Textural and Compositional Evidence for Magma Mixing in...

Textural and Compositional Evidence for Magma Mixing in theEvolution of the Çamlıdere Volcanic Rocks (Galatean Volcanic

Province), Central Anatolia, Turkey

ELİF VAROL1, ABİDİN TEMEL1 & ALAIN GOURGAUD2

1 Department of Geological Engineering, Hacettepe University, Beytepe, TR–06800 Ankara,Turkey

(e-mail: [email protected])2 Blaise Pascal University, OPGC, UMR-CNRS 6524 ‘Magmas et volcans’, 5 rue Kessler, 63038 Clermont-Ferrand Cedex, France

Abstract: The Çamlıdere area, in the Galatean Volcanic Province (Ankara), Turkey, is composed of rhyolitic, andesitic, trachytic,dacitic and locally basaltic rocks. The older volcanic rocks in the studied area are rhyolitic and the younger ones basaltic. Thephenocrysts from all the volcanic rocks exhibit some petrographic disequilibrium features such as: (a) coexistence of reversely,normally and oscillatory zoned sieved or unsieved plagioclase in the same rock; (b) wide compositional variation of An% in feldsparphenocrysts; (c) sieved, unsieved, normally and reversely zoned pyroxenes occur together in a single rock; (d) some orthopyroxenephenocrysts are surrounded by clinopyroxene; (e) reaction textures, and normal and reverse zoning of amphibole; (f) euhedralphenocrysts such as plagioclase, pyroxene coexist with resorbed phenocrysts of the same type.

Such features indicate that a wide change of melt composition and/or temperature occurred in the magma reservoir or conduitduring the production of the Çamlıdere volcanic rocks and may reflect an open-system process such as magma mixing. Injection ofmafic magma into a felsic magma could generate a chemically zoned magma chamber and subsequent magma mixing process. Thisprocess is also supported by major elements modelling. However, a simple mixing process is not consistent with the formation of allGalatean volcanic rocks, and fractionation of basaltic parental liquids led to evolved magmas.

Key Words: Çamlıdere, Turkey, zoning, sieved texture, reaction texture, magma mixing

Çamlıdere Volkanik Kayaçlarının Evriminde Magma Karışımı için Dokusal veBileşimsel Kanıt (Galatya Volkanik Provensi), Orta Anadolu, Türkiye

Özet: Galatya Volkanik Provensi (Ankara, Turkiye)’nde yeralan Çamlıdere bölgesi, riyolitik, andezitik, trakitik, dasitik ve bazaltikkayaçlardan oluşmaktadır. Çalışma bölgesindeki en yaşlı volkanik kayaçar riyolitik, en genç olanlar ise bazaltik karakterdedir. Tümvolkanik kayaçlardaki fenokristaller, petrografik açıdan bazı dengesizlik özellikleri sergilemektedir: (a) ters, normal ve salınımlızonlanmış elek dokulu veya elek dokusuz plajiyoklaz minerallerinin aynı kayaç içerisinde birarada bulunuşu; (b) feldispatfenokistallerinin %An içeriğindeki geniş bileşimsel değişimler; (c) aynı kayaç içerisinde, elek dokulu, elek dokusuz, normal ve terszonlanmış piroksenlerin birlikte bulunması; (d) çevresi klinopiroksenle çevrilmiş bazı ortopiroksen fenokristallerinin varlığı; (e)amfibollerde gözlenen normal, ters zonlanma ve reaksiyon dokusu; (f) plajiyoklaz, piroksen gibi özşekilli fenokristallerin aynı tiptekikemirilmiş fenokristallerle birarada bulunuşu.

Bu gibi özellikler, Çamlıdere volkanik kayaçlarının oluşumunda, magma odasında veya magmanın yükselimi sırasında gerçekleşeneriyiğin bileşimindeki ve/veya sıcaklığındaki değişimi göstermekte olup, bu durum magma karışımı gibi bir açık sistem sürecinidüşündürmektedir. Mafik bir magmanın daha felsik bir magma içine karışımı kimyasal olarak zonlanmış bir magma odası ve bunutakip eden magma karışım sürecini meydana getirebilir. Bu süreç aynı zamanda ana element modellemesiyle de desteklenmiştir.Bununla birlikte, sadece magma karışımı süreci değil, bazaltik ana magmanın fraksiyonel kristalleşmesi de Galatya VolkanikKayaçlarının oluşumunda etkendir.

Anahtar Sözcükler: Çamlıdere, Türkiye, zonlanma, elek dokusu, reaksiyon dokusu, magma karışımı

Introduction

Magma mixing is an ubiquitous process in the evolution of

arc magmas, caused by injection of a basic melt into an

acidic one, that occurs either in a magma chamber or in a

conduit (Eichelberger 1978; Dungan & Rhodes 1978;

Sakuyama 1979; Feeley & Dungan 1996; Geshi 2000).The evidence of magma mixing in a volcanic rock samplecan be recognized petrologically from disequilibriumfeatures such as sieve-textured phenocrysts, coexistenceof normal and reverse zoning of phenocrysts in a singlerock, reaction textures etc.

709

Turkish Journal of Earth Sciences (Turkish J. Earth Sci.), Vol. 17, 2008, pp. 709–727. Copyright ©TÜBİTAKFirst published online 14 March 2008

In this article, a detailed study of petrography, andmineral and major element chemistry of different types oflava flows from the Çamlıdere area, in the GalateanVolcanic Province (GVP), NW of Ankara, Turkey ispresented. The aim of this study is to identify the role ofmagma mixing in the evolution of the Çamlıdere volcanicrocks using textural, mineral and major elementcompositional evidence. Chemical modelling is carried outto quantify the process.

Geological Setting

The study area is located around the town of Çamlıdere, 80km NW of Ankara, in the Galatean Volcanic Province (GVP),situated within the Pontide Tectonic Unit (Ketin 1966)(Figure 1a). The development of the GVP started in theLate Cretaceous and is related to the closure of thenorthern branch of Neotethys and to the collision of theAnatolide-Tauride and Pontide platforms during LatePaleocene–Eocene time (Şengör & Yılmaz 1981; Koçyiğitet al. 1995, 2003). A number of previous studiessuggested that these subduction and collision processeswere continuing during the evolution of the GVP (Keller etal. 1992; Tankut et al. 1998; Wilson et al. 1997; Koçyiğitet al. 2003; Telsiz 2004; Muratçay-Varol 2006). This isan important area for the understanding of collision-relatedvolcanism.

The province consists mainly of lacustrine sedimentarydeposits, pyroclastic deposits (fall and flow deposits) andvolcanic lava flows and domes (Figure 1b). The lacustrinesedimentary deposits are seen in some isolated basins inthe southern part of the studied area. These basins aresurrounded by volcanic rocks. Toprak et al. (1996) andSüzen (1996) indicated that the deposition in the lacustrinebasin began in the Early Miocene and continued in thePliocene. These sedimentary deposits are interbedded withvolcanic units and pyroclastic deposits in some places, sothat the deposition of sedimentary units was coeval withthe volcanic activity. The volcanic activity started at the endof the Cretaceous (Keller et al. 1992; Koçyiğit et al. 2003)and resumed from the Early Miocene to the Late Miocene(Türkecan et al. 1991; Tankut et al. 1995, 1998; Wilsonet al. 1997; Süzen & Türkmenoğlu 2000; Adıyaman et al.2001; Schumacher et al. 2001; Telsiz 2004; Muratçay-Varol 2006). In the studied area, K-Ar ages for six volcanicsamples range from 22.5 Ma to 18.8 Ma (Early Miocene)(Muratçay-Varol 2006). The volcanic activity started withthe explosive eruption of rhyolitic pyroclastic deposits,

followed by rhyolitic, and then andesitic, trachytic anddacitic volcanism. The pyroclastic deposits, embedded inthe basin-fill deposits, were not observed extensively in thefield, because they are covered by younger volcanic rocks.These younger volcanic rocks are mainly rhyolitic, trachytic,commonly andesitic, dacitic and locally basaltic rocks. Therhyolitic volcanic rocks crop out in the northeast and thebasaltic rocks in the northwest of the studied area andwere emplaced respectively as lava flows, small domes anddikes. The andesitic lava flows are brecciated. Trachyticrocks exhibit rounded andesitic enclaves of various sizes.The dacitic lava flows display flow banding and are alsobrecciated. The andesitic and dacitic lava flows areobserved as block-and-ash flow in some places.Sedimentary deposition continued after the cessation ofvolcanism and Quaternary alluvium unconformably overliesthese sedimentary units.

