Mineral chemical constraints on the petrogenesis of mafic and intermediate volcanic rocks from the Erciyes and Hasandağ volcanoes, Central Turkey

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Mineral chemical constraints on the petrogenesis of mafic and intermediate volcanic rocks from the Erciyes and Hasanda˘g volcanoes, Central Turkey Nezihi Köprübas¸i a , Aykut Güc¸tekin a,∗ , Da˘ghan C¸elebi a , M. Ziya Kirmaci b a b

Department of Geological Engineering, Kocaeli University, TR-41380 I˙ zmit, Turkey Department of Geological Engineering, Black Sea Technical University, TR-61080 Trabzon, Turkey

a r t i c l e

i n f o

Article history: Received 14 February 2013 Accepted 26 November 2013 Keywords: Stratovolcanoes Magma evolution Magma mixing Hasanda˘g-Erciyes Central Anatolia

a b s t r a c t Hasanda˘g and Erciyes stratovolcanoes, which produced both calc-alkaline and alkaline eruptive products, are the two important volcanic complexes in Central Anatolia. There are three geochemical evolution stages in the history of the Hasanda˘g strato volcanic complex: (1) Kec¸ikalesi tholeiitic, (2) Hasanda˘g calc-alkaline and (3) Hasanda˘g alkaline. Volcanologic and petrologic characteristics of the Hasanda˘g and Erciyes calc-alkaline series show that water played an important role on the genesis of these rocks. These rocks are phenocryst-rich with vesicular texture, and contain hydrous mineral phases. The approximate pressure and temperature estimates obtained from the mineral chemistry studies of the Hasanda˘g strato volcanic complex indicate crystallization temperature of 1100 ◦ C with 2.5–3.4 kbar pressure interval for the first stage of Kec¸ikalesi tholeiitic volcanism, and about 850 ◦ C temperatures with 4.3–9.6 kbar pressure intervals for the second stage of Hasanda˘g calc-alkaline volcanism. The geochemical evolution of Erciyes volcanic complex also exhibits three distinct evolutionary stages: (1) Koc¸da˘g alkaline, (2) Koc¸da˘g calc-alkaline and (3) Erciyes calc-alkaline. The temperature of Koc¸da˘g alkaline volcanism is 1097–1181 ◦ C and in a range of 5.1–6.7 kbar pressure, for Koc¸da˘g calc-alkaline volcanism 850–1050 ◦ C temperature to 2.0–6.6 kbar pressure interval, and for Erciyes calc-alkaline volcanism about 950 ◦ C temperature, to 3.2–7.9 kbar pressure intervals were calculated. Polybaric origin of magma chambers for calc-alkaline and alkaline rocks and disequilibrium parameters observed in phenocrysts indicate that the rocks were affected by magma mixing processes in crustal magma chambers. The disequilibrium features of amphibole and plagioclase phenocrysts in these rocks point the latent heat in magma chambers and periodic recharging with mafic magma chambers and also show that magmas reequilibrate before the eruption. © 2013 Elsevier GmbH. All rights reserved.

1. Introduction The Central Anatolian Volcanic Province (CAVP) and Cappadocian Volcanic Provinces (CVP) are used synonymously in the literature (Toprak et al., 1994). The region known as the Cappadoccia Volcanics is located among Kırs¸ehir, Ni˘gde, Aksaray and Karapınar and covers an area of 20–25 km width and 300 km length with a NE–SW extension. Various volcanic complexes belong to this volcanic province and among the largest ones are the Hasanda˘g and Erciyes volcanoes which show tholeiitic, calc-alkaline and alkaline, and alkaline and calc-alkaline characteristics, respectively (e.g., Deniel et al., 1998; Kürkc¸üo˘glu et al., 1998; Güc¸tekin and Köprübas¸ı, 2009). These complexes contain many monogenetic and

∗ Corresponding author. Tel.: +90 2623033142. E-mail address: [email protected] (A. Güc¸tekin).

polygenetic structures such as stratovolcanoes, maar, cinder cones and domes (Aydar et al., 1995; Fig. 1). The calc-alkaline rocks are the most abundant products in these complexes. The calc-alkaline activity suggests that magmatic products were generated from a heterogeneous mantle source with varying melting conditions and affected by the crustal contamination at varying degrees (Güc¸tekin and Köprübas¸ı, 2009). Several studies stated that calc-alkaline rocks are the typical products of arc volcanism (Gill, 1981; Pearce, 1983). The main petrogenetic process responsible for the generation of calc-alkaline rocks is differentiation of basalt with fractional crystallization, but some other mechanisms are also important for crystallization of these rocks, such as partial melting of the crust, mixing of mafic and felsic magmas or the assimilation of crustal material (Gill, 1981). The evidence of magma mixing in these rocks can be recognized petrologically from disequilibrium features of phenocrysts. In the mixed magmas, the compositions and temperatures of the

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Fig. 1. (a) Map of Central Anatolia showing the location of ‘The Cappadocian Volcanic Province’ and distribution of volcanic products (modified from Toprak, 1998). Inset figure show location map of Cappadocian Volcanic Province. (b) Simplified map of Hasanda˘g stratovolcano (modified from Aydar and Gourgaud, 1998). (c) Simplified map of Erciyes stratovolcano (modified from S¸en et al., 2003).

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end-member magmas can be determined from the compositional and textural features of phenocrysts. Magma mixing processes and textural features of phenocrysts in Hasanda˘g and Erciyes volcanics have been previously discussed by several researchers (e.g., Aydar and Gourgaud, 1998; Kürkc¸üo˘glu et al., 1998). Disequilibrium phenocrysts and reaction textures were determined by some of these studies. The Hasanda˘g volcanics contain phenocrysts such as plagioclase, pyroxene, amphibole with strong disequilibrium features (Aydar and Gourgaud, 1993; Deniel et al., 1998). Another research based on the mineralogical features indicated that the isobaric–isenthalpic magma mixing of basalt and rhyolite is the major controlling process in the petrogenesis of the Hasanda˘g magmas (Do˘gan et al., 2008). Also, Do˘gan et al. (2011) suggest that the dacites from Erciyes volcano likely formed as mixing product between basaltic andesite and rhyolitic magmas. Phenocryst compositions and mineral-melt equilibria are affected by the changes in intensive parameters of magmatic systems such as temperature, pressure, water activity and oxygen fugacity. Furthermore, phenocryts crystallizing in a melt keep a record of changes in ambient conditions during their growth and so they provide an insight into the dynamics of the magmatic system during a particular period activity (Reubi et al., 2002). The main purpose of this study is to investigate crystallization conditions, such as crystallization temperatures and pressures of volcanic rocks of the Hasanda˘g and Erciyes volcanoes. Petrogenetic conditions of magma evolution are evaluated using the petrographic and mineral chemistry data from volcanic assemblages of the Hasanda˘g and Erciyes volcanoes.

2. Geological setting The Neogene-Quaternary volcanism in Central Anatolia is one of best examples of the volcanic activity related to the post-collisional stage (Notsu et al., 1995). New structural features were formed by the movement of the Arabian plate to north during Miocene (S¸engör, 1980). The Anatolian block formed by the new tectonic regime was bounded by the two important structural features, North Anatolian Fault and East Anatolian Fault (S¸engör et al., 1985). A continental collision following the closure of Neotethyan Sea along the Bitlis Suture Zone caused the westward escape and deformation of Anatolian block (McKenzie, 1972; McKenzie and Yılmaz, 1991). The volcanic activity occurred during Neogene-Quaternary in a NE–SW direction is related to this deformation (McKenzie and Yılmaz, 1991; Aydar et al., 1995). Distribution of volcanic centers along the regional scale strike-slip fault systems indicating additional effects of strike-slip faulting on melt production and eruption (Güc¸tekin and Köprübas¸ı, 2009). The total volume and areal extent of the Hasanda˘g volcano are estimated at 354 km3 and 760 km2 respectively (Aydar and Gourgaud, 2002). Products of the Hasanda˘g volcano are composed of basaltic, andesitic and pyroclastic rocks. The Kec¸ikalesi tholeiitic rocks, dated as 13 Ma (K/Ar method, Besang et al., 1977), are the first volcanic products of the Hasanda˘g stratovolcano. Kec¸ikalesi tholeiitic volcanism consists of rocks with basalt-andesite composition. The volcanism at the Hasanda˘g continued with calc-alkaline products (Aydar, 1992; Aydar and Gourgaud, 1998). Calc-alkaline volcanism is characterized mostly by andesitic, dacitic, rhyolitic rocks and widespread rhyolitic–rhyodacitic pyroclastic products as well (Deniel et al., 1998). The latest products of Hasanda˘g volcanoes are represented by alkaline rocks. The final stage of Hasanda˘g volcanism is represented by alkaline basaltic volcanism and linearly distributed cinder cones (Aydar and Gourgaud, 1998). The activity of Erciyes stratovolcano occurred in two different stages, which are of namely Koc¸da˘g and Erciyes (Kürkc¸üo˘glu et al., 1998; S¸en et al., 2003). The products of Erciyes volcanism include

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Fig. 2. Classification of the Hasanda˘g and Erciyes volcanic rocks from Central Anatolia on the total alkali versus silica (TAS) diagram of Le Bas et al. (1986). Dashed line is boundary between alkaline and subalkaline rocks of Irvine and Baragar (1971). Key to abbreviations: B, basalt; BA, basaltic andesite; A, andesite; D, dacite; R, rhyolite; TB, trachybasalt; BTA, basaltic trachyandesite; TA, trachyandesite; TD, trachydacite. Source: Data from Güc¸tekin and Köprübas¸ı (2009) and shaded area represents data from previous studies for comparison (Deniel et al., 1998; Kürkc¸üo˘glu et al., 1998).

