolia, magmatism occurred in distinct episodessince the early Eocene and appears to have changed in nature fromcalc-alkaline to alkaline over time. The interpretations explainingthe mode and nature of multiple episodes of Cenozoic magmatismthrough time are subject to discussions and further testing. The cur-rent models are; a) active subduction zone magmatism, b) region-wide extension and magmatism caused by orogenic collapse and c)syn-convergent extension and magma generation driven by slabbreak-off, delamination or convective removal of the lithosphere.The variations in tectonic regimes were a result of feedback mecha-nisms between the tectonically driven crustal processes and mantledynamics in the late-stage evolution of the western Anatolian oro-genic belt.

Current subduction zone models suggest that the Cenozoic mag-matism was either a product of the north-dipping subduction of a Te-thyan ocean floor (Borsi et al., 1972; Fytikas et al., 1984; Pe-Piper andPiper, 1989; Gülen, 1990; Delaloye and Bingöl, 2000; Okay and Satır,2000; 2006) or that the Cretaceous subduction along the Izmir–Anka-ra–Erzincan suture zone and the Miocene subduction along the Hel-lenic trench could have been related in space and time through slabretreat (Spakman, 1990; van Hinsbergen et al., 2005; Pe-Piper andPiper, 2006). Although magmatic rocks of western Anatolia displaya geochemical subduction fingerprint, there is no convincing geolog-ical evidence for a subduction event such as the formation of anophiolithic melange, accretionary prism or blueschist facies meta-morphic rocks synchronous with Cenozoic magmatic activity in theregion during the middle Eocene through middle Miocene (Harris etal., 1994; Genç and Yılmaz, 1997; Yılmaz et al., 2000, 2001 and refer-ences therein). Cretaceous subduction of the Tethyan seafloor be-neath the Sakarya continent was halted and terminated by thepartial subduction of the Anatolide–Tauride continental margin, fol-lowing the emplacement of the Cretaceous ophiolites exposed alongthe Izmir–Ankara–Erzincan suture zone (Harris et al., 1994; Okay etal., 1998; Sherlock et al., 1999; Dilek et al., 2007). The isostatic re-bound of this partially subducted continental material in the lowerplate was the driving force for the uplift and exhumation of the blues-chist rocks in the Paleogene (Sherlock et al., 1999). Time constraintson the obduction of the ophiolite fragments exposed along the colli-sion zone and accretionary processes (Harris et al., 1994; Okay andTüysüz, 1999; Sherlock et al., 1999; Önen and Hall, 2000) indicatethat the timing of collision SC and ATP in NW Anatolia was pre-early Eocene. Following the collision, the units of the SC and the su-ture zone units were covered unconformably by a continental to shal-low marine sedimentary rocks of Baslamis (Akdeniz, 1980) andGebeler Formations (Akyurek and Soysal, 1983) during middle Eo-cene. This stratigraphic relationship also supports the timing of colli-sion in NW Anatolia was earlier than the middle Eocene. Thiscontinental collision resulted in the development of the western An-atolian orogenic belt (Şengör et al., 1985; Dilek and Whitney, 2000).As subduction of African lithosphere beneath Eurasia along the Hel-lenic trench south of the Anatolide–Tauride and Cyclades belts startedaround ~12 Ma (Meulenkamp et al., 1988), the Eocene to middle


Miocene magmatism was not related to any active subduction pro-cesses at that time. Therefore, the Oligo–Miocene granitoids weremost likely generated in a post-collisional setting rather than in an ac-tive continental margin setting, and subduction-related enrichmentof the western Anatolian lithospheric mantle was associated withthe previous, late Cretaceous subduction of the Neo-Tethyan oceaniclithosphere beneath the Sakarya continent, as suggested by previousresearchers (Yılmaz and Polat, 1998; Yılmaz et al., 2000; Aldanmazet al., 2000; Altunkaynak and Genç, 2008).