Petrography

The Çamlıdere volcanic rocks consist of rhyolitic, andesitic,trachytic, dacitic and basaltic volcanic rocks in composition.The pyroclastic units are rhyolitic fall and flow deposits.

The oldest rhyolites contain plagioclase, biotite andquartz microphenocrysts in a glassy rhyolitic groundmass.The rhyolitic lava flows and domes are grey and exhibitporphyritic textures, with plagioclase, biotite and quartzphenocrysts in a groundmass of plagioclase, biotite, opaquemicrolites and brown glass. In some rhyolitic lava flows,clear, unsieved plagioclase phenocrysts occur. Some ofthem exhibit sieved textures: a clear core with a sieved rim(or vice versa); sometimes whole phenocryst is sieved. Theywere observed coexisting in the same rock. The biotitephenocrysts are reddish to dark brown in colour or havebeen completely replaced by Fe-Ti oxides. They occur asinclusions in some plagioclase phenocrysts. Rare quartzphenocrysts are corroded and embayed.

The andesitic lavas are porphyritic and containclinopyroxene, orthopyroxene, plagioclase and amphibolephenocrysts in a groundmass consisting either ofplagioclase and pyroxene microcrysts or totally of glass.The pyroxene phenocrysts are predominantly zoned. Thereare also typically normally zoned, clear, unsievedplagioclase phenocrysts. Some of them show sieved texturedominantly at the rims (Figures 2a, g, h). Pyroxene andplagioclase phenocrysts display typical glomeroporphyritictextures. The amphiboles have been completely replacedby Fe-Ti oxides. Inclusions of small crystals of the opaqueminerals are common in other phenocrysts.

MAGMA MIXING PROCESS IN GALATEAN PROVINCE

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Figure 2. Photomicrographs from different types of Çamlıdere volcanic rocks showingdisequilibrium textural features: (a) clear and sieve-cored and rimmedplagioclase phenocrysts in andesite; (b) clear, unsieved and completely sievedplagioclase phenocrysts and opacitized amphibole phenocrysts in dacite; (c)clear, unsieved and sieve-rimmed plagioclase phenocrysts in dacite; (d) sieved-core plagioclase phenocryst in dacite; (e) euhedral, clear and sieve-coredplagioclase phenocrysts and amphibole phenocrysts with reacted core andrim in a trachytic rock; (f) sieve-cored and rimmed plagioclase phenocrysts indacite; (g) oscillatory zoning in sieved and unsieved plagioclase phenocrystsin andesite; (h) zoned plagioclase phenocrysts with sieved texture in andesite;(i) euhedral, clear and sieve-cored plagioclase phenocrysts in dacite.

The trachytic lavas display typical flow banding textureswith aligned plagioclase microlites, and a porphyritictexture. Clinopyroxene ± orthopyroxene + plagioclase +amphibole + biotite generally occur as phenocrysts. Oxideminerals occur as inclusions in the phenocrysts. Thegroundmass contains the same minerals. Someorthopyroxenes are rimmed by clinopyroxene. Theclinopyroxene phenocrysts are sometimes coated by thinreaction zones of amphibole and contain abundant glassinclusions. Together with normal clear plagioclasephenocrysts, there are also sieved core or rim plagioclases(Figure 2e). The reddish amphibole phenocrysts exhibitreaction rims or are completely replaced by Fe-Ti oxides.Biotite occurs occasionally as inclusions in the amphibole.Fe-Ti oxides were observed as microphenocrysts. Thegroundmass contains microlites of the same minerals andoccasionally sub-spherical vesicles.

The dacitic rocks consist mainly of plagioclase ±clinopyroxene ± orthopyroxene + amphibole ± biotite ±quartz + Fe-Ti oxides. They formed in a groundmass ofplagioclase + amphibole ± biotite + opaque minerals andtransparent glass and exhibit porphyritic textures.Clinopyroxene and orthopyroxene were found in somedacitic samples as phenocrysts or microphenocrysts andare often zoned, although clear pyroxenes are lessabundant. Clear, unsieved, zoned, sieved rim and core or

completely sieved euhedral to subhedral plagioclases occurtogether dominantly in dacitic lava flows (Figures 2b, c, d,f, i). The amphiboles are characteristically reddish to darkbrown and are completely replaced or just rimmed by Fe-Ti oxides. Clear amphibole phenocrysts are also present.Rare biotite also exhibits reaction rims. These rocks containalso a small amount of quartz. The groundmass iscomposed of the same minerals.

The youngest basaltic lavas crop out as dikes andexhibit scarce phenocrysts of olivine, clinopyroxene,plagioclase ± orthopyroxene and opaque minerals. Olivinereaction rims of pyroxene were observed. Theclinopyroxenes are generally zoned and include glassinclusions. Zoned and sieved rim plagioclases also occur inthese rocks. Fe-Ti oxides are accessory minerals orinclusions.

Mineral Chemistry

Olivine

Olivine phenocrysts are scarce and limited to basaltic rocks.Representative olivine analyses are listed in Table 1. Thecompositions range from Fo74 to Fo68. Some crystals aresurrounded by reaction rims. All the crystals aredominantly normally zoned with Fo-rich cores.

E. VAROL ET AL.

713

Table 1. Representative olivine analyses from basaltic rocks (c– core; r– rim)(cations per 4 oxygens).

Basaltic rocks

GM-171

c--> r c--> r c--> r

SiO2 37.58 37.46 37.82 37.08 36.86 36.44TiO2 0.08 0.00 0.06 0.05 0.03 0.02Al2O3 0.04 0.02 0.02 0.02 0.01 0.01FeOt 24.19 25.92 23.78 27.42 25.96 27.88MnO 0.51 0.68 0.47 0.77 0.62 0.75MgO 37.58 36.29 37.82 34.74 36.43 34.84CaO 0.31 0.32 0.33 0.25 0.31 0.28

Total 100.29 100.68 100.31 100.33 100.21 100.22

Si 1.00 0.99 0.99 0.99 0.98 0.98Ti 0.00 0.00 0.00 0.00 0.00 0.00Al 0.00 0.00 0.00 0.00 0.00 0.00Fe(ii) 0.53 0.57 0.52 0.61 0.58 0.63Mn 0.01 0.02 0.01 0.02 0.01 0.02Mg 1.46 1.43 1.48 1.38 1.45 1.40Ca 0.01 0.01 0.01 0.01 0.01 0.01

Fo 73.1 70.9 73.5 68.7 71.0 68.4Fa 26.4 28.4 25.9 30.4 28.4 30.7

Pyroxene

The pyroxene phenocrysts include both ortho- and clino-pyroxene. Representative pyroxene analyses are listed inTables 2 and 3. Orthopyroxenes and clinopyroxenes in theandesitic rocks are enstatite, augite and diopside withcompositions of En78–81Wo3–4Fs16–18 and En39–50Wo39–46

Fs9–21, respectively. The ortho- and clino-pyroxenephenocrysts of dacitic rocks exhibit a compositional rangeof En71–82Wo2–3Fs15–26 and En40–49Wo41–46Fs8–18,respectively, and are also enstatite and augite, diopside incomposition. The clinopyroxene phenocrysts in the basalticand trachytic rocks have ranges of En40–44Wo42–45Fs13–16

and En43–56Wo39–46Fs9–15, respectively and are augite ordiopside in the classification of Morimoto (1989) (Figure3). Normally zoned pyroxene phenocrysts (ortho- andclino-pyroxene) with Mg-rich cores coexist with reverselyzoned pyroxenes phenocrysts with Mg-rich rims in a singlerock. Oscillatory zoning of pyroxenes is also common inthe lava flows. Some orthopyroxene phenocrysts arecoated by clinopyroxene rims (Figure 4).