volcanic rocks, pyroclastics and also some monogenetic vents such as dome, cinder cone and maar. The Erciyes stratovolcano, which occurred in two different stages, spread over an area of approximately 3000 km2 . Koc¸da˘g volcanism, which is the remnant of initial volcano, constitutes the eastern flank of Erciyes volcano (S¸en et al., 2003). The Koc¸da˘g stage began with alkaline volcanism and the following Erciyes stage continued with calc-alkaline volcanism. The first explosive activity was the ignimbrite eruption 2.8 Ma ago (Innocenti et al., 1975). The last dated eruption corresponding to a dacitic rocks generation in the Erciyes volcano took place 0.083 Ma ago (Notsu et al., 1995). Rocks of the Erciyes and Hasanda˘g stratovolcanoes show a broad range of composition as displayed in TAS diagram (Fig. 2) with the data as presented in Güc¸tekin and Köprübas¸ı (2009). 3. Sample selection and analytical methods Electron microprobe studies and detailed petrographic determinations were performed to acquire information on the formation conditions of minerals from representative samples from the Hasanda˘g and Erciyes volcanoes. Eight samples, which are consistent with the volcano-stratigraphical sequence, were collected from each of these volcanoes. Polished thin sections were prepared for Electron Probe Microanalysis (EPMA) at Purdue University (Indiana, USA) and Université Blaise-Pascal, Centre des Recherche Volcanologiques in France by following standard preparation and polishing steps (Picot and Johan, 1982). The composition of selected minerals was determined by wavelength dispersive X-ray analysis using a CAMECA SX50 electron microprobe. An accelerating voltage of 15 kV was used. Beam current and counting time for major elements were 20 nA and 20 s, respectively. The accuracy of the EPMA analyses was monitored using reference materials of similar composition. 4. Petrography The Hasanda˘g and Erciyes volcanic rocks have different mineralogical and textural characteristics. The petrography of Hasanda˘g volcanic rocks has already been described in detail by Aydar (1992) and Aydar and Gourgaud (1998). Petrographic characteristics of the volcanic rock samples used in analytical studies are summarized in Table 1. Phenocrysts in rocks of the Hasanda˘g volcanics observed in a wide compositional spectrum changing

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Table 1 Observed apparent mineral assemblage and modal composition of the Hasanda˘g and Erciyes stratovolcanoes. Area

˘ HASANDAG Kec¸ikalesi tholeiitic Kec¸ikalesi tholeiitic Hasanda˘g calc-alkaline Hasanda˘g calc-alkaline Hasanda˘g calc-alkaline Hasanda˘g calc-alkaline Hasanda˘g alkaline Hasanda˘g alkaline ERCI˙ YES Koc¸da˘g alkaline Koc¸da˘g alkaline Koc¸da˘g calc-alkaline Koc¸da˘g calc-alkaline Erciyes calc-alkaline Erciyes calc-alkaline Erciyes calc-alkaline Erciyes calc-alkaline

Age (Ma)

13.7 ± 0.3a

0.78b 0.034 ± 0.007c

4.39 ± 0.28d

0.9 ± 0.2e 0.15 ± 0.07f 0.9 ± 0.2e

Location

Sample no

Rock type

Texture

Apparent phenocryst assemblage (vol%) Amp

Plg

Bio

Cpx

Opx

Ol

Fe–Ti

Kec¸ikalesi Kec¸ikalesi Kale Hill Karakapı Hill Seki Hill Mahmutlu Hill Karaören Karacaören

H-26 H-28 H-2 H-14 H-36 H-42 H-49 H-72

Basalt B.andesite Andesite Andesite Andesite Basalt Basalt Basalt

Microlitic porp. Microlitic Microlitic porp. Microlitic porp. Microlitic porp. Microlitic porp. Intergranular Microlitic

– – 15 25 66 – – –

65 64 77 58 22 60 41 62

– – 1 – 4 – – –

23 16 4 5 3 10 15 9

10 8 2 10 4 5 – –

– 12 – – – 25 40 29

2 – 1 2 1 – – –

Yes¸ilyurt Yes¸ilyurt Koc¸da˘g Hill Koc¸da˘g Hill Mt. Ali Kulpak Develi S¸eyhs¸aban

E-148 E-150 E-102-b E-108 E-88 E-169 E-175 E-188

Basalt Basalt Andesite Andesite Andesite Dacite Andesite Andesite

Intergranular Intergranular Porphyritic Microlitic porp. Porphyritic Porphyritic Microlitic Microlitic

– – 7 14 24 56 – –

49 46 82 73 72 32 68 70

– – – – – – – –

10 8 1 3 3 20 16

– – 9 7 4 6 2 –

39 45 – – – – 8 12

2 1 1 3 – 3 2 2

Note: Vol %: phase present; –, phase absent; amp, amphibole; plg, plagioclase; bio, biotite; cpx, clinopyroxene, opx, orthopyroxene; ol, olivine; Fe–Ti, magnetite and ilmenite. a Besang et al. (1977). b Ercan et al. (1992). c Aydar (1992). d Ayrancı (1969). e Innocenti et al. (1975). f Ercan et al. (1994).

from basalt to rhyolite range in size between 0.3 and 2 mm. Hasanda˘g volcanic rocks include subhedral–anhedral phenocrysts and contain about 10–61 vol% phenocrysts. Calc-alkaline rocks of the Hasanda˘g volcanism include phenocrysts of plagioclase, amphibole and pyroxene. The groundmass in the rocks is microlite-rich and volcanic glass and opaque microphenocrysts also occur in some rocks. Some plagioclase phenocrysts exhibit concentric zoning and sieved texture dominantly at the rims in calc-alkaline volcanic rocks (Fig. 3a). Clinopyroxene and orthopyroxene were found in some volcanic rock of Hasanda˘g volcano as phenocrysts or

microphenocrysts and are often zoned, although clear pyroxenes are less abundant in calc-alkaline rocks. Amphiboles among the same group of rocks are widely distributed, forming euhedral and subhedral crystals. Reaction textures in amphiboles were observed in thin sections of some rocks (Fig. 3b). Slightly chloritized biotite grains are rarely present as phenocrysts in calc-alkaline volcanic rocks of Hasanda˘g. Garnet, which was described for the first time in the Hasanda˘g strato volcano by Aydar et al. (1995) and Aydar and Gourgaud (2002), occurs as euhedral microcrysts in alkaline rocks and microphenocrysts in the calc alkaline basaltic andesites.

Fig. 3. Microphotos for calc-alkaline rocks of the Hasanda˘g (a and b) and the Erciyes (c and d) volcanism: (a) clear and sieve-cored and rimmed plagioclase phenocrysts, (b) reaction textures in amphiboles, (c) euhedral, clear and sieve-cored plagioclase phenocrysts and amphibole phenocrysts with corona (d) amphibole crystals typically contain plagioclase and clinopyroxene inclusions; pl, plagioclase; am, amphibole.

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The Erciyes stratovolcano formed in two different stages as Koc¸da˘g and Erciyes volcanism (Kürkc¸üo˘glu et al., 1998). The volcanic rocks of these stages include subhedral–anhedral phenocrysts (8–56 vol%) ranging in size between 0.2 and 3.2 mm and contain phenocrysts of plagioclase, amphibole, pyroxene, olivine, and Fe–Ti oxides (Table 1). Plagioclase is the most abundant phenocryst phase, accounting for ∼46–73 vol% of the phenocryst assemblage in most of the rocks. The Koc¸da˘g volcanic rocks consist of basalt and andesite rocks with alkaline and calc-alkaline characteristics, respectively. The plagioclase phenocrysts in these rocks are concentric zoned and also typically normally zoned. Some of them exhibit sieve textures. Amphiboles belonging to calc-alkaline rocks of the Koc¸da˘g phase are abundant in andesitic rocks. Amphibole inclusions in the plagioclase phenocrysts are very common in andesites. Some basaltic samples have partially altered olivines as phenocrysts or microphenocrysts. Oxide minerals occur as inclusions in the phenocrysts of olivine and pyroxene. Calc-alkaline rocks of the Erciyes volcanism are composed of basaltic andesite, andesite, dacite, rhyodacite rocks and pyroclastic units. Regarding the textural features of these rocks, microlitic porphyritic and trachytic textures are seen in basaltic andesites but vesicular texture is also common for some samples. Plagioclase is abundant, and amphibole and biotite represent the hydrous assemblages in the Erciyes calc-alkaline rocks. Plagioclase phenocrysts show textural zoning, and sieve texture in these rocks (Fig. 3c and d). Some plagioclase phenocrysts also contain inclusions of apatite. Amphiboles are found in andesite, dacite and rhyodacite rocks. These amphiboles forming euhedral and subhedral crystals are very common. The hornblende crystals typically contain plagioclase and clinopyroxene inclusions and are characterized by common disequilibrium textures such as reaction coronas (Fig. 3d). Pyroxenes are present in most of the Erciyes calc-alkaline rocks. The abundance of orthopyroxene in dacitic rocks is remarkable. Glomeroporphyritic texture is associated with accumulation of these minerals. The textural characteristic of andesitic and dacitic rocks call attention to magma mixing process during the formation of these rocks. The Fe–Ti oxides are present as either accessory minerals or inclusions. 5. Mineral chemistry 5.1. Olivine Although olivine is common mineral in basaltic rocks, tholeiitic and calc alkaline rocks from these volcanoes contain only small amount of olivine as phenocryst and microphenocryst. No significant compositional difference was found for the rim to core of olivines from all rock types. The olivine composition of Hasanda˘g volcanics is in the following ranges; Fo77 –Fo75 for the Kec¸ikalesi tholeiitic volcanism; Fo71 for microphenocryst; Fo86 –Fo71 for the Hasanda˘g calc-alkaline volcanism, Fo82 –Fo72 for the Hasanda˘g alkaline volcanism and Fo69 for microlites. Composition of olivine for the Erciyes strato volcano ranges from Fo90 –Fo89 in calc-alkaline rocks and Fo89 –Fo87 in alkaline rocks (Table 2). 5.2. Pyroxene Pyroxenes exist in all the groups of rocks from the Hasanda˘g and Erciyes strato volcanoes. Orthopyroxene and clinopyroxene pairs occur in Kec¸ikalesi tholeiitic rocks in the Hasanda˘g suite and Koc¸da˘g calc-alkaline rocks in the Erciyes suite. Pyroxenes are augite and hypersthene in composition in the rocks of Kec¸ikalesi tholeiitic volcanism, and augite, bronzite and hypersthene in the Hasanda˘g calc-alkaline rocks. Pyroxenes also exist as diopside and