The orogenic collapse models suggest that the Late Oligocene–Miocene magmatism in western Anatolia was a consequence of ex-tensional tectonics associated with the collapse of the overthickenedwestern Anatolian orogenic belt (Seyitoğlu and Scott, 1991, 1992,1996; Seyitoğlu et al., 1997). The inferred catastrophic orogenic col-lapse caused crustal attenuation and magmatism associated withdecompressional melting. This model does not explain the modeand nature of earlier Eocene magmatism in the region and has limitedapplications to the Cenozoic evolution of western Anatolia.

Synconvergent extension and associatedmagmageneration iswide-ly recognized within the interiors of modern convergent orogens (e.g.,Dalmayrac and Molnar, 1981; Molnar and Chen, 1983; Molnar andLyon-Caen, 1988, England and Houseman, 1989; Platt and England,1994; McCaffrey and Nabelek, 1998; Seghedi and Downes, 2011) andthe young Tethyan orogen in Anatolia (Turkey) and the broader Aegeanregion (Aldanmaz et al., 2000; Keskin, 2003; Köprübaşı and Aldanmaz,2004; Dilek and Altunkaynak, 2007; Altunkaynak and Genç, 2008). Dif-ferent driving mechanisms such as slab break-off, extensive delamina-tion, partial delamination or convective removal of lithosphere haveall been invoked to explain the interplay between syn-convergent ex-tension and magma generation in the region. Some researchers havesuggested that the Cenozoic magmatism in western Anatolia displayscompositionally distinct magmatic episodes controlled by slab breakoff(Köprübaşı and Aldanmaz, 2004; Altunkaynak and Dilek, 2006;Altunkaynak 2007; Dilek and Altunkaynak, 2007; Boztuğ et al., 2009).Others have proposed that lithospheric delamination (Aldanmaz et al.,2000) and/or partial convective removal of the subcontinental litho-spheric mantle resulting in asthenospheric upwelling and decompres-sional melting were important processes during the post collisionalbuild up of Cenozoic western Anatolia (Altunkaynak and Genç, 2008).

We think that the long-lived Cenozoic magmatism in western An-atolia was spatially and temporally associated with different tectonicevents driven by crustal- and mantle-scale processes and their inter-actions. The first episode of granitoid magmatism and its volcanicequivalents evolved during the early to late Eocene (54–35 Ma) andproduced medium to high-K calc-alkaline I type granitoids. The em-placement of localized granitoid plutons along the IASZ and into theSakarya continent has been interpreted to have resulted from slabbreakoff-related asthenospheric upwelling and associated partialmelting of the subduction-metasomatized continental lithosphericmantle by previous studies (Köprübaşı and Aldanmaz, 2004;Altunkaynak, 2007; Dilek and Altunkaynak 2007). Partial underplat-ing of the leading edge of the buoyant Anatolide–Tauride platform be-neath the Sakarya continent jammed the north-dipping Tethyansubduction temporarily, while the continued sinking of lithosphericmantle resulted in slab breakoff in NW Anatolia. This interpretationis supported by the seismic tomography model of Dilek and Sandvol(2009) demonstrating the existence of a second high-velocity (cold)slab near the 660 km discontinuity in the lower mantle north of theHellenic slab, which is interpreted as a detached Tethyan slab dippingbeneath the western Anatolian orogenic belt. Slab detachment andbreakoff is a natural consequence of the gravitational settling of sub-ducted lithosphere in continental collision zones, as a result of a decreasein the subduction rate caused by the positive buoyancy of partially sub-ducted continental lithosphere (Davis and Von Blanckenburg, 1995;Von Blanckenburg and Davies, 1995; Wortel and Spakman, 2000;Gerya et al., 2004).




