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  • Syn-extensional granitoids in the Menderes core complex and the

    late Cenozoic extensional tectonics of the Aegean province

    YILDIRIM DILEK1*, ŞAFAK ALTUNKAYNAK2 & ZEYNEP ÖNER1

    1Department of Geology, 116 Shideler Hall, Miami University, Oxford, OH 45056, USA2Department of Geology Engineering, Istanbul Technical University, Maslak 80626,

    Istanbul, Turkey

    *Corresponding author (e-mail: [email protected])

    Abstract: The Miocene granitoid plutons exposed in the footwalls of major detachment faults inthe Menderes core complex in western Anatolia represent syn-extensional intrusions, providingimportant geochronological and geochemical constraints on the nature of the late Cenozoic mag-matism associated with crustal extension in the Aegean province. Ranging in composition fromgranite, granodiorite to monzonite, these plutons crosscut the extensional deformation fabrics intheir metamorphic host rocks but are foliated, mylonitized and cataclastically deformed in shearzones along the detachment faults structurally upward near the surface. Crystallization andcooling ages of the granitoid rocks are nearly coeval with the documented ages of metamorphismand deformation dating back to the latest Oligocene–early Miocene that record tectonic extensionand exhumation in the Menderes massif. The Menderes granitoids (MEG) are represented bymainly metaluminous-slightly peraluminous, high-K calc-alkaline and partly shoshonitic rockswith their silica contents ranging from 62.5 to 78.2 wt%. They display similar major and traceelement characteristics and overlapping inter-element ratios (Zr/Nb, La/Nb, Rb/Nb, Ce/Y)suggesting common melt sources. Their enrichment in LILE, strong negative anomalies in Ba,Ta, Nb, Sr and Ti and high incompatible element abundances are consistent with derivation oftheir magmas from a subduction-metasomatized, heterogeneous sub-continental lithosphericmantle source. Fractional crystalization processes and lower to middle crustal contaminationalso affected the evolution of the MEG magmas. These geochemical characteristics of the MEGare similar to those of the granitoids in the Cyclades to the west and the Rhodope massif to thenorth. Partial melting of the subduction-metasomatized lithospheric mantle and the overlyinglower-middle crust produced the MEG magmas starting in the late Oligocene–early Miocene.The heat and the basaltic material to induce this partial melting were provided by asthenosphericupwelling caused by lithospheric delamination. Rapid slab rollback of the post-Eocene Hellenicsubduction zone may have peeled off the base of the subcontinental lithosphere, triggering theinferred lithospheric delamination. Both slab retreat-generated upper plate deformation and mag-matically induced crustal weakening led to the onset of the Aegean extension, which has migratedsouthward through time.

    The Aegean extensional province is a rapidlydeforming and seismically active domain in theAfrica–Eurasia convergent zone in the easternMediterranean region and is considered to haveevolved as a backarc tectonic environment abovethe north-dipping Hellenic subduction zone(Fig. 1; Le Pichon & Angelier 1979; Jolivet 2001;Faccenna et al. 2003; van Hinsbergen et al. 2005;Jolivet & Brun 2008). Southward retreat of the sub-ducting African lithosphere along the Hellenictrench and the faster SW motion of the southernpart of the Anatolian block in the upper plate haveresulted in approximately north–south extensionin the Aegean region since the Oligo-Miocene(Jolivet et al. 1994; Jolivet & Faccenna 2000;Ring & Layer 2003). The thrust front associatedwith this subduction zone and its slab retreat hasalso migrated from the Hellenic trench to the

    south of the Mediterranean Ridge since then (LePichon et al. 2003). These observations suggestthat the driving forces for regional extensional tec-tonics in the broader Aegean region reside mainlywithin the retreating lithospheric slab. Subductionof the Tethyan mantle lithosphere northwardbeneath Eurasia was nearly continuous since thelatest Cretaceous, only temporarily punctuated bythe collisional accretion of several ribbon continents(i.e. Pelagonia, Sakarya, Anatolide–Tauride) to thesouthern margin of Eurasia and related slab breakoffevents (Rosenbaum et al. 2002; van Hinsbergenet al. 2005; Dilek & Altunkaynak 2007). Exhuma-tion of middle to lower crustal rocks and theformation of extensional metamorphic domesoccurred in the backarc region of this progressivelysouthward migrated trench and the Tethyan slabthroughout the Cenozoic.

    From: RING, U. & WERNICKE, B. (eds) Extending a Continent: Architecture, Rheology and Heat Budget.Geological Society, London, Special Publications, 321, 197–223.DOI: 10.1144/SP321.10 0305-8719/09/$15.00 # The Geological Society of London 2009.

  • Recent geochronological data from several corecomplexes (i.e. Menderes, Kazdag) and the syn-extensional granitoid plutons in them (Fig. 2) indi-cate that both extension and attendant magmatismin the Aegean region date back to the at leastlatest Oligocene–early Miocene (Bozkurt & Satir2000; Okay & Satir 2000; Ring et al. 2003; Işiket al. 2004; Thomson & Ring 2006). These findingssuggest that tectonic extension and magmatismwere synchronous events starting around 25–24 Ma. The Aegean extension thus appears to havestarted c. 25 Ma, long before the onset of theArabia–Eurasia collision-driven SW escape of theAnatolian microplate in the late Miocene (Barka &Reilinger 1997; Jolivet & Faccenna 2000).

    Syn-extensional magmatism during the early andmiddle Miocene produced widespread volcanicrocks and plutons in the Cyclades and western Ana-tolia (Altherr et al. 1988; Altherr & Siebel 2002;Pe-Piper & Piper 2002, 2006; Pe-Piper et al. 2002;Akay & Erdoğan 2004; Bozkurt 2004; Gessneret al. 2004; Işik et al. 2004; Köprübaşi & Aldanmaz2004; Innocenti et al. 2005; Ring & Collins 2005;Agostini et al. 2007; Dilek & Altunkaynak 2007;Akay 2008). The Oligo-Miocene volcanic rocks

    have medium- to high-K calcalkaline compositions(Pe-Piper & Piper 2006; Altunkaynak & Genç2008), and their trace-element and isotope geo-chemistry characteristics indicate that parentalmagmas were derived from partial melting of anenriched lithospheric mantle (Aldanmaz et al.2006; Altunkaynak & Genç 2008) and that theyunderwent decreasing subduction influence andincreasing crustal contamination through time(Altunkaynak & Dilek 2006; Dilek & Altunkaynak2007, and references therein). Mildly alkalinebimodal volcanic products that were erupted duringthe middle Miocene (16–14 Ma), on the otherhand, show a decreasing amount of crustal con-tamination and subduction influence through time(Altunkaynak & Dilek 2006; Dilek & Altunkaynak2007). Melting of a subduction-modified continen-tal lithospheric mantle and asthenospheric mantle-derived melt contribution both appear to haveplayed a major role in the generation of themagmas of these middle Miocene volcanic rocks.

    The Oligo-Miocene and middle Miocene plutonsin the region are represented by mainly I-typegranitoids, whose chemical compositions displaysignificant differences throughout the region

    Fig. 1. Tectonic map of the Aegean and eastern Mediterranean region, showing the main plate boundaries, major suturezones and fault systems. Thick, white arrows depict the direction and magnitude (mm a21) of plate convergence; greyarrows mark the direction of extension (Miocene–Recent). Orange and purple colours delineate Eurasian and Africanplate affinities, respectively. Key to lettering: BF, Burdur fault; CACC, Central Anatolian crystalline complex; DKF,Datça–Kale fault (part of the SW Anatolian Shear Zone); EAFZ, East Anatolian fault zone; EF, Ecemis fault; EKP,Erzurum–Kars Plateau; IASZ, Izmir–Ankara suture zone; IPS, Intra-Pontide suture zone; ITS, Inner-Tauride suture;KF, Kefalonia fault; KOTJ, Karliova triple junction; MM, Menderes massif; MS, Marmara Sea; MTR, Maras triplejunction; NAFZ, North Anatolian fault zone; OF, Ovacik fault; PSF, Pampak–Sevan fault; TF, Tutak fault; TGF,Tuzgölü fault; TIP, Turkish-Iranian plateau (modified from Dilek 2006).

    Y. DILEK ET AL.198

  • Fig. 2. Geological map of western Anatolia, showing the distribution of Menderes and Kazdag metamorphic massifs,Neotethyan ophiolites, Cenozoic sedimentary basins and igneous provinces, salient fault systems. Major tectonic blocksand suture zones are also depicted. AF, Acigöl fault; BFZ, Burdur fault zone; DF, Datça fault; IASZ, Izmir–Ankarasuture zone; IPSZ, Intra-Pontide suture zone; KDM, Kazdag massif; KF, Kale fault; NAFZ, North Anatolian fault zone;SWASZ, Southwest Anatolian shear zone. Key to lettering for the detachment faults: AD, Alasehir detachment; GD,Güney detachment; SD, Simav detachment. Key to lettering for the granitoid plutons: AG, Alasehir; BG, Baklan; CGD,Çataldag; EGP, Egrigöz; EP, Eybek; EVG, Evciler; GBG, Göynükbelen; GYG, Gürgenyayla; IGD, Ilica; KBG,Karabiga; KG, Kozak; KCG, Kusçayiri; KOP, Koyunoba; KSG, Kestanbol; KTG, Katrandag; OGD, Orhaneli; SG,Salihli; SVG, Sevketiye; TG,Turgutlu; TGD, Topuk; YCG, Yenice.

