Turkish Journal of Earth Sciences (Turkish J. Earth Sci.), Vol. 18, 2009, pp. 1–27. Copyright ©TÜBİTAK doi:10.3906/yer-0806-2 First published online 07 July 2008

Geochemical Characteristics of Mafic and Intermediate Volcanic Rocks from the Hasandağ and Erciyes Volcanoes (Central , )

AYKUT GÜÇTEKİN & NEZİHİ KÖPRÜBAŞI Department of Geological Engineering, Kocaeli University, TR–41040 İzmit, Turkey (E-mail: nezihi@ kocaeli.edu.tr)

Received 23 June 2007; revised typescript received 24 November 2007; accepted 07 December 2007

Abstract: Hasandağ and Erciyes stratovolcanoes, which are the two important stratovolcanoes in Central Anatolia, erupted volcanic products with both calc-alkaline and alkaline compositions, although the calc-alkaline activity is more widespread. There are three stages of geochemical evolution in the history of the Hasandağ stratovolcanic complex: (1) Keçikalesi tholeiitic volcanism, (2) Hasandağ calc-alkaline volcanism, and (3) Hasandağ alkaline volcanism. The geochemical evolution of Erciyes volcanic complex also exhibits three distinct evolutionary stages: (1) Koçdağ alkaline volcanism, (2) Koçdağ calc-alkaline volcanism and (3) Erciyes calc- alkaline volcanism. The volcanic rocks from both suites show enrichments in LREE relative to HREE. The rocks as a whole show enrichments in large ion lithophile elements (LILE) relative to high field strength elements (HFSE) in N-MORB normalized multi- element diagrams, although the thoeliitic and alkaline rocks have less pronounced effects of HFSE/LILE fractionation comparing to the calc-alkaline rocks. Theoretical fractionation models obtained using the whole-rock trace element data indicate two distinct fractionation trends for the Hasandağ volcanism: and fractionation for the tholeiitic and calc-alkaline rocks and plagioclase, and amphibole fractionation for the alkaline rocks. The alkaline and calc-alkaline rocks of Erciyes volcanism, on the other hand, indicate similar fractionation trends that can be explained by plagioclase and amphibole fractionation. AFC modelling indicate that the effect of crustal contamination on parental melt compositions is less pronounced in the Erciyes volcanic rocks compared to the Hasandağ volcanic rocks. Theoretical melting trends obtained using the non-modal batch melting model indicate degree of melting between 8–9% for the Keçikalesi tholeiitic rocks, 4–5% for the Hasandağ alkaline rocks and 3–8% for the Koçdağ alkaline rocks. The modeling also shows that the Central Anatolian volcanic rocks were originated by variable degree melting of a mantle source with +spinel lherzolite composition, although the effect of residual garnet in the source is more pronounced for the Hasandağ alkaline rocks. Geochemical modeling indicates that Central Anatolian volcanic rocks are likely to have originated by partial melting of a metasomatised lithospheric mantle. Delamination of TBL (termal boundary layer) may be considered as a potential mechanism that may cause thermal perturbation melting of continental lithospheric mantle. The distribution of volcanic centres along the region- scale strike-slip systems may also indicate additional effects of strike-slip faulting on melt production and eruption.

Key Words: Central Anatolia, collision volcanism, lithospheric delamination, Turkey

Hasandağ ve Erciyes Volkanlarının Mafik ve Ortaç Volkanik Kayaçlarının Jeokimyasal (Orta Anadolu, Türkiye)

Özet: Orta Anadolu’da iki önemli stratovolkan olan Hasandağ ve Erciyes stratovolkanları kalk-alkalen ve alkalen karakterli volkanizmalar olmasına rağmen, kalk-alkalen aktivite daha yaygındır. Hasandağ volkanik kompleksi jeokimyasal farklılıklarıyla Keçikalesi toleyitik, Hasandağ kalk-alkalen, Hasandağ alkalen volkanizması olmak üzere üç evrede gelişimini gerçekleşmiştir. Erciyes volkanik kompleksinin jeokimyasal gelişimi Koçdağ alkalen, Koçdağ kalk-alkalen, Erciyes kalk-alkalen volkanizması olmak üzere üç evredir. Volkanizmalara ait nadir toprak element (REE) içeriklerinde tüm ürünlerde, hafif nadir toprak elementler (LREE) ağır nadir toprak elementlere (HREE) göre göreceli bir zenginleşme göstermektedir. N-MORB’a göre normalize edilmiş çoklu element diyagramlarında tüm volkanik ürünlerde geniş iyonlu litofil (LIL) elementler ve hafif nadir toprak elementlerde (LREE) belirgin zenginleşme, Ta, Nb, Ti, Hf gibi kalıcılığı yüksek elementlerde (HFS) ise göreceli bir tüketilme görülmekle birlikte HFSE/LILE fraksiyonasyonunun etkileri kalk-alakali kayalarda daha yüksek ve toleyitik, alkali bileşimli kayalarda daha az oranlardadır. Tüm kayaç iz element içerikleri kullanılarak yapılan teorik kristalizasyon modellemeleri ile elde edilen eğilim, Hasandağ toleyitik ve kalk-alkalen kayaçlarda amfibol, plajiyoklas; alkalen kayaçlarda plajiyoklas, piroksen, amfibol; Erciyes alkalen ve kalk-alkalen kayaçlarda ise plajiyoklas, piroksen ve amfibolun baskın olduğu fraksiyonel kristalizasyon ile açıklanabilir. AFC modellemelerine göre Erciyes volkanında kıta kirlemesinin etkisi Hasandağ’a göre daha azdır. Modal olmayan yığın ergime modeliyle hesaplanan ergime dereceleri Keçikalesi toleyitik kayaçlarında yaklaşık %8–9, Hasandağ alkalen kayaçlarında %4–5, Koçdağ alkalen kayaçlarında ise %3–8 arasındadır. Teorik ergime modelleri Orta Anadolu volkanik kayaçları için granat ve spinel-lerzolit bileşimli manto kaynaklarından türeyen değişen miktarlarda karışımını önerirken, Hasandağ alkalen kayaçlarında ergime sürecinde artık granat etkisi daha baskındır. Metasomatize olmuş litosferik mantodan türediği düşünülen Orta Anadolu volkanizması, termal sınır düzeyinin (TSD) deleminasyonu ile oluşan geniş çaplı termal düzensizlik sonucu kıta altı litosferik mantonun ergimesiyle açıklanabilir. Bölgedeki volkanizmanın doğrultu atımlı tektonizmanın bulunduğu kuşaklar boyunca görülmesi bu sistemin magma yükselimine olası katkı sağladığını göstermektedir.

Anahtar Sözcükler: Orta Anadolu, çarpışma volkanizması, litosferik delaminasyon, Türkiye

1 GEOCHEMISTRY OF HASANDAĞ AND ERCİYES VOLCANOES

Introduction to be separated from the African plate (McKenzie 1972; Collision-related calc-alkaline and alkaline volcanisms are Cochran 1981; İzzeldin 1987; Bayer et al. 1988; Le observed in the Hasandağ and Erciyes volcanoes, which Pichon & Gaulier 1988). Northerly movement of the are two important stratovolcanoes in the Central Anatolia, Arabian plate during the middle–late resulted in continental collision which was responsible for shortening but calc-alkaline volcanism is more dominant. Tholeiitic and thickening of the in the eastern Anatolia rocks of small volumes comprise the first products of the between the Eurasian and Arabian plates (Şengör 1980; Hasandağ volcanism. The plate boundaries between Şengör & Yılmaz 1981; Fyitkas et al. 1984; Buket & African, Arabian and Eurasian plates, which represent the Temel 1998; Temel et al. 1998; Yılmaz et al. 1998; western part of the Alpine-Himalayan belt, are irregular in Yürür & Chorowicz 1998). The continental collision gave the Mediterranean region (Jackson & McKenzie 1984). rise to westward escape of the Anatolian block along Aeolian and Aegean volcanic arcs were formed in the (NAF) and East Anatolian Fault southern Italy and Aegean regions by of the (EAF) (McKenzie 1972; McKenzie & Yılmaz 1991). The African plate under the Eurasian plate (Keller 1982). In shortening and thickening of the crust in the eastern addition, geologic and geomorphologic characteristics of Anatolia via Arabia- collision and westward escape other areas in the Aegean-Anatolian region are mainly of the Anatolian block resulted in deformation of the shaped by the collision and post-collision tectonism (Notsu Anatolian block (McKenzie & Yılmaz 1991; Lyberis et al. et al. 1995). In most collision zones (Himalaya and 1992). The volcanic activity in Central Anatolia is related Anatolia), calc-alkaline and alkaline associations are found to this deformation (McKenzie & Yılmaz 1991; Aydar et together that are closely associated chronologically and al. 1995). The Central Anatolian region in Turkey has spatially (Pearce et al. 1990; Turner et al. 1996). Bonin been subjected to deformation and volcanism over the (1990) who studied magmatic rocks in the Alps stated past 10 Ma (Innocenti et al. 1982; Şengör et al. 1985; that magmatism changes from calc-alkaline to alkaline Pasquare et al. 1988; Aydar 1992; Temel 1992; Aydar et type due to decreasing water content; both types of al. 1993; Le Pennec et al. 1994). There are two major volcanics are derived from almost the same source. The active fault systems in the Central Anatolian volcanism Central Anatolian volcanism also is characterized by (Toprak & Göncüoğlu 1993). The first is the left-lateral products of calc-alkaline, alkaline and tholeiitic character Ecemiş fault zone and the right-lateral Tuz Gölü fault which developed at various stages of volcanic activity and zone and the second is N60–70° E-trending normal faults do not show any significant chronological and spatial that are consistent with main eruption centres as being systematic. parallel to the volcanic axis (Toprak & Göncüoğlu 1993). In this study we aimed to provide evidence for NE–SW-extending faults are central Kızılırmak and Niğde determining the petrogenetic processes that were faults (Toprak 1994). Some of these faults are covered effective during the formation and evolution of the with young volcanic rocks. volcanic suites. For this purpose, based on trace element Magmatic, metamorphic and ophiolithic rock data on volcanic rocks, a petrogenetic modeling was assemblages in Central Anatolia form the crystalline performed. During these studies, in order to determine complex. This complex is composed of crystallization processes of rocks, fractional crystallization ophiolithic units overlying Palaeozoic– medium- and assimilation effects were examined and then possible to high-grade metamorphic rocks and intrusive rocks source components of volcanoes were determined. This cutting those units (Akıman et al. 1993 & Göncüoğlu et was followed by melting modelling studies to delineate al. 1991b). There is no published geophyscial information percents of partial melting types which were effective regarding the thickness of crust and lithospheric mantle during the magma generation processes. beneath Central Anatolia. The products of the Hasandağ (Figure 1), Geological Setting which is one of the important stratovolcanoes in the Central Anatolia, are composed of flows, lava domes The Anatolian volcanism is one of the best examples of and pyroclastic rocks. According to Aydar & Gourgaud continental collision volcanism. With the opening of the (1998), volcanism was developed at four stages, namely, Suez Gulf in the Oligocene, the Arabian plate was started

2 A. GÜÇTEKİN & N. KÖPRÜBAŞI N oı 35 30 E E KAYSERİ fied from Toprak 1998). Basin

Sultansazlığı

cmşFutZone Fault Ecemiş ııımkriver Kızılırmak

major faults Hasandağ Erciyes stratovolcano deposits (Late Miocene-Quaternary) basement rocks (pre-Middle Miocene) volcanic complexes (Late Miocene- Quternary) continental clastics (Late Miocene-) eiky Fault Derinkuyu E HD Km N 300 Van 200 NİĞDE 100 Erzurum

Bitlis-Zagros suture zone 0 Derinkuyu

Trabzon inFault lian Arabian Plate

Tuz-Lake Fault Anato Sivas

SEA East

North Anatolian Fault Erciyes Ecemiş Fault Adana HD Tuzgölü Fault Mt. Hasan BLACK Basin İstanbul Bursa Tuzgölü Map of Central Anatolia showing the location ‘the Cappadocian volcanic province’ and distribution products (modi İzmir MEDİTERRANEAN SEA Karapınar A E G E A N S E A oı Figure 1. 33 30 E o o 39 N 38 N

3 GEOCHEMISTRY OF HASANDAĞ AND ERCİYES VOLCANOES

Keçikalesi volcano (13 Ma), Palaeovolcano (7 Ma), Based on the Le Bas et al. (1986) diagram, Hasandağ Mesovolcano and Neovolcano. alkaline rocks are and trachybasalt while the The Keçikalesi tholeiitic volcanism is composed of lava Koçdağ alkaline rocks plot in the basalt field. Except for flows of basalt and basaltic and lesser amount of these two groups, all other rocks are below the pyroclastic products while Hasandağ calc-alkaline subalkaline line. The Hasandağ calc-alkaline rocks are volcanism is characterized mainly by andesite lava domes represented by basaltic trachyandesite, and and type and widespread and andesite while Keçikalesi tholeiitic rocks are pyroclastic products. The latest stage of the Hasandağ represented by basaltic andesite. The Erciyes calc-alkaline volcanism is represented by basaltic alkaline volcanics and rocks show a wide compositional spectrum from linear scoria cones (Aydar & Gourgaud 1998). Products trachybasalt to dacite and calc-alkaline rocks of Koçdağ of the Erciyes volcano are composed of lava flows, volcanics mostly plot in the andesite field. pyroclastics and some monogenic structures such as Subalkali series are divided into several sub-groups dome, cone and . The volcanism was developed in based on K2O and SiO2 contents. This discrimination is two stages as Koçdağ and Erciyes (Kürkçüoğlu et al. shown in the Peccerillo & Taylor (1976) diagram (Figure 1998). The products of the Koçdağ volcanism at the 2b). It is shown in this diagram that samples plot in high eastern part of the Erciyes stratovolcano are alkali K-calcalkaline series and calc-alkaline series. Moreover, in , andesitic lava flows, basaltic and total alkali (Na2O + K2O)-total FeO-MgO triangular (Şen et al. 2003). Dark grey-black coloured diagram (Figure 3) proposed by Irvine & Baragar (1971), basaltic rocks are monocrystalline and show flow subalkali series can be discriminated as calc-alkaline and structure. According to Ayrancı (1969), their age is tholeiitic types. In Figure 3 where subalkali samples are 4.39±0.28 Ma. The Erciyes stratovolcano with an age used, the Keçikalesi volcanic rock samples plot in tholeiitic ranging from 3 Ma to historical times displays a wide field. compositional spectrum from basalt to rhyodacite In the major oxide covariation diagrams, for all of (Pasquare et al. 1988; Ayrancı 1991). samples, there is an increase in K2O and a decrease in

Fe2O3, MnO, CaO with increasing SiO2 (Figure 4). There is Analytical Methods also minor decrease in Al2O3 with SiO2 although the distributions are rather scattered for most of the samples. A total of 38 samples from lava and dome flows were Especially, the similar major oxide behaviour in calc- collected for chemical analyses, 17 from the Hasandağ alkaline porphyric rocks is probably due to fractionation volcanism and 21 from the Erciyes volcanism. The rock of plagioclase dominant mineral assemblages in the samples were powdered at the Mineralogy-Petrography shallow depth of long-lived magma chambers. laboratories of the Geology Department in the Kocaeli Consumption of CaO can be explained by crystallization of University. The major and trace element analyses were significant amount of plagioclase and clinopyroxene. conducted at the ALS Chemex (Toronto-Canada) analytical laboratory using ICP-MS and ICP-OES, respectively. The high Fe2O3 and TiO2 concentrations of Hasandağ Results of chemical analyses are shown in Table 1. and Erciyes alkaline rocks indicate that they are rich in iron. Especially, TiO2 contents of Hasandağ and Erciyes

alkaline rocks increase with SiO2, while there is a negative Geochemical Characteristics trend in other rock groups. MnO, MgO and CaO Classification of Volcanic Rocks concentrations of alkaline Hasandağ and Erciyes rock samples have high concentrations. There is an increase in The volcanic rocks in the region were classified using the MgO with increasing SiO in the Hasandağ alkaline classification scheme of Le Bas et al. (1986) based on the 2 volcanism and this can be explained by the accumulation total alkali (Na O + K O) vs SiO (TAS) diagram (Figure 2 2 2 of forsteritic which exists in the phenocrysts 2a). In this diagram, the dashed line separating the alkali assemblages of these rocks. and subalkali magma series was taken from Irvine & Baragar (1971).