The secondmagmatic episode produced widespread I-type plutonicand associated volcanic rocks in western Anatolia during the late Oligo-cene to middle Miocene. This time interval coincides with the exhuma-tion of lower to middle crustal rocks in western Anatolia (as in theMenderes and Kazdağ core complexes) and in the Aegean province(Naxos, Cyclades) (Fig. 19). The initial exhumation age of the Kazdağcore complex has been suggested as the latest Oligocene–earlyMiocene(Okay and Satır, 2000) and that of the Menderes core complex as theearliest Miocene (Işık et al., 2004; Thomson and Ring, 2006; Bozkurt,2007; Dilek and Altunkaynak, 2007; Altunkaynak and Genç, 2008). Ingeneral, tectonic extension also appears to have migrated southwardin time. Following the exhumation of the Kazdag and Menderes meta-morphic core complexes, the Tauride block in SWAnatolia was uplifted(Dilek et al. 1999b) and the blueschist rocks in Crete and the Cyclades inthe South Aegean region (Ring and Layer, 2003) were exhumed in theMiocene and onwards (Fig. 19).

Zircon SHRIMP U–Pb dating of NATPG and SCG groups yields agesbetween 19.48±0.29 and 23.94±0.31 Ma as the timing of their em-placement, whereas 39Ar/40Ar dating of hornblende and biotite sepa-rates from the SCG, RMG and NATPG groups reveals cooling ages of18.9±0.1–24.8±0.1. These results are consistent with the radiomet-ric ages (mostly K/Ar ages) obtained in previous studies and indicatethat the extensional deformation was spatially and temporally associ-ated with voluminous granitoid magmatism which is represented bymetaluminous to slightly peraluminous, I-type granitoids. The Sr–Ndisotopic signatures and trace element characteristics of these granit-oids indicate that the melts derived from both lithospheric mantleand depleted mantle (at least for the SCG and RMGmagmas) contrib-uted to magma source region of the parental magmas. The astheno-spheric melt contribution in addition to lithospheric mantle meltsmost likely resulted from lithospheric delamination or partial convec-tive removal of the subcontinental lithospheric mantle. Although theextensional tectonic regime was operating fully during the latest Oli-gocene–Early Miocene, the relationships between the isotopic com-positions and cooling ages as documented in this study indicate anincreasing crustal signature from 24 to 18 Ma (Fig. 16).

We propose that asthenospheric upwelling caused by partial de-lamination or convective thinning of lithospheric mantle led tounderplating of mantle-derived magmas providing melt and heat toinduce partial melting of the lithospheric mantle (Fig. 19). Invasionof the crust by melts derived from both asthenospheric (depleted)and enriched lithospheric mantle triggered open system processes(AFC and/or MASH (melting, assimilation, storage, homogenization;Hildreth and Moorbath, 1988)) in separate magma chambers, result-ing in the production of mildly to highly evolved Oligo–Miocenegranitoid magmas. This inferred melt source and magma evolutionreadily explains the I-type granitoid nature of most Cenozoic plutonsin western Anatolia, regardless of their temporal and spatial position.This widespread early to middle Cenozoic magmatism caused ther-mal weakening of the young orogenic crust and played a significantrole for the initiation of syn-convergent extension and crustal exhu-mation as early as in the latest Oligocene–early Miocene (Fig. 19).The absence of large volumes of alkaline basaltic lavas in western An-atolia during this period also contradict extensive lithospheric delam-ination models. Moreover, previous workers suggested that thecrustal thickness in the Aegean province ranges from 16 km in theCrete Sea to 25–35 km in the Cyclades and W Turkey (Makris andStobbe1984; Doglioni et al. 2002; Tirel et al. 2004; Zhu et al. 2006).Variations in crustal thickness may indicate that extensional thinninghas not been uniform in western Anatolia and the Aegean region, con-sistent with the proposed models of convective removal and partialdelamination of lithospheric mantle.

