International Geology Review, Vol. 50, 2008, p. 563–582. DOI: 10.2747/0020-6814.50.6.563Copyright © 2008 by Bellwether Publishing, Ltd. All rights reserved.

Geochemical Characteristics of the Sebinkarahisar Granitoidsin the Eastern Pontides, Northeast Turkey:

Petrogenesis and Tectonic ImplicationsNURDANE ILBEYLI1

Mustafa Kemal University, Faculty of Engineering, Hatay 31040, Turkey

Abstract

A series of Cretaceous to Eocene granitoids are present in the Eastern Pontides of northeasternTurkey. The Asarcik (Saplica, Catakhan), Eskine, and Saydere (Sebinkarahisar–Giresun) are theleast-studied, thus least-understood plutons in the orogen. Rock assemblages range from monzoniteto granite. They contain mainly K-feldspar, plagioclase, quartz, hornblende, biotite, and Fe-Tioxides. They are high-K, calc-alkaline, and I-type granites. Chondrite-normalized REE patterns arefractionated and have small negative Eu anomalies. They show enrichment in LILE and LREE rel-ative to HFSE, displaying features of arc-related granitoids. Low molar Al2O3/(FeO+MgO+TiO2) incombination with variable molar (Na2O+K2O)/(FeO+MgO+TiO2) ratios indicate that the magmaswere derived from mafic lower-crustal source rocks. The Eu and Sr anomalies and unfractionatedHREE suggest the presence of plagioclase and absence of garnet in the source.

Introduction

THE EASTERN PONTIDE magmatic arc in northernTurkey forms one of the largest Tethyan magmaticarcs in the Eastern Mediterranean (Okay andTüysüz, 1999). It also represents a very wellpreserved example of a paleo-island arc of LatePaleozoic age (e.g., Akin, 1978; Sengör and Yilmaz,1981; Akinci, 1984; Okay and Sahintürk, 1997;Yilmaz et al., 1997; Boztug et al., 2003, 2006,2007). This magmatic arc was produced during thenorthward subduction of the Izmir–Ankara–Erzin-can Ocean beneath the Eurasian plate (Sengör andYilmaz, 1981).

The east-west–oriented Pontide orogenic belt is40 km wide, and is characterized by a >2 km thicksection of volcanic rocks and intercalated sedimen-tary rocks, intruded by granitoids (e.g., Akin, 1978;Sengör and Yilmaz, 1981; Okay and Sahintürk,1997; Okay and Tüysüz, 1999). This belt is boundedby the Black Sea to the north and the Izmir–Ankara–Erzincan ophiolitic suture zone to the south(Fig. 1).

The Eastern Pontides consist of three zones:northern, southern and axial (Ketin, 1966; Bektas etal., 1995, 1999; Okay and Tüysüz, 1999). The north-

ern zone is governed by a Late Cretaceous–MiddleEocene magmatic island arc (Bektas et al., 1995;Okay and Tüysüz, 1999). However, the southernzone is dominated by rift-related Liassic sediments,Malm–Lower Cretaceous platform carbonates, andUpper Cretaceous flysch overlying the Hercynianbasement (Bektas et al., 1995). The axial zone or theback-arc basin is controlled by large bodies ofMesozoic peridotites and an accretionary complex(Okay and Tüysüz, 1999).

The intrusive rocks of the Eastern Pontides (Fig.1B) have been studied extensively (e.g., Yilmaz,1972; Yilmaz and Boztug, 1996; Okay andSahintürk, 1997; Karsli et al., 2004a, 2004b; Boztuget al., 2004, 2006; Yilmaz-Sahin et al., 2004; Topuzet al., 2005; Yilmaz-Sahin, 2005; Dokuz et al.,2006; Kaygusuz et al., in press). However, previousstudies involving major and trace geochemistry inthe Sebinkarahisar region are scarce (e.g., Oymanet al., 1995). These studies concentrate mainly onthe mining in the region (e.g., Calapkulu, 1982;Karaoglu, 1985; Ayan, 1991; Ozgenc, 1993, 1999;Sasmaz, 1993; Sasmaz and Sagiroglu, 1994).