4 A. GÜÇTEKİN & N. KÖPRÜBAŞI DL RSD (%) DL RSD ıı ıı 38 26 ı ı 14 03 asalt o o 38 34 ıı ıı 01 25 ı ı 13 04 o o 38 34 ğ Hasandağ Hasandağ ıı ıı 21 13 ı ı 14 08 o o 38 34 ıı ıı 46 32 ı ı t, RSD– Relative Standart Deviation. 13 08 ava flow Lava flow Lava flow Lava flow o o 38 34 ıı ıı 35 38 ı ı 07 02 o o 38 34 ıı ıı 45 03 ı ı 07 04 o o 38 34 ıı ıı 26 30 ı ı 08 06 o o 38 34 ıı ıı 09 24 ı ı 06 10 o o 38 34 ıı ıı 54 25 ı ı 05 10 o o 38 34 ıı ıı 37 44 ı ı 10 03 o o 38 34 ıı ıı 52 38 ı ı 13 08 o o 38 34 ıı ıı 47 40 ı ı 10 05 o o 38 34 ıı ıı 26 49 ı ı 11 11 o o 38 34 ıı ıı 59 51 ı ı 04 09 o o 38 34 ıı ıı 06 38 ı ı 01 15 o o 38 34 ıı ıı 23 35 ı ı 10 05 o o 38 34 ıı ıı 32 03 ı ı 03 06 o o Whole-rock major and trace element data for the representative samples from Hasandağ* Erciyes volcanoes. DL– Detection Limi 0.919.54 1.01 11.30 0.76 6.520.15 0.58 0.20 6.59 0.77 7.75 0.31 0.72 6.78 0.19 1.10 8.11 0.16 0.80 6.83 0.20 0.70 6.58 0.37 0.70 6.24 0.26 0.69 6.30 0.19 1.26 10.55 0.22 0.88 7.38 1.20 0.22 9.85 1.16 0.36 10.05 1.19 0.32 9.94 1.36 10.25 0.57 0.01 0.01 0.42 0.80 0.30 0.35 0.48 0.01 0.10 55.1217.10 53.33 16.65 60.10 15.50 60.50 16.00 57.71 16.40 61.09 15.65 54.23 15.60 56.02 15.60 60.70 16.30 61.29 16.05 60.30 16.15 47.96 17.40 52.34 17.25 48.36 16.55 48.66 48.26 15.95 49.05 16.55 16.10 0.01 0.01 0.10 0.90 3 3 5 O 2.97 2.70 3.95 3.72 3.58 3.85 3.73 3.67 3.78 3.80 3.82 3.57 4.17 3.47 3.54 3.34 3.86 0.01 0.70 2 2 O O 2 O 1.12 1.04 2.25 1.98 1.99 2.33 1.74 1.68 1.93 1.98 2.01 0.96 1.27 1.18 1.18 0.95 1.48 0.01 0.50 2 O 2 2 2 SiO TiO Fe Table 1. Sample NoLocality H-26Rock typeFlow type Hasandağ Basalt H-80 Hasandağ Lava flowLongitude 34 B. Andesite Lava flow Hasandağ H-36 Andesite Dome flow Hasandağ Dome flow Andesite Hasandağ H-20 Lava flow Andesite Hasandağ Lava flow H-7 Hasandağ Andesite Lava flow Hasandağ Basalt Dome flow H-4 HasandağP Dome flow Hasandağ Andesite Dome flow H-42 Dome flow Hasandağ Andesite Lava flow Hasandağ H-75 Andesite Lava flow Hasandağ L Andesite Hasandağ H-15 Hasanda Basalt H-14 Basalt H-2 Basalt H-72 Basalt Basalt H-70 B H-43 H-49 H-62 H-64 Latitude 38 K Al MnOMgOCaONa 0.15 3.87 7.88 0.16L.O.I 3.88Total 8.70 0.12Ppm 1.35 100.16 2.65VCo 4.65 100.06 0.79Cu 0.11Zn 2.88 99.17 346.6Ga 5.39 34.8 2.36 0.12 104.9Rb 299.3 3.56 99.3Sr 99.48 50.7 6.05 150.2 22.6Y 0.11 1.44Zr 38.1 100.8 2.36 99.14 38.9Nb 21.6 4.95 31.0 396.1 63.8Cs 0.13 1.05Ba 7.03 65.8 26.4 39.5 99.65 28.8 103.4 403.2 7.42 20.8 38.4 5.2La 0.11 72.0 1.61 100.06 28.0 105.6Ce 0.9 6.02 31.9 70.8 61.7 374.7 30.6Pr 7.34 0.11 49.0 6.3 115.2 20.5Nd 0.60 99.54 201.8 3.19 15.82 21.4 2.0Sm 338.4 65.1 5.1 32.95 392.0 62.5 5.73Eu 99.25 0.10 22.4 76.1 34.2 16.92 4.12Gd 17.6 1.21 17.35 2.95 138.6 35.38Tb 497.8 18.9 497.9 2.4 146.1 69.9 3.94 59.5 5.39 99.10Dy 4.35 0.11 65.8 42.7 30.69 18.62 0.04 21.7 1.14Ho 121.0 2.79 11.9 59.73 4.15Er 411.3 18.4 451.8 4.11 102.9 81.3 99.12 5.36 67.8 0.71Tm 0.16 2.2 1.12 6.18 22.46 20.8 52.5 0.47 37.9 24.47 4.39 149.0Yb 6.19 4.17 609.9 77.1 9.5 468.2 99.77 44.91 0.92Lu 11.00 19.4 0.71 4.64 67.9 44.9 0.13 2.48 61.7 32.7 4.25 20.17 2.2 152.4 1.12 1.37 0.35 18.38 20.0 4.73 5.02Hf 96.58 0.93 566.1 36.98 540.8 4.42 48.3 7.40 12.6 2.34 65.8 22.5Ta 2.49 0.15 0.69 50.3 3.61 0.37Pb 24.99 0.36 0.38 56.6 16.01 127.9 32.1 21.6 99.18 7.56 408.3 3.75 2.5 430.4 4.13 0.91 45.47Th 9.97 2.49 56.6 0.76 17.4 59.2 0.16 3.94 3.36U 18.0 63.9 0.38 99.06 142.5 29.11 2.03 3.51 8.20 0.53 0.71 18.82 0.52 49.4 398.1 30.7 20.6 0.31 55.56 137.7 11.17 9.43 234.5 1.03 5.13 3.10 1.4 0.15 100.18 3.34 2.14 20.6 55.5 3.35 6.94 0.63 9.4 151.2 66.1 7.88 22.37 0.51 25.01 0.32 0.39 397.1 99.8 54.4 3.85 459.0 0.52 99.38 11.30 7.23 1.69 20.6 2.43 156.3 42.72 0.16 6.47 0.26 3.02 1.12 6.58 92.6 5.34 1.8 25.77 6.90 19.8 137.1 12.5 0.64 9.21 3.48 671.0 0.31 1.71 64.2 19.21 489.6 201.6 60.7 46.52 33.1 4.70 1.04 0.01 1.83 21.8 0.53 1.79 16.53 0.27 0.01 0.26 1.31 130.5 4.98 3.20 0.01 26.20 75.1 0.27 619.1 2.3 19.21 17.6 139.9 9.90 13.4 1.50 19.6 4.47 0.67 1.71 460.0 85.4 52.6 4.35 48.51 19.9 3.63 1.20 0.67 3.30 0.27 1.91 0.86 0.70 10.33 116.5 0.85 5.13 676.1 238.6 22.76 89.5 3.59 0.28 1.05 20.24 25.3 356.8 100.8 23.5 60.4 11.5 44.21 1.2 0.74 3.17 4.34 1.82 21.0 9.38 3.84 52.5 147.3 665.9 0.01 13.47 1.92 0.49 27.74 0.74 0.28 85.4 2.74 5.36 1.04 85.4 16.86 0.27 240.2 2.89 18.0 52.3 52.94 25.9 14.2 3.42 19.9 147.5 656.7 1.90 0.61 1.2 7.34 0.1 4.34 3.89 20.99 114.2 11.37 0.54 90.5 24.53 387.4 0.29 63.4 1.68 0.86 2.43 4.71 41.55 1.01 705.6 25.6 3.16 23.3 136.9 0.24 20.8 11.3 2.1 3.89 0.69 30.82 83.3 0.1 0.5 4.23 1.62 384.4 9.34 3.51 7.28 17.73 164.5 0.52 0.1 60.95 1.98 0.1 1.08 19.0 24.9 6.14 20.2 0.25 0.95 2.93 0.29 3.26 18.3 31.12 361.9 1.5 0.1 3.53 0.72 27.17 1.78 59.76 0.1 4.83 0.8 7.23 30.4 4.99 0.9 10.25 1.4 24.8 0.52 0.1 2.03 0.29 4.65 387.2 28.45 1.45 18.4 0.67 1.95 0.29 3.11 1.5 27.32 58.97 4.34 0.2 0.65 11.37 24.9 0.1 1.83 29.38 3.72 4.97 1.6 0.6 0.73 7.99 0.1 7.21 15.8 1.79 56.41 0.27 0.84 25.16 1.16 4.34 0.27 2.66 0.01 3.73 0.1 0.90 0.8 12.40 5.34 1.79 26.73 20.4 2.7 4.35 0.01 9.97 0.61 0.5 7.03 2.32 1.49 0.28 0.85 0.10 3.53 0.32 3.04 4.82 2.2 27.90 0.01 5.23 2.10 0.71 0.1 2.11 6.37 0.73 4.88 0.5 9.35 1.45 1.92 0.29 4.12 0.83 0.50 0.27 4.96 10.63 2.93 5.15 6.59 0.84 2.0 0.78 1.78 0.5 4.12 1.45 2.25 9.88 4.42 0.27 5.17 0.92 4.35 0.31 10.33 0.01 0.94 3.18 0.69 1.47 2.07 0.1 4.92 2.56 5.12 4.02 4.71 0.01 10.33 0.31 2.20 0.37 0.76 0.83 0.72 1.18 0.01 2.51 2.0 4.22 2.16 4.56 2.50 0.01 7.48 3.92 0.36 0.30 0.85 1.02 0.01 1.10 1.71 2.01 2.15 1.20 0.01 4.41 0.31 7.21 0.30 5.56 0.01 0.10 1.14 2.01 1.40 0.01 1.47 7.23 4.12 0.30 0.01 2.40 5.41 1.09 0.01 0.10 1.48 4.78 2.70 0.01 0.01 5.12 1.24 0.80 2.80 1.08 0.01 0.10 5.78 0.01 1.72 5.20 0.01 1 0.01 0.70 0.20