The effects of convective removal or partial delamination of thecold mantle lithosphere and its replacement by hot asthenosphereare well documented in other orogenic belts and in eastern Anatolia,where the lower–middle crust has been remobilized upwards,


causing exhumation, surface uplift, and overall net extension (Bird,1979; England and Houseman, 1989; Molnar et al., 1993; Housemanand Molnar, 1997; Keskin 2003; Şengör et al., 2003; Dokuz, 2011).

The degree of crustal contribution appears to have increased inplutonic rocks by middle Miocene (Fig. 16). The age of the youngestgranitoid group (SATPG; 13–16 Ma; Hetzel et al., 1995), which dis-plays a strong crustal signature, corresponds to the time interval be-tween the initiation of, mildly alkaline (associated with bimodalvolcanism) and strongly alkaline volcanism in western Anatolia.Thus, both asthenospheric- and lithospheric mantle and crustalmelts were involved in the evolution of magmatism in the middleMiocene and onwards. Therefore, the geochemical variations in thelate Cenozoic post-collisional magmatism in western Anatolia reflectthe increasing intensity of regional extension through time (Altun-kaynak and Dilek 2006, Altunkaynak and Genç 2008, Altunkaynak etal., 2010). This shift in the geochemical affinity of magmatism is inter-preted as a result of tectonically driven asthenospheric upwelling be-neath this highly extended terrane, following a period of extremecrustal thinning after the exhumation of core complexes in westernAnatolia and the Aegean region in response to rapid slab rollback atthe Hellenic trench (Meulenkamp et al., 1988; Spakman et al., 1988;Pe-Piper and Piper 2006). Pn velocity and Sn attenuation tomographymodels indicate that the uppermost mantle is anomalously hot andthin, consistent with the existence of a shallow asthenosphere be-neath western Anatolia (Sandvol et al., 2003).

The close temporal and spatial relationships between the late Ce-nozoic tectonic extension and magmatism suggest that the wide-spread early to middle Cenozoic magmatism caused thermalweakening and played a significant role in the initiation of synconver-gent extension, crustal exhumation and thinning in the hinterland ofa young Tethyan orogen in western Anatolia and the broader Aegeanregion.

9. Conclusions

The majority of the Oligo–Miocene granitoids are represented bymetaluminous to slightly peraluminous, I-type granitoids. Isotopicsignatures and major-trace element characteristics of the RMG–SCGand NATPG granitoids which emplaced into different tectonic unitsof western Anatolia indicate that both lithospheric- and astheno-spheric mantle (at least partly for the SCG–RMG magmas) melts ap-pear to have contributed to source region of mafic parental magmaswhich evolve toward granodioritic to granitic compositions. The com-positional variations observed in the RMG, SCG and NATPG granitoidsare interpreted as a result of open-system processes during evolutionof these granitoids rather than a reflection of different compositionsof crustal lithologies through which the RMG and SCG, ATPG magmasmigrated. The TDM ages of the RMG and SCG suggest a high amount ofmantle-derived protoliths in the mixed source and the extraction ageof the mantle material to be younger than 1.2 Ga. The calculated TDMages of the NATPG samples are consistent with those of the Pan-African crustal rocks, and indicate that these granitoids, characterizedby stronger crustal signatures than the other groups, were affected bythe crystalline basement of the Anatolide–Tauride platform. By con-trast, the SATPG samples with crust-like geochemical signaturesmay have been produced by crustal melting or, at least, significantcontributions from the ATP crystalline basement.

The observed isotopic characteristics and variations with indicesof differentiation suggest that the crustal signature within theOligo–Miocene granitoids developed predominantly through simul-taneous assimilation of upper–middle crustal rocks and fractionalcrystallization (AFC) of mantle derived melts during magma ascent.Assimilation and fractional crystallization models explain the compo-sitions of the Oligo–Miocene granitoids slightly better than bulk mix-ing between different mantle and crustal components, althoughmixing between mantle-derived melts and partial crustal melts




cannot be entirely ruled out. Thus, the observed range in isotopic var-iations is not solely a feature of the inferred mantle melt source.