Plagioclase

Representative plagioclase analyses are presented in Table4 and shown in Figure 5. Plagioclase is the most abundantphenocryst phase in all lava types. The compositions rangefrom An27 to An59 as labradorite, andesine and oligoclase inandesitic rocks, An28 to An56 as labradorite, andesine andoligoclase in trachytic rocks, An24 to An67 as labradorite,andesine, oligoclase in dacitic rocks, An43 to An65 and islabradorite and andesine in basaltic rocks, respectively. Theplagioclase of the groundmass displays a widecompositional range (An20–63). Both normal, reverse (e.g.,labradorite cores to andesine rims or andesine cores tolabradorite rims) and oscillatory zoning were observed insieved and unsieved plagioclase phenocrysts in the samelava flows (Figures 2g, h & 6).

Amphibole

Euhedral and subhedral amphibole phenocrysts, foundmainly in trachytic and dacitic lava flows, are calcicamphiboles and classified as magnesio-hastingsite, andtschermakite using the Leake et al. (1997) classification(Figure 7). Representative chemical analyses are given inTable 5. Most of the crystals exhibit opaque rims and someof them become opaque either around the core orthroughout the crystal (Figures 2b, c, e, f, i). Unzoned

crystals have little difference in composition from core torim, but zoning when it occurs is normal and/or reversewith decrease or increase of Mg# from core to rim,respectively.

Biotite

Biotite phenocrysts occur in trachytes, dacites andrhyolites. The amount of biotite increases with increasingsilica content. Most of the crystals exhibit reaction rims andsome of them were observed as inclusions in otherphenocrysts. Together with the normally zoned crystals,reversely zoned biotite crystals were also observed to havenarrow Mg-rich rims. Representative biotite analyses arelisted in Table 6.

Oxide

The Fe-Ti oxides are mostly magnetite andtitanomagnetite, abundant in the groundmass and asinclusions in other phenocrysts. Ilmenite occurs rarely intrachytes as an accessory phase.

Discussion and Conclusion

The SiO2 contents of the Çamlıdere volcanic rocks rangefrom 49 to 72 wt% (Table 7), as basaltic to rhyolitic types.The observed disequilibrium features, chemical mineralcompositions and major element data are discussed belowin order to determine the effective processes controllingthe evolution of these volcanic rocks.

Some orthopyroxene phenocrysts are rimmed byclinopyroxene. For example, such a rim is attached to aresorbed, anhedral clinopyroxene phenocryst (Figure 4),and this type of feature was observed in many samples.Such features are not common with subhedral, rimmedphenocrysts after resorption of another phenocryst thathas the same composition. Nakamura & Kushiro (1970)suggested that orthopyroxene and clinopyroxene are in acotectic relationship and cannot be produced by simplefractional crystallization. Euhedral orthopyroxene andclinopyroxene phenocrysts also coexist with resorbedorthopyroxene and clinopyroxene. They display bothnormal and reverse zoning in the same rock.

Amphibole phenocrysts exhibit rounded reacted coresand rims (Figures 2e, f, h). These reaction textures indicatethe reduction of pH2O due to decompression and/ortemperature increase (Gill 1981). However, it is difficult to


714

E. VAROL ET AL.

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SiO

255

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54.3

855

.58

54.4

455

.69

54.4

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54.3

952

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55.6

654

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51.3

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53.8

354

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Al 2O

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122.

301.

311.

651.

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901.

462.

131.

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480.

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26.3

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27.1

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826

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30.1

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CaO

1.67

1.51

1.51

1.97

1.66

1.45

1.24

1.62

1.34

1.60

1.37

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1.29

1.26

1.37

1.55

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020.

040.

040.

020.

04

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0.00

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0.00

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0.00

0.00

0.00

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360.

120.

300.

160.

210.

220.

310.

190.

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180.

100.

200.

100.

180.

13

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0.23

0.31

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0.38

0.29

0.43

0.25

0.33

0.41

0.32

0.37

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0.22

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99.5

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99.9

310

0.06

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911.

951.

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951.

931.

931.

941.

931.

941.

981.

881.

941.

951.

951.

931.

95

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0.08

0.05

0.10

0.05

0.07

0.06

0.08

0.06

0.09

0.07

0.11

0.03

0.06

0.04

0.07

0.05

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0.05

0.07

0.06

0.06

0.04

0.05

0.07

0.03

0.08

0.02

0.00

0.14

0.10

0.04

0.07

0.06

0.05

Fe2+

0.25

0.27

0.27

0.28

0.24

0.32

0.40

0.31

0.43

0.28

0.43

0.35

0.28

0.43

0.29

0.24

0.24

Mg

1.62

1.60

1.61

1.56

1.64

1.56

1.48

1.56

1.43

1.59

1.45

1.47

1.60

1.45

1.59

1.63

1.64

Ca0.

060.

060.

060.

070.

060.

060.

050.

060.

050.

060.

060.

040.

050.

050.

050.

060.

06

Na

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

K0.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

00

Ti0.

010.

010.

000.

010.

000.

010.

010.

010.

010.

010.

000.

010.

000.

010.

000.

010.

00

Mn

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

Tota

l4.

004.

004.

004.

004.

004.

004.

004.

004.

003.

994.

004.

004.

004.

004.

004.

004.

00

Wol

last

onit

e3.

102.

862.

853.

743.

122.

772.

403.

142.

603.

062.

822.

042.

412.

472.

582.

912.

81

Ens

tati

te81

.02

79.9

580

.37

78.5

482

.65

78.2

373

.94

79.2

371

.49

81.3

174

.40

73.0

678

.88

73.1

678

.99

81.8

482

.34

Ferr

osili

te15

.88

17.1

916

.78

17.7

314

.23

19.0

023

.66

17.6

325

.91

15.6

322

.78

24.9

018

.71

24.3

718

.43

15.2

514

.85


716

Tabl

e 3.

R

epre

sent

ativ

e cl

inop

yrox

ene

anal

yses

fro

m b

asal

tic, a

ndes

itic,

tra

chyt

ic a

nd d

aciti

c ro

cks

(c–

core

; r–

rim

; mic

– m

icro

lite)

(ca

tions

per

6 o

xyge

ns).

Bas

alti

c ro

cks

And

esit

ic r

ocks

Trac

hyti

c ro

cks

Dac

itic

roc

ks

GM

-125

GM

-171

GM

-52

GM

-47

GM

-76

GM

-16

GM

-168

r-->

cc-

->r

c-->

rc-

->r

c-->

rr-

->c

r-->

cr-

->c

c-->

rc-

->r

c-->

rc-

->r

c-->

r

SiO

246

.00

46.1

050

.25

51.2

648

.70

48.0

750

.55

51.0

051

.30

53.3

052

.01

50.5

950

.15

50.5

150

.28

49.3

052

.52

52.9

151

.27

48.6

353

.38

51.8

050

.23

51.0

552

.64

51.6

4

Al 2

O3

9.06

9.21

2.82

2.45

4.07

4.97

1.85

4.00

4.09

1.53

1.77

3.06

4.11

4.29

3.26

4.52

1.85

2.21

2.85

5.25

1.47

2.76

4.79

2.71

1.34

2.50

FeO

t8.

128.

658.

087.

799.

138.

6612

.85

7.09

5.72

5.74

8.62

8.60

7.69

7.73

8.64

6.84

5.60

5.20

8.85

10.0

85.

017.

236.

4810

.54

10.1

46.