    SYN-EXTENSIONAL GRANITES, MENDERES MASSIF 199

  • (Altherr & Siebel 2002). However, similar to theirvolcanic counterparts (Altunkaynak & Genç 2008),these granitoids do not exhibit geochemical signa-tures of an active subduction zone magmatism forthe origin of their magmas. The melt sources, themagmatic evolution and the nature of the heatsupply for the production of syn-extensional grani-toids in the Aegean province remain, therefore,some of the most signifcant questions in the lateCenozoic geodynamic evolution of this region.Granitic plutons commonly exposed in the footwallsof major detachment faults of the metamorphic corecomplexes in the region provide critical informationto address some of these questions.

    In this paper we present new geochemical andisotope data as well as evaluating the extant geo-chemical data from the Miocene granitoid plutonsintruded into the Menderes metamorphic corecomplex in western Anatolia in order to constraintheir magma sources and tectonomagmatic evol-ution. We also present new field observations fromthe Menderes granitoids to document the syn-extensional nature of these intrusions. We com-pare the Menderes granitoid data with the availablegeochemical data from the granitoids emplaced intothe other core complexes in the Central Cycladesand the northern Aegean in order to understandbetter the melt evolution of syn-extensional grani-toids in western Anatolia. We then discuss the roleof the late Cenozoic magmatism in the onset andthe spatial and temporal progression of orogen-wideextension in the Aegean province within the frame-work of a regional tectonic model.

    Basement geology of Cenozoic granitoids

    in western Anatolia

    The Cenozoic granitoid plutons in western Anatoliaare intrusive into the crystalline basement rocks ofthe Sakarya continent and the Anatolide–Taurideblock. They also crosscut the Tethyan ophiolites(c. .92–90 Ma) and blueschist assemblages occur-ring along the Izmir–Ankara suture zone (IASZ)between the Sakarya and Anatolide–Tauride conti-nental blocks (Fig. 2; Önen & Hall 1993; Okay et al.1998; Önen 2003). The 40Ar/39Ar cooling ages(phengite crystallization during exhumation) of79.7 + 1.6–82.8 + 1.7 Ma (Sherlock et al. 1999)from the blueschist rocks along the IASZ indicatea latest Cretaceous timing of the HP–LT meta-morphism in the region. This event was followedby the collision of the Sakarya and Anatolide–Tauride blocks in the late Palaeocene–earlyEocene (Harris et al. 1994; Dilek & Altunkaynak2007). The Lycian ophiolite nappes structurallyoverlying the platform carbonates of the Taurideblock farther south (Fig. 2; Collins & Robertson2003; Ring & Layer 2003) represent the tectonic

    outliers of the Cretaceous oceanic crust derivedfrom the IASZ. These ophiolitic thrust sheets areinferred to have once covered the Menderes meta-morphic massif and then to have been removed asa result of the tectonic uplift and erosion associatedwith the exhumation of the Menderes core complexduring the late Cenozoic (Dilek & Whitney 2000;Ring & Layer 2003; Thomson & Ring 2006).

    The Sakarya continent consists of a Palaeozoiccrystalline basement with its Permo-Carboniferoussedimentary cover and Permo-Triassic rift oraccretionary-type melange units (Karakaya com-plex) that collectively form a composite continentalblock (Tekeli 1981; Okay et al. 1996). The Carbon-iferous felsic gneisses, amphibolites, marbles andmeta-ophiolitic units that are tectonically interca-lated with sillimanite-bearing gneisses and migma-tites in the western part of the Sakarya continentconstitute the Kazdag metamorphic massif exposedin the Biga Peninsula (KDM in Fig. 2; Okay et al.1991; Duru et al. 2004). The NE–SW-trendingKazdag massif forms a structural dome and rep-resents a metamorphic core complex. The high-grade metamorphic basement rocks in the massifare separated by the overlying unmetamorphosedmiddle Cretaceous accretionary melange (Çetmimelange) along a mylonitic shear zone (Alakeçishear zone) that defines a detachment surface(Bonev & Beccaletto 2007). The metamorphicassemblages in the footwall of this shear zonerecord amphibolite-facies metamorphic conditionsat 5 kbar and 640 8C that were reached around24 Ma as constrained by Rb–Sr mica ages (Okay &Satir 2000). Kinematic indicators and deformationpatterns in the mylonitic rocks suggest top-to-the-NNW (in general) normal shear sense and defor-mation mechanisms grading from ductile shear flowto brittle fracturing and cataclasis toward the top ofthe detachment zone (Bonev & Beccaletto 2007).The Kazdag core complex in the footwall of thisdetachment zone is inferred to have been exhumedstarting at c. 24 Ma from a depth of c. 14 km alongthe north-dipping Alakeçi mylonitic shear zone(Okay & Satir 2000).

    The Sakarya continental rocks and the ophioliticunits of the IASZ are intruded by a series of east–west trending Eocene and Oligo-Miocene plutonsthat are represented by I-type calc-alkaline grani-toids (Fig. 2; Harris et al. 1994; Genç 1998; Altun-kaynak & Yılmaz 1998; Köprübaşi & Aldanmaz2004; Altunkaynak 2007). The plutons straddlingthe IASZ (the suture zone granitoids, SZG, of Altun-kaynak 2007) range in composition from diorite,quartz diorite and granodiorite to syenite (Orhaneli,Topuk, Gürgenyayla and Göynükbelen plutons) andhave ages around 54–48 Ma (Ataman 1972; Bingölet al. 1982, 1994; Harris et al. 1994; Delaloye &Bingöl 2000; Yılmaz et al. 2001). The plutonsfarther north along the Marmara Sea (Marmara

    Y. DILEK ET AL.200

  • granitoids, MG, of Altunkaynak 2007) are com-posed of monzogranite, granodiorite and granite(Armutlu, Lapseki and Kapidag plutons) and haveages between 48 and 34 Ma (Ercan et al. 1985;Bingöl et al. 1994; Harris et al. 1994; Genç &Yılmaz 1997; Delaloye & Bingöl 2000; Köprübaşiet al. 2000; Köprübaşi & Aldanmaz 2004).

    The granitoid plutons intruded into the Kazdagcore complex farther west are Oligo-Miocene inage and crosscut the extensional foliation and linea-tion in the Kazdag massif, providing an upper ageconstraint for the timing of the extensional defor-mation in NW Anatolia. These plutons are composedof granite, granodiorite, quartz diorite and monzo-nite. They are metaluminous and subalkaline innature and have medium- to high-K calc-alkalinecompositions (Okay & Satir 2000; Genç & Altunkay-nak 2007). Rb–Sr biotite dating of the Evciler pluton(Fig. 2) revealed cooling ages of 20.7 + 0.2 Ma–20.5 + 0.2 Ma, nearly identical to the Rb–Srbiotite ages of 18–20 Ma from the gneissic rocksof the host Kazdag massif (Okay & Satir 2000).Birkle & Satir (1995) have also reported a Rb–Srbiotite age of 25 + 0.3 Ma from the northeasternpart of the Evciler pluton. These cooling ages of theEvciler pluton are nearly coeval with a single-grainzircon SHRIMP age of 23.94 + 0.31 Ma from theEybek pluton (Fig. 2; Altunkaynak and Dilek, unpub-lished data). These structural and temporal relationsindicate that the syn-extensional granitoids in theKazdag core complex were emplaced during thelatest Oligocene–early Miocene, shortly afterthe peak deformation and metamorphism.

    The Menderes metamorphic massif farther southin the Anatolide block is a NE–SW-oriented, sub-elliptical dome divided into northern, central andsouthern sections that are separated by nearlyeast–west-trending structural grabens (Fig. 2). Itconsists of a Precambrian ‘core’ and Palaeozoic–Cenozoic ‘cover’ (Satir & Friedrichsen 1986;Bozkurt & Park 1994; Bozkurt & Oberhänsli 2001and references therein). The core sequence includesaugen gneisses, metagranites, high-grade schistsand eclogitic metagabbros with metamorphic agesolder than 50 Ma (Candan et al. 2000; Bozkurt &Oberhänsli 2001). The cover sequence consists ofvarious schist types and metamorphosed carbonatesand the protoliths of the cover sequences range inage from Palaeozoic to the early Eocene (Loos &Rischmann 1999; Bozkurt & Oberhänsli 2001;Rimmelé et al. 2003). The core and cover sequencesof the Menderes massif collectively compriseseveral nappe systems that were assembled mainlyduring the late Mesozoic–early Cenozoic colli-sional events in the region (Gessner et al. 2001;Ring et al. 2001; Reignier et al. 2007).

    The main episode of metamorphism in the Men-deres massif is inferred to have resulted from theburial regime associated with the emplacement of

    the Lycian nappes and ophiolitic thrust sheets(Dilek & Whitney 2000; Yılmaz 2002). Imbricatestacking of the Menderes nappes beneath theLycian nappes and ophiolitic thrust sheets appearsto have migrated southwards throughout thePalaeocene–middle Eocene (Özer et al. 2001;Candan et al. 2005). The unroofing and exhumationof the Menderes massif may have started as early asthe latest Oligocene–early Miocene (25–21 Ma) asconstrained by the cooling ages of the syn-exten-sional granitoid intrusions crosscutting the meta-morphic rocks (Bozkurt & Satir 2000; Catlos et al.2002; Işik et al. 2003; Ring & Collins 2005;Thomson & Ring 2006). The Simav detachmentalong the northern edge of the northern submassif(Işik et al. 2003; Ring & Collins 2005) and theAlasehir and Büyük Menderes (or Güney) detach-ments along the northern and southern edges(respectively) of the central submassif (Fig. 2;Gessner et al. 2001) played a major role in the exhu-mation of the Menderes massif as a core complex.