Zircon SHRIMP U–Pb dating of the NATPG and SCG groups yieldsages between 19.48 and 23.94 Ma as the timing of their emplace-ment, whereas cooling ages of same granitoids range between 20.6and 18.9. 39Ar/40Ar dating of biotite separates from the SCG, RMGand NATPG groups reveals cooling ages of 18.9–28.0 Ma. The isotopiccompositions and cooling ages of the western Anatolian granitoidssuggest a progressive increase in the amount of crustal signature (as-similation of crustal rocks) from 24 to 18 Ma, coinciding with the tim-ing of crustal exhumation and core complex formation (Kazdağ andMenderes massifs) in western Anatolia. The heat and basaltic materialto induce partial melting, which led to the generation of granitoidmagmas, were provided by asthenospheric upwelling caused by par-tial lithospheric delamination and/or convective thinning beneathwestern Anatolia. This widespread early to middle Cenozoic magma-tism caused thermal weakening of the young orogenic crust andplayed a significant role for the initiation of syn-convergent extensionand crustal exhumation as early as in the latest Oligocene–earlyMiocene.

The age of the youngest granitoid group (SATPG; 13–16 Ma; Hetzel etal., 1995; Glodny andHetzel 2007), which displays a strong crustal signa-ture, corresponds to the time interval between the initiation of mildly al-kaline and strongly alkaline volcanism in western Anatolia. This shift inthe geochemical affinity ofmagmatism is interpreted as a result of tecton-ically driven asthenospheric upwelling beneath this highly extended ter-rane, following a period of extreme crustal thinning after the exhumationof core complexes in western Anatolia and the Aegean region.

Supplementarymaterials related to this article can be found onlineat doi:10.1016/j.gr.2011.10.010.

Acknowledgments

This study has been funded by grants from the Istanbul TechnicalUniversity (BAP Project No: 35691) and the Turkish Research Council(TUBITAK-CAYDAG-109Y010) that are gratefully acknowledged. Con-structive and insightful comments by P.T. Robinson and Y. Eyupogluhelped us to improve the paper. We would like to thank the Editor-in-Chief, Professor M. Santosh, for inviting us to prepare this contribu-tion as a Focus Paper in Gondwana Research.

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Şafak Altunkaynak is an Associate Professor in the Depart-ment of Geology at Istanbul Technical University (Turkey).She received her PhD from Istanbul Technical University in1997. She was a visiting scientist at the Open University(UK) in 2003 and the University of Nevada Las Vegas(USA) in 2009. She has worked on the geology, petrologyand geochemistry of post-collisional volcanic and plutonicrocks, volcanic–plutonic connections in Turkey, the Aegeanregion and the Lesser Caucasus (Azerbaijan). Her current re-search projects involve Cenozoic crustal evolution andman-tle dynamics of post-collisional magmatism in westernAnatolia and the Aegean extensional province; thermo-barometry and geochronology of magmatic and metamor-phic rocks of Çataldağ, Kazdağ and Menderes core com-plexes; and petrology and geodynamics of adakiticmagmatism in NW Turkey. She has published a number ofrefereed papers on these topics in international journals.

Yıldırım Dilek is a Professor of Tectonics in the Departmentof Geology and a Harrison Scholars Professor at Miami Uni-versity (USA). He received his PhD from the University ofCalifornia-Davis (1989), worked as a Senior Research Fellow(1989–90) at the Getty Conservation Institute (Los Angeles,CA), and taught at Vassar College (NewYork) until 1996. Thefocus of his research is mostly on the structure, petrology,and tectonics of modern oceanic crust and ophiolites, post-collisional igneous complexes in orogenic belts, and meta-morphic core complexes. He has also worked extensivelyin the western U.S. Cordillera, Northern Appalachians, Nor-wegian Caledonides, Caucasus Mountains, Arabian–NubianShield, and Central Asian orogenic belts. He is an expert sci-entist for the NATO Science for Peace Programme and amember of the United States Science Advisory Committee.