5

Fig. 4. Minor element variations of clinopyroxenes shown by plots of (a) stoichiometric Ti versus Al (per formula unit); and (b) MnO contents versus the molar percentage of ferrosilite (Fs).

salite in Koc¸da˘g alkaline rocks, as augite and bronzite in Koc¸da˘g calc-alkaline rocks and as augite, diopside, salite and hypersthene in Erciyes calc-alkaline rocks (Tables 3 and 4). Experimental and petrological investigations showed that Ti and Al contents of pyroxenes are strongly growth-rate dependent while the concentration of Ca, Mg and Fe may not be significantly affected by cooling rates (Grove and Bence, 1977; Gamble and Taylor, 1980). Slight positive correlation is observed between Al and Ti contents of clinopyroxenes analyzed from all the samples. However, Erciyes and Koc¸da˘g calc-alkaline, and Kec¸ikalesi tholeiitic rocks seem to have lower Ti and Al contents than Koc¸da˘g and Hasanda˘g alkaline, and Hasanda˘g calc-alkaline volcanics. Therefore, volcanic rocks containing higher Ti and Al bearing clinopyroxenes probably reflect more elevated cooling rates (Fig. 4a). Fig. 4b indicates that, almost for all rock groups, there is an increase in MnO concentration, and it coincides with an increase in Fs. Since Mn+2 can substitute for Fe+2 not only in pyroxene but also in olivine and/or Fe–Ti oxides, this may be explained by the olivine crystallization (with or without Fe–Ti oxides) prior to pyroxene crystallization for the later-formed volcanics from this rock. 5.3. Plagioclase Plagioclase crystallizes in all the stages of volcanic evolution of the Hasanda˘g and Erciyes volcanoes. Plagioclases in the rock groups are observed as pheno, micro and xenocrysts. Anorthite contents of plagioclase crystals in Hasanda˘g and Erciyes volcanics are 29–74 and 33–75, respectively (Table 5). The calc-alkaline volcanics from both stratovolcanoes contain plagioclase phenocrysts with complex (both normal and reverse) compositional zoning (Table 5). 5.4. Amphibole and biotite Amphiboles were analyzed for only the Hasanda˘g calc-alkaline, the Koc¸da˘g and Erciyes calc-alkaline rocks (Table 6a). Since all the analyzed amphiboles are (Ca + Na)MA > 1.34 and (Na)MA < 0.67, they are classified as calcic amphiboles according to Leake (1978)

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Table 2 Representative electron-microprobe analyses of olivine phenocrysts and microphenocrysts in volcanic rocks of Hasanda˘g and Erciyes. Olivine Sample no

H-28

(c)core/(r)rim

c

c

c

r

c

r

c

r

c

c

c

c

SiO2 FeO MnO MgO CaO

36.87 22.54 0.46 38.43 0.23

38.88 20.60 0.48 39.55 0.14

39.47 13.26 0.16 45.74 0.19

39.08 17.16 0.31 42.39 0.16

38.47 22.54 0.01 37.52 0.26

38.35 24.37 0.88 35.89 0.36

38.09 22.14 0.57 38.29 0.26

37.97 23.94 0.68 36.63 0.35

39.83 10.42 0.20 48.72 0.32

39.90 11.00 0.21 48.30 0.33

38.24 11.46 0.21 48.57 0.30

38.30 12.10 0.22 48.16 0.31

39.94 8.93 0.15 50.21 0.20

39.83 9.94 0.16 49.03 0.14

Total

98.67

99.79

99.20

99.43

98.95

99.96

99.49

99.75

99.82

99.99

99.11

99.33

100.09

99.46

Si Fe Mn Mg Ca

0.98 0.50 0.01 1.52 0.01

1.01 0.45 0.01 1.52 0.00

0.99 0.28 0.00 1.72 0.00

1.00 0.37 0.01 1.62 0.00

1.01 0.50 0.00 1.47 0.01

1.01 0.54 0.02 1.41 0.01

1.00 0.48 0.01 1.50 0.01

1.00 0.53 0.02 1.44 0.01

0.98 0.22 0.00 1.80 0.01

0.99 0.23 0.00 1.78 0.01

0.96 0.24 0.00 1.82 0.01

0.96 0.25 0.00 1.80 0.01

0.98 0.18 0.00 1.84 0.01

0.99 0.21 0.00 1.81 0.00

Total

3.02

2.99

3.00

3.00

2.99

2.99

3.00

3.00

3.01

3.01

3.04

3.04

3.02

3.01

75.24 24.76

77.39 22.61

86.02 13.98

81.49 18.51

74.80 25.20

72.42 27.58

75.51 24.49

73.17 26.83

89.29 10.71

88.67 11.33

88.31 11.69

87.65 12.35

90.93 9.07

89.79 10.21

Fo Fa

H-42

H-49

H-72

classification. As shown in Fig. 5a, where the amphibole analyses are plotted in Hawthorne (1981) classification diagram, the amphiboles in Koc¸da˘g calc-alkaline rocks fall into edenite and paragasite field, whereas the Hasanda˘g and Erciyes calc-alkaline rocks plot into edenite and edenitic hornblende fields. Experimental studies indicated that positive correlation between AlIV and (Na + K) content of amphiboles represent the temperature increase (Helz, 1973). Fig. 5b indicates that amphiboles of the Hasanda˘g and Erciyes calc-alkaline rocks were crystallized under different temperature and pressure conditions. Biotites were only found in some of the calc-alkaline volcanic rocks from the Hasanda˘g volcano. Regarding Ti, Al and Mg/Fe ratios of biotites, Mg/Fe ratios contents are shown Table 6b.

E-148

E-150

E-175 c

c

5.5. Fe–Ti oxides Compositions of Fe–Ti oxides are listed in Table 7. In the Hasanda˘g suite, Fe–Ti oxides occur in Kec¸ikalesi thoeliites and Hasanda˘g calc-alkaline volcanic rocks. Plotting of data on the triangular diagram for the Fe–Ti–O system shows that the major part of oxides from the Kec¸ikalesi and Hasanda˘g volcanics are formed as titanomagnetite with a lesser amount of ilmenite (Fig. 6). Fe–Ti oxides are observed in all rock groups of the Erciyes strato volcano. According to Bacon and Hirschmann (1988) triangular diagram, some of the samples from the Hasanda˘g calcalkaline, Erciyes calc-alkaline and Koc¸da˘g alkaline suites fall close to the ilmenite fields, whereas some samples from the Erciyes calc-alkaline rocks, Koc¸da˘g alkaline-calc-alkaline, Hasanda˘g calcalkaline and Kec¸ikalesi tholeiitic rocks plot close to the line of ulvospinel solid solution (Fig. 6). 6. Discussion 6.1. Mineral-melt equilibrium Phenocryst compositions and mineral-melt equilibrium are sensitive to variations in the critical intensive parameters of magmatic

Fig. 5. (a) Amphibole phenocrysts plotted on the classification diagram of Hawthorne (1981). (b) The Al[IV] versus (Na + K)A diagram shows site occupancy for amphibole phenocrysts.

Fig. 6. Triangular diagram for the Fe–Ti oxides in the Fe–Ti–O systems.