    Cenozoic granitoids in the Menderes

    Massif

    We have examined the occurrence, structure andgeochemistry of the Egrigöz, Koyunoba and Baklangranitoids in the northern submassif and the Salihli,Turgutlu and Alasehir granitoids in the central sub-massif (Fig. 2) in order to document the nature andpetrogenesis of syn-extensional magmatism duringthe exhumation of the Menderes core complex.Granitoid plutons in the Menderes massif aremainly exposed in the footwalls of major detach-ment faults and show structures and textures associ-ated with extensional deformation. Collectively, wegroup these plutons under a descriptive name ofMenderes Granitoids (MEG).

    Field relations and structure of the MEG

    The NNE-trending Egrigöz and Koyunoba grani-toids are intruded into the Precambrian–Palaeozoicgneiss, schist, amphibolite and gneissic mylonite inthe footwall of the Simav detachment in the northernsubmassif and are overlain by Neogene volcano-sedimentary rocks of the Akdere basin (Işik et al.2004; Ring & Collins 2005). They are composedof granite, granodiorite and monzonite, with lesscommon diorite and monzodiorite, and are cut byfine-grained dykes of similar compositions. Themajority of the plutonic rocks are medium- tocoarse-grained and isotropic. They become foliatedand mylonitic toward the Simav detachment fault tothe north and west, with a preferred alignment ofbiotite, quartz and feldspar defining a high-temperature foliation plane in a ductile shear zone.S-C fabrics, biotite fish structures, asymmetric

    SYN-EXTENSIONAL GRANITES, MENDERES MASSIF 201

  • porphyroclasts and oblique quartz grain-shape foli-ation all consistently suggest top-to-the-NW senseof shear, indicating extensional deformation parallelto the Simav detachment surface (Işik et al. 2003;Ring & Collins 2005; Thomson & Ring 2006).

    The timing of the mylonitic shear zone develop-ment along the northern edge of these plutons andtheir intrusion into the northern Menderes massifare nearly coeval as constrained by the recent geo-chronological studies. 40Ar/39Ar dating of meta-morphic muscovite grains from a mylonitic gneissin the extensional shear zone along the Koyunobapluton suggests that mylonitic deformation of thehost rock occurred around 22.86 + 0.47 Ma (Işiket al. 2004). Ring & Collins (2005) obtained second-ary ion mass spectrometry (SIMS) U–Th–Pb zirconages of 20.7 + 0.6 Ma and 21.0 + 0.2 Ma from theEgrigöz and Koyunoba granitoids, respectively.These intrusion ages are within error of the40Ar/39Ar biotite cooling ages of 20.19 + 0.28 Mafrom the Egrigöz granitoid (Işik et al. 2004). Thesegeochronological data, combined with the structuralobservations, demonstrate the syn-extensionalnature of the plutons and possibly their intrusion atshallow depths resulting in rapid cooling duringexhumation (Ring & Collins 2005; Thomson &Ring 2006). The c. 15 Ma volcanic interlayers inthe Akdere basin sedimentary srata, which rest onthe mylonitic gneiss and granitoids along the Simavdetachment (Ercan et al. 1997), suggest that thenorthern Menderes massif and the syn-extensionalEgrigöz and Koyunoba plutons were exhumed tothe surface by the early–middle Miocene.

    The Baklan granitoid to the SE of the Egrigözand Koyunoba plutons (Fig. 2) is intrusive into thePalaeozoic marble, schist and quartzite of the Men-deres massif and the tectonically overlying Murat-dagi ophiolitic melange (Aydogan et al. 2008).The lower Miocene Kürtköyü Formation consistingof sandstone and gravel deposits rest unconformablyon all these units, including the Baklan granitoid,indicating that the pluton was exposed at thesurface by the end of the early Miocene. Themajority of the Baklan pluton rocks are made ofmedium- to coarse-grained granodiorite composedof K-feldspar, plagioclase, quartz, biotite and horn-blende. Monzodioritic to monzogabbroic microgra-nular enclaves are common in the granodioritic hostrocks. K–Ar whole-rock dating of the granodioritehas revealed ages between 17.8 + 0.7 Ma and19.4 + 0.9 Ma (Aydogan et al. 2008).

    The Turgutlu, Salihli and Alasehir granitoidsfarther south occur along an approximately east–west-trending belt in the footwall of the Alasehirdetachment in the central submassif and are intrusiveinto the metasedimentary rocks and schists of theMenderes massif (Fig. 3). The shear zone beneaththe detachment surface includes mylonitized

    metamorphic and granitoid rocks that display well-developed foliation and stretching lineation in thelower sections and microbreaccia, breccia, cata-clasite, foliated cataclasite and pseudotachylitetoward the top (Işik et al. 2003; Öner & Dilek2007). The nearly 100 m thick cataclastic shearzone beneath the detachment surface contains S-Cfabrics, microfaults, Riedel shears and shear bands,all consistently indicating top-to-the-north-NEshearing (Fig. 4; Öner & Dilek 2007). The majorityof all three granitoids are composed of isotropicgranodiorites, which become increasingly myloniticupward into the detachment shear zone. The myloni-tic foliation in these deformed granitoids is definedby the alignment of biotite and feldspar porphyclasts(Fig. 5c), whereas the lineation is marked bystretched quartz and preferred orientations of feld-spar and biotite grains plunging to the north–NE at12–148 (Işik et al. 2003; Öner & Dilek 2007).

    Kinematic indicators in the mylonitic granitoidsand their host metamorphic rocks include S-Cfabrics, asymmetric porphyroclasts, biotite fish,fractured and displaced grains and asymmetricenclaves that consistently show top-to-the-north–NE normal sense of shearing (Işik et al. 2003;Öner & Dilek 2007). The similar orientation ofthe mylonitic foliation and stretching lineation(Fig. 4), the same top-to-the-north–NE normalshear sense and a corresponding retrogradegreenschist-facies metamorphic overprint in boththe deformed granitoid and its host metamorphicrocks indicate that the plutons and the Menderesmetamorphic rocks were affected by the sameextensional deformation. The progression from rela-tively undeformed isotropic granodiorite at depth tomylonitic-ultramylonitic plutonic rocks within thedetachment shear zone at the surface (Fig. 4)further show that these plutons are syn-extensionalintrusions (Hetzel et al. 1995; Işik et al. 2003;Öner & Dilek 2007).

    The oldest sedimentary units overlying theAlasehir detachment surface and the granitoids arethe lower–middle Miocene shale and limestone oflacustrine and fan-delta facies (Gerentas andKaypaktepe Units). Stratigraphically upward theserocks are overlain by the upper Miocene AcidereFormation and the Plio-Pleistocene Göbekli,Yenipazar, Asartepe and Erendali Formations(Figs 4 & 5; Öner & Dilek 2007). Several majorunconformities exist in these Miocene–Pleistocenestrata that likely developed as a result of extensionaltilt-block faulting during the evolution of theAlasehir supradetachment basin.

    Geochronology of the MEG

    The geochronology of both the Salihli and Turgutlugranitoids and their metamorphic host rocks provide

    Y. DILEK ET AL.202

  • significant constraints on the timing of the exten-sional deformation and the synchronous magmatismin the footwall of the central Menderes massif.Igneous biotites from the Turgutlu and Salihligranodiorites yielded 40Ar/39Ar cooling ages of13.2 + 0.2 Ma and 12.2 + 0.4 Ma, respectively(Hetzel et al. 1995). U–Pb monazite ages of16.1 + 0.2 Ma from the Turgutlu and U–Pb allaniteages of 15.0 + 0.3 Ma from the Salihli granodioritedate the crystallization ages of these two granitoidbodies as the early–middle Miocene (Glodny &Hetzel 2007). These crystallization ages are closeto the matrix monazite ages of 17 + 5 Ma (Catlos &Çemen 2005) from metamorphic rocks in theeastern part of the Alasehir detachment that areinterpreted to record tectonic extension. Morerecently, Catlos et al. (2008) reported in situTh–Pb ion microprobe monazite ages of21.7 + 4.5 Ma to 9.6 + 1.6 Ma (+1s) from the

    Salihli and Turgutlu granitoids and 31.5 + 2.7 Mato 22.8 + 2.4 Ma (+1s) from garnet-bearingschists from the Bozdag nappe. These new agesdemonstrate an older exhumation history of themiddle crustal rocks and their syn-extensionalplutons in the central Menderes massif, goingback to the early Miocene and possibly to theOligocene.

    Geochemistry

    We present new major and trace element analysesand isotope data from the Salihli granitoid occurringon the southern shoulder of the Alasehir graben(Figs 2 & 3). These new data, combined with thepreviously published geochemical data from theSalihli, Turgutlu, Egrigoz and Baklan plutons, areused to constrain the magma sources and tectono-magmatic evolution processes of the MEG. We

    Fig. 3. Geological map of the Menderes massif and its environs in western Anatolia. The Menderes massif consists ofseveral nappe systems (Bozdag, Çine and Bayindir) that are stacked up along north-directed thrust sheets in the fieldarea. The Alasehir granitoid (AG), Salihli granitoid (SG) and Turgutlu granitoid (TG) are intrusive into differentbasement units in the Menderes massif.