Here I examine the Asarcik (Saplica, Catakhan),Eskine, and Saydere (Sebinkarahisar–Giresun)plutons, which are geochemically the least-studiedplutons in the Eastern Pontides. This work repre-sents the first geochemical approach for the genesis1Email: ilbeyli@mku.edu.tr; nurilbeyli@yahoo.com

5630020-6814/08/1005/563-20 $25.00

564 NURDANE ILBEYLI

of these plutons. I present new major- and trace-element data from the plutons to constrain granitoidmagma sources and magma producing processes inan arc-related setting. These geochemical data alsocan reveal the origin of high-K, calc-alkaline (I-type) intrusive rocks in this setting.

Geological Setting

General Geology of the Eastern Pontides

The Anatolian plate is located along the collisionzone between the Eurasian and Afro-Arabian plates,and contains a number of continental blocks, each

FIG. 1. A. Location map and position of the Neo-Tethyan sutures in Turkey (after Okay, 2000). Abbreviations: IPS =Intra-Pontide suture; IAES = Izmir–Ankara–Erzincan suture; CACC = Central Anatolian Crystalline Complex; ITS =Intra-Tauride suture; AS = Antalya suture; BS = Bitlis suture. B. Distributions of the granitoids in the Eastern Pontides(simplified from Bingöl, 1989).

SEBINKARAHISAR GRANITOIDS 565

of which is surrounded by different branches ofTethys (Fig. 1A). The northern Neo-Tethys (known asthe Izmir–Ankara–Erzincan Ocean) opened duringthe Lias between the Tauride–Anatolide Platformand the Sakarya Continent, and began to close at thebeginning of the Late Cretaceous by the consump-tion of its floor along two north-dipping subductionzones (Tüysüz et al., 1995). The initiation of arcmagmatism is related to this northward subductionof the northern branch of Neo-Tethys (e.g., Akin,1978; Sengör and Yilmaz, 1981; Okay andSahintürk, 1997; Yilmaz et al., 1997). The oceanicand continental terranes of the Anatolian plateunderwent thickening related to closure of thenorthern branch of Neo-Tethys and subsequent col-lision of the Tauride–Anatolide Platform with theEastern Pontides during the Late Cretaceous–EarlyTertiary period (Dixon and Robertson, 1984; Deweyet al., 1986). The collision resulted in thrust imbri-cation of the active margin (Okay and Tüysüz,1999).

The basement of the Eastern Pontides consistsmainly of two rock types (Dokuz et al., 2006); (1)medium- to high-grade metamorphic complexes ofCarboniferous age; and (2) granitoid complexes ofpre-/Early Jurassic age. This basement is overlainby Lower–Middle Jurassic volcanosedimentaryrocks, and Upper Jurassic–Lower Cretaceous car-bonates (e.g., Yilmaz, 1972; Sengör and Yilmaz,1981; Okay and Sahintürk, 1997; Yilmaz et al.,1997). These rocks are covered by Upper Mesozoic–Early Cenozoic ophiolitic mélange + volcanic rocksand granitoid plutons (e.g., Tokel, 1977; Yilmaz andBoztug, 1996; Boztug et al., 2004). The complex isoverlain in part by Upper Paleocene–Lower Eoceneflysch and post-Eocene terrigeneous units (e.g.,Okay and Sahintürk, 1997).

The basement in the Eastern Pontides isintruded by numerous granitoid plutons (Fig. 1B).They are formed in different geodynamic settingswith three distinct ages: (i) Early Cretaceous (e.g.,Delaloye et al., 1972; Giles, 1974; Taner, 1977;Gedikoglu, 1979; Moore et al., 1980; Boztug et al.,2003); (2) Late Cretaceous (Taner, 1977; Moore etal., 1980; JICA, 1986; Okay and Sahintürk, 1997;Yilmaz et al., 1997; Köprübasi et al., 2000, Boztuget al., 2006); and (3) Eocene (Boztug, 2001; Boztuget al., 2001, 2004, 2006; Karsli, 2002; Arslan et al.,2004; Yilmaz-Sahin, 2005; Topuz et al., 2005). Inaddition, the compositions of the plutons rangefrom low-K tholeiitic through high-K calc-alkalinemetaluminous-peraluminous granites to alkaline

syenites (e.g., Karsli et al., 2002; Boztug et al.,2003; Yilmaz-Sahin et al., 2004; Arslan and Aslan,2006; Boztug et al., 2006; Boztug and Harvalan,2008). The emplacements of these plutons alsooccurred in a wide range of tectonic settings, such asfrom arc-collisional through syn-collisional to post-collisional (e.g., Yilmaz and Boztug, 1996; Okay andSahintürk, 1997; Yilmaz et al., 1997; Yegingil et al.,2002; Boztug et al., 2002, 2003; Karsli et al., 2004a,2004b; Topuz et al., 2005; Yilmaz-Sahin, 2005;Boztug and Harvalan, 2008).