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H-2

(c)core/(r)rim

c

c

H-14 c

c

H-26 c

r

H-28

SiO2 TiO2 Al2 O3 FeO MnO MgO CaO Na2 O

51.03 0.99 4.35 8.21 0.20 15.85 18.75 0.36

49.40 0.99 4.27 9.03 0.26 14.90 19.17 0.34

51.43 1.00 4.27 8.05 0.19 14.42 19.12 0.34

49.80 1.00 4.18 8.85 0.24 13.56 19.55 0.32

50.96 0.67 1.73 11.45 0.33 15.15 18.02 0.25

50.72 0.76 2.07 10.95 0.30 14.44 19.28 0.27

Total

99.80

98.43

99.19

97.54

98.61

Si Ti Al Fe Mn Mg Ca Na

1.89 0.03 0.19 0.25 0.01 0.87 0.74 0.03

1.87 0.03 0.19 0.29 0.01 0.84 0.78 0.02

1.91 0.03 0.19 0.25 0.01 0.80 0.76 0.02

1.90 0.03 0.19 0.28 0.01 0.77 0.80 0.02

Total

4.01

4.02

3.98

Mg# En Fs Wo

77.47 46.70 13.58 39.72

74.64 44.17 15.01 40.83

76.15 44.12 13.82 42.06

c

H-36

H-42

H-49

E-102b

E-108

E-148

E-150

E-175

E-188

r

c

c

c

c

c

c

c

c

c

c

c

c

c

c

c

c

c

c

52.65 0.31 1.27 10.63 0.61 14.74 19.56 0.24

51.97 0.49 2.04 9.21 0.39 14.60 20.64 0.25

50.03 0.94 4.15 8.38 0.19 15.38 19.33 0.36

49.90 0.95 4.07 9.21 0.25 14.47 19.76 0.33

49.08 1.38 3.04 9.15 0.31 14.81 19.58 0.39

51.66 0.76 3.50 7.42 0.21 17.25 17.94 0.24

48.37 1.13 4.16 8.33 0.30 13.50 22.16 0.39

46.41 1.56 6.98 6.24 0.17 13.45 23.20 0.32

50.97 0.46 1.44 9.26 0.33 14.53 20.75 0.41

49.96 0.93 3.21 10.22 0.28 14.91 18.19 0.54

51.42 0.43 1.40 9.25 0.33 14.37 21.99 0.44

50.46 0.88 3.05 10.21 0.28 14.74 19.46 0.54

49.33 1.19 4.81 6.76 0.14 14.02 22.60 0.27

51.01 0.60 3.43 4.28 0.10 15.74 22.98 0.27

47.85 1.20 4.57 6.55 0.12 14.44 23.05 0.25

49.34 1.13 4.04 8.11 0.22 13.90 22.60 0.35

50.72 0.73 1.94 9.86 0.30 13.58 19.40 0.34

50.30 0.92 3.09 10.49 0.26 14.78 18.47 0.53

48.99 0.57 3.95 9.85 0.47 12.46 22.28 0.63

49.43 0.65 4.41 7.02 0.16 14.07 22.73 0.39

98.78

100.01

99.62

99.14

98.95

97.81

99.15

98.38

98.41

98.19

98.30

99.70

99.69

99.13

98.47

98.06

99.72

96.94

98.91

99.25

98.94

1.93 0.02 0.08 0.36 0.01 0.86 0.73 0.02

1.93 0.02 0.09 0.35 0.01 0.82 0.78 0.02

1.97 0.01 0.06 0.33 0.02 0.82 0.78 0.02

1.94 0.01 0.09 0.29 0.01 0.81 0.83 0.02

1.87 0.03 0.18 0.26 0.01 0.86 0.77 0.03

1.88 0.03 0.18 0.29 0.01 0.81 0.80 0.02

1.88 0.04 0.14 0.29 0.01 0.84 0.80 0.03

1.91 0.02 0.15 0.23 0.01 0.95 0.71 0.02

1.84 0.03 0.19 0.27 0.01 0.77 0.91 0.03

1.76 0.04 0.31 0.20 0.01 0.76 0.94 0.02

1.94 0.01 0.06 0.30 0.01 0.83 0.85 0.03

1.90 0.03 0.14 0.32 0.01 0.84 0.74 0.04

1.94 0.01 0.06 0.29 0.01 0.81 0.89 0.03

1.89 0.02 0.13 0.32 0.01 0.83 0.78 0.04

1.85 0.03 0.21 0.21 0.00 0.78 0.91 0.02

1.90 0.02 0.15 0.13 0.00 0.87 0.92 0.02

1.82 0.03 0.21 0.21 0.00 0.82 0.94 0.02

1.85 0.03 0.18 0.25 0.01 0.78 0.91 0.03

1.95 0.02 0.09 0.32 0.01 0.78 0.80 0.03

1.90 0.03 0.14 0.33 0.01 0.83 0.75 0.04

1.87 0.02 0.18 0.31 0.02 0.71 0.91 0.05

1.86 0.02 0.20 0.22 0.01 0.79 0.92 0.03

3.99

4.02

4.02

4.01

4.01

4.02

4.02

4.03

4.00

4.04

4.05

4.03

4.03

4.04

4.03

4.02

4.02

4.05

4.04

4.00

4.02

4.05

4.04

73.21 41.63 15.23 43.13

70.24 43.89 18.60 37.51

70.16 41.94 17.83 40.23

71.20 42.40 17.15 40.45

73.87 42.19 14.93 42.88

76.59 45.28 13.84 40.88

73.69 42.76 15.27 41.97

74.26 43.53 15.09 41.37

80.57 50.30 12.13 37.58

74.29 39.59 13.70 46.70

79.35 40.00 10.41 49.59

73.66 41.95 15.00 43.05

72.23 44.22 17.00 38.78

73.46 40.63 14.68 44.69

72.03 42.79 16.62 40.60

78.72 41.17 11.13 47.70

86.78 45.43 6.92 47.65

79.70 41.63 10.60 47.77

75.33 40.06 13.12 46.82

71.06 41.08 16.73 42.18

71.52 43.55 17.34 39.11

69.28 36.65 16.25 47.10

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Table 3 Representative microprobe analyses of clinopyroxene phenocrysts and microphenocrysts in volcanic rocks of Hasanda˘g and Erciyes.

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Table 4 Representative microprobe analyses of orthopyroxene phenocrysts and microphenocrysts in volcanic rocks of Hasanda˘g and Erciyes. Orthopyroxene Sample no

H-2

H-14

H-26

H-36

E-88

(c)core/(r)rim

c

c

c

c

SiO2 TiO2 Al2 O3 FeO MnO MgO CaO

52.84 0.15 0.60 20.08 1.05 24.10 0.67

53.26 0.15 0.59 19.67 0.96 21.93 0.68

52.49 0.22 1.01 15.75 0.36 24.46 1.40

52.67 0.41 1.13 19.04 0.45 23.27 2.11

Total

99.51

97.29

95.78

Si Ti Al Fe Mn Mg Ca

1.97 0.00 0.03 0.62 0.03 1.34 0.03

2.02 0.00 0.03 0.62 0.03 1.24 0.03

Total

4.02

Mg# En Fs Wo

68.15 67.24 31.42 1.34

c

c

c

r

c

c

c

c

53.18 0.37 1.11 18.70 0.45 23.10 2.07

53.92 0.14 0.57 19.68 1.00 23.40 0.69

52.70 0.15 1.66 21.71 0.66 22.85 0.61

52.70 0.17 0.86 19.83 0.65 23.46 0.76

52.41 0.36 1.04 18.03 0.56 24.31 1.63

53.28 0.24 0.82 15.22 0.42 26.81 1.54

52.93 0.35 0.99 18.01 0.55 24.04 1.78

53.81 0.23 0.78 15.20 0.42 26.50 1.67

99.13

99.04

99.41

100.38

98.47

98.42

98.41

98.76

98.71

1.99 0.01 0.05 0.50 0.01 1.38 0.06

1.96 0.01 0.05 0.59 0.01 1.29 0.08

1.97 0.01 0.05 0.58 0.01 1.28 0.08

2.00 0.00 0.02 0.61 0.03 1.29 0.03

1.95 0.00 0.07 0.67 0.02 1.26 0.02

1.97 0.00 0.04 0.62 0.02 1.31 0.03

1.96 0.01 0.05 0.56 0.02 1.35 0.07

1.96 0.01 0.04 0.47 0.01 1.47 0.06

1.97 0.01 0.04 0.56 0.02 1.33 0.07

1.97 0.01 0.03 0.47 0.01 1.45 0.07

3.97

3.99

4.00

3.99

3.99

4.01

4.00

4.01

4.02

4.01

4.01

66.52 65.55 32.98 1.47

73.47 71.31 25.75 2.94

68.55 65.62 30.11 4.28

68.76 65.85 29.91 4.24

67.94 66.98 31.60 1.42

65.23 64.42 34.34 1.24

67.83 66.78 31.67 1.55

70.62 68.30 28.41 3.29

75.84 73.55 23.43 3.03

70.41 67.87 28.52 3.61

75.65 73.14 23.54 3.32

systems and these variations can be used to constrain the crystallization environments of phenocrysts in basaltic rocks (Damasceno et al., 2002). During magma storage and ascent, changes in melt composition occur due to fractional crystallization or magma mixing, and changes in the physical conditions of crystallization occur due to cooling, decompression or magma mixing (Aldanmaz, 2006). The reason for the changes in melt compositions is the magma mixing or fractional crystallization during magma storage or ascend. There may be also changes in physical conditions of crystallization because of cooling due to the magma mixing or decompression. Mixing processes due to convections may occur between different zones of the same chamber or different magma groups (Couch et al., 2001). The signs of these processes can be determined with compositional and textural zoning of phenocrysts (Hibbard, 1981; Davidson et al., 1998; Ginibre et al., 2002; Troll and Schmincke, 2002). Such compositional and textural zoning in phenocrysts shows that mineral groups are in disequilibrium with each other before or during the eruptions of magma groups. There are several petrographic signs, which indicate disequilibrium parameters of phenocrysts in the rocks. Zoning in plagioclase and pyroxene phenocrysts and reaction rims around amphibole phenocrysts are the signs of disequilibrium. Plagioclase zoning records physical and chemical changes in magmatic liquidus from which the crystals grow (e.g., Vance, 1965; Wiebe, 1968; Loomis and Welber, 1982; Pearce et al., 1987; Blundy and Shimizu, 1991). Experimental investigations examined the effects of cooling and quenching (Lofgren, 1974), thermal and compositional disequilibrium produced by magma mixing (Lofgren and Norrıs, 1981; Tsuchıyama, 1985). Sieve texture exists in dissolved parts of plagioclases and is considered to be originated from the reaction with magma (MacKenzie et al., 1998; Shelley, 1993). In a group of plagioclases, the presence of sieve texture in some plagioclases indicates a magmatic corrosion. On the contrary, the absence of this texture in some plagioclases implies that plagioclase crystallization occurred at different periods. According to Gill (1981), the reaction of an amphibole phenocryst with interstitial melt takes place when the lava reaches to the surface, or due to the rise of the temperature in magma chamber during the eruption. The occurrence of opaque reaction

E-102b

E-108

corona around the amphiboles is facilitated by the low pressure of disequilibrium (Wilson, 1993). The early formed amphiboles break down as a result of decompression, incongruent melting, eventually forming corona-textured xenocryst (Aldanmaz, 2006).