    SYN-EXTENSIONAL GRANITES, MENDERES MASSIF 203

  • Fig. 4. Geological cross-section from the northern part of the central Menderes core complex showing the spatial relations between the high-grade metamorphic rocks, the Salihlipluton, the cataclastic zone of the detachment fault and the Upper Miocene-Pleistocene supradetachment sedimentary strata (tilted southward into the detachment fault). Thecataclastic zone associated with the Alasehir detachment is up to 150 m in thickness and encompasses the exposed upper surface of the Salihli granitoid. Note the decreasing strainstructurally down-section into the pluton. Outcrop photos 1 and 2 show the internal fabric in a relatively less-deformed and a highly-deformed granodiorite from two differentelevations in the pluton. Both the cataclastic zone and the Salihli granitoid rocks display similar extensional fault and foliation geometries. South-dipping foliation in both unitsrepresents the extensional fabric in south-tilted fault blocks.

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  • Fig. 5. Field photos of the Salihli granitoid in the Menderes core complex. (a) Gently north-dipping slope in thebackground represents the Alasehir detachment surface, overlain by the Upper Miocene Acidere Formation. The surfacein the foreground shows the cataclastic zone of the detachment surface. View to the East. (b) The Alasehir detachmentdips gently to the North and overlain by the red fluvial clastic rocks of the Upper Miocene Acidere Formation. Deformedplutonic rocks of the Salihli granitoid are seen along the detachment surface in the foreground. View to the NW. (c)North-dipping mylonitic foliation and banding in the Salihli plutonic rocks beneath the cataclastic zone.

    SYN-EXTENSIONAL GRANITES, MENDERES MASSIF 205

  • also compare the geochemical features of the MEGwith those granitoids that are emplaced into othermetamorphic core complexes in the northern(Rhodope massif) and central (Cyclades) AegeanProvince.

    Analytical techniques

    Multi-element concentration was determined byusing polarized energy dispersive XRF. The spec-trometer used in this study is the Spectro XLAB2000 PEDXRF that is equipped with an Rh anodeX-ray tube and 0.5 mm Be side window andhoused in the Department of Geological Engineeringat the University of Ankara (Turkey). The detector ofspectrometer is Si (Li), cooled by liquid N2, with aresolution of ,150 eV at Mn Ka, 5000 cps. Thespectrometer was calibrated with two standardrocks, G01-MA-N and K03-MRG-1, Canadian Cer-tified Reference Materials and Centre de RecherchesPétrographiques et Géochimiques (CRPG) ofFrance, based on the certificated concentrations ofthe elements under investigation. The sampleswere ground into fine powder in an agate mortarthat was sieved to pass through of 200 mm andthen pressed into thick pellets of 32 mm diameterusing wach as blinder. USGS standards, GEOL,GBW 7109 and GBW-7309 Sediment were equallypressed into pellets in a similar manner as thesamples and these standards were used for qualityassurance (La Tour 1989; Johnson et al. 1999).Total analysis time for each additional element was30 minutes. Sr and Nd isotope ratios were deter-mined by thermal ionization mass spectrometry(TIMS) (Thermo Quest Finnigan MAT 261) at theUniversity of Texas at Dallas.

    Major and trace element characteristics

    Major and trace element compositions of the MEGare given in Table 1. Different intrusive units ofthe MEG (Salihli, SG; Turgutlu, TG; Egrigöz, EG;Baklan granitoids, BG) show moderate variationsof major element compositions, with their silicacontent ranging from 62.5 to 78.2 wt%. The MEGare composed mainly of tonalite, granodiorite andgranite (de la Roche et al. 1980; Fig. 6), consistentwith their modal mineralogy. The A/CNK[Al2O3/(CaOþNa2OþK2O) molecular ratio]values range between 0.81 and 1.27. The vastmajority of the MEG are metaluminous and slightlyperaluminous; rocks having peralkaline compo-sitions are absent among the analysed samples(Fig. 7). The least-evolved members are predomi-nantly metaluminous (tonalite and hornblende–biotite granodiorite with A/CNK ,1), whereassome more-evolved biotite granodiorite andtwo-mica granodiorites exhibit slightly to mildly

    peraluminous signatures (A/CNK ¼ 1.1–1.27).However, the metamorphic basement rocks intowhich these granitoids were emplaced are stronglyperaluminous (A/CNK ¼ 1.45–1.91) (Fig. 7).

    The MEG are all subalkaline in nature anddisplay a calc-alkaline trend in an AFM ternarydiagram (Irvine & Baragar 1971; Fig. 8a). Themajority of the MEG belong to the high-Kcalc-alkaline series, although a few samplesbelong to the shoshonitic and medium-K series(Fig. 8b). Their K2O/Na2O ratio ranges between0.68 and 2.67 and they have moderate Mg-numbers(average: 35–57) (Fig. 9).

    The major element variations of the MEG definelinear trends as seen in Figure 9. Their TiO2, MgO,Al2O3, FeO, CaO and P2O5 contents decrease andK2O contents and A/CNK, K2O/Na2O ratiosincrease with increasing SiO2 contents (Fig. 9).The trace element compositions also show moderatevariations, some of which (e.g. Sc, Zr, Rb and Sr)correlate well with the SiO2 contents (Table 1;Fig. 10). Samples with SiO2 . 70 wt% mostlyhave 102–250 ppm Rb, 241–279 ppm Sr and103–154 ppm Zr, whereas samples withSiO2 , 70 wt% have 95–144 ppm Rb, 216–372 ppm Sr and 108–239 ppm Zr. Other traceelements display more scattered variations (e.g. Y,La, Ce ) with SiO2 (not shown here). There is a con-siderable overlap among all four groups of theplutons (SG, TG, EG, BG) for inter-element ratios,such as Zr/Nb, La/Nb, Rb/Nb and Ce/Y (Fig. 9).This similarity is supported by the abundance andthe shape of trace element patterns on thePM-normalized and chondrite-normalized REE dia-grams (Figs 10a & 11a).

    Primitive mantle (PM)-normalized trace elementpatterns of representative rock samples from theMEG, Cyclades and Rhodope granitoids and meta-morphic basement rocks of the Menderes massifare shown in Figure 10. Elemental patterns ofupper (UC), middle (MC) and lower continentalcrust (LC) are also plotted in Figure 10a for thepurpose of comparison (UC, MC, LC values aretaken from Taylor & Mc Lennan 1985). The MEGdisplay enrichment in LILE (K, Rb,Cs), in someHFSE (Th, U) and in Pb over LREE and MREEand show strong negative anomalies in Ba, Nb, Sr,P and Ti. These depletions are more pronouncedin two-mica granitoids. Trace element patterns ofthe MEG are similar to the trends displayed by thegranitoids in the Cyclades, such as the plutons onMikanos, Naxos, Delos and Ikeria (Pe-Piper et al.1997, 2002; Pe-Piper & Piper 2001; Alther &Siebel 2002) and in the Rhodope massif (Fig. 10b;Christofides et al. 1998). These patterns are alsopartly similar to those of the metamorphic basementrocks of the Menderes massif (Fig. 10c; Catlos et al.2008). The REE distributions of the MEG show

    Y. DILEK ET AL.206

  • Table 1. Major and trace element compositions and Sr and Nd isotopes of selected samples from the Salihli granitoid in the Menderes metamorphic massif, western Turkey

    01DEG07 02DEG07 03DEG07 04DEG07 05DEG07 06DEG07 07DEG07 08DEG07 09DEG07 10DEG07 11DEG07 12DEG07 13DEG07 14DEG07 15DEG07 16DEG07 17DEG07 18DEG07 19DEG07

    SiO2 63.92 70.25 68.43 67.45 69.17 67.77 67.87 68.58 69.08 65.85 65.08 63.92 66.51 67.66 68.29 67.06 67.67 66.62 69.58Al2O3 19.11 14.66 14.9 14.49 14.76 15.21 14.02 15.33 14.31 15.26 15.72 14.94 15.07 14.73 14.35 14.73 14.62 15.25 14.33Fe2O3 3.89 3.1 3.26 4.18 3.29 3.63 3.96 2.98 3.18 3.98 4.31 5.47 4.18 3.88 3.81 3.97 3.77 4.05 3.2MnO 0.07 0.06 0.06 0.07 0.06 0.07 0.07 0.06 0.06 0.07 0.07 0.13 0.08 0.07 0.07 0.07 0.06 0.07 0.06MgO 1.71 1.14 1.57 2.09 1.62 2.05 2.24 1.24 1.48 1.99 2.39 3.04 2.39 1.85 1.63 2.3 1.64 2.02 1.86CaO 3.94 2.77 3.77 3.93 2.91 4 3.84 2.56 3.43 4.23 4.11 5.02 4.16 3.46 3.97 4.03 3.59 4.13 3.04Na2O 1.75 3.04 3.58 3.04 4.27 3.18 4.33 4.05 3.67 3.4 3.5 2.83 3.01 3.14 2.69 3.01 3.2 3.42 3.01K2O 4.66 3.46 3.13 3.21 3.09 2.78 2.91 3.8 3.15 3.71 2.99 2.95 2.99 3.48 4.1 3.24 3.59 2.78 3.71TiO2 0.67 0.47 0.48 0.61 0.46 0.53 0.59 0.45 0.5 0.55 0.64 0.58 0.57 0.57 0.57 0.55 0.53 0.62 0.46P2O5 0.15 0.16 0.16 0.17 0.15 0.18 0.15 0.13 0.19 0.19 0.22 0.16 0.2 0.17 0.18 0.19 0.17 0.2 0.18LOI 0.58 0.82 0.57 0.64 0.15 0.53 0.63 0.75 0.82 0.86 0.82 0.85 0.72 0.85 0.86 0.73 0.95 0.71 0.93Total 100.44 99.93 99.92 99.87 99.93 99.92 100.61 99.93 99.87 100.08 99.85 99.89 99.88 99.87 100.51 99.89 99.8 99.88 100.35