Local geological setting and petrology

The basement of the Sebinkarahisar region iscomposed of undifferentiated volcanic rocks con-taining lavas and pyroclastic rocks (e.g., andesite,latite, thrachyte, basalt, rhyolite, and dacite) (Ayan,1991) (Fig. 2). They are cut by plutonic rocks rang-ing from monzonite through syenite to granite (Ayan,1991). Old valley sediments overlie undifferentiatedvolcanic rocks and granitoids (Oyman et al., 1995).Middle–Upper Paleocene andesite and basaltsoverlie the Upper Cretaceous units. The Eocenevolcano-sedimentary units begin with conglomerateat the base and continue with basalt, andesite, pyro-clastics, and agglomerates at the upper level.Miocene–Pliocene-aged volcanic rocks are com-posed of basalt, andesite, and agglomerate, with tuffintercalations (Fig. 2).

In the Sebinkarahisar region around Mt. Tutak(Fig. 2), Pb-Zn and alunite deposits were identifiedby many authors (e.g., Calapkulu, 1982; Karaoglu,1985; Ayan, 1991; Ozgenc, 1993; Sasmaz, 1993;Sasmaz and Sagiroglu, 1994; Ozgenc, 1999).According to Sasmaz and Sagiroglu, the Pb-Zn bod-ies formed as ore veins along faults in the UpperCretaceous volcanic rocks. On the other hand, thealunite deposits are locally abundant in the center ofargillic alteration zones that developed throughoutthe Upper Cretaceous volcanic rocks (Ozgenc,1993) (Fig. 2).

The Asarcik (Saplica, Catakhan) (ASC), Eskine(ESK), and Saydere (SAY) plutons (Fig. 2) aremainly monzonite, quartz monzonite, syenite, andgranite. The rocks are grey, dark grey, and pinkish,and are medium to coarse grained. They are cut byaplitic and pegmatitic dikes. Enclaves are commonin the plutons (Table 1). Field and petrographiccharacteristics of the intrusive rocks from the ASC,ESK, and SAY plutons are summarized in Table 1.

K-Ar (alkali feldspar, biotite) determinationsfrom the ASC plutons gave age results from 75.7 ±

566 NURDANE ILBEYLI

1.6 to 60.0 ± 1.3 Ma (Oyman et al., 1995). In con-trast, K-Ar (alkali feldspar, biotite, hornblende) agedeterminations from the ESK intrusive rocksyielded ages from 82.4 ± 1.8 to 45.2 ± 1.0 Ma(Oyman et al., 1995). K-Ar (alkali feldspar) determi-nation on one sample from the SAY pluton gave aresult of 64.5±1.7 Ma (Oyman et al., 1995).

Analytical Methods

Fifty-five samples were analyzed for major andtrace analyses by X-ray fluorescence (XRF) at KeeleUniversity, UK. Major oxides and minor element

abundances from 15 samples were determined usingan ICP-MS following LiBO2 fusion and dilute nitricacid digestion. Loss on ignition (LOI) is by weightdifference after ignition at 1000°C. REE contents ofthese 15 samples were measured by ICP-MS at theAcme Analytical Laboratories, Canada. Represen-tative chemical analyses of the Eastern Pontideintrusive rocks are listed in Table 2.

Geochemistry

The investigated intrusive rocks from the EasternPontides have a range from ~56 to 77 wt% SiO2,

FIG. 2. Geological map of the studied area (after Ayan, 1991; Ozgenc, 1999).