45

MgO

13.4

113

.53

14.9

115

.25

14.4

513

.87

13.4

915

.88

15.9

917

.91

16.3

713

.98

14.2

414

.98

14.8

214

.36

18.3

817

.68

15.1

413

.50

17.3

216

.50

14.7

113

.87

14.4

415

.62

CaO

19.3

118

.41

21.5

721

.00

20.8

321

.51

18.9

120

.36

21.1

620

.00

19.4

520

.59

21.6

921

.01

19.9

321

.53

19.5

520

.76

20.3

119

.91

21.3

020

.21

21.8

120

.48

19.9

222

.35

Na 2

O1.

021.

230.

600.

650.

760.

540.

620.

450.

510.

260.

310.

800.

520.

540.

660.

450.

340.

390.

440.

470.

310.

310.

700.

600.

400.

29

K2O

0.00

0.00

0.00

0.00

0.00

0.02

0.01

0.02

0.00

0.01

0.00

0.01

0.00

0.01

0.00

0.03

0.01

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TiO

21.

902.

001.

000.

981.

291.

580.

690.

800.

740.

300.

641.

201.

511.

271.

171.

310.

310.

260.

561.

160.

380.

310.

780.

440.

530.

46

MnO

0.20

0.18

0.16

0.33

0.23

0.20

0.26

0.17

0.21

0.17

0.27

0.28

0.24

0.20

0.25

0.13

0.20

0.13

0.27

0.30

0.17

0.23

0.14

0.32

0.42

0.22

Tota

l99

.02

99.3

199

.39

99.7

199

.46

99.4

299

.23

99.7

799

.72

99.2

299

.44

99.1

110

0.2

100.

599

.01

98.4

798

.75

99.5

499

.69

99.3

099

.34

99.3

799

.64

100.

099

.83

99.5

3

Si1.

711.

711.

871.

901.

811.

791.

911.

881.

881.

961.

931.

881.

851.

851.

881.

851.

931.

931.

901.

821.

961.

911.

831.

901.

971.

91

Al

0.40

0.40

0.12

0.11

0.18

0.22

0.08

0.17

0.18

0.07

0.08

0.14

0.18

0.19

0.14

0.20

0.08

0.10

0.13

0.23

0.06

0.12

0.21

0.12

0.06

0.11

Fe3+

0.15

0.17

0.13

0.10

0.18

0.15

0.10

0.06

0.06

0.02

0.05

0.09

0.07

0.08

0.09

0.07

0.07

0.05

0.08

0.09

0.02

0.06

0.14

0.10

0.01

0.07

Fe2+

0.10

0.10

0.12

0.15

0.10

0.12

0.31

0.16

0.12

0.16

0.22

0.18

0.17

0.16

0.18

0.15

0.11

0.11

0.20

0.23

0.14

0.16

0.06

0.23

0.31

0.13

Mg

0.74

0.75

0.83

0.84

0.80

0.77

0.76

0.87

0.87

0.98

0.91

0.78

0.78

0.82

0.83

0.80

1.01

0.96

0.84

0.75

0.95

0.91

0.82

0.77

0.80

0.86

Ca0.

770.

730.

860.

830.

830.

860.

770.

800.

830.

790.

770.

830.

860.

830.

800.

860.

770.

810.

810.

800.

840.

800.

870.

820.

800.

89

Na

0.07

0.09

0.04

0.05

0.06

0.04

0.05

0.03

0.04

0.02

0.02

0.06

0.04

0.04

0.05

0.03

0.02

0.03

0.03

0.03

0.02

0.02

0.05

0.04

0.03

0.02

K0.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

000.

00

Ti0.

050.

060.

030.

030.

040.

040.

020.

020.

020.

010.

020.

030.

040.

040.

030.

040.

010.

010.

020.

030.

010.

010.

020.

010.

020.

01

Mn

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.00

0.01

0.00

0.01

0.01

0.01

0.01

0.00

0.01

0.01

0.01

Tota

l4.

004.

004.

004.

004.

004.

004.

004.

004.

004.

004.

004.

004.

004.

004.

004.

004.

004.

004.

004.

003.

993.

994.

004.

004.

004.

00

Wol

last

onit

e43

.60

41.7

144

.25

43.2

443

.18

45.0

739

.48

42.3

044

.04

40.3

839

.58

43.8

445

.47

43.7

541

.95

45.8

639

.39

41.9

041

.87

42.5

543

.12

41.2

645

.97

42.4

441

.27

45.3

6

Ens

tati

te42

.13

42.6

342

.55

43.7

141

.67

40.4

539

.18

45.9

446

.32

50.3

346

.34

41.4

141

.50

43.3

843

.42

42.5

751

.51

49.6

943

.43

40.1

548

.74

46.8

543

.17

40.0

041

.64

44.0

8

Ferr

osili

te14

.27

15.6

613

.20

13.0

515

.16

14.4

821

.34

11.7

69.

649.

2914

.08

14.7

513

.02

12.8

714

.63

11.5

79.

108.

4114

.70

17.3

18.

1511

.89

10.8

617

.56

17.0

910

.56

E. VAROL ET AL.

717

Tabl

e 4.

R

epre

sent

ativ

e pl

agio

clas

e an

alys

es f

rom

bas

altic

, and

esiti

c, t

rach

ytic

and

dac

itic

rock

s (c

– co

re; r

– ri

m; m

ic–

mic

rolit

e) (

catio

ns p

er 3

2 ox

ygen

s).

Bas

alti

c ro

cks

And

esit

ic r

ocks

GM

-125

GM

-170

GM

-25

GM

-52

c-->

rc-

->r

c-->

rm

icc-

->r

c-->

rc-

->r

c-->

rc-

->r

c-->

rc-

->r

mic

r-->

cc-

->r

SiO

252

.59

50.6

750

.97

51.6

050

.29

52.5

352

.52

55.3

150

.98

51.9

855

.65

52.9

350

.46

52.6

352

.14

53.4

654

.33

55.8

653

.26

52.3

755

.42

52.8

258

.82

52.4

354

.91

55.8

7

TiO

20.

090.

070.

090.

070.

100.

080.

120.

090.

090.

120.

100.

050.

080.

080.

160.

080.

170.

050.

000.

000.

000.

000.

120.

050.

040.

07

Al 2

O3

28.2

929

.82

29.8

128

.86

29.8

528

.66

28.3

627

.04

28.7

528

.33

26.1

427

.90

29.4

928

.03

28.3

827

.38

27.0

527

.05

28.2

328

.40

26.7

228

.31

24.0

828

.89

28.9

826

.51

Fe2O

30.

640.

760.

720.

850.

680.

600.

660.

591.

020.

761.

160.

730.

830.

580.

890.

761.

170.

100.

620.

430.

360.

740.

770.

660.

000.

65

FeO

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.57

0.00

MnO

0.01

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.00

0.01

0.05

0.02

0.01

0.00

0.00

0.00

0.02

0.00

0.00

0.04

0.01

0.03

0.00

0.00

MgO

0.

050.

060.

020.

010.

000.

030.

030.

090.

040.

070.

040.

100.

040.

040.

050.

050.

060.

000.

040.

060.

040.

030.

020.

020.

020.

04

CaO

11.5

113

.31

12.8

312

.25

13.1

611

.30

11.6

29.

3212

.74

11.9

99.

1711

.91

12.9

011

.26

11.9

210

.95

9.40

9.42

11.3

512

.07

9.68

11.7

57.

3211

.87

11.4

29.

32

Na 2

O4.

763.

824.

144.

674.

054.

954.

795.

914.

344.

546.

314.

774.

145.

154.

385.

225.

966.

095.

015.

176.

014.

707.

244.

564.

666.