5 GEOCHEMISTRY OF HASANDAĞ AND ERCİYES VOLCANOES ıı ıı 38 35 ı ı 27 13 o o 38 35 ıı ıı 20 51 ı ı 24 27 o o Erciyes Erciyes 38 35 ıı ıı 22 54 ı ı te B.Andesite Andesite 40 32 o o 38 35 ıı ıı 22 43 ı ı 39 33 o o 38 35 ıı ıı 26 23 ı ı 29 15 o o 38 35 ıı ıı 17 41 ı ı 27 21 o o 38 35 ıı ıı 24 15 ı ı flow Lava flow Lava flow Dome flow Dome flow Lava flow Lava flow 19 38 o o 38 35 ıı ıı 00 26 ı ı 36 16 o o 38 35 ıı ıı 49 49 ı ı 25 34 o o 38 35 ıı ıı 55 17 ı ı 32 32 o o 38 35 ıı ıı 18 08 ı ı 33 33 o o 38 35 ıı ıı 20 04 ı ı 34 39 o o 38 35 ıı ıı 09 57 ı ı 20 38 o o 38 35 ıı ıı 36 10 ı ı 17 38 o o 38 35 ıı ıı 41 09 ı ı 19 37 o o 38 35 ıı ıı 36 10 ı ı 17 38 o o 38 35 ıı ıı 08 41 ı ı 18 37 o o 38 35 ıı ıı 46 03 ı ı 19 38 o o 38 35 ıı ıı 24 15 ı ı 19 38 o o 1.77 1.67 1.730.40 1.74 0.36 1.75 0.39 1.70 0.42 0.68 0.39 0.98 0.35 0.76 0.21 0.75 0.24 0.72 0.19 1.23 0.20 0.52 1.42 0.18 0.65 0.39 0.49 0.22 0.49 0.39 0.96 0.18 0.70 0.14 0.14 0.36 0.16 47.9617.05 47.7612.45 17.15 47.96 11.65 16.75 47.76 11.90 16.85 47.26 12.25 16.85 47.56 61.39 12.15 16.85 58.61 11.75 16.35 58.71 5.35 15.75 62.19 7.17 16.05 57.31 6.31 15.60 53.83 5.31 17.15 64.08 17.00 51.24 6.79 60.00 15.05 7.92 62.19 17.40 4.73 64.08 16.35 53.03 8.78 15.50 60.40 15.90 5.93 17.10 4.40 16.65 4.73 7.67 5.96 (Continued) 3 3 5 O 3.93 3.80 3.79 3.92 3.86 3.81 4.06 4.01 3.43 3.77 3.36 3.96 3.76 3.92 3.61 3.74 3.85 3.52 3.95 2 2 O O 2 O 0.77 0.67 0.73 0.77 0.73 0.73 2.07 2.16 1.96 2.94 1.41 1.62 2.47 1.34 1.69 1.98 2.03 1.14 1.83 2 O 2 2 2 K Rock typeFlow TypeLatitude 38 Basalt Lava flow Lava flow Basalt Lava flow Basalt Lava flow Lava flow Basalt Lava flow Basalt Lava flow Lava flow Basalt Lava flow Lava flow Andesite Lava flow Andesite Lava flow Dome Andesite Andesite Andesite B.Andesite Dasite Basalt Andesite Andesite Dasi Table 1. Sample noLocality E-146 Erciyes E-148Longitude 35 Wt % ErciyesSiO E-149 Erciyes E-150 Erciyes E-152 Erciyes E-233P Erciyes E-141 Erciyes E-102-b Erciyes E-108 Erciyes E-103 Erciyes E-133 Erciyes E-194 Erciyes E-169 Erciyes E-196 Erciyes E-185 Erciyes Erciyes E-88 Erciyes E-86 E-175 E-188 TiO Fe MnOMgOCaONa 0.19 6.28 8.56 0.17 6.79 8.90 0.18 6.78 8.75 0.19 6.52 8.55 0.18 6.59 8.49 0.18 6.75 8.74 0.08 2.71 4.85 0.10 3.12 5.19 0.15 3.46 5.72 0.09 2.04 4.04 0.10 4.34 7.33 0.12 4.29 6.49 0.08 2.17 4.32 0.13 5.59 7.41 0.10 3.15 5.81 0.07 2.01 0.08 4.70 1.91 4.63 0.12 6.14 0.09 8.17 3.08 5.84 Al L.O.ITotalPpm 0.43V 99.79Co 0.07Cu 98.99Zn 171.8Ga 61.1 0.40 99.36 96.7Rb 237.6 101.8Sr 54.5 20.7 99.33Y 0.36 72.0 101.8 271.5Zr 17.8Nb 21.0 51.2 99.70 491.8Cs 1.45 66.9 109.0 174.9Ba 29.5 26.2 204.1 515.2 99.89 21.7 58.2 14.2La 1.47 210.9 27.6 99.8 93.6 185.5Ce 0.4 17.1 99.07 193.4 556.9Pr 11.2 57.6 20.6 1.32Nd 228.3 100.8 90.5 199.2 19.73 31.2 222.8 1.1Sm 99.98 487.7 15.2 42.87Eu 12.4 115.2 21.1 54.3 17.63 5.11 2.65Gd 97.7 99.41 199.7 71.1 21.16 148.7 37.72 29.0Tb 451.1 0.5 27.3 5.12Dy 4.65 60.7 22.4 2.67 21.1 13.1 20.11 20.92 1.72Ho 99.72 56.6 194.7 39.1 299.5 45.58 5.34 471.4 28.5Er 4.83 26.5 0.89 65.8 0.3Tm 1.52 2.79 2.81 35.6 99.19 5.49 12.2 22.67 19.64 194.5 5.56Yb 68.9 271.9 4.91 317.7 85.4 42.64 1.19 28.0Lu 0.80 5.61 70.5 99.63 45.3 3.21 34.6 0.50 18.63 0.5 4.83 202.8 22.5 21.88 1.80 12.2 59.7 0.47 5.24 303.6 67.9 329.9Hf 40.88 1.04 5.43 19.2 3.18Ta 99.69 2.83 87.4 0.91 5.31 93.6 2.78 19.12 24.1 0.49 229.6 21.4Pb 20.59 0.43 375.7 400.7 11.5 5.37 60.7 0.6 1.68 5.04 40.12 48.3Th 2.76 99.90 1.15 5.15 28.3 5.25 60.7 126.5U 179.0 20.97 0.43 2.29 4.91 3.11 0.84 37.3 19.16 300.4 0.93 22.9 380.3 41.19 0.45 64.8 99.22 14.2 1.57 5.03 2.5 74.1 4.79 5.17 5.32 20.7 2.98 23.7 5.12 1.06 260.6 2.25 97.9 2.28 33.99 378.2 16.97 35.5 396.1 0.75 98.12 4.89 0.44 0.87 20.8 2.92 84.3 55.92 12.5 0.67 54.5 5.11 4.59 0.43 5.24 1.47 129.6 99.13 2.9 32.2 131.0 22.93 2.88 1.75 500.9 5.49 1.08 4.71 43.8 2.87 432.4 23.37 25.6 45.55 21.7 3.61 0.83 0.71 46.3 0.78 2.87 0.44 14.7 99.34 51.4 46.3 167.5 0.99 0.41 5.17 6.13 4.71 2.90 29.41 279.0 0.9 18.6 18.97 321.0 42.9 3.44 39.3 2.49 1.02 99.73 2.68 57.24 5.33 21.8 82.3 5.52 0.57 50.4 80.2 10.4 0.41 2.81 0.82 1.29 0.82 148.2 558.0 5.03 19.86 376.2 3.42 1.13 0.41 22.9 25.81 7.23 29.7 95.8 39.14 3.3 0.74 5.49 21.0 13.4 62.7 2.65 5.85 2.33 3.94 66.9 188.5 1.13 352.3 18.4 24.85 0.92 2.01 0.82 0.39 518.3 6.75 0.82 1.12 16.48 18.4 0.29 21.3 49.31 24.9 4.95 148.1 5.17 55.5 20.8 3.89 1.07 295.3 152.0 35.0 1.4 1.04 1.93 2.85 5.94 5.03 26.72 333.2 12.6 0.62 22.9 20.26 66.9 0.29 2.79 0.84 315.6 22.5 4.51 48.65 45.5 44.3 1.24 1.07 3.64 165.5 20.8 44.2 0.39 10.33 5.31 0.75 22.57 303.6 1.3 18.3 6.18 2.51 39.6 3.59 2.94 530.5 18.28 153.0 0.86 47.89 2.02 72.0 69.4 18.2 20.6 5.43 0.86 57.6 0.39 1.02 0.29 4.77 1.12 11.37 353.7 20.64 377.7 31.8 133.5 3.24 1.02 21.37 11.4 1.91 41.55 4.26 55.5 65.1 11.18 3.4 7.76 60.7 19.1 20.2 373.1 0.53 2.74 5.15 22.63 0.29 1.24 153.5 0.95 13.45 3.32 3.20 0.39 16.87 45.28 10.5 4.26 26.3 21.5 19.6 323.0 0.68 23.36 3.81 2.70 15.76 6.64 0.6 0.67 5.56 46.82 1.93 18.88 0.46 0.96 9.63 0.88 10.1 3.78 342.4 62.7 0.28 25.54 5.00 18.2 3.83 0.84 9.64 4.71 48.65 18.93 1.79 1.7 7.89 4.59 0.59 2.21 19.46 1.45 16.3 13.43 0.28 18.4 0.93 3.51 0.31 39.43 3.13 4.58 17.98 3.61 0.75 14.89 2.31 5.03 0.72 2.5 9.4 4.98 0.99 2.04 16.49 0.30 9.30 4.31 0.73 0.31 3.64 4.07 4.89 5.14 0.89 7.98 1.0 0.59 2.01 0.91 5.83 2.36 9.32 3.41 0.30 3.81 3.62 1.02 0.34 5.13 0.72 2.45 0.62 4.83 0.89 2.32 1.0 1.95 5.81 3.72 3.58 3.68 12.40 0.38 4.35 0.28 0.82 0.76 0.61 1.08 2.05 14.81 2.3 1.88 3.34 2.01 3.54 3.38 5.71 11.37 0.29 0.29 0.72 1.12 0.98 0.56 4.71 1.99 5.04 2.02 3.35 3.29 10.33 5.60 0.29 0.31 0.72 0.53 0.83 1.98 3.22 6.60 2.01 13.57 1.47 5.82 0.30 0.29 0.69 0.73 13.43 1.87 1.87 10.82 2.40 5.71 0.28 0.29 0.72 10.71 7.23 1.80 3.25 4.62 0.28 9.30 6.62 1.01 3.37 5.20 10.20 0.75 2.01 3.23

6 A. GÜÇTEKİN & N. KÖPRÜBAŞI

16 a Hasandağ alkaline volcanism Erciyes calc-alkaline volcanism 14 Hasandağ calc-alkaline volcanism Koçdağ calc-alkaline volcanism Keçikalesi tholeiitic volcanism Koçdağ alkaline volcanism 12 PH TPP

10 PT TD Alkaline TA R 8 TP BTA 6 TB

22

Na O+K O (wt%) 4 Denielet al. (1998) Subalkaline Kürkçüoğluet al. (1998) 2 PC B BA A D 0 40 45 50 55 60 65 70 75 80

SiO2 (wt%) 6 b Hasandağ alkaline volcanism Erciyes calc-alkaline volcanism Hasandağ calc-alkaline volcanism Koçdağ calc-alkaline volcanism 5 Keçikalesi tholeiitic volcanism Koçdağ alkaline volcanism

4

Banakite

Absarokite

Shoshonite 3 High-K High-K basaltic andesite andesite 2 Rhyolite

K O (wt%) 2 Basalt Dasite Andesite Low-K et al. 1 basaltic andesite Basaltic Deniel (1998) andesite Low-K et al. Low-K basalt andesite Kürkçüoğlu (1998) 0 40 45 50 55 60 65 70 75 80

SiO2 (wt%)

Figure 2. Classification of the volcanic rocks from Central Anatolia. (a) TAS diagram of Le Bas et al. (1986). Key to abbreviations: PC– picrobasalt; B– basalt; BA– basaltic andesite; A– andesite; D– dacite; R– rhyolite; TB– trachybasalt; BTA– basaltic trachyandesite; TA– trachyandesite; T– trachyte; TD– trachydacite; BS– basanite; TP– tephrite; TPPH–

tephriphonolite; PHTP– phonotephrite; PH– phonolite; F– foidite. (b) K2O vs SiO2 diagram of Peccerillo & Taylor (1976). Data from Deniel et al. (1998) and Kürkçüoğlu et al. (1998) are also plotted for comparison.

Trace Element Characteristics there is an increasing trend in Nb, Sr, Zr and Y with

In trace element diagrams an increase is observed in Rb increasing SiO2 contents for the samples with over 60% SiO2. Similar trends are also observed for Rb, Ba, Th in and Ba concentrations with increasing SiO2 for all of the samples but there is not a prominent trend defined for this rock suite. the rest of the elements (Figure 5). However, concentrations of Rb, Zr and Nb indicate positive Rare Earth Element Characteristics correlations with silica contents of the rocks when the Hasandağ and Erciyes alkaline samples are examined Chondrite normalized rare earth element diagrams were separately. Also, for the Hasandağ calc-alkaline rocks prepared separately for the Hasandağ and Erciyes volcanic rocks (Figures 6a, b). These diagrams were used to

7 GEOCHEMISTRY OF HASANDAĞ AND ERCİYES VOLCANOES

and b, respectively. In multi-element diagram of the FeOt Hasandağ strato volcano, there is significant enrichment of large ion lithophile elements (LIL) (e.g., Rb, Ba, Th, U

Erciyes calc-alkaline volcanism Koçda and K) and light rare earth elements and a relative

ğ calc-alkaline volcanism depletion of high field strength elements (HFS) (e.g., Ta, Tholeiitic Nb, Ti and Hf) and heavy rare earth elements (HREE). In comparison to other rock suites, concentrations of large ion lithophile elements (LIL) such as Rb, Ba, Th, U and K in samples from the Hasandağ alkaline volcanism

Hasandağ calc-alkaline volcanism display variable depletion trends. In addition, they display Keçikalesi tholeiitic volcanism Calc-alkaline Ta and Nb negative anomalies smaller than the other rock groups, suggesting that the source of the Hasandağ Denielet al. (1998) alkaline lavas is different from those of the other rock Kürkçüoğluet al. (1998) groups. This may indicate that the source of the Hasandağ Na2O+K2O MgO alkaline rocks contained less significant subduction component when compared to the other rock groups or Figure 3. Distrubution of the samples from the Central Anatolian volcanic rocks on Irvine & Baragar (1971) AFM diagram. that their derivative melts have not been significantly Data from Deniel et al. (1998) and Kürkçüoğlu et al. (1998) affected by subsequent crustal contamination. These are also plotted for comparison. rocks are significantly enriched in large ion lithophile compare the composition of rock samples of present elements (LIL) and high field strength elements (HFS; Ta, study with average OIB and MORB compositions of Sun & Nb, Zr) in comparison to mid-ocean ridge basalts (N- McDonough (1989). In addition to rock samples, OIB and MORB) and this can be explained by different MORB compositions were also normalized to chondrite mechanisms: (1) enrichment of lithospheric mantle source values of Boynton (1984). In these diagrams, one or two with small melts fractions derived from asthenosphere; samples were used for each rock group. Symbols and SiO2 (2) melting of lithospheric source which is depleted in contents of these patterns are shown in the same figures. large ion lithophile elements (LIL) and light rare earth In samples from the Hasandağ stratovolcano, light rare elements (LREE) by previous melting events and earth element patterns are flat and show sub-parallel formation of tholeiitic and calc-alkaline ; (3) low- trends and they are more enriched with respect to heavy degree partial melting of the asthenospheric mantle rare earth elements (Figure 6a). There is a negative Eu source. In some samples of the Keçikalesi tholeiitic anomaly in a sample with SiO2 content of 60.1% from the volcanism and Hasandağ calc-alkaline volcanism, depletion Hasandağ calc-alkaline volcanism (Figure 6a). Rare earth in Ta, Nb and P is much more than that of other rock element patterns of the Erciyes stratovolcano closely suites. These negative Ta and Nb anomalies resemble resemble those of Hasandağ samples (Figure 6b). In this subduction-related active continental margins and diagram, negative Eu anomalies are noticeable in samples enrichment in large ion lithophile elements (LIL) can be from the Koçdağ calc-alkaline volcanics. The most explained by metasomatism in the mantle source with negative Eu anomalies are the product of plagioclase effect of subduction component (Pearce 1983). fractionation. Patterns in multi-element variation diagram for the LREE enrichment in REE patterns of samples from the Erciyes stratovolcano are similar to those of the Hasandağ Hasandağ and Erciyes stratovolcanoes could be originated stratovolcano. In this diagram, concentrations of large ion from a low-degree partial melting or due to contributions lithophile elements (LIL) (Th, U and K) in samples of the from subducting slab or crustal components. Koçdağ and Erciyes calc-alkaline volcanism are significantly enriched in comparison to other samples. Depletion of Hf and Ti with respect to other high field Multi Element Characteristics strength elements (HFS) is attributed to mantle N-type MORB normalized multi-element diagrams for the enrichment due to intra-continental processes or Hasandağ and Erciyes volcanisms are shown in Figure 7a derivation from a source with low-degree partial melts.