SEBINKARAHISAR GRANITOIDS 567

corresponding to a compositional variation frommonzonite to granite (Fig. 3A). Asarcik (Saplica, Cat-akhan) (ASC) plutonic rocks cover the compositionalspectrum from monzonite to granite (Fig. 3A). How-ever, Eskine (ESK) intrusive rocks have a narrowcompositional range from quartz monzonite to graniteon the total alkali versus silica diagram (Fig. 3A). Onthe other hand, the Saydere (SAY) plutonic rocks fallinto the monzonite and quartz monzonite fields (Fig.3A). All rock types are mainly high-K, alkaline, andcalcic (not shown here). All samples have a predom-inantly metaluminous character (Fig. 3B).

The SAY samples tend to have the highest con-tents of TiO2, Fe2O3, and MgO for given silica values(Fig. 4). In the ASC, ESK, and SAY plutons, TiO2,Al2O3, Fe2O3, MgO, and P2O5 (not shown) decrease

with increasing SiO2 (Fig. 4). Na2O scatters some-what for the SAY samples. However, it decreasesslightly for the ASC and ESK samples. In selectedHarker trace element diagrams (Fig. 5), Rb, Zr, andNb increase slightly with increasing silica for theASC, ESK, and SAY samples, whereas the samplesare depleted in Sr and Ba (Fig. 5). Y remains con-stant for the SAY samples (Fig. 5C); it remainsconstant up to ~75 wt% SiO2 and then decreases forthe ASC and ESK samples.

Chondrite-normalized REE patterns of theselected samples from the ASC, ESK, and SAYplutons, and corresponding to various SiO2 contents,are shown in Figure 6. All samples are mainly simi-lar in patterns with differences in abundances. Theyare all LREE-enriched and HREE-depleted, with

TABLE 1. Main Field, Petrographic, and Geochemical Characteristics of the Asarcik, Eskine, and Saydere Plutons from the Eastern Pontides1

Pluton:Asarcik (Saplica, Catakhan)

(ASC)Eskine(ESK)

Saydere(SAY)

Field

Rock unit mz, qmz, sy, gr qmz, gr mz

Grain size Medium to coarse Medium to coarse Medium to coarse

Enclave/dikes Igneous/aplitic-pegmatitic Igneous/aplitic-pegmatitic Igneous/aplitic-pegmatitic

Petrography

Mineral composition Ksp+Pl+Qtz+Hbl+Bt Ksp+Pl+Qtz+Hbl+Bt Ksp+Pl+Qtz+Hbl+Bt

Texture Hypidiomorphic Hypidiomorphic Hypidiomorphic

Mafic phase Hbl+Bt Hbl+Bt Hbl+Bt

Accessory phase Titanite, apatite, zircon, opaques Titanite, apatite, zircon, opaques

Titanite, apatite, zircon, opaques

Alteration Sericite, chlorite, epidote, clay minerals

Sericite, chlorite, epidote, clay minerals

Sericite, chlorite, epidote, clay minerals

Geochemistry

Alkali-lime index Calc-alkalic Calc-alkalic Calc-alkalic

Shand’s index Mainly metaluminous (A < CNK)

Mainly metaluminous Mainly metaluminous

Na2O+K2O (%) ~ 7–11 ~ 9–10 ~ 8–11

Granite type I I I

References This study This study This study

1Abbreviations: mz = monzonite; qmz = quartz monzonite; sy = syenite; gr = granite; ksp = alkali feldspar; pl = plagioclase; qtz = quartz; hbl = hornblende; bt = biotite.

568 NURDANE ILBEYLI

TAB

LE 2

. Maj

or (w

t %) a

nd T

race

(ppm

) Ele

men

t Abu

ndan

ces

of R

epre

sent

ativ

e Sa

mpl

es fr

om th

e E

aste

rn P

ontid

e Pl

uton

ic R

ocks

1

Sam

ple

no.

ASC

-42

ASC

-9A

SC-5

1A

SC-7

4A

SC-2

3A

SC-9

4A

SC-7

2A

SC-2

4A

SC-8

3A

SC-1

2E

SK-3

ESK

-4

SiO

2 57

.34

58.9

159

.65

61.4

462

.47

63.5

565

.26

66.7

572

.19

75.9

457

.49

64.5

8Ti

O2

0.63

0.60

0.51

0.49

0.55

0.39

0.36

0.39

0.31

0.22

0.63

0.49

Al 2O

3 17

.90

16.9

816

.64

16.2

616

.22

16.2

115

.86

15.3

713

.91

12.4

317

.15

15.8

5Fe

2O3

(tot)

6.86

6.58

5.56

5.51

5.20

4.58

3.98

3.98

2.76

1.67

7.42

4.51

MnO

0.16

0.15

0.11

0.11

0.18

0.13

0.12

0.11

0.16

0.02

0.21

0.14

MgO

2.43

2.44

1.70

1.87

1.29

1.41

1.05

1.02

0.06

0.59

2.17

1.06

CaO

5.09

4.88

4.22

3.94

1.73

2.80

2.51

2.34

0.12

0.30

5.04

2.38

Na 2O

3.