    Ba 578.9 625.8 633.9 511.5 556.1 531.3 396.1 607.6 597.5 474.5 477.6 472.8 608.6 624.5 639.5 581.9 686.9 481.9 995.5Sr 216 243.7 326.8 297.7 302.4 350.7 306.3 302.4 285.7 349.4 355.7 319.4 346.7 292.4 291.9 350.9 323.8 312.8 296.4Y 19.2 21.2 17.5 24.5 16.5 16.9 17.3 19.3 13.6 17.8 18.6 34.4 14.7 16.8 16.3 16.4 18.1 23.5 11.5Zr 220.8 197.3 193.2 205.3 203.3 203.8 170.5 154.4 202.9 218 227.5 173.6 210.5 184.8 214.3 212.8 191.3 217.4 207.2Co 24 44.9 37.7 41.1 59.2 63.1 44.9 50.4 41.9 50 42.6 47.6 46.1 37.2 41 44.3 30.6 64.7 46Zn 43 57.6 51.9 61.7 63.7 55.4 60.6 52.4 55.6 55.2 64.1 79.7 60.1 67.9 60.7 54.3 46.3 61.2 52.4Ga 26.4 20.9 18.6 20.7 19.8 18.5 20.3 20.5 19.5 21.4 22 18.8 20.9 21.7 20.7 20.4 19.1 21 21.5Ge 1.1 1.8 1.3 1.33 2.4 1.93 2.6 1.3 2.4 2.4 1.32 1.3 1.3 2.3 1.4 1.3 1.3 1.3 1.3Rb 162.2 139.9 110 121.1 112.7 92.2 122.3 120.4 95.6 110.5 105 111.7 101.5 135.4 139.2 97.9 95.8 91 113.3Nb 14.7 15.2 14.6 19.9 14.5 16.2 13.6 13.9 15.1 16.5 16.8 14.7 11.9 18.7 15.9 12 13.4 18.3 16Sn 8.2 4.5 5.4 5.6 4.6 4.2 6 6.5 1.2 5 3.5 5.4 3.4 3.1 4.1 3.9 3.2 4.1 0.9Cs 9 22.3 14.3 17.7 21.7 16.5 22.8 17.3 22.5 7.8 3.52 16.3 29.1 26.1 20.5 19.2 23.1 16.9 23.6La 25.7 78.3 53.3 60 73 80.7 43.1 37.7 74.9 41.6 18.9 42.8 96.5 61 39 78.5 117.5 65.7 79.3Ce 55 130.2 92.6 101.8 113.2 119.3 63.4 70.3 129.8 78.9 35.5 80.6 150 107.6 81 122.5 191.4 111.7 126.7Hf 2.5 2.8 2.9 4.2 2.9 3 3.1 3 2.8 3.2 3.3 4.7 3.5 4.6 3.8 2.5 3.1 3.1 3Ta 3.6 4.2 10.7 9.1 4.2 4.9 4.5 4.2 3.7 4.3 4.6 9.9 3.8 5.7 4 3.9 3.3 4.5 4.2Tl 1.4 2.3 2.7 2.5 1.4 2.4 1.3 1.3 1.9 1.1 1.7 1.4 1.7 1.4 1.1 2.4 1.7 1.9 1.4Pb 56.4 64.7 50 38 45.7 39.3 44.2 54 44 40.9 41.9 38.8 42.6 48.7 53.3 38.1 42.1 38.2 53.7Bi 1 1.7 0.9 0.9 1.1 1.1 0.9 0.7 0.7 0.7 1.2 1.2 0.5 0.4 0.7 1.5 0.8 1.6 0.6Th 12 14.2 13.7 15.3 17.7 14.1 9 11.4 13.4 15.4 14.2 9.5 13 10.4 10.8 12.9 10.3 15.6 12.1U 7.6 10.8 8.2 7.7 6.8 7.7 18.3 7.3 6.8 15.6 15.3 8 9.5 8.2 8.3 9.2 7.5 7.8 887Sr/86Sr 0.71096 n.d. n.d. n.d. n.d. n.d. n.d. 0.71141 n.d. n.d. n.d. 0.7109 n.d. n.d. n.d. n.d. n.d. n.d. n.d.143Nd/144Nd 0.51223 n.d. n.d. n.d. n.d. n.d. n.d. nd. n.d. n.d. n.d. 0.51222 n.d. n.d. n.d. n.d. n.d. n.d. n.d.

    (Continued )

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  • Table 1. Continued

    20DEG07 21DEG07 22DEG07 23DEG07 24DEG07 25DEG07 26DEG07 27DEG07 28DEG07 29DEG07 30DEG07 31DEG07 32DEG07 33DEG07 34DEG07 35DEG07 36DEG07

    SiO2 69.86 69.44 68.4 69.47 71.52 66.48 67.48 66.25 65.92 66.96 71.66 67.34 67.1 66.21 66.48 73.95 67.17Al2O3 14.2 14.22 14.21 14.34 14.25 15.49 14.95 15.34 15.23 15.25 13.44 15.03 15.32 15.22 15.71 13.1 15.06Fe2O3 3.23 3.82 3.94 3.56 2.21 4.12 3.73 4.28 4.68 3.96 2.89 3.47 3.81 4.18 3.83 1.77 3.8MnO 0.06 0.06 0.08 0.06 0.05 0.07 0.06 0.07 0.08 0.07 0.06 0.07 0.07 0.07 0.06 0.03 0.07MgO 1.39 1.35 1.88 1.63 0.97 2.04 1.93 2.18 2.31 2.04 1.18 1.84 1.5 2.53 2.13 0.97 1.87CaO 3.12 3.14 3.79 3.62 2.97 3.95 3.68 4.19 4.54 4.1 2.69 3.88 3.76 3.66 3.41 2.96 4.01Na2O 3.21 3.07 3.06 2.79 3.25 3.28 3.2 3.27 2.85 3.34 2.86 3.34 4.22 3.43 3.51 2.75 3.78K2O 3.17 3.98 2.83 2.94 3.69 2.98 3.36 2.7 2.38 2.77 3.91 3.3 3.27 2.99 3.38 4.1 2.82TiO2 0.48 0.42 0.56 0.56 0.3 0.64 0.55 0.61 0.7 0.59 0.43 0.54 0.47 0.68 0.57 0.28 0.57P2O5 0.19 0.15 0.17 0.16 0.11 0.22 0.2 0.24 0.24 0.21 0.17 0.18 0.16 0.2 0.19 0.09 0.19LOI 0.94 0.91 0.94 0.79 0.82 0.62 0.76 0.69 0.82 0.62 0.65 0.9 0.72 0.68 0.62 0.34 0.54Total 99.85 100.57 99.87 99.93 100.14 99.89 99.91 99.82 99.76 99.91 99.94 99.89 100.4 99.85 99.89 100.35 99.88

    Ba 555.9 652.4 454.4 487.2 534 609.9 777.9 511.1 620 607.3 564.8 731 601 460.8 618.3 376.3 481.8Sr 282.4 274 282 292.5 279.8 372.8 352.6 370 384 369.7 256.8 337.8 319 338.3 345.7 269.2 326.2Y 17.9 15.7 16.9 20.9 12.7 18.5 17.2 19.9 17.8 21.2 21.9 19.6 22.5 24 23.5 12.4 21.9Zr 222.7 172.6 196.6 206.3 131.4 222.2 202.6 218 239.4 231.7 154.6 196.9 188.4 215.8 193.3 103.4 223.9Co 45 29.3 32.5 39.4 52 45.2 41.8 12 28.7 41.7 58.7 59 42.8 45.4 56.7 46.6 39.7Zn 58.4 50.6 68.9 55.8 41.7 61.6 56.4 58.2 60.9 58.1 50.6 50.2 57.6 61 56.9 29.9 57.4Ga 21.9 20.8 21.3 18.1 19.6 21.6 20.3 21.4 19.4 19.6 20.2 19.8 19.5 20 21.1 15.8 21.2Ge 1.1 0.3 1.9 1.34 0.8 2 0.34 1.8 1.32 0.63 1.3 1.7 1.1 2.3 0.67 1.78 0.32Rb 104.8 144.2 120.1 121.1 102 101 102.3 93.7 70.4 86.2 132.7 103.7 108.9 108 116 85.6 95.3Nb 20.2 14.8 17.1 18.1 8 15.4 14.8 16.8 15.5 15.7 12.8 12.3 23.5 17.9 16.4 12.5 17.3Sn 2 4.3 10.1 3.9 3.5 4.1 1.7 2.9 5 4.7 4 3.2 6.9 7.6 1 1 4.4Cs 3.9 17.4 17.4 21.2 13.6 15.3 18.5 3.54 9.4 3.21 22.4 20.7 3.11 12.3 33.4 3.5 16.8La 8.5 62.2 44.1 39.6 42.1 60.9 73.7 10.9 64.3 11.3 59.5 68.4 20.3 47.1 103 7.4 69.1Ce 135.4 108.1 80.3 67.2 64 111.9 113.4 88.7 108.9 104.6 94.6 95.5 32.5 85 166.2 12.2 124.8Hf 2.9 3.2 3.3 3.1 3.1 3.3 3.3 4.5 3.2 3 3 3.1 3.2 4.3 3 2.8 3.3Ta 4 4.3 3.8 7.6 4.3 3.7 4 4.2 4.8 4 3.4 4.1 8.1 5.2 4 4.1 4.9Tl 1.2 2.3 1.6 1.7 1.6 1 1.8 1.1 1.1 1.6 1.2 1.5 2.2 1.8 1.5 1.5 1.5Pb 50.6 58 48.4 42.9 60.3 40.7 44.6 39.4 41.4 39.5 50.7 44.8 45.4 41.8 43.4 54.2 42.6Bi 1 0.9 1 1.1 2 1 1 1.4 1.3 1.1 1.7 1 1.1 1.2 0.8 0.8 1.2Th 10.3 14.4 13.5 8.9 8.1 13.8 12.6 13 12.5 15.1 12.3 10.5 16.2 12.3 11.6 14.9 15.5U 10.6 7 6.7 7.3 9 6.6 7.2 20.8 7.3 10.6 8 10.7 16.1 10.1 6.9 20.6 10.387Sr/86Sr n.d. n.d. n.d. n.d. 0.71132 n.d. n.d. n.d. 0.71104 n.d. n.d. n.d. 0.71106 n.d. n.d. 0.71103 n.d.143Nd/144Nd n.d. n.d. n.d. n.d. 0.5122 n.d. n.d. n.d. 0.51223 n.d. n.d. n.d. 0.51223 n.d. n.d. 0.51224 n.d.