8 A. GÜÇTEKİN & N. KÖPRÜBAŞI

18 14

Al23 O 12 Fe O 17 23 10 16 8

15 6 4 14 2 13 0 45 50 55 60 65 70 45 50 55 60 65 70 0.20 10 MnO 8 MgO 0.15 6 0.10 4 0.05 2

0.00 0 45 50 55 60 65 70 45 50 55 60 65 70 12 6 Na O 10 CaO 2 5 8 6 4 4 3 2 0 2 45 50 55 60 65 70 45 50 55 60 65 70

4.0 2.0 3.5 KO2 TiO2 3.0 1.5 2.5 2.0 1.0 1.5 1.0 0.5 0.5 0.0 0.0 45 50 55 60 65 70 45 50 55 60 65 70

SiO2 (wt%) SiO2 (wt%) Hasandağ alkaline volcanism Erciyes calc-alkaline volcanism Hasandağ calc-alkaline volcanism Koçdağ calc-alkaline volcsnism Keçikalesi tholeiitic volcanism Koçdağ alkaline volcsnism

Figure 4. Major element variation of the Central Anatolian volcanic rocks.

Post-collisional within plate origin is also reported in melting. This diagram proposed by Pearce (1983) makes previous works (Kürkçüoğlu et al. 1998). a distinction between rocks derived from regular mantle Concentrations of large ion lithophile elements (LIL) such as ocean island basalts (OIB) or mid-ocean ridge (Rb, Ba, Th, U and K) in samples of the Koçdağ alkaline basalts (MORB) which generally lie on a diagonal line of volcanism are relatively less enriched compared to those mantle array, and rocks derived from mantle which is in other rock suites. However, Ta and Nb display negative enriched via subduction process or rocks affected by the anomalies. These patterns are similar to those of the crustal contamination. Hasandağ alkaline volcanism and can be evaluated in the The deviation observed along the diagonal mantle same way. array for all the samples from the Hasandağ and Erciyes stratovolcanoes could be explained with subduction- related metasomatism or mantle-derived melts that are Trace Element Ratios significantly modified by the crustal melts (Figure 8). The Diagrams where Th/Yb and Ta/Yb trace element ratios are trend of samples from the Hasandağ alkaline volcanism is used can determine fractional crystallization and/or partial almost parallel to that diagonal mantle array. Although

9 GEOCHEMISTRY OF HASANDAĞ AND ERCİYES VOLCANOES

400 120 V 100 Rb 300 (ppm) (ppm) 80 200 60 40 100 20 0 0 45 50 55 60 65 70 45 50 55 60 65 70

800 40 Sr Y (ppm) 600 30 (ppm)

400 20

200 10

0 0 45 50 55 60 65 70 45 50 55 60 65 70

300 30 Nb 250 Zr (ppm) (ppm) 200 20 150 100 10 50 0 0 45 50 55 60 65 70 45 50 55 60 65 70

18 600 Th Ba (ppm) 500 (ppm) 14 400 10 300 200 6 100 2 0 45 50 55 60 65 70 45 50 55 60 65 70 SiO (wt%) SiO2 (wt%) 2

Hasandağ alkaline volcanism Erciyes calc-alkaline volcanism Hasandağ calc-alkaline volcanism Koçdağ calc-alkaline volcanism Keçikalesi tholeiitic volcanism Koçdağ alkaline volcanism

Figure 5. Trace element variation of the Central Anatolian volcanic rocks.

this does not rule out variable effect of crustal Petrogenetic Modeling contamination, the relative enrichment of LILEs observed Interpretation of Crystallization Process in Volcanic even in the least modified mafic compositions suggests a Rocks subduction influence in the source of Hasandağ alkaline volcanics. The effect of subduction modified mantle Changes in trace element concentrations can be modelled source is also observed in the alkaline series of Erciyes using binary vector diagrams which show direction and volcanism but the effect of crustal contamination is less amount of variation occurring as a result of certain pronounced. processes. The mineral vectors used in modeling

10 A. GÜÇTEKİN & N. KÖPRÜBAŞI

1000 Hasandağ volcanism

5: H-49 (48.66 % SiO2 ), Hasandağ alkaline volcanism

3: H-62 (48.26 %SiO2 ), Hasandağ alkaline volcanism

2: H-7 (55.71 % SiO2 ), Hasandağ calc-alkaline volcanism 4: H-36 (60.10 %SiO ), Hasandağ calc-alkaline volcanism 100 2 1: H-26 (55.12 % SiO2 ), Keçikalesi tholeiitic volcanism

(C1) normalised

10

Chondrite average OIB a average N-MORB 1 La Ce Pr Nd (Pm) Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 1000 Erciyes volcanism

3: E-169 (64.08 % SiO2 ), Erciyes calc-alkaline volcanism 2: E-196 (51.24 % SiO2), Erciyes calc-alkaline volcanism

6: E-102-b (58.61 % SiO2 ), Koçdağ calc-alkaline volcanism 5: E-103 (62.19 % SiO2), Koçdağ calc-alkaline volcanism

100 1: E-148 (47.76 % SiO2 ), Koçdağ alkaline volcanism

(C1) normalised 10

average OIB

Chondrite b average N-MORB 1 La Ce Pr Nd (Pm) Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Figure 6. Chondrite-normalised REE element patterns for the Central Anatolian volcanic rocks. Chondrite normalising values are from Boynton (1984). represent the compositions arising from fractionation of Fractionation effects of amphibole and plagioclase are any mineral phase or assemblage. Theoretically, the very distinct in the Hasandağ calc-alkaline rocks (Figure fractionation trends are computed using the ‘Rayleigh’ 9a–c). equation. The Hasandağ alkaline rocks, which are the youngest The mineral vectors used in modeling were formed products of volcanism, are conformable with trend no. 2 with computer software by Keskin (2002). In fractional in Figure 9 and also mineral assemblages (plag[%50] + crystallization modeling, Rb and Th were used as the amp[%30] + cpx[%10] + opx[%10]) determined in petrographic fractionation index since they are incompatible elements. studies (Figure 9a–c). The phenocrystal assemblage in Other elements used in diagrams include Y and Sm. these rocks are composed of olivine, plagioclase and Yttrium was used to examine the fractionation effect clinopyroxene and do not contain amphibole. This can be during the formation of the volcanic rocks. As known, attributed to earlier amphibole fractionation and amp-liquid ≈ amp-liquid ≈ yttrium has a high distribution coefficient in garnet and depletion of Y( KdY 1.1) and Sm( KdSm 2.3) amphibole. Samarium was used for discrimination of elements in magmas. Previous studies report the presence anhydrous and hydrous crystallization assemblages. of little garnet in these rocks (Aydar et al. 1995; Aydar & In general, two different trends are found in rock Gourgaud 2002). However, in trace element modeling, suites of the Hasandağ stratovolcanism (Figure 9). no garnet fractionation was observed that could affect the

11 GEOCHEMISTRY OF HASANDAĞ AND ERCİYES VOLCANOES

1000 Hasandağ volcanism 5 4 1: H-49 (48.66 % SiO2 ), Hasandağ alkaline volcanism 2: H-62 (48.26 %SiO ), Hasandağ alkaline volcanism 3 2 100 4: H-7 (55.71 % SiO2 ), Hasandağ calc-alkaline volcanism 2 1 5: H-36 (60.10 % SiO2), Hasandağ calc-alkaline volcanism

3: H-26 (55.12 % SiO2 ), Keçikalesi tholeiitic volcanism

10

N-Morb normalised 1

a 0.1 Cs Ba U Ta La Pr Nd Hf Ti Tb Y Er Yb Rb Th K Nb Ce P Zr Sm Gd Dy Ho Tm Lu

1000 6 5 Erciyes volcanism 4

6: E-169 (64.08 % SiO2 ), Erciyes calc-alkaline volcanism

3 1: E-196 (51.24 %SiO2 ), Erciyes calc-alkaline volcanism

100 2 4: E-102-b (58.61 % SiO2 ), Koçdağ calc-alkaline volcanism 1 5: E-103 (62.19 %SiO2 ), Koçdağ calc-alkaline volcanism

3: E-148 (47.76 % SiO2 ), Koçdağ alkaline volcanism

10

N-Morb normalised 1

b 0.1 Cs Ba U Ta La Pr Nd Hf Ti Tb Y Er Yb Rb Th K Nb Ce P Zr Sm Gd Dy Ho Tm Lu

Figure 7. N-MORB normalised multi-element patterns for the Central Anatolian volcanic rocks. N-MORB normalising values are from Sun & McDonough (1989). trace element concentrations. The presence of pyroxene Assimilation-fractional Crystallization Effect cpx- and plagioclase is supported by decreasing Y ( As a result of heat transfer from hot magma to the cold liquid ≈ plg-liquid ≈ KdY 1.2, KdY 0.15) contents vs Th. crust, magmas, which are undergone fractional Fractionation trends of rock suites from the Erciyes strato crystallization and assimilated around the crust, are very volcano are quite similar and consistent with common (De Paolo 1981; Spera & Bohrson 2001; petrographically proposed fractionation trends Thompson et al. 2002; Kuritani et al. 2005). Most of (plg[%50]+amp[%50]) (Figure 10a–c). large-volume continental silicic magmas are combination of continental rocks and mantle-derived basaltic melts (De

12 A. GÜÇTEKİN & N. KÖPRÜBAŞI

assimilation to fractional crystallization) was used as the 100 Hasandağ alkaline volcanism AFC numeric index. Hasandağ calc-alkaline volcanism average Since mantle xenoliths are absent in rocks of the Keçikalesi tholeiitic volcanism crust Erciyes calc-alkaline volcanism Hasandağ and Erciyes stratovolcanoes, alkaline rocks Koçdağ calc-alkaline volcanism elting comprising the most primitive rocks in the region were 10 Koçdağ alkaline volcanism used in studies regarding end-member of the mantle of partial m source. The average crust values provided by Taylor & McLennan (1985) were used as the crust composition. Distribution coefficients (D) used in AFC modeling decreasing degree 1.0 ARRAY were computed from mineral/melt distribution Th/Yb coefficients (Kd) which were used in previous fractional

subduction enrichment MANTLE crystallization modeling (Keskin 1994; Keskin et al. 1998). AFC vectors for the Hasandağ and Erciyes stratovolcanoes were separately computed. All 0.1 distribution coefficients were calculated considering N-MORB fractional assemblages of (plg[50%]+amp[50%]) for the

Hasandağ stratovolcano and (plg[505%]+amp[50%]) for the Erciyes stratovolcano. 0.01 0.01 0.1 1.0 10 Assimilation and fractional crystallization effects of all Ta/Yb the rock samples from the Hasandağ and Erciyes stratovolcanoes were studied on the Rb vs Rb/Th Figure 8. Th/Yb against Ta/Yb log±log diagram (after Pearce 1983) diagrams. In the AFC modeling, Rb/Th ratio was used for the Central Anatolian volcanic rocks. Average OIB and since Rb and Th are not affected significantly by MORB values used for comparasion are from Sun & crystallizing phases. Rb/Th ratio of the crust is higher McDonught (1989). than basaltic lavas and increases in this ratio may be possible reflections of the crustal assimilation. Rubidium Paolo et al. 1992). Although physical mixing formed by was used as the fractionation index. Rb is strongly hybridization is preserved in xenoliths and xenocrysts, retained in biotite which is not involved significantly in the most workers state that chemical evidence (particularly crystallization assemblages of volcanic rock suites except radiogenic isotopes) are important for mixing between for some high silica rocks. Calculated theoretical curves magmas with contrasting geochemical compositions were included to the Rb vs Rb/Th diagrams. In this (Beard et al. 2005). By the early 1970’s it was recognized modeling, due to potential variations in distribution that isotopic variations in the Sierra Nevada batholith, for coefficient values during the course of fractional example, correlated with the character of the basemenet crystallization and uncertainties in end-member and, implicitly, required mixing of crustal- and mantle- compositions, ‘r’ values represent rather broad derived melts (Kistler 1974). Recent geochemical works approximations. However, r values significantly reflect indicated that fractional crystallization and assimilation the most primitive composition of rocks and AFC effects are the most important processes for differentiation of between the rocks. Similar trends and assimilation ratios volcanic rocks (De Paolo 1981; Spera & Bohrson 2001). are also reported by Keskin et al. (1998) for the East Mantle-derived magmas are subjected to contamination Anatolian post-collisional volcanic rocks. when they rise through the thick crust and therefore, are As shown from the diagram, the Hasandağ alkaline affected by the contamination with certain degree. rocks is the rock group which is the least contaminated by In order to examine the effects of magma mingling the crust. This rock group is found between r= 0.01 and and assimilation processes in rocks of the Hasandağ and 0.2 theoretical curves. Most of the Keçikalesi tholeiitic Erciyes stratovolcanoes, theoretical AFC models (De Paolo and Hasandağ calc-alkaline rock samples are observed at 1981) were used that are based on trace element r= 0.2–0.3 while a few samples are at r>0.4 (Figure chemistry. In the modeling, ‘r’ value (the ratio of 11a).

13 GEOCHEMISTRY OF HASANDAĞ AND ERCİYES VOLCANOES

100 100 10 9 11 1 1 11 6 6 2 2 3 alkaline rocks 3 4 alkaline rocks 4 tholeiitic and calc-alkaline rocks 9

Y Y 10 8 10 7,8

5 5

a 7 b 1 1 1 10 100 110100 Rb Th 10 10 11 Hasandağ alkaline volcanism 1 Hasandağ calc-alkaline volcanism 6 Keçikalesi tholeiitic volcanism 2 1) %65 pl+%25 cpx+%10 opx (I) 7 4 2) %50 pl+%30 am+%10 cpx+%10 opx (I) 3) %50 pl+%50 cpx (A) Sm 3 4) %50 pl+%50 am (I) 5) %50 pl+%50 am (A) 6) %20 pl+%60 cpx+%10 opx+%10 ol (I) 8 7) gt (I) 8) am (I) 9) cpx (A) 9 10) %50 pl+%15 cpx+%35 ol (B) c 5 11) %50 pl+%15 cpx+%20 ol+%15 gt (B) 1 1 10 100 Rb

Figure 9. Trace-element diagrams used to study the petrogenesis of the Hasandağ strato volcanic rocks. Diagram showing theoretical Rayleigh fractionation vectors for 50% crystallisation of the phase combinations indicated in the inset (a– logRb–logY; b– logTh–logY; c– logRb– logSm). Thick marks on each vector correspond to 5% crystallization intervals am– amphibole; pl– plagioclase; ol– olivine; cpx– clinopyroxene; opx– orthopyroxene; gt– garnet; B– basic; I– intermediate; A– acidic; numbers refer to phase proportions.