21

K2O

0.33

0.23

0.21

0.19

0.22

0.27

0.24

0.57

0.28

0.30

0.45

0.31

0.27

0.38

0.28

0.44

0.49

0.32

0.19

0.10

0.20

0.20

0.47

0.28

0.36

0.55

Tota

l98

.27

98.7

498

.79

98.5

098

.35

98.4

298

.34

98.9

298

.24

98.1

099

.02

98.7

198

.26

98.1

798

.21

98.3

498

.63

98.8

998

.72

98.6

098

.43

98.5

998

.85

98.7

910

1.0

99.2

2

Ano

rthi

te56

.165

.062

.358

.563

.454

.956

.545

.060

.958

.343

.457

.062

.253

.559

.052

.345

.345

.255

.059

.046

.657

.334

.958

.056

.343

.9

Alb

ite

42.0

33.7

36.4

40.4

35.3

43.5

42.1

51.7

37.5

39.9

54.1

41.3

36.2

44.3

39.3

45.1

51.9

53.0

43.9

40.4

52.3

41.5

62.4

40.3

41.6

53.0

Ort

hocl

ase

1.9

1.3

1.2

1.1

1.3

1.5

1.4

3.3

1.6

1.7

2.5

1.7

1.6

2.2

1.7

2.5

2.8

1.8

1.1

0.6

1.1

1.2

2.7

1.6

2.1

3.1

Trac

hyti

c ro

cks

Dac

itic

roc

ks

GM

-136

GM

-121

GM

-76

GM

-43

GM

-44

c-->

rc-

->r

c-->

rc-

->r

c-->

rr-

->c

c-->

rc-

->r

c-->

rc-

->r

c-->

rc-

->r

c-->

r

SiO

257

.66

54.7

053

.75

54.0

556

.15

54.1

953

.75

60.3

953

.75

57.5

559

.17

51.0

459

.06

56.2

555

.26

58.1

757

.07

53.2

662

.38

52.3

955

.92

53.3

053

.74

56.9

657

.84

54.3

1

TiO

20.

060.

030.

050.

030.

050.

090.

010.

030.

050.

090.

080.

770.

080.

070.

020.

080.

000.

000.

030.

050.

030.

080.

050.

000.

010.

00

Al 2

O3

24.9

526

.80

28.0

027

.75

27.3

028

.03

27.6

223

.24

28.0

024

.41

23.4

525

.48

24.0

125

.72

27.9

125

.46

26.7

228

.86

23.5

228

.43

26.2

328

.69

27.5

025

.94

25.4

127

.18

Fe2O

30.

520.

440.

440.

730.

080.

000.

270.

210.

440.

970.

496.

010.

530.

430.

490.

580.

250.

640.

000.

520.

240.

190.

510.

450.

260.

64

FeO

0.00

0.00

0.00

0.00

0.66

0.66

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.16

0.00

0.00

0.00

0.00

0.00

0.00

0.00

MnO

0.

020.

000.

000.

000.

000.

000.

000.

020.

000.

000.

010.

020.

020.

010.

000.

000.

000.

000.

000.

010.

000.

010.

030.

020.

030.

00

MgO

0.

030.

030.

040.

020.

110.

080.

030.

010.

040.

180.

030.

140.

030.

060.

050.

030.

010.

030.

000.

020.

030.

030.

050.

030.

010.

02

CaO

7.

4010

.03

11.4

210

.08

10.1

011

.26

10.6

45.

9311

.42

7.84

5.99

9.33

6.76

8.76

10.4

47.

479.

0511

.78

5.06

12.1

99.

1611

.60

11.0

98.

087.

7510

.50

Na 2

O6.

955.

594.

795.

395.

574.

865.

207.

644.

796.

147.

424.

996.

596.

055.

587.

556.

004.

938.

054.

666.

294.

805.

276.

896.

975.

30

K2O

0.

720.

540.

320.

460.

310.

270.

250.

780.

321.

171.

490.

421.

590.

730.

470.

790.

680.

270.

950.

170.

360.

200.

200.

540.

520.

35

Tota

l98

.31

98.1

698

.80

98.5

110

0.3

99.4

497

.78

98.2

498

.80

98.3

398

.12

98.2

098

.65

98.0

810

0.2

100.

199

.76

99.7

610

0.2

98.4

498

.26

98.9

098

.44

98.9

198

.80

98.3

0

Ano

rthi

te35

.548

.255

.849

.449

.155

.352

.328

.755

.838

.628

.349

.532

.842

.649

.533

.843

.756

.024

.458

.543

.756

.553

.138

.136

.951

.2

Alb

ite

60.4

48.6

42.3

47.8

49.0

43.2

46.2

66.9

42.3

54.6

63.4

47.9

58.0

53.2

47.9

61.9

52.4

42.4

70.2

40.5

54.3

42.3

45.7

58.8

60.1

46.8

Ort

hocl

ase

4.1

3.1

1.8

2.7

1.8

1.6

1.5

4.5

1.8

6.8

8.4

2.6

9.2

4.2

2.7

4.2

3.9

1.5

5.5

1.0

2.0

1.1

1.1

3.0

2.9

2.0


718

Tabl

e 5.

R

epre

sent

ativ

e am

phib

ole

anal

yses

fro

m t

rach

ytic

and

dac

itic

rock

s (c

– co

re; r

– ri

m; m

ic–

mic

rolit

e) (

catio

ns p

er 2

2 ox

ygen

s).

Trac

hyti

c ro

cks

Dac

itic

roc

ks

GM

-121

GM

-160

GM

-39

GM

-44

r-->

cc-

->r

mic

c-->

rc-

->r

c-->

rc-

->r

c-->

rc-

->r

c-->

rc-

->r

SiO

240

.16

42.1

640

.53

40.5

342

.41

41.6

643

.89

43.4

542

.71

43.6

744

.81

42.6

443

.67

43.5

544

.35

41.4

242

.40

40.8

542

.65

43.5

442

.98

Al 2O

311

.89

10.3

912

.65

12.4

710

.20

11.7

911

.90

9.42

9.79

10.8

99.

1711

.15

10.8

510

.53

9.69

11.7

311

.19

11.1

610

.14

9.56

9.25

FeO

t12

.44

13.8

49.

7310

.59

11.9

711

.03

10.7

612

.08

12.6

613

.20

13.1

512

.67

13.3

913

.97

13.2

712

.92

13.7

814

.70

13.2

012

.90

12.5

8

MgO

13.5

113

.07

14.6

514

.64

13.9

113

.75

13.1

514

.39

13.8

614

.30

15.1

414

.92

14.4

214

.57

15.0

713

.68

13.2

913

.28

14.5

014

.35

14.3

1

CaO

11.2

011

.20

11.4

011

.50

11.1

211

.30

11.1

611

.30

10.9

911

.22

10.9

610

.63

11.3

211

.16

10.9

811

.20

11.2

510

.97

10.9

111

.26

11.2

5

Na 2

O2.

482.

222.

592.

732.

302.

522.

532.

583.

062.

131.

921.

952.

132.

152.

042.

452.

482.

241.

952.

202.

98

K2O

0.85

0.92

0.82

0.90

0.97

0.88

0.80

0.65

0.70

0.42

0.44

0.40

0.41

0.37

0.43

0.83

0.84

0.72

0.70

0.73

0.75

TiO

24.

532.

854.

224.

054.

144.

254.

292.

902.

952.

151.

872.

512.

472.

652.

123.

342.

502.

902.

223.

043.

04

MnO

0.20

0.39

0.18

0.15

0.21

0.18

0.21

0.31

0.18

0.23

0.33

0.16

0.25

0.26

0.24

0.21

0.26

0.30

0.19

0.27

0.30

Tota

l97

.27

97.0

496

.77

97.5

597

.23

97.3

698

.69

97.0

896

.90

98.2

197

.79

97.0

398

.91

99.2

198

.19

97.7

897

.99

97.1

296

.46

97.8

597

.44

Si5.

916.

235.

945.

926.

236.

116.

356.

386.

326.

266.

416.

126.

226.

186.

336.

046.

196.

006.

226.

326.