253.

283.

153.

254.

203.

513.

393.

143.

240.

143.

103.

19K

2O

5.50

4.98

6.22

5.77

5.39

6.21

6.48

6.31

6.58

6.86

5.50

6.64

P 2O5

0.34

0.29

0.25

0.20

0.18

0.16

0.14

0.13

0.04

0.03

0.28

0.13

L.O

.I.

0.58

0.75

1.96

0.90

2.28

0.99

0.51

0.59

0.79

1.41

0.84

0.45

Tota

l10

0.08

99.8

499

.97

99.7

499

.69

99.9

499

.66

100.

1310

0.16

99.6

199

.83

99.4

2

V11

812

999

9690

7949

4925

2013

050

Cr

1716

1614

1613

1110

1112

1713

Ni

710

88

77

64

33

97

Cu

7860

3547

1834

1614

1271

6344

Zn12

180

6048

8957

6740

4224

176

100

Ga

1617

1414

1612

1315

1412

1615

Rb

190

206

245

314

366

315

289

377

436

250

284

442

Sr65

560

449

844

119

240

634

929

366

132

566

247

Y25

2927

3141

3130

3641

2529

40Zr

142

159

175

278

348

291

240

319

333

287

306

532

Nb

1215

1430

4128

2041

5443

2546

Ba

716

562

558

523

465

469

380

380

222

416

813

372

La30

.00

44.0

067

.00

30.0

087

.00

24.0

058

.00

Ce

67.0

086

.00

152.

0062

.00

169.

0082

.00

113.

00N

d9.

408.

8010

.30

8.80

7.70

9.30

13.1

0Pr

24.0

023

.43

27.3

027

.89

25.5

130

.00

21.3

5Sm

3.60

4.40

4.40

4.00

3.20

4.80

5.30

Eu

0.50

0.90

0.80

0.70

0.30

0.30

0.40

Gd

2.40

2.20

1.70

2.90

1.80

1.70

2.40

Dy

1.50

1.60

2.20

2.20

1.50

2.20

2.40

Ho

0.13

0.12

0.15

0.16

0.12

0.18

0.13

Er

0.14

0.15

0.16

0.14

0.12

0.13

0.19

Tm0.

010.

010.

010.

010.

010.

010.

02Y

b0.

100.

130.

120.

140.

140.

110.

13Lu

0.01

0.01

0.01

0.01

0.01

0.01

0.01

Pb74

4334

3134

4563

4025

712

265

Th17

4124

8490

111

6614

221

512

843

158

Tabl

e co

ntin

ues

SEBINKARAHISAR GRANITOIDS 569

TA

BLE

2. C

ontin

ued

Sam

ple

no.

ESK

-6E

SK-7

ESK

-11

ESK

-10

ESK

-8SA

Y-9

SAY

-8SA

Y-1

SAY

-5SA

Y-4

SAY

-6SA

Y-3

SiO

2 68

.50

69.1

570

.07

71.5

676

.98

55.8

055

.93

56.3

556

.52

59.6

265

.38

65.5

0Ti

O2

0.32

0.33

0.32

0.35

0.14

0.75

0.74

0.74

0.72

0.69

0.58

0.53

Al 2O

3 15

.25

14.5

414

.49

14.5

112

.03

17.0

517

.23

17.5

917

.39

17.2

815

.77

15.5

2Fe

2O3

(tot)

3.05

2.95

2.79

2.62

1.76

7.70

7.94

7.75

7.89

6.01

4.07

4.40

MnO

0.08

0.05

0.05

0.05

0.01

0.16

0.19

0.20

0.22

0.10

0.07

0.10

MgO

0.46

0.59

0.62

0.13

0.09

2.38

2.80

2.88

2.77

1.80

0.21

0.56

CaO

1.26

1.07

1.12

0.30

0.13

4.57

3.86

4.32

3.40

3.21

0.90

0.97

Na 2O

3.