AFC effects on samples from the Erciyes stratovolcano Mantle-melting Modeling are examined in Figure 11b. In this diagram, the Koçdağ In mantle melting modeling, non-modal batch melting alkaline rocks that comprise the most primitive rocks of equations of Shaw (1970) were used. REE abundances volcanism are found between theoretical vectors of r= and their ratios were used for limiting the source 0.01 and 0.1. All the calc-alkaline rocks are found characteristics of magmas. Distribution coefficients of between similar vectors. In diagram, Rb/Th ratios span a REE were taken from McKenzie and O’Nions (1991, rather narrow range particularly for the Koçdağ alkaline 1995). Values proposed by Kostopoulos & James (1992) and Erciyes calc-alkaline rocks, although there is a were utilized for the modal mineralogies and melting significant increase in Rb concentrations indicating that ratios. fractional crystallization was an effective process during the magmatic evolution. In the modeling, we first attempted to test whether the trace element composition of depleted MORB mantle

14 A. GÜÇTEKİN & N. KÖPRÜBAŞI

100 100 6, 10 9 3 6 2 3 1 2 4 1 4 9

Y 8 10 Y 10 7,8

5 5

a b 1 7 1 1 10 100 1 10 100 Rb Th 10

6 Erciyes calc-alkaline volcanism 10 Koçdağ calc-alkaline volcanism 2 Koçdağ alkaline volcanism 1 7 4 1) %45 pl+%15 cpx+%10 opx+%30 am (I) 3 2) %50 pl+%25 am+%25 cpx+ (I)

Sm 3) %50 pl+%50 cpx (A) 4) %50 pl+%50 am (I) 5) %50 pl+%50 am (A) 8 6) %50 pl+%30 cpx+%20 ol (I) 7) gt (I) 8) am (I) 9 9) cpx (A) c 5 10) %50 pl+%15 cpx+%35 ol (B) 1 1 10 100 Rb

Figure 10. Trace-element diagrams used to study the petrogenesis of the Erciyes strato volcanic rocks. Diagram showing theoretical Rayleigh fractionation vectors for 50% crystallisation of the phase combinations indicated in the inset (a– logRb–logY; b– logTh–logY; c– logRb– logSm). Thick marks on each vector correspond to 5% crystallization intervals am– amphibole; pl– plagioclase; ol– olivine; cpx– clinopyroxene; opx– orthopyroxene; gt– garnet; B– basic; I– intermediate; A– acidic; numbers refer to phase proportions.

(DMM) can be a suitable source for the Central Anatolian melting modeling (Figure 12). Melting degrees and source volcanic rocks. DMM was assumed to represent the compositions used in calculations are shown on the asthenospheric mantle circulation which is characterized melting curves. As shown from diagrams in Figure 12, by a theoretical depleted MORB source proposed by melting degrees of the Keçikalesi tholeiitic rocks, the McKenzie and O’Nions (1991, 1995). Since the mantle Hasandağ alkaline rocks and Koçdağ alkaline rocks are 8– source mineralogy is not accurately known, the modelling 9%, 4–5% and 3–8%, respectively. was based on a mixture of three different source In order to determine the source mineralogy, La- compositions; garnet lherzolite, spinel lherzolite and La/Sm and La/Sm-Sm/Yb diagrams (MREE/HREE and garnet-spinel lherzolite (50%: 50%). In the modelings, LREE/MREE ratios are considered) were used (Figure priority was given to incompatible element concentrations 13). Since La and Sm are not significantly affected by (LRE) which are not significantly affected by changes in changes in the source mineralogy, they may be very useful the source mineralogy. for determination of bulk chemical composition of the Theoretic melting curves in the La-Ce, La-La/Nd and source (Aldanmaz et al. 2000). These diagrams were used La/Ce-La/Yb diagrams are computed based on the batch to distinguish the melting of garnet-lherzolite and spinel-

15 GEOCHEMISTRY OF HASANDAĞ AND ERCİYES VOLCANOES

10 r =0.5 r =0.4 (D-1) A 6 5 r =0.3 a r7 =0.7 4 r8 =0.85 C/C=FL0 r3 =0.2

r2 =0.1

B r1 =0.01 composition component A:

Rb/Th Taylor & McClennan (1985) Rb= 91; Th= 1.4 D(Rb)= 0.1; D(Th)= 0.08 Hasandağ alkaline volcanism composition component B: Hasandağ calc-alkaline volcanism C94-14 (Şenet al. 2004) Rb= 14.13; Th= 4 Keçikalesi tholeiitic volcanism 1 10Rb 100 100 composition component A: b Taylor & McClennan (1985) (D-1) A Rb= 91; Th= 1.4 C/C=FL0 D(Rb)= 0.1; D(Th)= 0.08

composition component B: r7 =0.7 et al. r8 =0.85 ER-24 (Notsu 1995) r6 =0.5 r5 =0.4 Rb= 6; Th=1.5 r4 =0.3 r3 =0.2 10 r2 =0.1

Rb/Th r =0.01 B 1 Erciyes calc-alkaline volcanism Koçdağ calc-alkaline volcanism Koçdağ alkaline volcanism 1 1 10 100 Rb

Figure 11. Rb/Th vs Rb diagram for the Central Anatolian volcanc rocks showing the results of AFC (assimilation-fractional crystallization modelling) as discussed in the text. lherzolite sources. Melting of spinel-lherzolite source C1 chondrite-normalized REE diagram including causes only a small change in La/Sm ratio of the melt, depleted MORB mantle (DMM), primordial mantle (PM) because none of these elements is fractionated by spinel and estimated using the above approach Central Anatolian facies melting. Likewise, only a small change occurs in mantle is shown in Figure 14. As shown from this figure, Sm/Ym ratio of the melt. Therefore spinel-lherzolite the computed Central Anatolian mantle composition is melting is observed as a horizontal trend. Melting of more enriched in LREE’s with respect to DMM and PM. In garnet-lherzolite source, on the other hand, produces addition, LREE concentrations are not affected by garnet melt with La/Sm ratio higher than the mantle array and or spinel lherzolite source while M-HREE concentrations the melt fraction produced from such a source will be are significantly affected by the source mineralogy. Figure displaced from the mantle array towards higher La/Sm 14 indicates that the mantle sourcing the Central and Sm/Yb ratios on a La/Sm-Sm/Yb diagram. The results Anatolian volcanic rocks is represented by a source with are given in Table 2, together with estimated mantle garnet + spinel lherzolite composition and the abundance source composition for the Central Anatolian volcanic of garnet component is more pronounced for the rocks. Hasandağ alkaline rocks.

16 A. GÜÇTEKİN & N. KÖPRÜBAŞI

100 from the Dikili-Ayvalık-Bergama area (Aldanmaz et al. Ce garnet lherzolite 2% Koçdağ alkaline volcanism partial melting curve 2000) and Big Pine volcanic rocks (Ormerod et al. 1991) Hasandağ alkaline volcanism 4% 4% spinel lherzolite which are generally derived from lithospheric mantle Keçikalesi tholeiitic volcanism 6% partial melting curve 6% enriched in subduction components (Şen et al. 2004). The 8% 8% alkaline rocks resemble within plate oceanic island basalt 10% 10% (OIB) and to some extent they also indicate mantle source

15% 15% with a subduction component. 20% 20% source composition 25% La: 1.44 The Central Anatolian Quaternary volcanism is mainly a 25% Ce: 3.14 La related to an extensional tectonism without an active 10 1 10 100 subduction process (Deniel et al. 1998; Şen et al. 2004). 10 As mentioned previously, considering the trace element La/Nd source composition La: 1.44 Nd: 1.86 content of volcanic rocks in MORB normalized multi- garnet lherzolite partial melting curve 1% element diagrams, LIL element concentrations are 2% 4% 1% 10% 8% 6% 2% significantly enriched with respect to HFS elements which 1 4% 10% 8% 6% garnet-spinel lerzolite can be attributed to either the addition of subduction spinel lherzolite partial melting curve partial melting curve component to the source or crustal contamination on mantle-derived primary magmas. b La 0.1 10 100 As shown from the Th/Yb-Ta/Yb diagram, most of samples have compositions indicative of derivation from 100 garnet-spinel lerzolite subduction modified source and resulting melts possibly La/Yb garnet lherzolite 2% partial melting curve partial melting curve 0.01% modified further by crustal contamination. Alkaline rocks 4% 0.5% 6% 1% seem to be less affected from these processes. In 0.01% 8% 2% 10% 0.5% addition, low Zr/Nb (Hasandağ alkaline rocks: 8–10, 4% 10 1% 15% 8% 2% Erciyes alkaline rocks: 14–17) and high La/Yb (Hasandağ 4% 20% 8% spinel lherzolite alkaline rocks: 13–15, Erciyes alkaline rocks: 6–14) source composition 25% 10% 25% partial melting curve La: 1.44 ratios observed in alkaline rocks of the Hasandağ and Ce: 3.14 Yb: 0.41 c La/Ce Erciyes stratovolcanoes may indicate derivation from a 1 0.1 1 mantle source similar to those of alkaline OIB magmas. In formation of calc-alkaline series, a combination of

Figure 12. Plots of (a) Ce and (b) La/Nd against La shows melting assimilation and fractional crystallization processes are curves obtained using the non-modal batch melting effective. equations (Shaw 1970) and data from Central Anatolian rocks. The absolute abundances of plotted incompatible Alkaline rocks of the Hasandağ stratovolcano are elements are unaffected by the mantle mineralogy, characterized by low Sr isotopic ratios and the crust therefore the sole control is the bulk chemical composition contribution is decreased in time (Deniel et al. 1998). of the source. (c) Variation of La/Yb vs La/Ce showing melting curves obtained using non-modal batch melting Alkaline rocks of the Erciyes stratovolcano have been equations for varying proportions of source mineralogy. reported to have 87Sr/86Sr ratios higher than the typical The points on the curves represent degree of partial MORB but significantly lower than the chondritic silicate melting. Mineral/matrix partition coefficients are from the compilation of McKenzie & O’Nions (1991, 1995). earth compositions and this may indicate the presence of an OIB source in the development of this magma Source Characteristics and Melting Mechanisms (Kürkçüoğlu et al. 1998). The Central Anatolian volcanism is characterized by calc- Hofmann & White (1982) state that enriched isotope alkaline, alkaline and tholeiitic type volcanic rocks which compositions of oceanic island basalts is due to old crust were formed at various stages of volcanic activity and do material sent back to the mantle. On the other hand, not show any systematic relationships. Based on McKenzie and O’Nions (1983) suggest that lower parts of geochemical characteristics, the Central Anatolian calc- the lithosphere thickening in the orogenic belts are alkaline and tholeiitic volcanism is reported to be similar detached in time and separated from the lithosphere and to Andean basalts (Hickey et al. 1986), basaltic rocks

17 GEOCHEMISTRY OF HASANDAĞ AND ERCİYES VOLCANOES

10 gt-lherzolite 2% 4% 1% La/Sm 6% gt+sp-lerzolite 2% 15% 10% 4% enrichmentCAM 25%20% 15% 10% OIB WAM 25% 20% 1% sp-lherzolite 2% depletion PM gt-lherzolite E-MORB 0.1% 4% 1% N-MORB 2% 1 10% DMM 30% 20% 4% 70% 50% 10% 6% sp-lherzolite 70% 50% 30% 20%

source composition Koçdağ alkaline volcanism La: 1.44 Hasandağ alkaline volcanism a Sm: 0.42 Keçikalesi tholeiitic volcanism La 0.1 0.1 1 10 100

10 1% 0.5% gt-lherzolite 2% 2% 1% Sm/Yb 4% 4% 6% OIB 6% gt+sp-lherzolite 8% 8% 10% 10% 1% 0.5% 0.01% 15% 2% 15% 10% E-MORB 20% 6%4% 20% 2% 1% 0.5% 15% 0.01% 10%4% 2% 1%0.5% 1 8% 4% PM WAM CAM sp-lherzolite DMM N-MORB sp-lherzolite enrichment source composition depletion La: 1.44 Sm: 0.42 Yb: 0.41 b La/Sm 0.1 0.1 1 10 100

Figure 13. Plots of La/Sm vs La and Sm/Yb vs La/Sm showing melt curves (or lines) obtained using the non-modal batch melting equations of Shaw (1970). Melt curves are drawn for spinel-lherzolite (with mode and

melt mode of ol0.578 + opx0.270 + cpx0.119 + sp0.033 and ol0.10 + opx0.270 + cpx0.50 + sp0.13) and for garnet-lherzolite (with mode and melt mode of ol0.598 + opx0.211 + cpx0.076 + gt0.115 and ol0.05 + opx0.20 +

cpx0.30 + gt0.45; respectively; Kostopoulos & James 1992). Mineral/matrix partition coefficients and DMM are from the compilation of McKenzie & O’Nions (1991, 1995); PM, N-MORB and E-MORB compositions are from Sun & McDonough (1989). Western Anatolian Mantle (WAM) composition is from Aldanmaz et al. (2000). The heavy line represents the mantle array defined using DMM and PM compositions. Solid curves (or lines) are the melting trends from DMM and Central Anatolian Mantle (CAM), respectively. Tick marks on each curve (or line) correspond to degrees of partial melting for a given mantle source.

added to convectional currents in the asthenosphere and, enriched in incompatible elements and volatiles and also they rise as plumes in certain places thus forming the upward migration of such melts which may result in source of oceanic island basalts. metasomatism at the base of SCLM and the combination McKenzie (1989) defined the continental basaltic of low-degree partial melt of the asthenospheric mantle magmas as those derived probably from the material under the continents. Anderson (1994) proposed metasomatized subcontinental lithospheric mantle convective mantle that is represented by trace element (SCLM). He also described melts that are significantly and isotope characteristics (like DMM) depleted prior to