33

Al

2.06

1.81

2.19

2.14

1.77

2.04

2.03

1.63

1.71

1.84

1.55

1.89

1.82

1.76

1.63

2.02

1.93

1.93

1.74

1.64

1.61

AlIV

2.06

1.77

2.06

2.09

1.77

1.89

1.65

1.62

1.68

1.74

1.55

1.88

1.78

1.76

1.63

1.96

1.81

1.93

1.74

1.64

1.61

AlVl

0.00

0.04

0.12

0.06

0.00

0.15

0.37

0.01

0.03

0.10

0.00

0.00

0.05

0.00

0.00

0.06

0.12

0.00

0.00

0.00

0.00

Fe3+

0.71

0.73

0.54

0.59

0.51

0.36

0.03

0.55

0.50

1.07

1.25

1.46

1.08

1.25

1.26

0.81

0.76

1.21

1.23

0.79

0.52

Fe2+

0.83

0.98

0.65

0.70

0.96

0.99

1.27

0.93

1.07

0.52

0.32

0.06

0.52

0.41

0.33

0.76

0.92

0.59

0.38

0.77

1.03

Mg

2.97

2.88

3.20

3.19

3.05

3.01

2.83

3.15

3.06

3.06

3.23

3.19

3.06

3.08

3.20

2.97

2.89

2.91

3.15

3.11

3.14

Ca1.

771.

771.

791.

801.

751.

781.

731.

781.

741.

721.

681.

631.

731.

701.

681.

751.

761.

731.

711.

751.

78

Na

0.71

0.64

0.74

0.77

0.66

0.72

0.71

0.73

0.88

0.59

0.53

0.54

0.59

0.59

0.56

0.69

0.70

0.64

0.55

0.62

0.85

K0.

160.

170.

150.

170.

180.

170.

150.

120.

130.

080.

080.

070.

080.

070.

080.

150.

160.

140.

130.

140.

14

Ti0.

500.

320.

470.

450.

460.

470.

470.

320.

330.

230.

200.

270.

270.

280.

230.

370.

280.

320.

240.

330.

34

Mn

0.03

0.05

0.02

0.02

0.03

0.02

0.03

0.04

0.02

0.03

0.04

0.02

0.03

0.03

0.03

0.03

0.03

0.04

0.02

0.03

0.04

Mg#

0.78

0.75

0.83

0.82

0.76

0.75

0.69

0.77

0.74

0.86

0.91

0.98

0.86

0.88

0.91

0.80

0.76

0.83

0.89

0.80

0.75

E. VAROL ET AL.

719

explain the rounded reaction zone with decreasing of pH2Obecause Mazzone et al. (1987) suggested that themorphology of amphibole phenocrysts remains undersubsolidus dehydration reactions.

The plagioclase and pyroxene phenocrysts exhibitnormally, reversely and oscillatory zoning in terms of An%and Mg#, respectively and have a wide compositional range(An% 24–67) from core to rim. In the Çamlıdere volcanicrocks, clear, unzoned, normally, reversely and oscillatoryzoned, sieved and unsieved plagioclase and pyroxenephenocrysts coexist in a single rock (Figures 2a–c, e–i).Both normal, reverse and oscillatory zoning are found insieved and unsieved phenocrysts. Sieved ones contain meltinclusions in either core or rim (Figure 2f). Melt inclusionsin the phenocrysts can be trapped with either increasingtemperature (e.g., dissolution) or rapid crystallization dueto rapid cooling (e.g., decompression) (Roedder 1984;Nelson & Montana 1992) or increasing pH2O. IncreasingpH2O reduces the melting temperature of phenocrysts andcan generate a melt of more calcic composition. Theseevents can explain resorbed, embayed phenocrysts andreverse and oscillatory zoning of plagioclase, but cannotexplain the wide compositional variation and coexistenceof normal, reverse zoned, sieved and unsieved plagioclaseand pyroxene phenocrysts in the same sample (Sakuyama1984; Tsuchiyama 1985; Halsor & Rose 1991).

Such features may reflect an open-system process suchas assimilation, magma mixing, etc. and indicate a physicaland/or chemical change in the magma chamber or conduit.This is because experimental studies show that such sieved,dusty textures and complex zoning within phenocrystsdemonstrate that temperature and chemical compositionvariations are the determinant parameters for formingthese disequilibrium textures (Tsuchiyama 1985;Nakamura & Shimakita 1996). Furthermore, according toGerbe & Thouret (2004), wide An% variations andresorption may be caused by injection of a more maficmagma into a more differentiated magmas in the reservoir.A simple fractional crystallization process cannot explainall the petrographic features observed above. A reasonableexplanation for the changes of these parameters and thewide compositional variations and disequilibrium featuresof phenocrysts, could be magma mixing process. However,the formation of all rocks from rhyolite to basaltic andesitecannot be explained by a simple magma mixing process.There are also clear, unsieved and unzoned phenocrysts inthe rocks, suggesting that fractional crystallization ofparental basaltic magmas occurred before the mixingevent. The injection of more mafic magmas at the base ofa felsic reservoir may constitute the subsequent mixingevent. Our observations may imply that the petrographicfeatures of the Çamlıdere volcanic rocks were essentially

En

Wo

Pigeonite

FerrosillitEnstatite

Diyopsite

Augite

Hedenbergite

Wo

Pigeonite

FerrosillitEnstatite

Diyopsite

Augite

Hedenbergite

Andesitic RocksBasaltic Rocks

Fs

Wo

Pigeonite

FerrosilliteEnstatite

Diyopsite

Augite

Hedenbergite

Dacitic Rocks

Core

Rim

Figure 3. Plot of ortho- and clino-pyroxene compositions on the Wo-En-Fs diagram (after Morimoto 1989).


720

formed by fractional crystallization coupled with asubsequent mixing between mafic and felsic magmas.Although the effects of fractional crystallization can befurther examined for the origin of the magma source anddetailed evolution of the rocks, our purpose in this studyis especially to demonstrate the effects of magma mixing.Hence, major element modelling was done using least-squares mass balance calculations (Bryan et al. 1969). Thewhole-rock chemistry in the modelling is summarized inTable 7. These data are consistent with a dominant processof magma mixing. The acid end-member of the suggested

mixture is a rhyolite, and the mafic one a basalt (Muratçay-Varol 2006). The blended mixes tested are trachyandesites.A series of models were calculated using proceduresproposed by Wright & Doberty (1970). Four tests arepresented in Table 8. The results clearly indicate that themixing model is compatible with the available data becauseof the low value of the sum of residual square (ΣR2 < 1).So, thorough chemical hybridization is a possible means ofgenerating trachyandesites, after mechanical mixingbetween basaltic and rhyolitic magmas. Such a result fitsthe mineralogical data.

A

B

ba

Distance /

60

40

20

0

5 10 15 20 25

A B

Ca

Mg

c

Figure 4. (a) SEM micrograph of a small orthopyroxene coated by a clinopyroxene rimattached to resorbed orthopyroxene phenocrysts; (b) mapping image of anenlargement of the circled area in a); (c) compositional profile of Mg, Ca in thepyroxene.

E. VAROL ET AL.

721

On the basis of these data, the scenario could beconceived as follows: The mafic magma is presumably theproduct of partial melting of the mantle and the felsicreservoir could be the product of partial melting of crustalmaterial and/or fractional crystallization of mafic magma.The fractionation of these two end-members continuedover a period of time. After the separation of olivinephenocrysts through the basic magma, the magma densitydecreased and the magma started to rise, intruding therhyolitic reservoir (Sparks & Huppert 1984). This intrusionresulted in the formation of a stratified magma chambercontaining a mafic magma injected into a felsic magma

chamber, which could be stratified upward from basalt torhyolite, as explained by Huppert & Sparks (1980). Basedon this scenario, as explained before, it can be concludedthat the rhyolitic magma overlay the basaltic magma in astratified magma chamber and the volcanic activity startedwith the explosive eruption of the rhyolitic pyroclasticdeposits, followed by rhyolitic lava flows and domes.Subsequent mixing of the rhyolitic and basaltic liquids mayhave generated andesitic, trachytic and dacitic magmas,while the youngest basaltic dikes that crop out locally inthe studied area, are interpreted as mafic magma emplacedat the base of the chamber.