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  • moderately fractionated REE patterns with LaN/YbN ratios of 4.2–23.3 (average: 7–14), regardlessof the rock types (Fig. 11a).

    Samples from the Salihli pluton have minor Euanomalies with Eu*/Eu values of 0.68 and 0.88,whereas others (TG, EG, BG) have medium tostrong negative Eu anomalies ranging from 0.22 to0.55 that show similar Eu*/Eu ratios to those ofthe Cyclades granitoids (Fig. 11a, b). The magnitude

    of the negative Eu anomalies of the MEG samplesincreases with the increasing SiO2 content.

    Petrogenesis of the Menderes granitoids

    Previous studies and interpretations

    The origin of the MEG has been a subject of variousstudies. Delaloye & Bingöl (2000) have suggestedthat the western Anatolian plutons, including theSalihli granitoid, originated from the Palaeoceneand younger magmatism associated with the Helle-nic subduction zone. Işik et al. (2004) have reportedthat the syn-extensional Egrigöz and Koyunobaplutons in the footwall of the Simav Detachmentwere emplaced in the early stages of continentalextension in the Aegean province. These granitoidsare hybrid in nature with dominantly upper crustalcompositions similar to the coeval Oligo-Miocenegranitoids in the central Aegean Sea region. Hasöz-bek et al. (2004) and Akay (2008) argued for a

    Fig. 6. Chemical variation in the MEG shown on a plotby de la Roche et al. (1980). Data sources include Salihligranitoid: this study and Catlos et al. (2008); Turgutlugranitoid and metamorphic basement rocks: Catlos et al.(2008); Baklan granitoid: Aydogan et al. (2008); Egrigözgranitoid: Akay (2008), Özgenç & İlbeyli (2008), Işiket al. (2004) and Delaloye & Bingöl (2000).

    Fig. 7. The Shand’s index diagram for the MEG (Shand1927). A/CNK: molar Al2O3/(CaOþNa2OþK2O);A/NK: molar Al2O3/(Na2OþK2O). Fields for I-andS-type granitoids are taken from Chappell & White(1974, 1992). See Figure 6 for the data sources.

    Fig. 8. (a) AFM diagram diagram of Irvine & Baragar(1971); (b) K2O v. Na2O diagram of the MEG using theclassification scheme of Peccerillo & Taylor (1976). SeeFigure 6 for the data sources.

    SYN-EXTENSIONAL GRANITES, MENDERES MASSIF 209

  • Fig. 9. Harker diagrams of the MEG illustrating the variations of major oxides and trace elements with SiO2. SeeFigure 6 for the data sources.

    Y. DILEK ET AL.210

  • hybrid magma source produced under compres-sional regime for the same granitoids. Özgenç &İlbeyli (2008) have proposed that the Egrigözpluton formed by partial melting of mafic lower-crustal rocks during post-collisional extensional tec-tonics in the region. Aydogan et al. (2008) haveargued that parental magmas of the Baklan plutonwere produced by partial melting of a juvenilelower crust, and that the underplated mantle-derivedbasaltic magmas, which provided the necessary heatfor partial melting, had chemical and isotopic signa-tures similar to those of an enriched mantle. Catloset al. (2008) have argued that the trace-element geo-chemical features of the Salihli and Turgutlu grani-toids are consistent with their continental arc originand that their magmas were produced under a com-pressional regime above the north-dipping Hellenicsubduction zone. The existing interpretations of themelt source and the magmatic evolution of the MEGare, therefore, varied.

    Fig. 11. Chondrite-normalized REE patterns for theMEG (a) and Cyclades granitoids (b). Chondritenormalizing values are from Boynton (1984). Datasources for Cyclades granitoids are from Pe-Piper et al.(2002), Pe-Piper & Piper (2001) and Altherr & Siebel(2002). Upper crust (UC), lower crust (L) and middlecrust (MC) values are from Taylor & McLennan (1985).

    Fig. 10. PM (Primitive mantle) normalizedmulti-element patterns for the MEG (a), Cyclades andRhodope granitoids (b) and metamorphic basementrocks of the Menderes massif (c). PM normalizing valuesare from Sun & McDonough (1989). Data sources for theCyclades: Pe-Piper & Piper (2001), Pe-Piper et al.(2002), Alther & Siebel (2002); Rhodope granitoids:Christofides et al. (1998). See Figure 6 for the datasources for the other granitoids.

    SYN-EXTENSIONAL GRANITES, MENDERES MASSIF 211

  • Melt sources and evolution of the MEG

    The Salihli, Turgutlu, Egrigöz and Baklan plutonsare all intrusive into the high-grade metamorphicrocks of the Menderes core complex. They showsimilar major and trace element characteristics andoverlapping Zr/Nb, La/Nb, Rb/Nb and Ce/Y,suggesting that their melt source(s) were similar(Figs 9, 10 & 11a).

    The A/CNK molecular ratios of the MEGbetween 0.81 and 1.27 indicate that these plutonsare made predominantly of metaluminous, I-typegranitoids (Özgenç & İlbeyli 2008; Aydogan et al.2008) and slightly to mildly peraluminous, rareS-type (Işik et al. 2004), two-mica granitoids(White & Chappell 1977; Chappell & White1992). The MEG samples display similar traceelemental patterns to middle-upper continentalcrust and metamorphic basement rocks (Fig. 10a, c)that were likely inherited from crustal melts of vari-able sources and compositions. However, the higherA/CNK values and lower Mg-numbers of the meta-morphic basement rocks in comparison to the MEGare not consistent with derivation of the MEGmagmas from these basement units alone. Giventhat the metamorphic basement rocks are stronglyperaluminous (Fig. 7), large amounts of crustalcomponent contribution into the magmas wouldincrease their A/CNK ratio and would cause the for-mation of strongly peraluminous S-type granitoids;yet, we do not see these features in the MEG.Thus, the metaluminous I-type character of theMEG eliminates the metapelitic rocks as suitablesource material and points to, instead, an igneousprotolith such as metabasalt, juvenile K-rich basal-tic underplate and/or mantle rocks (Roberts &Clemens 1993; Tepper et al. 1993; Pearce 1996;Patino Douce & McCarthy 1998; Von Blancken-burg et al. 1998; Ashwal et al. 2002; Altherr &Siebel 2002).

    Experimental studies suggest that hydrousmelting of basalts or amphibolites could yield tona-litic magmas, which evolve toward granodioritic togranitic compositions by crustal interaction and/orfractional crystallization (Wyllie 1984; Rapp &Watson 1995; Petford & Gallagher 2001). Althoughsome chemical features [such as (Na2OþK2O)/(FeOþMgOþ TiO2) and CaO/(FeOþMgOþTiO2)] of the MEG, as shown in Figure 12 (a & b)appear to be derived from metabasalts (PatinoDouce 1996, 1999), partial melts of metabasaltsare characterized by relatively high contents ofNa2O and low Mg numbers (Fig. 12c, d), regardlessof the degree of partial melting. These features arenot displayed by the MEG samples. Furthermore,Roberts & Clemens (1993) and Ashwal et al.(2002) have argued that metabasaltic rocks are notsuitable source rocks for the generation of high-K,

    calc-alkaline, I-type granitoids because such maficrocks contain low-K2O and insufficient incompati-ble elements to form appreciable volumes of grani-tic melts. Therefore, we infer that high-K,calc-alkaline and incompatible element-enrichednature of the MEG is inconsistent with derivationof their magmas solely from melting of metabasalts.