18 A. GÜÇTEKİN & N. KÖPRÜBAŞI fferent mineral modes as garnet-lherzolite, spinel– Estimation of mantle source composition the Central Anatolia suite Concentration of trace element in tle liquid (garnet-lherzolite) Concentration of trace element in tle liquid (spinel-lherzolite) Concentration of trace element in tle liquid (spinel+gt-lherzolite) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu lherzolite and garnet+spinel-lherzolite (50%– 50%). Mantle source compositions for the central Anatolian volcanic rocks. Trace element concentrations were estimated using three di (F) Degree of partial 1.44melting 0.25 3.140.200.150.10 5.760.08 0.40 7.150.06 9.450.04 13.90 1.860.02 17.130.01 12.52 22.320.005 15.48 32.01 0.420.0001 20.29 56.59 29.40 1.59 91.87 35.85 133.46 1.95 239.93 45.91 0.14 2.52 63.84 3.570.25 7.41 104.71 4.280.2 9.01 154.01 201.42 11.50 0.50 5.340.15 288.47 15.88 7.11 1.680.1 10.62 18.74 5.76 2.010.08 14.09 22.85 16.85 2.490.06 20.85 7.15 3.28 0.09 29.26 40.68 9.42 0.580.04 3.76 50.55 57.53 13.79 0.680.02 4.40 66.53 16.93 0.82 0.610.01 12.55 5.30 1.04 6.65 21.93 1.960.005 1.17 7.64 8.24 31.11 15.49 2.270.0001 8.94 20.21 1.33 53.53 2.68 0.13 29.10 1.55 3.28 1.84 1.60 83.69 35.30 116.51 3.60 0.35 2.04 189.22 2.15 44.87 1.96 2.28 4.00 0.40 2.53 0.40 61.55 0.450.25 7.45 4.48 5.11 3.57 0.53 97.97 4.270.2 2.40 5.49 0.57 9.07 139.14 5.70 176.15 11.57 5.320.15 2.62 5.93 238.27 0.06 0.61 2.87 15.98 7.04 1.700.1 3.18 0.66 18.86 0.72 5.76 10.43 0.530.08 3.32 13.72 2.05 23.00 16.30 0.41 2.59 0.75 0.55 0.770.06 19.98 7.15 3.48 0.58 0.79 29.47 3.51 9.43 0.61 0.58 41.000.04 4.10 3.65 3.84 1.54 50.98 58.04 0.62 13.84 0.06 0.02 4.92 67.16 3.95 0.70 1.55 17.03 4.00 0.87 0.63 1.550.01 12.54 4.05 6.15 22.12 1.16 1.55 8.19 0.64 1.980.005 0.66 1.34 10.92 9.83 0.23 31.56 15.49 1.55 12.250.0001 0.66 20.25 1.59 0.67 0.22 2.38 55.06 2.98 1.55 0.67 0.20 29.25 1.94 1.59 87.78 0.19 3.98 1.55 1.54 35.58 2.50 1.55 124.99 3.19 4.60 0.36 2.92 214.58 0.18 1.32 3.50 45.39 1.95 1.55 1.55 5.45 1.15 2.53 0.18 1.55 0.43 62.69 1.02 0.54 0.23 7.43 6.68 3.57 101.34 0.17 0.17 8.62 0.98 0.71 11.02 4.28 0.18 2.44 10.08 0.82 9.04 12.12 146.57 0.14 188.79 0.17 0.94 11.54 0.17 5.33 0.12 263.37 0.97 0.17 2.92 3.63 0.90 15.93 7.08 0.87 1.69 0.11 10.52 1.18 18.80 4.79 0.54 1.91 0.85 1.51 0.84 1.76 0.11 5.49 13.91 2.03 22.92 16.58 2.10 2.54 0.84 20.41 0.65 0.10 6.44 0.81 0.10 29.37 3.40 40.84 0.58 3.93 7.77 1.07 0.10 1.58 12.22 0.09 50.77 11.30 57.78 9.82 1.23 13.28 0.09 4.66 66.84 0.69 0.85 1.89 1.44 2.36 5.72 7.42 1.10 1.75 1.97 2.79 3.12 1.26 2.57 8.73 0.24 9.58 2.23 3.04 3.59 10.59 1.46 2.32 2.83 4.23 0.29 0.36 1.74 2.17 3.63 5.13 1.60 8.20 0.48 7.55 4.10 6.52 0.36 8.94 2.48 2.67 0.55 2.89 1.91 4.72 2.37 0.64 0.41 0.50 0.24 5.58 3.13 6.86 0.77 1.23 3.59 0.62 1.13 2.42 0.98 1.33 7.79 0.69 0.28 8.36 0.35 9.03 4.21 0.79 2.77 0.46 3.25 5.08 7.97 7.37 0.53 6.41 0.92 8.66 1.12 3.99 0.54 0.61 4.41 1.26 1.34 1.44 0.60 0.74 4.96 1.13 0.69 1.05 0.92 1.22 5.71 0.84 6.83 1.56 0.92 7.62 8.11 8.67 1.72 1.04 1.95 1.20 2.34 1.44 0.24 2.57 1.62 1.73 1.86 2.89 0.25 0.28 3.34 1.57 4.04 0.33 0.36 4.55 4.87 1.61 5.25 1.76 0.41 0.23 2.08 0.47 0.58 2.28 0.23 0.25 0.65 2.57 0.70 0.75 0.29 2.99 3.64 0.32 4.11 4.41 0.36 4.75 0.42 0.51 0.57 0.61 0.66 Table 2.

19 GEOCHEMISTRY OF HASANDAĞ AND ERCİYES VOLCANOES

1000 garnet-lherzolite spinel-lherzolite 2% Hasandağ alkaline volcanism garnet+spinel lherzolite 4% DMM 100 6% CAM 8% 10% PM 2% 4% 6% Keçikalesi tholeiitic volcanism 8% 10% 10 Koçdağ alkaline volcanism 10% 2% 8% 4% 6%

Chondrite (C1) normalised 1

CL0 /C =1/[D 0 +F(1-P)] 0 La Ce Pr Nd (Pm) Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Figure 14. Chondrite (C1) normalised REE patterns showing the compositions of modelled batch melts produced by melting of a CAM source with mineral proportions of garnet-lherzollite, spinel- lherzolite and garnet (%50) + spinel (%50) lherzolite. The modal mineral proportions and distribution coefficients used same as figure 13. Normalised values are srom Boynton (1984) and the batch melting equation is from Shaw (1970). ascension and interacted at the beginning with shallow continental lithosphere has a mechanical boundary layer and enriched mantle. This portion proposed by Anderson (MBL) of varying thickness and is separated from the (1994) is below the thermal boundary layer or within the convective asthenosphere with a thermal boundary layer asthenosphere. The same author also states that enriched (TBL). Bailey (1987) suggests that geothermal gradient part of the shallow mantle may correspond to chemical of MBL cuts the lithospheric solidus which is characteristics of a source region similar to continental metasomatized by small melt pockets ascending from basaltic or OIB magmatism. In order to explain asthenosphere to the lithosphere and it is metasomatized composition of all oceanic and continental within plate in lower parts of the region. basic volcanics which necessitate an enriched source, The potential mechanisms of magma generation in the McKenzie and O’Nions (1995) proved that SCLM could be (subduction component bearing) heterogeneously enriched and remelted afterwards. enriched mantle source of the Central Anatolian volcanism No evidence was found for spatial and chronologic may include: (a) mantle-plume, (b) slab break-off, (c) systematic variation of the source component and the extension and associated strike-slip faulting, and (d) magmatism sourcing alkaline and calc-alkaline volcanics in lithospheric delamination and associated orogenic the Central Anatolia. Therefore, it is thought that alkaline collapse. These possible options are discussed below. and calc-alkaline magmatic products were represented by (a) Melting of lithospheric mantle as a result of magmas derived from a heterogeneous mantle source thermal perturbation in association with ascending mantle with melts of varying rates and affected from crustal plume or asthenospheric mantle may give rise to contamination at varying rates. formation of widespread volcanism in the Central In order to examine melting mechanisms which gave Anatolia. It was proposed by McKenzie & Bickle (1988) rise to generation of Central Anatolian post-collisional that asthenosphere could start to melt at a potential volcanism, P-T diagram of Pearce et al. (1990) proposed temperature of 1280 ºC and at an initial depth of 50 km for the Eastern Anatolia was taken into consideration. under a stress factor of 2.5. Under hot mantle conditions, Pearce et al. (1990) state that a typical non-cratonic mantle plume can also start melting at great depths without substantial stress (at 100 km, potential

20 A. GÜÇTEKİN & N. KÖPRÜBAŞI

temperature is 1480 ºC) and affects the regional zone in this region, however, the volcanism in Central topography. The typical mantle plume is described by Anatolia is unlikely to be directly affected by the White and McKenzie (1989) as a spreading center (limited subduction process that resulted in formation of the to 150–200 km) forming a mushroom-shaped hot spot Eastern Anatolia collision system. One can infer that the with a diameter of 1000–2000 km that dynamically closure of inner-Tauride Ocean could be a possible uplifts an area of 1000–2000 km in diameter. There is no subduction. Geochemical characteristics of Paleocene– regional stress evidence that could be associated with a Eocene volcanic and intrusive products in the region and mantle plume responsible for the post-collisional Central their radiometric ages may indicate that these volcanics Anatolian volcanism and there are no topographic are cogenetically formed (Gürer & Aldanmaz 2002). In indicators necessary for such a mantle plume either. most of previous works, these events are evaluated in the (b) Melting of lithospheric mantle due to thermal concept of arc magmatism associated with closure of the perturbation arising from ascending asthenospheric inner-Tauride Ocean (Şengör &Yılmaz 1981; Görür et al. mantle by slab breakoff could be an alternative 1984; Gökten & Floyd 1987; Erdoğan et al. 1996). More mechanism for the source of Central Anatolia volcanism. recent studies, however, showed that the regional According to Davies and Von Blanckenburg (1995), slab magmatic activity took place in a post-collisional breakoff is very common for many orogenic belts and it environment and may have an intra-plate character explains the coexistence of ultra-high pressure (Gürer & Aldanmaz 2002). This is evident from the metamorphics and mantle-derived magmatism. Slab temporal evolution of the activity that changes from a should be separated at the early stages of continental syn-collisional episode (e.g., S-type, peraluminous collision (Davies & Von Blanckenburg 1995; Wong A Ton granites) through a post-collisional, calc-alkaline episode & Wortel 1997). This is due to decrease in subduction (e.g., I-type, high-K, metaluminous granites) to a post- rate by the positive lifting power of continental collisional, within-plate alkaline episode (e.g. A-type, lithosphere intruded into the subduction zone (Gerya et peralkaline granites) (e.g., Göncüoğlu & Türeli 1993; al. 2004). İlbeyli & Pearce 1997; Boztuğ 2000, 2008; Köksal & In contrast to previously proposed several models for Göncüoğlu 2008). the Eastern Anatolia, Şengör et al. (2003) and Keskin The age of tholeiitic volcanism of the Hasandağ strato (2003, 2007) suggested the model of slab breakoff and volcano ranges from 12.4±0.6 to 13.7±0.3 Ma (Besang steepening under widely spread subduction accretionary et al. 1977) and alkaline type latest products are dated as complex. In the model proposed by Davies & Von 34000±7000 years (Aydar 1992). Alkaline rocks as the Blanckenburg (1995), if the subduction rate is 1 cm/year, first products of the Erciyes stratovolcano are of the breakoff was stated to occur at a depth of 50–120 4.39±0.28 Ma old (Ayrancı 1969). Since the volcanism in km. The volcanism was thought to start as a result of both regions is not a subduction-type volcanism related to release of this substantial load and upwelling of less dense the closure of inner-Tauride Ocean and the subsequent asthenospheric mantle. Unlike the model of ‘original slab slab breakoff event is not evidenced by significant breakoff’ proposed by Davies & Von Blanckenburg chronological and spatial systematic, this model is not (1995), Keskin (2003), Şengör et al. (2003) suggest a suitable one. In addition, considering the alkaline lavas of new model where subducting oceanic lithosphere beneath varying ages, the presence of a heterogeneous mantle the accretionary prism gets steepened and eventually source is reasonable. detached from the continental lithosphere. According to these workers, the melting occurs in the asthenospheric (c) Another alternative mechanism is that regional mantle and eventually volcanic activity spreads in a large extension developing in association with strike-slip faults area apart from the suture zone. and the melting of mantle lithosphere due to thermal perturbation could be related to tectonic regime in the Under the light of above information, a similar Central Anatolia. Formation of lithospheric melting in mechanism can be discussed for Central Anatolia continental extensional environments is studied by several considering its closeness to Eastern Anatolia and similar workers (Latin et al. 1989; Hawkesworth & Norry 1982; geochemical characteristics of the two regions. Given the Menzies & Hawkesworth 1987). Lithospheric thermal distance of the volcanic centres to any possible subduction perturbation arising from upwelling of hot asthenosphere

21 GEOCHEMISTRY OF HASANDAĞ AND ERCİYES VOLCANOES

is the reason for lithospheric extension necessary for the of thermal boundary layer (TBL) could be proposed as the melting of lithospheric mantle material (Dixon et al. more efficient mechanism (Pearce et al. 1990). In 1981) or the position of solidus above the metasomatized general, one of the fundamental consequences of the level. Since melting point of these rocks will be lower in lithospheric delamination is the collapse event associated metasomatized mantle conditions, small thermal with rapid uplifting and extensional system which occurs irregularities could be sufficient for starting of melting. as a result of isostatic replacing of relatively dense (cold) Thus, even small-size extensions can trigger volcanism. lithospheric mantle by the less dense (hot) asthenospheric mantle (Dewey 1988; England & Houseman 1998; The magma generation in pull-apart basins in Nelson 1992; Platt & England 1993). Thickening TBL is association with N–S-trending fractures and strike-slip denser and colder than the surrounding medium and since regimes in the Eastern Anatolia is attributed to fast thickened levels of metasomatized lithosphere are in close lithospheric extension and small-scale delamination under contact with the asthenosphere, they are convectively the pull-apart basins (Dewey et al. 1986). Although replaced by the asthenosphere (Houseman et al. 1981; Pearce et al. (1990) suggest that delamination process is England & Houseman 1998). Due to thermal the dominant mechanism for widespread magma perturbation arising from direct contact between generation in the same region they also state that other metasomatized mantle lithosphere and hot mechanisms such as formation of pull-apart basins asthenosphere, delamination of TBL could result in accompany these processes. Cooper et al. (2002) melting of metasomatized mantle lithosphere. proposed that mantle upwelling and melting under the Pearce et al. (1990) stated that the close contact strike-slip fault systems could be the origin of mafic between thickened metasomatized lithospheric mantle magmas in northwest Tibet. Likewise, Aldanmaz et al. and asthenosphere is an effective mechanism for (2005, 2006) mention partial effect of strike-slip faults collisional magma generation developed in the Eastern in generation of alkaline volcanics in NW Turkey. Anatolia. While delaminated block of the mantle The first group of active fault systems extending lithosphere sinks into the asthenosphere, increasing through the Central Anatolian volcanism is left-lateral melting may release water (Elkins-Tanton 2004). These Ecemiş fault zone and right-lateral Tuz Gölü fault zone two mechanisms play an important role in formation of and the second is N60–70° E-trending normal faults that common partial melt in the mantle and can produce are parallel to the volcanic axis and concordant with the widespread volcanism in the region. main eruption centres (Toprak & Göncüoğlu 1993). The As a result, delamination of TBL and associated Erciyes basin is a pull-apart basin with an important substantial thermal perturbation could be alternative strike-slip component (Koçyiğit & Beyhan 1998). Due to models that facilitate melting of continental lithosphere lateral stress arising from transtensional tectonic regime responsible for initiation of Central Anatolia volcanism. In in the Central Anatolia coupled with regional extension, addition, the close association of volcanism with the formation of thermal perturbation in the mantle strike-slip tectonism in the region indicates that this lithosphere could be a possible mechanism. In addition, as system possibly contributes to the magma rising. mentioned previously, little effect of AFC on the Erciyes strato volcano could be explained with crustal thinning as a result of extensional tectonism in the region associated Conclusion with pull-apart basin. The Hasandağ and Erciyes stratovolcanoes represented by (d) Another alternative mechanism could be thermal widespread calc-alkaline volcanism are two important perturbation and melting triggered by lithospheric members of collisional volcanism in the Central Anatolia. delamination and associated orogenic collapse following The calc-alkaline products are accompanied by tholeiitic the post-collisional lithospheric thickening. Thermal and alkaline rocks in the Hasandağ volcano and by alkaline perturbation and melting arising from lithospheric rocks in the Erciyes stratovolcano. Rocks of both delamination could be the reason of volcanism in the volcanisms show a wide composition spectrum from Central Anatolia. Although thermal perturbation in basalt to rhyolite. association with strike-slip faults in lithosphere can be In the chondrite normalized diagrams the rocks from thought as the mechanism to start melting, delamination the Hasandağ and Erciyes stratovolcanoes, display