Basaltic Rocks

Ab

An

Andesitic Rocks

An

Trachytic Rocks

An

Dacitic Rocks

Or

An

Albite

Oligoclase

Andesine

Labradorite

Bytownite

AnorthiteCore

Rim

Na

Ca

30

20

10

0

500 1000 1500 2000 2500

Distance /

A

B

A B

ba

Figure 5. Plot of plagioclase composition on the Ab-An-Or diagram of basaltic, andesitic, trachytic and dacitic rocks.

Figure 6. (a) SEM micrograph of an oscillatory zoned plagioclase phenocryst; (b) compositional profile of Ca, Na in this plagioclase.


722

0,0

0.0

0,5

0.5

0.9

1,0

1.0

Mg

/(M

g+

Fe

2+

)M

g/(

Mg

+F

e2

+)

Si

Si

5.50

5,50

5.00

5.00

4.506.00

6.008.00

6.50

6.50

7.00

7.007.50

0.0

0.5

1.0

7.50

Edenite

Ferro-edenite

Hastingsite

Magnesiohastingsite

(Al >Fe )

(Al <Fe )

(Al <Fe )

VI

VI

VI

3+

3+

3+

Tremolite

ActinoliteMagnesiohornblende

Ferrohornblende

Tschermakite

FerrotschermakiteFerro-actinolite

Ca > 1.50 ; (Na+K) > 0.50B A

Ca > 1.50 ; (Na+K) < 0.50B A

Ti < 0.50

Core

Core

Dacitic RocksRim

Rim

Magnesiosadanagaite

Sadanagaite

Ferro-pargasite

Figure 7. Plot of amphibole compositions (after Leake 1997).

E. VAROL ET AL.

723

Tabl

e 6.

R

epre

sent

ativ

e bi

otite

ana

lyse

s fr

om t

rach

ytic

, dac

itic

and

rhyo

litic

roc

ks (

c– c

ore;

r–

rim

; mic

– m

icro

lite)

(ca

tions

per

22

oxyg

ens)

.

Trac

hyti

c ro

cks

Dac

itic

roc

ksR

hyol

itic

roc

ks

GM

-121

GM

-71

GM

-160

GM

-37

GM

-100

c-->

rm

icc-

->r

c-->

rc-

->r

r-->

cc-

->r

mic

r-->

cr-

->c

r-->

cc-

->r

r-->

c

SiO

236

.48

37.2

236

.36

40.3

238

.28

37.0

136

.11

37.0

337

.62

42.0

537

.72

37.5

540

.03

36.9

435

.95

37.8

037

.19

37.6

636

.85

36.6

636

.93

37.7

637

.22

36.8

6

Al 2O

313

.30

13.5

113

.16

11.9

716

.51

15.6

514

.29

14.0

913

.94

13.0

814

.31

13.0

611

.79

13.0

113

.71

13.5

713

.80

13.4

413

.43

13.6

713

.28

13.6

913

.25

13.2

4

FeO

t17

.08

17.4

617

.24

4.87

7.31

7.42

9.95

13.2

08.

2911

.12

8.56

14.2

714

.81

14.9

814

.96

14.1

015

.90

13.9

814

.55

14.9

713

.73

12.2

813

.90

15.0

7

MgO

13.5

813

.42

12.7

322

.49

16.6

118

.19

17.8

814

.68

17.7

213

.06

17.6

015

.24

13.5

214

.67

14.5

515

.20

14.4

314

.96

15.4

015

.33

16.1

816

.55

15.9

914

.87

CaO

0.03

0.04

0.08

0.03

0.01

0.01

0.00

0.03

0.05

0.34

0.00

0.05

0.20

0.03

0.00

0.05

0.01

0.02

0.01

0.04

0.03

0.02

0.03

0.03

Na 2

O0.

620.

740.

421.

050.

850.

910.

910.

380.

970.

420.

670.

740.

630.

480.

760.

750.

850.

770.

810.

820.

670.

530.

630.

41

K2O

9.11

8.93

8.34

8.89

8.39

8.65

9.00

9.81

9.08

5.95

9.39

8.87

8.15

9.26

9.04

8.96

9.14

8.93

8.80

8.59

8.79

9.18

8.73

8.67

TiO

24.

614.

694.

644.

386.

435.

334.

696.

506.

694.

566.

945.

234.

565.

095.

495.

345.

895.

694.

364.

384.

284.

444.

744.

26

MnO

0.17

0.18

0.24

0.10

0.16

0.12

0.14

0.06

0.11

0.05

0.04

0.03

0.05

0.11

0.21

0.25

0.27

0.23

0.22

0.24

0.13

0.10

0.19

0.37

Tota

l94

.99

96.1

893

.21

94.1

094

.55

93.2

992

.97

95.7

894

.47

90.6

395

.23

95.0

493

.74

94.5

794

.67

96.0

297

.48

95.6

894

.43

94.7

094

.02

94.5

594

.68

93.7

8

Si5.

615.

615.

625.

945.

685.

535.

475.

545.

586.

625.

565.

696.

155.

665.

525.

635.

585.

635.

615.

575.

635.

635.

675.

65

AlIV

2.39

2.39

2.39

2.06

2.32

2.47

2.53

2.46

2.42

1.38

2.44

2.31

1.86

2.34

2.48

2.37

2.42

2.37

2.39

2.43

2.37

2.37

2.33

2.35

AlVI

0.02

0.02

0.01

0.02

0.56

0.28

0.02

0.02

0.02

1.05

0.05

0.02

0.28

0.01

0.00

0.01

0.02

0.00

0.02

0.02

0.02

0.03

0.05

0.04

Fe3+

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

Fe2+

2.20

2.20

2.23

0.60

0.91

0.93

1.26

1.65

1.03

1.47

1.06

1.81

1.90

1.92

1.92

1.76

2.00

1.75

1.85

1.90

1.75

1.53

1.77

1.93

Mg

3.11

3.02

2.93

4.94

3.67

4.05

4.04

3.27

3.92

3.07

3.87

3.44

3.09

3.35

3.33

3.37

3.23

3.34

3.49

3.47

3.68

3.68

3.63

3.40

Ca0.

010.

010.

010.

010.

000.

000.

000.

010.

010.

060.

000.

010.

030.

010.

000.

010.

000.

000.

000.

010.

010.

000.

010.

01

Na

0.19

0.22

0.13

0.30

0.24

0.26

0.27

0.11

0.28

0.13

0.19

0.22

0.19

0.14

0.23

0.22

0.25

0.22

0.24

0.24

0.20

0.15

0.19

0.12

K1.

791.

721.

641.

671.

591.

651.

741.

871.

721.

201.

771.

721.

601.

811.

771.

701.

751.

701.

711.

661.

711.

751.

701.

70

Ti0.

530.

530.

540.

490.

720.

600.

530.

730.

750.

540.

770.

600.

530.

590.

630.

600.

660.

640.

500.

500.

490.

500.

540.

49

Mn

0.02

0.02

0.03

0.01

0.02

0.02

0.02

0.01

0.01

0.01

0.01

0.00

0.01

0.01

0.03

0.03

0.03

0.03

0.03

0.03

0.02

0.01

0.03

0.05

Mg#

0.59

0.58

0.57

0.89

0.80

0.81

0.76

0.66

0.79

0.68

0.79

0.66

0.62

0.64

0.63

0.66

0.62

0.66

0.65

0.65

0.68

0.71

0.67

0.64


724

Tabl

e 7.

Maj

or e

lem

ent

cont

ents

of

sele

cted

vol

cani

c ro

cks

from

Çam

lıder

e re

gion

.

T.ba

salt

Bas

alti

ctra

chya

ndes

ite

Trac

hyan

desi

teTr

achy

teA

ndes

ite

GM

-57

GM

-125

GM

-170

GM

-175

GM

-41

GM

-47

GM

-70

GM

-74

GM

-75

GM

-87

GM

-98

GM

-121

GM

-55

GM

-71

GM

-76

GM

-82

GM

-7G

M-5

1

SiO

248

.37

53.0

849

.37

50.7

559

.24

53.9

760

.26

60.1

956

.32

60.3

060

.47

60.7

065

.36

60.1

065

.27

64.4

659

.64

59.3

2

TiO

21.