    Intermediate to felsic products of the MEG showPM-normalized multi-element patterns (e.g. enrich-ment in Rb, Th and K and negative anomalies in Ba,Sr, P and Ti), suggesting their possible derivationfrom basaltic magmas through crystal fractionation(Fig. 10a). Trace-element patterns of this group areconsistent with derivation of their magmas from anincompatible element-enriched source, as evi-denced by negative Ta and Nb anomalies, enrichedLREE, and low Rb/Sr ratios. These features of theMEG are similar to those of igneous rocksforming at convergent margin settings (Thorpeet al. 1982; Davidson et al. 1991; Pearce & Peate1995). High incompatible element abundances(e.g. K, Rb, Nb and Ba) and inter-element relation-ships (e.g. Ce/Y, Zr/Ba, Th/Yb and Ba/Nb ratios;Figs 9 & 10a) of the MEG indicate asubduction-enriched, heterogeneous sub-conti-nental lithospheric mantle source (see Pearce et al.1990; McCulloch & Gamble 1991; McDonough1990; Thirlwall et al. 1994; Pearce & Peate 1995).Moreover, the (La/Yb)n and (Gd/Yb)n ratios ofthe MEG are in the ranges 6.5–14.5 (Fig. 11a) and1.3–2.1, respectively, that are consistent with deri-vation from lithospheric mantle melts (Thirlwallet al. 1994). Partial melting model suggested byThirlwall et al. (1994) shows that the effects ofpartial melting were more important than fractionalcrystallization in controlling the compositionalvariations within the MEG (Fig. 13).

    The subduction-related enrichment of thewestern Anatolian lithospheric mantle may havebeen an artifact of either arc-derived magmas or asubduction component inherited from earlier con-vergent margin events. Source enrichment throughprevious subduction events in the region has beensuggested for the western Anatolian plutons andrelated volcanism by some authors (Seyitoğluet al. 1997; Genç & Yılmaz 1997; Yılmaz & Polat1998; Altunkaynak & Yılmaz 1998; Yılmaz et al.2000, 2001; Aldanmaz et al. 2000; Köprübaşi &Aldanmaz 2004; Altunkaynak & Dilek 2006;Altunkaynak 2007; Dilek & Altunkaynak 2007).However, although subduction-induced mantlemetasomatism can account for enriched sourcecharacteristics of the MEG rocks, the Nb/Laversus Ba/Rb variations observed in these samples(Fig. 14) cannot be explained solely by this mechan-ism. The vertical continental crust versusN-MORB-OIB mantle trend indicate mixing of amantle derived magma with a crustal component,

    Y. DILEK ET AL.212

  • rather than the sole influence of subduction-generated fluids (Wang et al. 1999; Tatsumi et al.1986; Peccerillo 1999; Marchev et al. 2004). A criti-cal evaluation of possible contamination by crustalmaterials is, therefore, necessary. If the MEGmagmas acquired their chemical compositions byassimilation of any crustal material as discussedabove, it is more likely that these assimilants werecomposed of lower to middle crustal componentsrather than the upper crustal host basement meta-morphic rocks alone.

    Sr–Nd isotopes

    Nd–Sr isotopic compositions of the Salihli(Table 1) and Baklan granitoids (Aydogan et al.

    2008) are consistent with a hybrid origin of theirmagmas. The Baklan granitoid has low 87Sr/86Sr(i)(0.70331–0.70452) and high 143Nd/144Nd(i)(0.512305–0.512336) ratios and negative 1Nd(t)(25.0 to 25.6) values that are compositionallysimilar to EMI-type source. These isotope valuespoint to the production of the Baklan granitoidmagmas from interaction of mantle-derived meltwith lower crustal amphibolites or granulites(Aydogan et al. 2008). However, the Salihli grani-toid displays higher 87Sr/86Sr(i) (0.7107–0.7116),lower 143Nd/144Nd(i) (0.512218–0.512220) and1Nd(t) (27.5 to 28.3), indicating a dominantcrustal component for the origin of its magmas(Fig. 14). These geochemical features and isotopiccompositions of the Salihli granitoid are similar to

    Fig. 12. Chemical compositions of the MEG. Outlined fields are adapted from Altherr & Siebel (2002 and referencestherein) and illustrate compositions of partial melts obtained from experimental studies of dehydration melting ofMetabasalts (MB), Metagreywackes (MGW), Metapelites (MP) (Rapp & Watson 1995; Patino Douce 1996, 1999;Patino Douce & McCarthy 1998; and references therein). See Figure 6 for the data sources.

    SYN-EXTENSIONAL GRANITES, MENDERES MASSIF 213

  • those of the granitoids in the Cyclades and in theRhodope massif (Figs 11c, 12b & 15). Pe-Piper &Piper (2001) and Pe-Piper et al. (2002) havesuggested that mafic magma fractionation and/ormixing with felsic crustal material, some of whichwas derived by crustal anatexis (Alther & Siebel2002), could produce the granitoid plutons of theCyclades. On the other hand, felsic magmas of theRhodope granitoids were most likely derived fromsome crustal melts that originated from dehydrationmelting at mid- to deep-crustal levels (Christofideset al. 1998).

    The most reasonable model for the origin of theMEG magmas involves, therefore, partial melting of

    a mixed source including varying proportions of anenriched lithospheric mantle and assimilated-melted lower and middle crustal components(Figs 14 & 15). We infer that crustal-scale shearzones facilitated the uprising of melts derivedfrom a previously enriched lithospheric mantleand their transport to lower to mid-crustal levels,where further melting and magma mixing occurredwithin the crust.

    Fractional crystallization processes

    The observed linear variations in the Harker dia-grams (Fig. 9) and REEcn patterns (Fig. 11a) indicatethat fractional crystallization was an importantprocess during the evolution of the MEG magmas.The negative covariances between SiO2 and FeO*(FeOþ Fe2O3), MgO and CaO (Fig. 9) indicate frac-tionation of olivine and clinopyroxene during theevolution of the MEG magmas. Variations in CaOwith silica are almost the same in all groups(Fig. 9). Decreasing CaO with increasing silica indi-cates that Ca-rich phases such as hornblende andCa-plagioclase were progressively formed and thenremoved from the granitic melt. The lack ofnotable negative Eu and Sr anomalies suggests thatplagioclase fractionation was insignificant duringthe evolution of the Salihli granitoid. However, theEu/Eu* ratios (Eu/Eu*: 022–088) and theirrelationship with the increasing silica content ofthe Turgutlu and Egrigöz granitoids indicate thatplagioclase fractionation was important during for-mation of the more siliceous members of the MEG

    Fig. 14. Nb/La versus Ba/Rb diagram illustrating theeffects of crustal contamination and subductionmetasomatism during evolution of the MEG. The valuesfor CC (Average Continental Crust) are from McLennan(2001) and for N-MORB and OIB are from Sun &McDonough (1989). See Figure 6 for the data sources.

    Fig. 15. Epsilon-Nd(i) versus87Sr/86Sr(i) diagram

    showing isotopic compositions of the MEG andCyclades granitoids. Data for asthenospheric andlithospheric mantle melting array are from Davis & vonBlanckenburg (1995), for Aegean metamorphicbasement from Briqueu et al. (1986), for Aegean Seasediments from Altherr et al. (1988) and for Global RiverAverage from Goldstein & Jacobsen (1988). See Figure 6for the data sources.

    Fig. 13. La/Yb versus La (ppm) diagram illustrating theeffects of partial melting and fractionation. Vectors forFC and PM are from Thirlwall et al. (1994). See Figure 6for the data sources.

    Y. DILEK ET AL.214

  • (Fig. 11). The increasing Rb and decreasing Sr con-tents of the MEG vary with increasing SiO2, pointingout significant feldspar fractionation during the evol-ution of the MEG. The depletion of Ti and P is alsoconsistent with fractional crystallization of Fe–Tioxides and apatite (Fig. 10a).

    Geodynamics of late Cenozoic magmatism

    and its effects on extensional tectonics in

    the Aegean region

    The collision of the Sakarya and Anatolide–Tauridecontinental blocks in the late Palaeocene–earlyEocene caused crustal thickening and orogen-wideburial metamorphism. This collision-driven regionalmetamorphism was responsible for the developmentof high-grade rocks in the Menderes metamorphicmassif. Partial underplating of the buoyantAnatolide–Tauride block beneath the Sakaryacontinent jammed the north-dipping Tethyan sub-duction temporarily, while the continued sinkingof lithospheric mantle resulted in slab breakoff(Fig. 16a). The emplacement of the widespreadmiddle to late Eocene granitoid plutons (i.e. Orha-neli, Topuk, Gürgenyayla, Kapidag) along theIASZ and into the Sakarya continent has been inter-preted to have resulted from slab breakoff-relatedasthenospheric upwelling and associated partialmelting of the subduction-metasomatized continen-tal lithospheric mantle (Fig. 16a; Altunkaynak 2007;Dilek & Altunkaynak 2007).

    Resumed Tethyan subduction and associated slabrollback triggered upper plate extension, leading atectonic collapse of the thermally weakened oro-genic crust in western Anatolia during the lateOligocene–Miocene. This tectonic phase coincideswith bimodal volcanism and widespread ignimbriteflare-up in the region (Pe-Piper & Piper 2006 andreferences therein). The Kazdag core complex inNW Anatolia began its initial exhumation in thelatest Oligocene–early Miocene (Okay & Satir2000) and the Menderes core complex in CentralWestern Anatolia underwent its initial exhumationin the earliest Miocene (Işik et al. 2004; Thomson &Ring 2006; Bozkurt 2007; Dilek & Altunkaynak2007). Some of the collision-generated thrust faultsmay have been reactivated during this time ascrustal-scale low-angle detachment faults, (i.e.Simav detachment fault, SW Anatolian shear zone)facilitating the region-wide extension (Thomson &Ring 2006; Çemen et al. 2006).