22 A. GÜÇTEKİN & N. KÖPRÜBAŞI

uniform and sub-parallel light rare earth element patterns The Central Anatolian volcanic rocks are generated by a and show relatively enrichment in LREE. In the multi- mantle source of garnet + spinel lherzolite composition element diagram normalized to N-MORB, tholeiitic and while Hasandağ alkaline rocks are dominated by the calc-alkaline rocks of the Hasandağ strato volcano show a garnet composition. The calculated Central Anatolian significant enrichment in LIL elements (Rb, Ba, Th, U and mantle composition is more enriched in LREE’s in K) and LREE’s and relatively depletion in HFS elements comparison to DMM and PM. (Ta, Nb, Ti and Hf). In the calc-alkaline rocks of the Accordingly, it is believed that alkaline and calc- Erciyes stratovolcano that are characterized by similar alkaline magmatic products were generated from a patterns, LIL elements such as Th, U and K as well as heterogeneous mantle source under varying melting LREE’s also show a distinct enrichment. In the alkaline conditions and affected by the crustal contamination at rocks of the both stratovolcanoes, LIL elements are in varying degrees. lower concentrations in comparison to other rock groups and they do not have negative Ta and Nb anomalies Considering its geochemical characteristics, the indicating that alkaline rocks are derived from a different Central Anatolian volcanism seems to be derived from a source. In MORB normalized multi-element diagrams of lithospheric mantle that is enriched in subduction the same rocks, it was observed that LIL elements are components. Solutions which are strongly enriched by significantly enriched compared to HFS elements. This incompatible elements and volatiles result in enrichment may be attributed to the effect of subduction metasomatism at the base of continental lithosphere. TBL component in the source region or crustal contamination. which is thickened by lithospheric thickening in Depletion of Hf and Ti with respect to other HFS elements association with collisional tectonism is denser and colder can be explained with mantle enrichment in than its environs. When thickened levels of metasomitized intracontinental processes or derivation from a source lithosphere are in close contact with asthenosphere, it can with small degree partial melts. be convectively replaced by the asthenosphere. Delamination of TBL may result in melting due to thermal According to fractionation vectors constructed on the perturbation arising from direct contingence of basis of variations in trace element concentrations, rocks metasomitized mantle lithosphere to hot asthenosphere. of the Hasandağ volcanism generally display two different Hence, the Central Anatolian volcanism can be generated trends. Tholeiitic and calc-alkaline rocks are modified by by melting of continental lithosphere as a result of a fractionation of amphibole and plagioclase while alkaline substantial thermal perturbation occurring by rocks are represented by fractionation effects of delamination of TBL. In addition, the observation that plagioclase, pyroxene and amphibole minerals. In alkaline volcanism is closely associated with strike-slip tectonism and calc-alkaline rocks of the Erciyes volcano, in the region may indicate that this system possibly fractionation trends are similar and conformable with contributes to the magma rising. The mechanism those of plagioclase and amphibole. suggested for the melt generation is rather similar to that Theoretically constructed AFC modelings show that proposed by Pearce et al. (1990) and Keskin et al. (1998) Hasandağ alkaline rocks are less affected from the crustal for the east Anatolian and by the Aldanmaz et al. (2000) contamination in comparison to tholeiitic and calc-alkaline for the west Anatolian volcanisms. rocks. However, in alkaline and calc-alkaline rocks of the Erciyes volcano which display similar AFC trends, the effect of crustal contamination is less than that of Acknowledgements Hasandağ volcanics. This research was financially supported by the Research According to theoretical melting curves calculated with Fund of Kocaeli University (Project No: 2003/74). We are non-modal batch melting model, the melting degrees of grateful to Dr. Ercan Aldanmaz for his constructive Hasandağ and Erciyes volcanic rocks are 8–9% for the discussion. We thank the guest editors, Prof. Nilgün Güleç Keçikalesi tholeiitic rocks, 4–5% for the Hasandağ and Prof. Durmuş Boztuğ, for the editorial handling of alkaline rocks and 3–8% for the Koçdağ alkaline rocks. the paper.

23 GEOCHEMISTRY OF HASANDAĞ AND ERCİYES VOLCANOES

References

AKIMAN, O., ERLER, A., GÖNCÜOĞLU, M.C., GÜLEÇ, N., GEVEN, A., TÜRELİ, K. BEARD, J.S., RAGLAND, P.C. & CRAWFORD, M.L. 2005 Reactive bulk & KADIOĞLU, Y. 1993, Geochemical characteristics of granitoids assimilation: a model for crust-mantle mixing in silicic magmas. along the western margin of the Central Anatolian Crystalline Geology 33, 681–684. Complex and their tectonic implications. Geological Journal 28, BESANG, C., ECKHARDT, F.J., HARRE, W., KREUZER, H. & MULLER, P. 1977. 371–382. Radiometrische Altersbestimmungen an Neogenen ALDANMAZ, E., PEARCE, J.A., THIRWALL, M.F. & MITCHELL, J.G. 2000. Eruptivegesteinen der Turkei. Geologisches Jahrbuch B25, 3–36. Petrogenetic evolution of Late Cenozoic post-collision volcanism in western Anatolia, Turkey. Journal of and Geothermal BONIN, B. 1990. From orogenic to anorogenic settings: evolution of Research 102, 67–95. granitoid suites after a major orogenesis. Geologica Journal 25, 261–270. ALDANMAZ, E., GOURGAUD, A. & KAYMAKCI, N. 2005. Constraints on the composition and thermal structure of the upper mantle beneath BOYNTON, W.V. 1984. Geochemistry of the rare earth elements: NW Turkey: evidence from mantle xenoliths and alkali primary meteorite studies. In: HENDERSON, P. (ed), Rare Earth Element melts. Journal of Geodynamics 39, 277–316. Geochemistry, Elsevier Amsterdam, 63–114.

ALDANMAZ, E, KÖPRÜBAŞI, N., GÜRER, Ö.F., KAYMAKCI, N. & GOURGAUD, A. BOZTUĞ, D. 2000. S-I-A-type intrusive associations: geodynamic 2006. Geochemical constraints on the Cenozoic, OIB-type alkaline significance of synchronism between metamorphism and volcanic rocks of NW Turkey: implications for mantle sources and magmatism in Central Anatolia, Turkey. In: BOZKURT, E. melting processes. Lithos 86, 50–76. WINCHESTER, J.A. & PIPER, J.D.A. (eds), Tectonics and Magmatism in Turkey and the Surrounding Area. Geological Society, London, ANDERSON, D.L. 1994. The sublithospheric mantle as the source of continental flood basalts; the case against the continental Special Publications 173, 441–85. lithosphere and plume had reservoirs. Earth and Planetary Science BOZTUĞ, D. 2008. Petrogenesis of the Kösedağ pluton, Suşehri NE Sivas, Letters 123, 269–280. East-Central Pontides, Turkey. Turkish Journal of Earth Sciences

AYDAR, E. 1992. Etude volcano-structurale et magmatologique du 17, 241–262.

stratovolcan Hasan Dagi, Anatolie Centrale, Turquie. PhD Thesis, BUKET, E. & TEMEL, A. 1998. Major-element, trace element and Sr-Nd Universite Blasie Pascal Clermont-Ferrand France [unpublished]. isotopic geochemistry, and genesis of Varto (Muş) volcanic rocks, AYDAR, E. & GOURGAUD, A. 1998. The geology of Mount Hasan eastern Turkey. Journal of Volcanology and Geothermal Research stratovolcano, Central Anatolia, Turkey. Journal of Volcanology 85, 405–22. and Geothermal Research 85, 129–152. COCHRAN, C.R. 1981. The Gulf of Aden: structure and evolution of a AYDAR, E. & GOURGAUD, A. 2002. Garnet-bearing basalts: an example young ocean basin and continental margin. Journal of Geophysical from Mt. Hasan, Central Anatolia, Turkey. Mineralogy and Research 86, 263–287. Petrology 75, 185–201. COOPER, K.M., REID, M.R., DUNBAR, N.W. & MCINTOSH, W.C. 2002. Origin AYDAR, E., GOURGAUD, A., DENIEL, C., LYBERIS, N. & GÜNDOĞDU, M.N. 1995. of mafic magmas beneath nortwestern Tibet: constraints from Le volcanisme quaternaire d’Anatolie central Turquie: association 230Th–238U disequilibria. Geochemistry, Geophysics 3, article de magmatisme calco-alcalin et alcalin en domaine de convergence. no.1065. Canadian Journal of Earth Sciences 327, 1058–1069. DAVIES, J.H. & BLANCKENBURG, V.F. 1995. Slab breakoff: A model of AYDAR, E., GÜNDOĞDU, M.N., BAYHAN, H. & GOURGAUD, A. 1993. Kapadokya lithosphere detachment and its test in the magmatism and bölgesinin Kuvaterner yaşlı volkanizmasının volkanik, yapısal ve deformation of collisional orogens. Earth and Planetary Science petrolojik incelenmesi [Volcanic, stuctural and petrologic study of Letters 129, 85–102. the Quaternary volcanism in Cappadocia region]. Doğa Türk Yerbilimleri Dergisi 3, 25–42 [in Turkish with English abstract]. DENIEL, C., AYDAR, A. & GOURGAUD, A. 1998. The Hasan Dağı stratovolcano Central Anatolia, Turkey: evolution from calc- AYRANCI, B. 1969. Zur Petrologie und Geologie des Erciyes-Vulkan- alkaline to alkaline magmatism in a collision zone. Journal of Geibetes bei Kayseri in Zentralanatolien/Türkei. Ph.D. Thesis, Volcanology and Geothermal Research 87, 275–302. Würzburg University, Germany [unpublished]. DE PAOLO, D. 1981. Trace element and isotopic effects of combined wall AYRANCI, B. 1991. The magnificent volcano of central Anatolia: Mt. Erciyes near Kayseri. Bulletin of Technical University of İstanbul rock assimilation and fractional crystallization. Earth and 44, 375–417. Planetary Science Letters 53, 189–202.

BAILEY, D.K. 1987. Mantle metasomatism-perspective and prospect. In: DE PAOLO, D.J., PERRY, F.V. & BALDRIDGE, W.S. 1992. Crustal vs mantle FITTON, J.G. & UPTON, B.G.J. (eds), Alkaline Igneous Rocks. sources of granitic magmas: A two parameter model based on Nd Geological Society, London, Special Publications 30, 1–13. isotopic studies. Royal Society of Edinburgh Transactions, Earth Sciences 83, 439–446. BAYER, H.J., HOTZL, H., JADO, A.R., ROCHER, B. & VOGGENREILER, W. 1988. Sedimentary and structural evolution of the northwest Arabian DEWEY, J.F. 1988. Extensional collapse of orogens. Tectonics 7, 1123– Red Sea Margin. Tectonophysics 204, 1–15. 1139.

24 A. GÜÇTEKİN & N. KÖPRÜBAŞI

DEWEY, J.F., HEMPTON, M.R., KIDD, W.S.F. & ŞENGÖR, A.M.C. 1986. HOFMANN, A.W. & WHITE, W.M. 1982. Mantle plums from acient oceanic Shortening of continental lithosphere; the neotectonics of eastern crust. Earth and Planetary Science Letters 58, 44–62. Anatolia, a young collision zone. In: COWARD, M.P. & RIES, A.C. HOUSEMAN, G.A., MCKENZIE, D.P. & MOLNAR, P. 1981. Convective (eds), Collision Tectonics. Geological Society Special Publications 19, 3–36. instability of a thickened boundary layer and its relevance for the thermal evolution of continental convergent belts. Journal of DIXON, J.E., FITTON, J.G. & FROST, R.T.C. 1981. The tectonic significance Geophysical Research 86, 6115–6132. of post–Carboniferous igneous activity in the North Sea basin. In: ILLING, L. & HOBSON, G.D. (eds), Petroleum Geology of the INNOCENTI, F., MANETTI, P., MAZZUOLI, R., PASQUARE G. & VILLARI, L. 1982. Continental Shelf of North West Europe. Blackwell London, 29– Anatolia and North-Western Iran. In: THORPE, R.S. (ed), Andesites: 52. Orogenic Andesites and Related Rocks. The Open University,

ELKINS-TANTON, L.T. 2004. Continental magmatism caused by Department of Earth & Environmental Sciences, Milton Keynes, lithospheric delamination. http://www.mantleplume.org/ UK, 327–349.