391.

871.

631.

261.

201.

630.

910.

811.

130.

760.

900.

910.

440.

880.

520.

520.

740.

91

Al 2O

318

.13

17.7

717

.41

17.0

817

.18

19.3

216

.44

16.6

417

.41

15.4

818

.08

15.7

017

.51

16.9

115

.63

15.5

016

.80

16.3

9

Fe2O

3*9.

447.

529.

048.

015.

438.

025.

575.

256.

924.

825.

195.

021.

965.

363.

423.

445.

625.

41

MnO

0.17

0.08

0.25

0.16

0.05

0.06

0.07

0.05

0.09

0.11

0.06

0.09

0.10

0.04

0.04

0.04

0.15

0.14

MgO

4.41

2.54

2.51

5.34

2.01

0.74

2.58

1.53

2.97

1.60

1.48

2.93

0.10

0.74

0.74

0.89

1.53

3.10

CaO

8.81

8.36

9.12

8.31

5.80

5.53

5.11

4.73

7.24

6.00

5.16

5.12

1.53

4.23

2.56

2.72

5.58

5.40

Na 2

O4.

854.

854.

313.

824.

484.

704.

144.

724.

014.

014.

383.

945.

794.

723.

273.

284.

014.

23

K2O

1.79

1.57

1.85

2.29

2.63

2.71

2.88

3.29

2.03

2.69

2.32

3.00

4.26

3.28

4.62

4.59

2.09

2.12

P 2O

50.

860.

810.

750.

800.

600.

700.

480.

430.

420.

320.

300.

330.

160.

450.

230.

250.

340.

33

LOI(

1050

°C)

1.78

1.49

2.28

0.70

1.19

1.66

1.12

1.05

0.42

4.12

1.45

1.01

1.06

1.15

2.80

2.67

2.21

0.83

Tota

l10

0.00

99.9

498

.51

98.5

299

.79

99.0

499

.56

98.7

098

.96

100.

2099

.80

98.7

498

.17

97.8

599

.10

98.3

598

.70

98.1

8

Dac

ite

Rhy

olit

e

GM

-52

GM

-72

GM

-73

GM

-99

GM

-42

GM

-43

GM

-62

GM

-77

GM

-104

GM

-105

GM

-106

GM

-107

GM

-109

GM

-110

GM

-5G

M-6

GM

-86

GM

-100

SiO

257

.80

60.4

056

.26

61.5

265

.38

62.8

263

.35

64.9

561

.15

64.0

564

.81

64.0

563

.53

62.9

671

.83

69.8

470

.13

71.6

4

TiO

20.

820.

810.

960.

750.

650.

740.

630.

610.

900.

740.

660.

730.

870.

990.

190.

180.

760.

34

Al 2O

315

.85

16.2

714

.22

14.8

916

.73

16.1

315

.48

16.0

716

.55

16.5

216

.35

16.1

916

.28

16.7

014

.39

13.9

615

.29

14.9

6

Fe2O

3*6.

755.

326.

995.

422.

854.

734.

034.

045.

214.

664.

254.

674.

193.

941.

281.

211.

172.

14

MnO

0.15

0.08

0.10

0.06

0.02

0.12

0.06

0.07

0.06

0.06

0.07

0.05

0.04

0.03

0.06

0.05

0.01

0.02

MgO

3.31

2.89

5.36

3.82

0.38

2.74

2.09

2.22

1.55

1.68

1.73

1.73

1.00

0.47

0.05

0.00

0.04

0.13

CaO

5.50

5.66

8.04

5.43

3.93

5.27

4.59

4.74

4.09

4.30

4.08

4.60

4.09

4.14

0.92

0.76

3.42

1.91

Na 2

O3.

743.

713.

293.

774.

373.

743.

984.

303.

094.

064.

264.

043.

743.

374.

643.

593.

934.

02

K2O

1.86

2.08

2.17

2.40

2.25

2.53

2.42

2.10

3.47

2.78

2.14

2.73

3.14

3.04

4.41

4.85

2.79

3.30

P 2O

50.

400.

400.

470.

270.

210.

290.

220.

200.

460.

230.

210.

250.

320.

370.

020.

010.

290.

09

LOI(

1050

°C)

3.29

2.53

2.06

0.90

1.41

1.26

3.74

0.38

3.35

1.04

1.31

1.12

2.27

3.74

0.78

3.79

1.16

1.52

Tota

l99

.46

100.

1599

.92

99.2

398

.17

100.

3710

0.59

99.6

699

.87

100.

1299

.87

100.

1499

.46

99.7

598

.56

98.2

499

.00

100.

07

E. VAROL ET AL.

725

Table 8. Mixing tests results for selected volcanic rocks from Çamlıdere region.

Test 1 Test 2Basaltic Rhyolitic Observed Calculated Basaltic Rhyolitic Observed Calculated

end-member end-member trachyandesite trachyandesite end-member end-member trachyandesite trachyandesiteGM 57 GM 100 GM 70 GM 57 GM 100 GM 41

SiO2 48.37 71.64 60.26 60.26 48.37 71.64 59.24 59.35TiO2 1.39 0.34 0.91 0.84 1.39 0.34 1.20 0.90Al203 18.13 14.96 16.44 16.43 18.13 14.96 17.18 16.65Fe2O3 9.44 2.14 5.57 5.63 9.44 2.14 5.43 6.01MnO 0.17 0.02 0.07 0.09 0.17 0.02 0.05 0.10MgO 4.41 0.13 2.58 2.18 4.41 0.13 2.01 2.40CaO 8.81 1.91 5.11 5.21 8.81 1.91 5.80 5.57Na2O 4.85 4.02 4.14 4.40 4.85 4.02 4.48 4.46K2O 1.79 3.30 2.88 2.57 1.79 3.30 2.63 2.50P2O5 0.86 0.09 0.48 0.46 0.86 0.09 0.60 0.50

% Basalt 47.9 53.0% Rhyolite 51.8 47.0SR2 0.35 0.96

Test 3 Test 4Basaltic Rhyolitic Observed Calculated Basaltic Rhyolitic Observed Calculated

end-member end-member trachyandesite trachyandesite end-member end-member trachyandesite trachyandesiteGM 175 GM 100 GM 72 GM 175 GM 100 GM 51

SiO2 50.75 71.64 60.40 60.45 50.75 71.64 59.32 59.39TiO2 1.26 0.34 0.81 0.87 1.26 0.34 0.91 0.87Al203 16.08 14.96 16.27 15.78 16.08 14.96 15.99 15.58Fe2O3 8.01 2.14 5.32 5.54 8.01 2.14 5.41 5.54MnO 0.16 0.02 0.08 0.10 0.16 0.02 0.14 0.10MgO 5.34 0.13 2.89 3.13 5.34 0.13 3.10 3.15CaO 8.31 1.91 5.66 5.61 8.31 1.91 5.40 5.61Na2O 3.82 4.02 3.71 3.95 3.82 4.02 4.23 3.90K2O 2.29 3.30 2.08 2.76 2.29 3.30 2.12 2.71P2O5 0.80 0.09 0.40 0.50 0.80 0.09 0.33 0.50

% Basalt 57.6 57.9% Rhyolite 43.6 41.9SR2 0.88 0.73

In conclusion, our petrographic observations, such asdisequilibrium textures and complex zoning in all rocks,combined with geochemical data and modelling canreasonably be explained by magma mixing that continuedthroughout the generation of the Çamlıdere volcanism.

Acknowledgments

This study was financially supported by TÜBİTAK (researchproject number: 101Y043), Hacettepe University and the

French Embassy in Ankara. The authors thank T. Yürür, C.Deniel, S. Telsiz for their help in the field and E. Aydar forconstructive comments on mineral chemistry. We wouldlike to thank T. Druit, C. Whipp and D. Whipp for thereviews of the manuscript. We are also grateful to I.Seghedi and an anonymous referee for their helpfulcomments. John A. Winchester edited the English of thefinal text.


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

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