423.

233.

172.

982.

623.

293.

063.

643.

233.

403.

062.

28K

2O

6.63

6.11

6.02

6.71

5.88

5.33

5.50

5.06

5.58

6.00

7.48

6.83

P 2O5

0.06

0.07

0.06

0.05

0.01

0.34

0.33

0.31

0.33

0.30

0.19

0.15

L.O

.I.

0.55

1.49

1.47

0.96

0.48

2.53

2.00

1.06

2.00

1.27

1.69

2.92

Tota

l99

.58

99.5

810

0.18

100.

2210

0.13

99.9

099

.58

99.9

010

0.05

99.6

899

.40

99.7

6

V28

3936

2914

175

172

171

172

143

5377

Cr

1217

1713

1317

1821

1619

1311

Ni

55

34

47

109

106

45

Cu

518

813

1292

8990

8279

3461

Zn61

4949

5327

8294

9811

269

4077

Ga

1614

1514

1318

1718

1718

1617

Rb

414

413

411

483

420

257

271

240

269

307

494

419

Sr15

616

116

110

244

600

612

646

576

596

149

120

Y52

3537

419

3032

3037

3345

33Zr

338

308

302

387

113

186

266

179

262

349

670

421

Nb

4648

4663

3621

1917

2128

5939

Ba

278

265

265

194

4679

688

573

580

574

241

939

4La

90.0

075

.00

50.0

036

.00

30.0

050

.00

55.0

055

.00

Ce

137.

0014

5.00

181.

0070

.00

74.0

084

.00

95.0

012

1.00

Nd

11.9

013

.30

12.2

08.

8011

.20

9.80

9.80

9.60

Pr20

.76

19.2

720

.16

17.1

918

.97

18.0

818

.38

18.6

8Sm

5.80

3.90

5.60

4.00

3.60

4.30

4.50

3.60

Eu

0.30

0.60

0.40

0.70

0.80

0.50

0.20

0.20

Gd

2.60

2.80

2.40

2.40

3.00

2.80

2.60

2.80

Dy

2.10

1.70

1.60

2.10

1.80

2.20

2.00

2.30

Ho

0.13

0.15

0.19

0.22

0.15

0.17

0.20

0.18

Er

0.20

0.20

0.21

0.19

0.17

0.16

0.16

0.16

Tm0.

010.

010.

020.

010.

010.

010.

010.

01Y

b0.

160.

110.

120.

110.

100.

180.

170.

14Lu

0.01

0.02

0.02

0.02

0.02

0.01

0.02

0.02

Pb69

4953

4322

3736

6032

4869

54Th

216

150

152

265

7450

5143

6276

232

123

1 Abb

revi

atio

ns: A

SC =

Asa

rcik

; ESK

= E

skin

e; S

AY =

Say

dere

.

570 NURDANE ILBEYLI

small to moderate negative Eu anomalies (Fig. 6).There is no significant correlation between LREEcontents or LREE/HREE ratios and SiO2 values.

The ORG (ocean ridge granite)–normalized(Pearce et al., 1984) spider diagrams of representa-tive samples (>5% modal quartz) from the EasternPontide intrusive rocks in proportion to various SiO2contents are presented in Figure 7. The samples

display enrichment in the LIL elements (K, Rb, Ba,Th), and the LREE (Ce) relative to the HFSelements (Nb, Hf, Zr, Sm, Y, Yb).

Petrogenesis

The Asarcik (Saplica, Catakhan), Eskine, andSaydere samples display linear trends in Harker

FIG. 3. A. Classification of the Asarcik (Saplica, Catakhan), Eskine, and Saydere intrusives: total alkali versus SiO2diagram (Middlemost, 1994). B. Shand’s index values (Shand, 1951).

SEBINKARAHISAR GRANITOIDS 571

diagrams (Figs. 4 and 5). In addition, there is a lackof distinctive compositional gaps in Figures 4 and 5,indicating that the origin of these rocks is related toeither crystal fractionation of mantle-derived mag-mas or to partial melting of lower crust (e.g., Cox etal., 1987; Wilson, 1991).