LithDelam.html. IRVINE, T.N. & BARAGAR, W.R.A. 1971. A guide to the chemical ENGLAND, P.C. & HOUSEMAN, G.A. 1988. The mechanics of the Tibetan classification of the common volcanic rocks. Canadian Journal of Plateau. Philosophical Transactions of the Royal Society, London Earth Sciences 8, 448–523. A326, 301–320. İLBEYLİ, N. & PEARCE, J. A. 1997. Petrogenesis of the collision-related ERDOĞAN, B., AKAY, E. & UĞUR, S.M. 1996. Geology of the Yozgat region Anatolian granitoids, Turkey. European Union of Geosciences and evolution of the collisional Çankırı basin. International (EUG), Strasbourg, France 9, p. 502. Geology Review 38, 788–806. IZZELDIN, A.Y. 1987. Seismic gravity and magnetic surveys in central part FYITKAS, M., INNOCENTI, F., MANETTI, P., PECCERILLO, A. & VILLARI, L. 1984. of the Red Sea: their interpretation and implications for the Tertiary to Quaternary evolution of volcanism in the Aegean structure and evolution of the Red Sea. Tectonophysics 143, 269– region. In: DIXON, J.E. & ROBERTSON, A.H.F. (eds), The Geological Evolution of the Eastern Mediterranean. Geological Society, 306. London, Special Publications 17, 687–699. JACKSON, J.A. & MCKENZIE, D.P. 1984. Active tectonics of the Alpine-

GERYA, T.V., YUEN, A.D. & MARECSH, W.V. 2004. Thermomechanical Himalayan belt between western Turkey and Pakistan. modelling of slab detachment. Earth and Planetary Science Letters Geophysical Journal of Royal Astronomical Society 77, 185–264. 226, 101–116. KELLER, J. 1982. Mediterranean island arcs. In: THORPE, R.S. (ed), GÖKTEN, E. & FLOYD, P. 1987. Geochemistry and tectonic environment of Andesite: Orogenic Andesite and Related Rocks. Wiley, New York, the Şarkışla area volcanic rocks in Central Anatolia: Turkey. 307–325. Mineralogical Magazine 51, 553–559. KESKİN, M. 1994. Genesis of Collision-related Volcanism on the GÖNCÜOĞLU, M.C., TOPRAK, V., KUŞÇU, I., ERLER, A. & OLGUN, E. 1991b. Erzurum–Kars Plateau, Northeastern Turkey. PhD Thesis, Orta Anadolu Masifi Batı Kesiminin Jeolojisi, Bölüm I: Güney University of Durham, UK [unpublished]. Kesim [Geology of Western Part of the Central Anatolian Massif, Part I: Southern Section]. Türkiye Petrolleri Anonim Ortaklığı KESKİN, M. 2002. FC-Modeler: A Microsoft Excel spreadsheet program (TPAO) Rapor no. 2909 [in Turkish, unpublished]. for modeling Rayleigh fractionation vectors in closed magmatic systems. Computers & Geosciences 28, 919–928. GÖNCÜOĞLU M.C. & TÜRELİ, T.K. 1993. Petrology and geodynamic interpretation of plagiogranites from Central Anatolian KESKİN, M. 2003. Magma generation by slab steepening and breakoff (Aksaray, Turkey). Turkish Journal of Earth Sciences 2, 195– beneath a subduction-accretion complex: an alternative model for 203. collision-related volcanism in Eastern Anatolia, Turkey. GÖRÜR, N., OKTAY, F.Y., SEYMEN, İ. & ŞENGÖR, A.M.C. 1984. Paleotectonic Geophysical Research Letters 30 (24), 8046, doi: 10.1029/2003 evolution of the Tuzgölü basin complex; Sedimentary record of a GL0180019. Neotethyan closure. In: DIXON, J.E. & ROBERTSON, A.H.F. (eds), The KESKİN, M. 2007. Eastern Anatolia: a hotspot in a collision zone withouth Geological Evolution of the Eastern Mediterranean. Geological a mantle plume. In: FOULGER, G.R. & JURDY, D.M. (eds), Plates, Society, London, Special Publications 17, 467–82. Plumes and Planetary Processes. Geological Society of America GÜRER, Ö.F. & ALDANMAZ, E. 2002. Origin of the Upper Cretaceous– Special Paper 430, 693–722, doi:10. 1130/2007. 2430 (32). Tertiary sedimentary basins within the Tauride-Anatolide platform in Turkey. Geological Magazine 139, 191–197. KESKİN, M., PEARCE, J.A. & MITCHELL, J.G. 1988. Volcano-stratigraphy and geochemistry of collision-related volcanism on the Erzurum- HAWKESWORTH, C.J. & NORRY, M.J. 1982. Continental Basalts and Mantle Kars Plateau, northeastern Turkey. Journal of Volcanology and Xenoliths. Shiva, Cheshire, U.K. 230–249. Geothermal Research 85, 355–404. HICKEY, R.L., FREY, F.A., GERLACH, D.C. & ESCOBAR, L.J. 1986. Multiple source basaltic arc rocks from the southern volcanic zone of the KISTLER, R.W. 1974. Phanerozoic batholiths in western North America: Andes (34o–41oS): trace element and isotopic evidence for a summary of some recent work on variations in time, space, contributions from subducted oceanic crust. Journal of chemistry, and isotopic compositions. Annual Review of Earth and Geophysical Research 91, 5963–5983. Planetary Sciences 2, 403–417.

25 GEOCHEMISTRY OF HASANDAĞ AND ERCİYES VOLCANOES

KURITANI, T., KITAGAWA, H. & NAKAMURA. E. 2005. Assimilation and MCKENZIE, D.P. & O’NIONS, R.K. 1995. The source regions of ocean fractional crystallization controlled by transport process of crustal island basalts. Journal of Petrology 36, 133–159. melt: implications from an dacite suite from Rishiri MENZIES, M.A. & HAWKESWORTH, C.J. 1987. Mantle Metasomatism. Volcano, Japan. Journal of Petrology 46, 1421–1442. Academic Press, London. KOÇYİĞİT, A. & BEYHAN, A. 1998. A new intracontinental transcurrent NELSON, K.D. 1992. Are crustal thickness variations in old mountain belts structure: the Central Anatolian Fault Zone, Turkey. like the Appalachians a consequence of lithospheric delamination? Tectonophysics 284, 317–336. Geology 20, 498–502.

KOSTOPOULOS, D.K. & JAMES, S.D. 1992. Parameterization of the melting NOTSU, K., FUJITANI, UI, T., MATSUDA, J. & ERCAN, T. 1995. Geochemical regime of the shallow upper mantle and the effects of variable features of collision-related volcanic rocks in central and eastern lithospheric stretching on mantle modal stratification and trace- Anatolia, Turkey. Journal of Volcanology and Geothermal element concentrations in magmas. Journal of Petrology 33, Research 64, 171–192. 665–691. ORMEROD, D.S., ROGERS, N.W. & HAWKESWORTH, C.J. 1991. Melting of the KÖKSAL, S. & GÖNCÜOĞLU, M.C. 2008. Sr and Nd isotopic charaesterictic lithosphere mantle: Inverse modeling of alkali olivine basalts from of some S-, I- and A- type granitoids from Central Anatolia. the Big Pine , California. Contributions to Mineralogy Turkish Journal of Earth Sciences 17, 111–127. and Petrology 108, 305–317.

KÜRKÇÜOĞLU, B., ŞEN, E., AYDAR, E., GOURGAUD, A. & GÜNDOĞDU, N. 1998. PASQUARE, G., POLI, S., VEZZOLI, L. & ZANCHI, A. 1988. Continental arc Geochemical approach to magmatic evolution of Mt. Erciyes volcanism and tectonic setting in Central Anatolia, Turkey. stratovolcano, Central Anatolia, Turkey. Journal of Volcanology Tectonophysics 146, 217–230. and Geothermal Research 85, 473–494. PEARCE, J.A. 1983. Role of the sub-continental lithosphere in magma LATIN, D.M., DIXON, J.E. & FITTON, J.G. 1989. Rift related magmatism in genesis at active continental margins. In: HAWKESWORTH, C.J. & the North Sea basin. In: BLUNDELL, D.J. & GIBBS, A. (eds), Tectonic NORRY, N.J. (eds), Continental Basalts and Mantle Xenoliths. Shiva, Evolution of the North Sea Rifts. Oxford University Press, Oxford, Cheshire, UK, 230–249. 101–104. PEARCE, J.A., BENDER, J.F., DE LONG, S.E., KIDD, W.S.F., LOW, P.J., GÜNER, LE BAS, M.J., LE MAITRE, R.W., STRECKEISEN, A. & ZANETTIN, B. 1986. A Y., ŞAROĞLU, F., YILMAZ, Y., MOORBATH, S. & MITCHELL, J.G. 1990. chemical classification of volcanic rocks based on the total Genesis of collision volcanism in Eastern Anatolia, Turkey. Journal alkalisilica diagram. Journal of Petrology 27, 445–450. of Volcanology and Geothermal Research 44, 189–229.

LE PENNEC, J.L., BOURDIER, J.L., FROGER, J.L., TEMEL, A., CAMUS, G. & PECCERILLO, A. & TAYLOR, S.R. 1976. Geochemistry of Eocene calcalkaline GOURGAUD, A. 1994. Neogene ignimbrites of the Nevşehir plateau volcanic rocks from the Kastamonu area, Northern Turkey. Central Turkey: stratigraphy, distribution and source constraints. Contributions to Mineralogy and Petrology 58, 63–91.

Journal of Volcanology and Geothermal Research 63, 59–87. PLATT, J.P. & ENGLAND, P.C. 1993. Convective removal of lithosphere

LE PICHON, X. & GAULIER, J.M. 1988. The rotation of Arabia and the beneath mountain belts: thermal and mechanical consequences. Levant fault system. Tectonophysics 153, 271–294. American Journal of Science 293, 307–336.

LYBERIS, N., YÜRÜR, T., CHOROWICZ, J., KASAPOĞLU, E. & GÜNDOĞDU, N. SHAW, D.M. 1970. Trace element fractionation during anatexis. 1992. The East Anatolian Fault: an oblique collisional belt. Geochimica et Cosmochimica Acta 34, 237–243. Tectonophysics 204, 1–15. SPERA, F.J. & BOHRSON, W.A. 2001. Energy-constrained open system magmatic processes I: General model and energy-constrained MCKENZIE, D. 1989. Some remarks on the movement of small melt fractions in the mantle. Earth and Planetary Science Letters 95, assimilation and fractional crystallization (EC-AFC) formulation. 53–72. Journal of Petrology 42, 999–1018. SUN, S.S. & MCDONOUGH, W.F. 1989. Chemical and isotopic systematics MCKENZIE, D. & YILMAZ,Y. 1991. Deformation and volcanism in western of oceanic basalts: implications for mantle composition and Turkey and the Aegean. Bulletin of Technical University 44, 345– processes. In: SAUNDERS, A.D. & NORRY, M.J. (eds), Magmatism in 373. the Ocean Basins. Geological Society, London, Special Publications MCKENZIE, D.P. 1972. Active tectonics of the Mediterranean region. 42, 313–345. Geophysical Journal of Royal Astronomical Society 30, 109–185. ŞEN, E., KÜRKÇÜOĞLU, B., AYDAR, E., GOURGAUD, A. & VINCENT, P.M. 2003. MCKENZIE, D.P. & BICKLE, M.J. 1988. The volume and composition of Volcanological evolution of stratovolcano and origin melt generated by extension of the lithosphere. Journal of of the Valibaba Tepe (Central Anatolia, Turkey). Petrology 29, 625–679. Journal of Volcanology and Geothermal Research 261, 1–22.

MCKENZIE, D. P. & O’NIONS, R. K. 1983. Mantle reservoirs and ocean ŞEN, P.A., TEMEL, A. & GOURGAUD, A. 2004. Petrogenetic modeling of island basalts. Nature 301, 229–231. Quaternary post-collisional volcanism: a case study of central and eastern Anatolia. Geological Magazine 141, 81–98. MCKENZIE, D.P. & O’NIONS, R.K. 1991. Partial melt distributions from inversion of rare earth element concentrations. Journal of ŞENGÖR, A.M.C. 1980. Principles of Turkey Neotectonics. Geological Petrology 32, 1021–1091. Association Conference Series no. 2, [in Turkish].

26 A. GÜÇTEKİN & N. KÖPRÜBAŞI

ŞENGÖR, A.M.C., GÖRÜR, N. & ŞAROĞLU, F. 1985. Strike-slip faulting and TOPRAK, V. 1994. Central Kızılırmak fault zone: northern margin of the related basin formation in zones of tectonic escape: Turkey as a Central Anatolian volcanics. Turkish Journal of Earth Sciences 3, case study. In: BIDDLE, K.T. & CHRISTIE-BLICK, N. (eds), Strike-Slip 29–38. Deformation, Basin Formation and Sedimentation. Society of TOPRAK, V. & GÖNCÜOĞLU, M.C. 1993. Tectonic control on the Economic Palaeontologists Mineralogists, Special Publications 37, development of Neogene-Quaternary Central Anatolian Volcanic 227–264. Province, Turkey: Geological Journal 28, 357–369. ŞENGÖR, A.M.C., ÖZEREN, S., ZOR, E. & GENÇ, T. 2003. East Anatolian TURNER, S., ARNAUD, N., LIU, J., ROGERS, N., HAWKESWORTH, G., HARRIS, N., high pleteau as a mantle-supported, N–S shortened domal KELLEY, S., VAN CALSTEREN, P. & DENG, M. 1996. Post-collision, structure. Geophysical Research Letters 30 (24), doi: shoshonitic volcanism on the Tibetan Plateau: implications for 10.1029/2003GL017858, convective thinning of the lithosphere and the source of ocean ŞENGÖR, A.M.C. & YILMAZ, Y. 1981. Tethyan evolution of Turkey; a plate island basalts. Journal of Petrology 37, 45–71. tectonic approach. Tectonophysics 75, 181–241. WHITE, R. & MCKENZIE, D.P. 1989. Magmatism at rift zones: the TAYLOR, S.R. & MCLENNAN, S.M. 1985. The Continental Crust: Its generation of volcanic continental margins and flood basalts. Composition and Evolution. Blackwell Scientific, Oxford. Journal of Geophysical Research 94, 7685–7729.

TEMEL, A. 1992. Kapadokya Eksplozif Volkanizmasının Petrolojik ve WONG, S.Y.M., TON, A. & WORTEL, M.J.R. 1997. Slab detachment in Jeokimyasal Özellikleri [Petrologic and Geochemical continental collision zones: an analysis of controlling parameters. Characteristics of Cappadocian Explosive Volcanism]. PhD Thesis, Geophysical Research Letters 24, 2095–2098. Hacettepe Üniversitesi [in Turkish with English abstract, YILMAZ, Y., GÜNER, Y. & ŞAROĞLU, F. 1998. Geology of the Quaternary unpublished]. volcanic centers of the east Anatolia. Journal of Volcanology and TEMEL, A., GÜNDOĞDU, N., GOURGAUD, A. & LE PENNEC, J.-L. 1998. Geothermal Research 85, 173–210. Ignimbrites of Cappadocia, Central Anatolia, Turkey: petrology, YÜRÜR, T. & CHOROWICZ, J. 1998. Recent volcanism, tectonics and plate geochemistry and evolution through time. Journal of Volcanology kinematics near the junction of the African, Arabian and Anatolian and Geothermal Research 85, 447–441. plates in the eastern Mediterranean. Journal of Volcanology and THOMPSON, A.B., MATILE, L. & ULMER, P. 2002. Some thermal constraints Geotermal Research 85, 1–15. on crustal assimilation during fractionation of hydrous, mantle- derived magmas with examples from central Alpine batholiths. Journal of Petrology 43, 403–422.

27