6.1.1. Olivine-liquid equilibrium In their experimental work on olivine-melt equilibria in basaltic systems, Roeder and Emslie (1970) state that the exchange coefficient (KD = [Fe/Mg]rock ) associated with the distribution of Mg and Fe between olivine and liquid must be 0.3 ± 0.03 if equilibrium is attained. These KD variations, at least in part, reflect melt compositional control on the relative activity of iron and magnesium oxides in silicate melts (e.g., Doyle and Naldrett, 1986; Doyle, 1989; Gaillard et al., 2001, 2003). Olivine-melt pairs in terms of Fe–Mg exchange between olivine and coexisting melt indicate that KD varies with bulk composition and oxygen fugacity (Kılınc¸ and Gerke, 2003). To understand the olivine/liquid equilibria relationship, the diagram was formed using Fe+2 Mg–1 ratio for the all rocks samples. In this diagram, Fe2 O3 /FeO whole rock weight ratios were used and the temperature was taken as 1000 ◦ C and Fe expression was assumed as 0.24 in nickel–nickel oxide oxygen fugacity according to Kılınc¸ et al. (1983) (Ni–NiO; Huebner and Sato, 1970). Fig. 7 illustrates that among the calc-alkaline rocks of the Hasanda˘g, only few olivine crystals are within equilibrium range and all the olivine grains from all the other samples of Hasanda˘g and Erciyes volcanoes are found to be out of equilibrium range. This situation can be explained that the olivine grains were either formed as accumulated xenocrysts or crystallized from relatively evolved magmas.

6.1.2. Clinopyroxene-liquid equilibrium In Fig. 8, compositions of clinopyroxene phenocryst cores are compared with those of whole rocks. The relationships illustrated are consistent with equilibrium KD = [Fe/Mg]cpx /[Fe2+ /Mg]rock = 0.2 and 0.3 which are similar to the values (0.20–0.25) found experimentally at 1 atm for silica-saturated and undersaturated rocks (Grove and Baker, 1984; Kennedy et al., 1990). In this figure, the majority of the samples from the Hasanda˘g and Erciyes volcanoes

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H-2

H-14

H-26

(c)core/(r)rim

c

c

c

c

r

c

r

c

r

c

r

SiO2 TiO2 Al2 O3 FeO CaO Na2 O K2 O

57.15 0.01 26.02 0.23 6.58 7.62 0.49

52.83 0.02 29.16 0.76 10.43 5.22 0.30

57.43 0.00 25.50 0.23 6.71 7.16 0.50

53.20 0.07 27.96 0.92 11.58 4.78 0.19

50.63 0.04 29.94 0.92 13.65 3.64 0.20

49.47 0.06 31.16 0.87 15.03 2.68 0.11

48.91 0.05 28.24 2.41 13.74 2.51 0.15

59.53 0.00 24.78 0.23 6.92 7.54 0.54

59.71 0.01 24.23 0.27 6.23 7.74 0.76

53.65 0.01 28.85 0.30 11.85 4.59 0.23

52.78 0.15 28.12 0.80 11.58 4.40 0.32

50.82 0.00 30.74 0.81 14.46 3.09 0.09

50.57 0.01 30.28 0.77 14.30 3.05 0.21

49.83 0.05 31.46 0.78 14.91 2.91 0.08

49.58 0.07 30.99 0.74 14.74 2.88 0.17

Total

98.19

98.88

97.61

98.86

99.12

99.52

97.63

99.60

99.01

99.49

98.25

100.21

99.35

100.19

Si Ti Al Fe Ca Na K

2.61 0.00 1.40 0.01 0.32 0.67 0.03

2.42 0.00 1.58 0.03 0.51 0.46 0.02

2.63 0.00 1.38 0.01 0.33 0.64 0.03

2.44 0.00 1.51 0.04 0.57 0.43 0.01

2.34 0.00 1.63 0.04 0.67 0.33 0.01

2.28 0.00 1.69 0.03 0.74 0.24 0.01

2.31 0.00 1.57 0.10 0.69 0.23 0.01

2.67 0.00 1.31 0.01 0.33 0.66 0.03

2.70 0.00 1.29 0.01 0.30 0.68 0.04

2.44 0.00 1.55 0.01 0.58 0.40 0.01

2.44 0.01 1.53 0.03 0.57 0.39 0.02

2.32 0.00 1.65 0.03 0.71 0.27 0.01

2.33 0.00 1.64 0.03 0.70 0.27 0.01

Total

5.04

5.03

5.01

5.01

5.02

5.00

5.02

5.02

5.02

5.00

5.00

5.00

31.40 65.82 2.78

51.53 46.71 1.76

33.11 63.95 2.93

56.59 42.29 1.12

66.65 32.19 1.16

75.12 24.26 0.62

74.42 24.59 0.99

32.64 64.34 3.02

29.47 66.25 4.27

57.99 40.67 1.34

58.11 39.96 1.93

71.74 27.73 0.53

An Ab Or

H-28

H-36

H-42

H-49 c

H-72

E-102b

E-108

E-148

E-150

E-169

E-175

r

c

c

c

c

c

c

c

c

c

c

52.75 0.01 29.82 0.48 13.10 4.15 0.13

52.87 0.00 28.98 0.47 12.27 4.53 0.13

57.16 0.01 26.03 0.32 8.57 6.30 0.55

57.73 0.01 26.08 0.31 8.91 6.24 0.48

48.47 0.07 31.08 1.12 15.01 2.67 0.22

48.80 0.06 31.23 1.10 15.64 2.75 0.23

50.74 0.06 28.32 1.23 13.95 3.56 0.41

52.22 0.01 29.85 0.49 12.83 4.01 0.14

50.32 0.05 29.82 0.61 13.57 3.56 0.33

52.36 0.07 27.56 0.81 11.40 4.52 0.53

58.15 0.03 25.42 0.26 7.83 6.73 0.68

54.77 0.04 26.90 0.58 10.17 4.27 1.29

99.35

100.49

99.28

99.01

99.85

99.00

99.90

98.38

99.63

98.42

97.58

99.14

98.12

2.28 0.00 1.69 0.03 0.73 0.26 0.00

2.28 0.00 1.68 0.03 0.73 0.26 0.01

2.39 0.00 1.59 0.02 0.63 0.36 0.01

2.42 0.00 1.56 0.02 0.60 0.40 0.01

2.59 0.00 1.39 0.00 0.41 0.55 0.03

2.60 0.00 1.38 0.01 0.43 0.54 0.03

2.25 0.00 1.70 0.04 0.74 0.24 0.01

2.25 0.00 1.70 0.04 0.77 0.25 0.01

2.37 0.00 1.56 0.05 0.70 0.32 0.02

2.38 0.00 1.60 0.02 0.63 0.35 0.01

2.33 0.00 1.63 0.02 0.67 0.32 0.01

2.44 0.00 1.51 0.03 0.56 0.40 0.03

2.62 0.00 1.35 0.00 0.37 0.58 0.03

2.52 0.00 1.46 0.02 0.50 0.38 0.07

5.00

5.01

5.00

5.00

5.01

5.00

5.00

5.02

5.03

5.03

5.00

5.01

5.01

5.00

4.97

71.28 27.51 1.22

73.55 26.01 0.44

73.16 25.83 1.01

63.10 36.15 0.75

59.48 39.75 0.77

41.55 55.27 3.17

42.90 54.35 2.75

74.69 24.02 1.29

74.88 23.80 1.32

66.83 30.86 2.31

63.39 35.80 0.80

66.49 31.56 1.95

56.40 40.47 3.13

37.63 58.48 3.90

52.32 39.79 7.89

c

c

E-88 r

c

E-188

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Sample no

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Table 5 Representative microprobe analyses of plagioclase phenocrysts and microphenocrysts in volcanic rocks of Hasanda˘g and Erciyes.