Ş. Can Genç is a Professor of Geology at the Istanbul Tech-nical University, Istanbul (Turkey) since 2004. Genc re-ceived his BSc (1981) and MSc (1987) from IstanbulUniversity, and PhD (1993) from the Istanbul TechnicalUniversity, Turkey. Genc's main research topics includemagmatic petrology, petrogenesis, and volcanology. Hehas published over 20 research papers.

Gürsel Sunal is an Assistant Professor in the Departmentof Geology at İstanbul Technical University, İstanbul,Turkey, since 2009. Sunal received his BSc (1993) and MSc(1997) from Istanbul Technical University, Turkey, andPhD (2008) from the University of Tübingen, Germany. Hismain research interests include geochronology of metamor-phic and magmatic rocks and exhumation history of tecton-ically active belts. He has published a number of researchpapers on these topics.


Ralf Gertisser is a lecturer in Mineralogy and Petrology atKeele University, UK, since 2005. He studied geology atthe University of Freiburg, Germany, and the University ofOregon, USA, and received his diploma (M.Sc.) in geologyfrom the University of Freiburg in 1996. In 2001, he wasawarded a doctorate (Dr. rer. nat.) “with highest honors”(summa cum laude) in Earth Sciences from the Universityof Freiburg. Before joining Keele University, he held postdoc-toral positions at the University of Freiburg and The OpenUniversity, UK. Gertisser's main research interests includemagma generation and differentiation in subduction-zone(and other geodynamic) settings, rates and timescales ofmagmatic processes using short-lived isotopes, magmachamber processes, volatile behavior in volcanic systems,and the generation and emplacement mechanisms ofsmall-volume pyroclastic flows. Study areas have includedthe Aeolian Islands (Italy), the Azores (Portugal), Santorini(Greece), the Sunda arc in Indonesia and the Chilean Andes.

Harald Furnes is Professor at the Department of Earth Sci-
ence, University of Bergen, Norway, since 1985. He re-ceived his D.Phil. at the University of Oxford, UK, in1978. His main research interest has been connected tovolcanic rocks. This involves physical volcanology, geo-chemistry and petrology of volcanic rocks, mainly con-nected to ophiolitic and island arc development ofvarious ages. Another research focus has been related tothe alteration of volcanic glass, which again led to along-term study on the interaction between micro-organisms and glassy rocks, and the search for traces ofearly life. On these topics he has published a number ofrefereed papers in international journals.
Kenneth A. Foland is Professor Emeritus in the School ofEarth Sciences at Ohio State University. He received a B.S.from Bucknell University (1967) and M.S. (1969) and Ph.D.(1972) degrees from Brown University. He joined Geologyfaculty at the University of Pennsylvania in 1972, leaving in1980 for Ohio State University in Columbus. There he devel-oped new facilities for high-precision, low-blank measure-ments of radiogenic isotopes and noble gases. After morethan 40 years of research in isotope geochemistry and geo-chronology, he recently retired from active lab work andteaching. His research includes laboratory, experimental,field, and clinical studies on isotopic compositions of a broadrange of natural andmodifiedmaterials including rock,min-eral, water, gas, and blood samples.

Jingsui Yang graduated from Dalhousie University in
Canada in 1992 with a PhD in geology. In 1995 he be-came a Research Professor and now is a chief scientistat the National Key Laboratory for Continental Tectonicsand Dynamics, Institute of Geology, Chinese Academy ofGeological Sciences. He has carried out a number of re-search projects on the tectonics and petrology of the oro-genic zones of the Qinghai-Tibet Plateau. His researchwork has mainly been focused on the ultra-high pressuremetamorphic zones, terrane amalgamation and collision,and deep mantle processes. Yang with collaborators haspublished 325 research papers and two books and be-came GSA Fellow in 2011.


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