    Starting in the middle Miocene, the subcontinen-tal lithospheric mantle beneath the Aegean regionwas delaminated as a result of peeling of its basedue to rapid slab rollback at the Hellenic trench(Fig. 16b). Asthenospheric upwelling caused bythis lithospheric delamination led to melting of the

    subduction-metasomatized lithospheric mantle thatin turn provided heat to the overlying crust. Invasionof the lower and middle crust by lithosphericmantle-derived melts triggered MASH-type pro-cesses (melting, assimilation, storage, homogeniz-ation; Hildreth & Moorbath 1988), resulting in theproduction of hybrid magmas of the MEG(Fig. 17a). Thus, lithospheric mantle and crustalmelts were involved in the evolution of hybrid mag-matism in the middle Miocene. Thermal relaxationassociated with this magmatic phase inducedlithospheric-scale extension and accelerated lowercrustal exhumation and doming across the Aegeanregion (Figs 16b & 17a; Lips et al. 2001). Sufficientcooling of the exhumed mid–lower crustal rocks(including the MEG plutons) in the Menderes corecomplex was followed around 7 + 1 Ma by thedevelopment of high-angle normal faults forminggraben structures (Hetzel et al. 1995, 1998;Gessner et al. 2001; Lips et al. 2001). These faultscrosscut the low-angle detachment surfaces andthe earlier extensional deformational fabrics in thegranitoid plutons and their metamorphic host rocks(Fig. 17b). This late-stage normal faulting causedrelative uplifting of the graben shoulders andfurther exhumation of the detachment footwalls.The MEG plutons continued to be deformed cata-clastically and brittlely during this phase as boththeir metamorphic host rocks and they werefurther uplifted tectonically.

    The development of the major graben systems(i.e. Büyük Menderes, Küçük Menderes, Alasehir,Simav; Fig. 17b) during the advanced stagesof extensional tectonics in the late Miocene–Quaternary further attenuated the continental crustin the region. This extensional phase, accompaniedby increased geothermal gradients, resulted in asth-enospheric upwelling and corresponding decom-pression melting of the sub-asthenospheric mantle.This melting episode generated magmas with highconcentrations of LILE and HFSE, radiogenic Nd,unradiogenic Sr and MORB and OIB-like Pb signa-tures (Alici et al. 2002; Dilek & Altunkaynakunpublished data) that produced the Kula volcanicserupted on the Menderes massif (Fig. 16c). Graben-bounding faults and lithospheric-scale shear zonesfacilitated the upward transport of these alkalinemagmas to the surface with little or no crustal con-tamination. Hydrous melting of the mantle wedgeperidotites above the southward-retreating Hellenicsubduction zone produced the South Aegean arcvolcanism farther south since the late Miocene(Fig. 16c; Pe-Piper & Piper 2006).

    The close temporal and spatial relationshipsbetween the late Cenozoic tectonic extension andmagmatism in the broader Aegean province indicatethat lithospheric-scale melting played a significantrole in weakening the young orogenic crust,

    SYN-EXTENSIONAL GRANITES, MENDERES MASSIF 215

  • facilitating vertical crustal flow and exhumation ofcore complexes (Fig. 17a). Similar close relationsbetween magmatism and extension have been docu-mented from farther south on the Aegean islands(Avigad & Garfunkel 1991; Vanderhaeghe 2004)

    and from other extended terranes such as the Basinand Range in the North American Cordillera(Gans et al. 1989) and the D’Entrecasteaux Islandsof Papua-New Guinea in the SW Pacific (Baldwinet al. 1993).

    Fig. 16. Cenozoic geodynamic evolution of the western Anatolian region through collisional and extensional processesin the upper plate of north-dipping subduction zone(s) within the Tethyan realm. (a) Collision and partial subduction ofthe Anatolide–Tauride continent (ATC) beneath the Sakarya continent leads to slab break-off of the Tethyanlithosphere. Asthenospheric upwelling through the breakoff-induced window facilitates partial melting of thesubduction-metasomatized mantle beneath the suture zone and the Sakarya continent that in turn generates the Eocene toOligo-Miocene volcanoplutonic complexes in NW Anatolia. (b) Rapid slab reatreat of the northward subductingSouthern Tethyan oceanic lithosphere triggers lithospheric delamination in the middle Miocene. Associatedasthenospheric upwelling results in asthenospheric and lithospheric mantle melting. Produced melt reacts with the lowerand middle crust where it undergoes fractional crystallization, assimilation, storage and further melting, generatinghybrid magmas of the MEG granitoids. This phase of magmatism was synchronous with and facilitatedlithospheric-scale extension in the region. Similar melting processes, magmatism and extension are inferred for theKazdag and Rhodope massifs to the north. (c) Advanced stages of tectonic extension and crustal attenuation induceasthenospheric upwelling, leading to decompression melting of the asthenospheric or sub-asthenospheric mantle. Thismelting event in turn generates MORB- and OIB-like magmas of the Kula volcanic domain. Menderes, Kazdag andRhodope massifs are substantially cooled off (due to their unroofing) by this time period and have undergone high-anglenormal faulting. The South Aegean arc volcanism is fed by hydrous melting of the mantle wedge above the Hellenicsubduction zone. Key to lettering: ATC, Anatolide–Tauride continent; IASZ, Izmir–Ankara suture zone;IPSZO, Intra-Pontide suture zone ophiolites; LO, Lycian ophiolites; MBL, Mechanical boundary layer; NAFZ, NorthAnatolian fault zone; RM, Rhodope massif; RPC, Rhodope-Pontide continent; SC, Sakarya continent; TBL, Thermalboundary layer.

    Y. DILEK ET AL.216

  • Conclusions

    The Miocene granitoid plutons in the metamorphiccore complexes in western Anatolia are syn-extensional intrusions, indicating close spatial andtemporal relations between magmatism ad exten-sional tectonics during the late Cenozoic geody-namic evolution of this region. This interpretationis supported by: (1) the nearly coeval crystallizationand cooling ages of the granitoid plutons and thedeformation ages of their host metamorphic rocksand (2) the spatial progression from undeformedgranitoid rocks at depth toward highly deformed,mylonitic–ultramylonitic and cataclastic plutonicrocks structurally upward into the shear zonesassociated with the detachment surfaces in thecore complexes. This granitic magmatism wasinstrumental in crustal weakening that led to the col-lapse and tectonic thinning of the early Cenozoicorogenic belt in the Aegean region, in tandem with

    rapid rollback of the north-dipping Hellenic subduc-tion zone.

    The compositional variations of the syn-extensional MEG are likely to have resulted fromdifferent degrees of partial melting of a mixedsource including varying proportions of an enrichedlithospheric mantle component and assimilated-melted lower and middle crustal components.Crustal-scale extensional shear zones gave rise touprising of melts derived from previously enrichedlithospheric mantle to lower- and mid-crustallevels, where further melting and mixing occurredwithin the crust. At the present level of exposures,there is no evidence of basic intrusive rocks withinthe Menderes massif. Nevertheless, mantle-derivedmagmas likely contributed to the granite petrogen-esis by invading the crust.

    Partial melting of the subduction-metasomatizedlithospheric mantle and the overlying lower crustthat led to the formation of the MEG magmas was

    Fig. 17. Schematic sequential cross-sections, depicting the inferred tectonomagmatic evolution of the metamorphiccore complexes in western Anatolia during the middle Miocene (a) and late Miocene (b). See text for discussion. Key tolettering: AG, Alasehir graben; BMG, Büyük Menderes graben; CGD, Çataldag granitoid; DF, Datça fault;IASZ, Izmir–Ankara suture zone; IGD, Ilica granitoid; KDCC, Kazdag core complex; KMG, Küçük Menderes graben;LON, Lycian ophiolite nappes; MEG, Menderes granitoids; SG, Simav graben; TBS, Tavsanli blueschists;TO, Tethyan ophiolites.

    SYN-EXTENSIONAL GRANITES, MENDERES MASSIF 217

  • induced by asthenospheric upwelling caused bylithospheric delamination. This inferred lithosphericdelamination was triggered by peeling of the base ofthe subcontinental lithosphere as a result of the rapidslab retreat of the newly established post-EoceneHellenic subduction zone. The combination of theslab rollback-generated upper plate extension andlithospheric-scale partial melting, aided by astheno-spheric upwelling, migrated southward in time,resulting in the younging of core complex formationand associated magmatism toward the Hellenictrench.

    This study was supported by research grants from theScientific & Technical Research Council of Turkey(TUBITAK-CAYDAG-101Y006), Istanbul TechnicalUniversity (Bilimsel Arastirma ve Gelistirme DesteklemeProgrami – BAP) and Miami University Committee onFaculty Research. The fieldwork of Z. O. in westernTurkey was supported by the Geological Society ofAmerica and the American Association of PetroleumGeology Grant-in-Aid research funds. We thankY. K. Kadioglu for his help with the geochemical analysesof the Salihli granotoid samples in his laboratory in theUniversity of Ankara (Turkey). Constructive and thoroughreviews by Uwe Ring, Stuart N. Thomson and an anon-ymous referee helped us improve the paper greatly.

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