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10

(a) Amphibole

(b) Biotite H-14

E-102b

E-88

E-169

E-108

H-2

H-36

H-2

(c)core/(r)rim

c

c

c

c

c

r

c

c

c

c

r

c

c

c

c

c

SiO2 TiO2 Al2 O3 FeO MnO MgO CaO Na2 O K2 O

45.82 1.17 9.28 12.66 0.32 14.50 12.08 1.49 0.49

44.93 2.17 9.20 12.33 0.24 14.58 11.89 2.02 0.39

45.47 2.13 9.11 12.08 0.22 13.27 12.13 1.90 0.40

45.12 2.66 9.99 12.37 0.16 12.63 12.07 1.92 0.43

45.57 2.00 9.01 13.33 0.24 13.93 10.93 1.78 0.34

45.92 2.07 8.60 12.85 0.22 14.39 10.98 1.80 0.35

45.28 1.51 7.76 14.37 0.44 13.14 11.46 1.44 0.80

46.38 1.40 7.26 13.55 0.43 13.90 11.59 1.37 0.68

45.73 1.43 7.78 14.38 0.44 15.11 11.46 1.34 0.81

46.85 1.33 7.01 13.56 0.43 15.29 11.59 1.40 0.60

45.72 1.46 7.61 13.39 0.39 13.97 11.53 1.46 0.77

44.48 2.26 9.03 12.20 0.24 16.01 11.43 2.12 0.42

SiO2 TiO2 Al2 O3 FeO MnO MgO Na2 O K2 O

41.27 4.56 14.18 13.65 0.09 15.62 0.72 8.38

41.04 4.54 13.94 13.44 0.06 15.59 0.69 8.16

37.52 4.75 13.77 14.07 0.08 15.17 0.72 9.21

37.31 4.74 13.53 13.85 0.06 15.14 0.68 8.97

Total

97.84

97.81

96.77

97.36

97.15

97.21

96.19

96.61

98.49

98.08

96.33

98.24

Total

98.53

97.51

95.34

94.31

6.71 0.13 1.28 0.31 1.55 0.04 3.17 1.90 0.42 0.09

6.60 0.24 1.40 0.19 1.51 0.03 3.19 1.87 0.58 0.07

6.73 0.24 1.27 0.32 1.49 0.03 2.93 1.92 0.54 0.08

6.64 0.29 1.36 0.37 1.52 0.02 2.77 1.90 0.55 0.08

6.72 0.22 1.28 0.29 1.65 0.03 3.06 1.73 0.51 0.06

6.76 0.23 1.24 0.25 1.58 0.03 3.16 1.73 0.51 0.07

6.82 0.17 1.18 0.20 1.81 0.06 2.95 1.85 0.42 0.15

6.91 0.16 1.08 0.18 1.69 0.05 3.09 1.85 0.40 0.13

6.73 0.16 1.27 0.07 1.77 0.05 3.31 1.81 0.38 0.15

6.87 0.15 1.12 0.08 1.66 0.05 3.34 1.82 0.40 0.11

6.84 0.16 1.16 0.18 1.68 0.05 3.12 1.85 0.42 0.15

6.51 0.25 1.49 0.06 1.49 0.03 3.49 1.79 0.60 0.08

Si Ti Al Fe Mn Mg Na K

5.84 0.49 2.37 1.62 0.01 3.30 0.20 1.51

5.86 0.49 2.35 1.61 0.01 3.32 0.19 1.49

5.59 0.53 2.42 1.75 0.01 3.37 0.21 1.75

5.61 0.54 2.40 1.74 0.01 3.39 0.20 1.72

Total

15.34

15.32

15.64

15.61

Total

15.62

15.69

15.55

15.51

15.55

15.56

15.61

15.56

15.71

15.63

15.61

15.80

Mg#

0.67

0.68

0.66

0.65

0.65

0.66

0.61

0.64

0.65

0.67

0.65

0.70

Mg/Fe

2.03

2.06

1.92

1.94

Si Ti AlIV AlVI Fe Mn Mg Ca Na K

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Table 6 (a) Representative microprobe analyses of amphibole phenocrysts and microphenocrysts in volcanic rocks of Hasanda˘g and Erciyes. (b) Representative microprobe analyses of biotite phenocrysts.

E-108

E-148

E-150

Ilm

Titano-mag

Ilm

Titano-mag

Titano-mag

Titano-mag

Titano-mag

Ilm

Mag

Ilm

Mag

Titano-mag

Ilm

Titano-mag

Ilm

Ilm

Titano-mag

Titano-mag

Titano-mag

Titano-mag

SiO2 TiO2 Al2 O3 Fe2 O3 FeO MnO MgO Cr2 O3

0.09 44.38 0.11 14.24 35.00 0.58 2.31 0.00

0.07 12.09 0.99 42.58 38.65 0.49 1.27 0.16

0.09 44.83 0.10 14.36 35.02 0.54 2.10 0.15

0.07 12.22 0.95 43.40 39.45 0.45 1.16 0.16

0.03 9.76 2.41 46.3 36.9 0.47 1.7 0.44

0.08 9.41 2.34 46.4 35.6 0.5 2.09 0.33

0.08 12.59 0.96 42.7 40.1 0.47 1.23 0.16

0.00 46.22 0.1 13.2 36.9 0.56 2.24 0.00

0.09 3.28 1.72 63.02 33.81 0.48 0.59 0.00

0.08 4.63 1.48 1.6 100.6 0.37 1.23 0.00

0.89 4.25 1.03 58.29 35.28 0.87 0.04 0.00

0.08 22.45 2.64 23.53 48.60 0.81 1.99 0.18

0.08 43.86 0.07 18.35 34.45 0.61 2.19 0.18

0.07 21.78 2.67 25.23 47.71 0.82 2.19 0.16

0.06 43.42 0.05 20.34 33.68 0.63 2.41 0.15

0.03 39.40 0.31 17.61 30.98 0.34 2.30 0.01

0.17 10.52 3.37 45.21 38.04 0.75 1.78 0.12

0.50 9.56 3.35 45.63 37.01 0.72 1.77 0.13

0.05 16.98 2.78 33.26 43.12 0.85 2.25 1.43

0.05 20.18 2.36 28.07 46.31 0.77 1.87 0.05

Total

96.87

96.41

98.17

97.98

93.42

92.09

94.13

98.05

103.12

100.07

100.88

100.38

100.10

100.73

101.05

91.02

100.06

98.89

100.94

99.78

Si Ti Al Fe+3 Fe+2

H-2

H-14

H-26

H-36

E-102b

0.002 0.860 0.003

0.003 0.354 0.045

0.002 0.859 0.003

0.003 0.352 0.043

0.001 0.278 0.108

0.003 0.271 0.106

0.003 0.361 0.043

0.001 0.873 0.003

0.003 0.091 0.074

0.002 0.082 0.041

0.034 0.120 0.046

0.003 0.616 0.113

0.002 0.825 0.002

E-169

E-175

E-188

0.003 0.595 0.114

0.001 0.809 0.001

0.003 0.815 0.015

0.006 0.292 0.146

0.019 0.268 0.147

0.002 0.464 0.119

0.002 0.559 0.102

0.276

1.244

0.275

1.249

1.321

1.335

1.224

0.25

1.741

1.789

1.645

0.645

0.345

0.689

0.374

0.363

1.255

1.279

0.909

0.778

Mn Mg Cr

0.753 0.013 0.088 0.000

1.255 0.016 0.074 0.005

0.763 0.012 0.080 0.003

1.262 0.015 0.066 0.005

1.167 0.015 0.096 0.013

1.138 0.016 0.119 0.010

1.277 0.015 0.07 0.005

0.775 0.012 0.084 0.000

1.038 0.015 0.032 0.000

0.031 0.007 0.043 0.000

1.118 0.028 0.002 0.000

1.481 0.025 0.108 0.005

0.720 0.013 0.082 0.004

1.448 0.025 0.118 0.005

0.703 0.013 0.089 0.003

0.710 0.011 0.074 0.001

1.173 0.023 0.098 0.003

1.153 0.023 0.098 0.004

1.310 0.026 0.122 0.041

1.426 0.024 0.103 0.001

Total

2

3

3

2

3

2

2

2

3

2

3

3

2

3

2

2

3

3

2

3

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Table 7 Microprobe analyses of coexisting magnetite and ilmenite in volcanic rocks of Hasanda˘g and Erciyes.

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Fig. 7. Fe2+ /Mg in cores of olivine plotted versus Fe2+ /Mg in the host rock. Lines in diagrams represent equilibrium between minerals and whole rock compositions. Equilibrium range was calculated using equilibrium Fe/Mg KDmin/liq values from Roeder and Emslie (1970). Whole rock Fe2 O3 /FeO ratio is assumed to be ∼0.24 based on the Kılınc¸ et al. (1983) expression Fe speciation, an f(O2 ) of NNO Huebner and Sato (1970) and a temperature of 1000 ◦ C.

Fig. 10. Pyroxene quadrilateral with data points representing the compositions of cores (white) and rims (gray) of pyroxenes of Hasanda˘g and Erciyes volcanic rocks. Correction methods for Na and Al and 1-bar isotherms are after Lindsley and Andersen (1983). The liquidus temperatures of pyroxenes plotted on the Di-En-HdFs quadrilateral of Lindsley (1983); calibrated to 1 atm pressure and contoured at 100 ◦ C intervals.

except for some plagioclases in calc-alkaline rocks of Hasanda˘g and Erciyes, all other plagioclase cores exist in the equilibrium range of KD . These values imply early crystallization of most plagioclase cores with low to moderate magmatic water contents. From an experimental investigation of plagioclase crystallization with variable Ca numbers and H2 O contents, it has been shown that all these variables directly control the composition of liquidus plagioclase (Panjasawatwong et al., 1995). The value of the Ca number ratio operates the strongest control on the An number. The An-rich phenocrysts precipitate from melts with high CaO/Na2 O ratios or high H2 O contents (Sisson and Grove, 1993; Panjasawatwong et al., 1995). 6.2. Estimates of temperature and pressure conditions

Fig. 8. Fe2+ /Mg in cores of clinopyroxene plotted vs. Fe+2 /Mg in host rock. The parameters used in the diagram are the same as Fig. 6.

seem to be within the equilibrium range, with some samples displaying compositional disequilibrium. 6.1.3. Plagioclase-liquid equilibrium The relationships between the cores of plagioclase phenocrysts and whole-rock Ca/Na ratios are illustrated in Fig. 9. In this figure, KD values at equilibrium are found by the equation of [KDCa-Na = (Ca/Na)plag /(Ca/Na)rock ]. Sisson and Grove (1993) showed that KD varies with water content of melt, from 1.0 at anhydrous conditions to 5.5 for melts with 6% water at 2 kbar. As seen in Fig. 9,

Fig. 9. Plot of Ca/Na in cores of plagioclase phenocrysts vs. Ca/Na of host rock. Lines represent exchange KD based on experimental studies discussed in text.

The mineral chemical data can be used to estimate the pressure, temperature, and redox conditions that prevailed during and after the crystallization of the volcanic rocks. The results not only help place useful estimates on the P–T conditions of the volcanic rocks, but also demonstrate that in most cases the minerals are not in equilibrium. In these studies, only one mineral or coexisting minerals were used in evaluation of temperature and pressure conditions. 6.2.1. Pyroxene thermometry Electron-microprobe data on pyroxenes from the Central Anatolian rocks were used to calculate Wo-En-Fs end members according to the projection scheme of Lindsley and Andersen (1983). The amount of Fe3+ in clinopyroxenes calculated from the mass balance (Lindsley, 1983) is very low. In Fig. 10, samples are plotted on the Di-En-Hd-Fs quadrilateral of Lindsley (1983) calibrated to 1 atm pressure and contoured equal temperature curves of 100 ◦ C intervals. Coexisting minerals of pyroxene and calculated temperatures of volcanic rocks found in balance by the help of quadrilateral diagram of Lindsley (1983). The temperature of coexisting pyroxenes was also calculated for comparison using the QUILF program of Andersen et al. (1993), and obtain similar results. Among the Hasanda˘g volcanics which are represented by rock groups containing both ortho and clinopyroxene, the Kec¸ikalesi tholeiitic rocks yield temperature estimates between 1090 and 1110 ◦ C while the samples of the Hasanda˘g calc-alkaline rocks give a temperature estimates between 835 and 1068 ◦ C. For the Koc¸da˘g calc-alkaline rocks of the Erciyes stratovolcano, estimated temperatures range from 1000 to 1080 ◦ C. 6.2.2. Amphibole-plagioclase thermometer Amphiboles are widely used for mineral chemistry studies as a temperature-pressure indicator for many metamorphic and

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13

In calculations of oxygen fugacity during crystallization, the equilibrium concentrations of Fe–Ti oxides and Fe–Mg silicates were used. Illustration shown above the QFM buffer curve indicates the conditions of intermediate oxidation for all samples.

Fig. 11. Temperature (T) and oxygen fugacity (fO2 ) conditions calculated from the composition of coexisting cubic (titanomagnetite) and rhombohedral (ilmenite) solid solutions. Curves define solid oxygen buffers corresponding to hematite–magnetite (HM; Myers and Eugster, 1983); quartz–fayalite–magnetite (QFM; Berman, 1988); magnetite–wüstite (MW; Myers and Eugster, 1983); and nickel–nickel oxide (NNO; Huebner and Sato, 1970).

magmatic rocks. Holland and Richardson (1979) and Graham and Powell (1984) analyzed crystallization temperatures of metamorphic rocks using the amphibole minerals. Blundy and Holland (1990) later used published and experimental data to develop a thermometer which was based on AlIV content of amphiboles and composition of coexisting plagioclases in the silica saturated systems. Holland and Blundy (1994) improved two new plagioclase amphibole thermometers. These thermometers can be used in different natural systems such as at a temperature range of 400–1000 ◦ C and 1–15 kbar pressure. In present study, the microprobe data on amphiboles are available only for the rocks of the Erciyes stratovolcano and the Hasanda˘g calc-alkaline rocks. For this reason, the plagioclase-amphibole geothermometer could only be applied to these rocks. For these calculations, core compositions of amphibole and plagioclase phenocrysts were selected assuming that they are coexisting phases. Temperature estimates were made using the equation given by Holland and Blundy (1994). The results show that the estimated temperature range is between 792 and 879 ◦ C for the Koc¸da˘g calcalkaline rocks and 863–1020 ◦ C for the Erciyes calc-alkaline rocks. The temperature ranges for the Hasanda˘g calc-alkaline rocks have been found to be 747–821 ◦ C. 6.2.3. Fe–Ti oxide thermometry and oxygen fugacity Fe–Ti oxide geothermometry is widely used in magmatic and metamorphic rocks. In thermodynamic calculation of coexisting Fe–Ti oxides, Buddington and Lindsley (1964) experimentally calibrated the balance on the FeO–Fe2 O3 –TiO2 system and also developed oxygen barometer with graphical Fe–Ti oxide thermometer. In the following years, the use of Fe–Ti oxide geothermometer and oxygen barometer became very common and simple. Among these methods, the double projection algorithm developed by Lindsley and Spencer (1982) and Lindsley et al. (1990) and the thermodynamic analysis of Fe–Mg–Ti oxides calibrated by Andersen (1988) are widely used. Only samples that were likely to have preserved equilibrium conditions, as determined from Mg and Mn partitioning (e.g., Bacon and Hirschmann, 1988), were used to calculate temperatures. Since some analyzed samples from the Hasanda˘g and Erciyes stratovolcanoes do not have sufficient ilmenite crystals coexisting with magnetite, the results of fO2 and temperature are quite limited. The results are shown in Table 8. The temperature estimates and fO2 values (Fig. 11) were obtained with the use of QUILF program which is based on Andersen and Lindsley (1988) model and developed by Andersen et al. (1993).

6.2.4. Clinopyroxene geobarometer Nimis (1995) combined the structural and experimental data to form crystal-structure simulation which assists to calculate structural parameters from chemical compositions of clinopyroxenes. Nimis and Taylor (2000) calibrated the clinopyroxene geobarometer which is based on the relationship between the cell volume (Vc) and M1-site volume (VM1) under the upper mantle-crust pressure conditions with the experimental study of tholeiitic and weakly alkaline rocks. The temperature values must be known to calculate the pressure for both geobarometers. Calculations were accomplished by using the CpxBar computer program made by Nimis (1995). The pressure estimates from the clinopyroxene barometer range between 2.5–3.4 kbar for the Kec¸ikalesi tholeiitic rocks and 4.3–9.6 kbar for the Hasanda˘g calcalkaline rocks. Pressure range is 5.1–6.7 kbar for the Koc¸da˘g alkaline rocks, 2.0–6.6 kbar for the Koc¸da˘g calc-alkaline rocks and 3.2–6.6 kbar for the Erciyes calc-alkaline rocks. 6.2.5. Al-in-hornblende geobarometer Crystallization pressure of the Koc¸da˘g and Erciyes calc-alkaline rocks was calculated by Schmidt (1992) barometer using the available electron microprobe data for amphibole phenocrysts (Table 8). The pressure range for the Hasanda˘g calc-alkaline rocks are between 4.5 and 5.2 kbar. Two different pressure ranges are found for amphibole phenocrysts in of the Koc¸da˘g calc-alkaline rocks. The first range is between 3.0 and 3.5 kbar and another pressure value is about 6.5 kbar, which can be explained by amphibole crystallization in magma chambers at different depths. Likewise, the Erciyes calc-alkaline rocks yield two different pressure intervals as 4.4–5.3 kbar and 4.3–7.9 kbar. 6.3. Magmatic evolution of the volcanic systems In the Hasanda˘g and Erciyes stratovolcanoes, the calc-alkaline character forms the major part of the volcanism. They contain explosive products with vesicular texture, eruptions of phenocrystrich rocks with common crystallization of hydrous mineral phases. Such volcanological and petrological characteristics indicate that water played an important role in the genesis of the calc-alkaline series in both the Hasanda˘g and Erciyes. In their experimental study, Foden and Green (1992) show the possible role of crystallization of hydrous mineral phases on the magma genesis in basaltic and andesite systems in island arc and continental environments. They attempted to define the amphibole stability field and composition of the liquids which coexist with amphibole in high-Al basalt system using a melting range between 1 atm and 10 kbar pressure. The calculated P–T values from the phenocrysts indicate polybaric origin for magma chambers. Location of magma chambers and the P–T path of magma path have been evaluated using the experimentally determined P–T diagram of Foden and Green (1992). From basalt and basaltic andesites of the Kec¸ikalesi tholeiitic volcano which represents the first product of Hasanda˘g strato volcano, 1100 ◦ C temperature and 2.5–3.4 kbar pressure values were obtained that correspond to 10–12 km depth intervals. Plagioclases and pyroxene phenocrysts widely occur in the same rocks and basaltic andesites contain few olivine minerals. Petrogenetic indicators show that amphibole is not in equilibrium under these P–T conditions (Foden and Green, 1992) and anhydrous mineral phases

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Table 8 Calculated temperatures and pressures of crystallization and oxygen fugacity of the melts. Area

Sample no

Rock type

T (◦ C)a

˘ HASANDAG Kec¸ikalesi tholeiitic Kec¸ikalesi tholeiitic Hasanda˘g calc-alkaline Hasanda˘g calc-alkaline Hasanda˘g calc-alkaline Hasanda˘g calc-alkaline

H-26 H-28 H-2 H-14 H-36 H-42

Basalt B.andesite Andesite Andesite Andesite Basalt

1090–1110

ERCI˙ YES Koc¸da˘g alkaline Koc¸da˘g alkaline Koc¸da˘g calc-alkaline Koc¸da˘g calc-alkaline Erciyes calc-alkaline Erciyes calc-alkaline Erciyes calc-alkaline Erciyes calc-alkaline

E-148 E-150 E-102-b E-108 E-88 E-169 E-175 E-188

Basalt Basalt Andesite Andesite Andesite Dacite Andesite Andesite

a b c, f d e

853–1068 845–1033 835

T (◦ C)b

773–821 747–758

T (◦ C)c

869–861 860–867 859

1181 1097–1165 1000–1080 1016–1044

792–886 806–879 901–1020 863–944

P (kbar)d 2.6–3.2 2.5–3.4 8.0–9.5

P (kbar)e

4.5–5.2 4.5–5.2

7.8–8.6 4.3–9.6 5.3–6.7 5.1–6.2 2.1–6.6 2.0–6.0

(Log fO2 )f

(−12.27) to (−12.53) (−12.24) to (−12.28) (−12.54)

(−8.08) to (−8.70) (−8.16) to (−8.75) 3.0–3.5 2.7–6.5 4.4–5.3 4.3–7.9

3.2–6.6 4.1–6.4

Two-pyroxene thermometer of Lindsley (1983). Amphibole-plagioclase thermometer of Holland and Blundy (1994). Oxide thermobarometry. Calculations were using with the ILMAT program of Lepage (2003) using the solution models of Andersen and Lindsley (1988). Clinopyroxene barometer of Nimis (1995). Al-in-hornblende barometer of Schmidt (1992).

such as pyroxene, plagioclase and small amount of olivine are crystallized in magmas of these chambers. Microprobe analyses of pyroxenes from andesites in the Hasanda˘g calc-alkaline volcanics conducted in accordance with the temperature range of 835–960 ◦ C, revealed crystallization depths between 15 and 32 km corresponding to a 4.5–8.6 kbar pressure interval. Amphibole-plagioclase thermometer yields temperature range of 747–821 ◦ C and Al-in-hornblende geobarometer gives 4.5–4.8 kbar polybaric pressure and 9–25 km depth. All these pressure and depth calculations indicate a polybaric origin and show more than one petrogenetic process. In the basaltic products of the same volcanism, magma shows a polybaric genesis with a depth of 16–36 km in a phenocryst assemblage consisting of olivine, clinopyroxene and plagioclase. Zoning and sieve texture in plagioclase, in these rocks may indicate disequilibrium conditions. The amphibole-free crystallization assemblages may indicate a continuous adiabatic decompression and an ascending magma that is in equilibrium with amphibole in the depth may simply erupt with an anhydrous pyroxene-feldspar assemblage as the ascending path will not cross the amphiboleout curve (Foden and Green, 1992). The resorption of plagioclase indicates that late-stage heating may be resulted from either the entrainment of hotter mafic magmas by cooler felsic magmas during the eruption of layered magma chambers or release of latent crystallization heat during enforced decompressive precipitation of plagioclase. In both cases, late-stage heat causes amphibole to be instable and formation of amphibole-free crystallization (Foden and Green, 1992). The crystallization assemblages in this phase are probably dominated by pyroxenes and plagioclase. In the Erciyes stratovolcano which started its activity with the Koc¸da˘g alkaline volcanism, the depth ranges of 19–23 km are found for alkaline basalts composed of anhydrous minerals such as plagioclase, pyroxene and olivine. These anhydrous assemblages were crystallized in deep magma chambers in the middle crustal levels. The Koc¸da˘g calc-alkaline volcanism consists generally of basaltic andesitic, andesitic rocks and dacitic (Temel et al., 1998) ignimbrites. Two pyroxene thermometers on andesitic rocks of this suite yield about 1050 ◦ C, while amphibole-plagioclase thermometer yields temperature estimates of 850 ◦ C. The andesitic rocks of Koc¸da˘g calc-alkaline volcanism indicate crystallization pressures in the range of 2.0–6.6 kbar corresponding to a depth of 8–25 km. Alin-hornblende geobarometer, on the other hand, gives 3.0–6.5 kbar polybaric pressure and 9–23 km depth. While plagioclase,

amphibole and pyroxene mineral assemblages occur mostly in andesitic rocks, pyroxene and plagioclase crystallization are widespread in basaltic andesite rocks. Zoning in plagioclase minerals, sieve textures, mantling along with the formation of xenocryst and zoning in pyroxene minerals are the disequilibrium parameters for these rocks. Corona texture in amphiboles is related to rising temperature which could traverse the amphibole-out curve during the magma ascent. The existence of the edenitic amphiboles in the rocks which represent the products of shallow level magma chambers indicates the ascend of magma to more shallow levels, reaching the amphibole stability field. Plagioclase and pyroxenes are widespread but amphibole is absent in basaltic andesite rocks that were erupted Koc¸da˘g calcalkaline phase. Disequilibrium crystallization signs such as sieve and zoning textures are very common in plagioclase and there are also mantled plagioclases. The amphibole-free crystallization phases that are dominated by pyroxene cause plagioclases to occur in this assemblage. Existence of mantled and unmantled plagioclase in the same sample indicates that thermal changes are formed by self-mixing magma (Couch et al., 2001). The Erciyes stage is characterized by more felsic products. The last part of volcanism is composed of rhyodacitic domes and pyroclastic products as well. Rhyodacitic domes which were settled after the pyroclastic explosions are associated with degassing and contribution from meteoric water, and the Al-in hornblende geobarometer indicates that amphiboles were crystallized at a pressure of 3.1 kbar (S¸en et al., 2003). The Erciyes calc-alkaline dacitic and andesitic rocks indicate a crystallization temperature in the range of 863–1020 ◦ C with amphibole-plagioclase thermometer. These rocks also indicate crystallization pressures in the range of 4.3–5.3 and 7.9 kbar Al-in-hornblende geobarometer, respectively. These temperature and pressure values indicate that the crystallization histories of the Koc¸da˘g and Erciyes calc-alkaline magmas are approximately similar. Phenocrysts with disequilibrium textures are widespread in andesitic and dacitic rocks. Zoning in pyroxene and plagioclases, reaction textures in most of the phenocrysts such as corona textures on amphibole crystals can be regarded as the signs of disequilibrium. The pressure estimates from different rock associations indicate variable depths for the crystallization of different units. Assemblages containing amphibole in dacitic and andesitic rocks crystallized at 10–18 km depths are polybaric. Corona texture observed on amphiboles of the same rocks, the temperature

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increase intersecting the amphibole out-curve during magma ascend and sieve textures in plagioclase are the indicators of the late-phase heating. The depths of crystallization which were obtained from the anhydrous mineral assemblages of the andesite rocks range between 12 and 25 km. Sieve texture and zoning and mantled phenocrysts are the disequilibrium textures developed in plagioclases. Aphyric and weakly porphyritic texture observed in most rocks indicate the rapid ascent of magma.

7. Conclusions The Hasanda˘g and Erciyes stratovolcanoes that are mainly represented by calc-alkaline rocks are the two important components of collision volcanism in the central Anatolia. Rocks in both stratovolcanoes show a broad range of composition from basalt to rhyolite. As a result of mineral chemistry studies, temperature estimates were calculated using the magnetite–ilmenite, hornblende-plagioclase and double pyroxene geothermometers. The pressure was estimated using single pyroxene and Al-inhornblende geobarometer. The temperatures and pressures are 1100 ◦ C and 2.5–3.4 kbar for the Kec¸ikalesi tholeiitic stage of Hasanda˘g stratovolcano, and 850 ◦ C and 4.3–9.6 kbar for the Hasanda˘g calc-alkaline volcanism. The temperature and pressure values are 1097–1181 ◦ C and 5.1–6.7 kbar for the Koc¸da˘g alkaline volcanism of the Erciyes stratovolcano, 850–1050 ◦ C and 2.0–6.6 kbar for the Koc¸da˘g calc-alkaline volcanism, and 950 ◦ C and 3.2–7.9 kbar for the Erciyes calc-alkaline volcanism. Zoning in plagioclase and pyroxene phenocrysts, sieve texture in plagioclases and reaction rims on amphibole phenocrysts particularly in calc-alkaline rocks are the petrographic signs of disequilibrium parameters. The existence of amphibole xenocrysts in rocks indicates that primary magmas were ponded in deep crustal reservoirs (35 km) where fractional crystallization and crustal assimilation or mixing with crustal melts also took place. Magma ascend with the early fractional assemblage from deep magma chambers can form high level magma chambers at variable depths with various amounts of fractional assemblage. Different crystallization pressures in calc-alkaline rocks indicate polybaric origin for magma chambers and disequilibrium parameters observed in phenocrysts show that the rocks were affected by more than one petrogenetic process. Corona texture in amphiboles is related to the rising temperature or decompression breakdown which could intercept the amphibole-out curve during the magma ascent. The resorption of plagioclase indicates late-stage heating that may be resulted either from the entrainment of hotter mafic magmas by relatively cooler felsic magmas during the eruption of layered magma chambers or release of latent crystallization heat during enforced decompressive precipitation of plagioclase. All these observations imply that the magma chambers were recharged with mafic magma and magmas were reequilibrated before the onset of eruption. Volcanologic and petrologic characteristics of the Hasanda˘g and Erciyes calc-alkaline series show that water played an important role on the genesis of these rocks which mainly consist of phenocryst-rich explosive products with vesicular texture containing hydrous mineral phases.

Acknowledgments This research was financially supported by the Research Fund of Kocaeli University (project code 2003/74). We would like to thank Emin C¸iftc¸i for providing microprobe analyses of this study in Purdue University (Indiana). We are grateful to Ercan Aldanmaz for his

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invaluable contribution to this study, and also help of Selc¸uk Tokel is much appreciated.

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Please cite this article in press as: Köprübas¸i, N., et al., Mineral chemical constraints on the petrogenesis of mafic and intermediate volcanic rocks from the Erciyes and Hasanda˘g volcanoes, Central Turkey. Chemie Erde - Geochemistry (2013), http://dx.doi.org/10.1016/j.chemer.2013.11.003