In variation diagrams (Figs. 4 and 5), K2O andRb increase, whereas TiO2, Al2O3, Fe2O3, MgO,

and CaO decrease with increasing silica, which iscompatible with their evolution through fractionalcrystallization processes in the analyzed samples.Depletions in P2O5 (not shown), Sr, Hf, Zr (Fig. 5),and TiO2 (Fig. 4) can be explained by the fraction-ation of apatite, plagioclase, zircon, and titanite,respectively. Trace elements (e.g., Rb, Sr, Ba) areuseful indicators for fractionation of the major

FIG. 4. Selected major element (A–F) variation diagrams for the Asarcik (Saplica, Catakhan), Eskine, and Sayderesamples.

572 NURDANE ILBEYLI

phases (e.g., feldpars, amphibole, biotite) in thesource rocks. Therefore the Eastern Pontide sam-ples are plotted on Ba-Rb and Sr-Ba diagrams (Fig.8). The variations in Figure 8 show fractionation ofalkaline feldspar, plagioclase, hornlende, andbiotite in the samples. Hallidey et al. (1991) sug-gested that the crystal fractionation model causeshigh Rb/Sr ratios; however, the Eastern Pontidesamples have low Rb/Sr ratios. Thus, this model

cannot explain the constant or decreasing negativeEu anomaly with increasing silica (Fig. 6). Crystalfractionation also requires a large volume of maficparental magma, which is not found in the region.Moreover, volcanic and intrusive rock compositionsin the Eastern Pontides have not differentiatedfrom basalt to granite; therefore for the genesis ofthe Eastern Pontide intrusive rocks, the crystalfractionation model can be excluded. Bearing in

FIG. 5. Selected trace element (A–F) variation diagrams for the Asarcik (Saplica, Catakhan), Eskine, and Sayderesamples.

SEBINKARAHISAR GRANITOIDS 573

FIG. 6. Chondrite-normalized REE patterns for the Asarcik (Saplica, Catakhan), Eskine, and Saydere samples.Normalization factors are taken from Boynton (1984).

574 NURDANE ILBEYLI

FIG. 7. Ocean-ridge granite (ORG)–normalized diagram illustrating the geochemical characteristics of the Asarcik(Saplica, Catakhan), Eskine, and Saydere rocks (samples >5% modal quartz are plotted; normalizing factors fromPearce et al., 1984).

SEBINKARAHISAR GRANITOIDS 575

mind that the generation of these intrusive rocks byfractional crystallization of a mantle-derived maficmagma is excluded, their evolution through frac-tional crystallization remains possible.

The Eastern Pontide plutons formed from severalmagma pulses, but they display little internal com-positional variation, and there is no compositionaloverlap among them (Figs. 3–5). They may also indi-cate the co-magmatic nature of these rocks. This isalso supported by the similarity of the REE patternsand spidergrams of the intrusive rocks.

The samples in Figure 8 plot on almost lineartrends, and bulk-rock compositions could be relatedto partial melting (Caskie, 1984). A crustal origin ofmagmas therefore can be considered for the EasternPontide intrusive rocks. Experimental data (e.g.,Roberts and Clemens, 1993) suggest that high-K,

calc-alkaline granitoids can be produced from par-tial melting of amphibolites, metagreywackes, andmetapelites (e.g., Patiño Douce, 1996, 1999). Thesource variation (e.g., partial melting of amphi-bolites, metagreywackes, metapelites) can be distin-guished using major oxides molar ratios (Fig. 9).Partial melts generated from mafic source rockshav e l owe r A l 2 O 3 / (FeO+M gO+TiO 2 ) and(Na2O+K2O)/(FeO+MgO+TiO2) ratios compared tothose resulting from acidic source rocks. In Figure9, most of the Eastern Pontide intrusive rocks plotinto the low Al2O3/(FeO+MgO+TiO2) field for par-tial melts from amphibolites. An origin from a mixedamphibolite/metagreywacke source for the intru-sives is also possible.

However, as can be seen from Figure 9, ametapelitic source can be excluded. Variation of

FIG. 8. A and B. Log-log fractional crystallization vector diagrams (Ba-Rb, Sr-Ba) for the Eastern Pontide intrusiverocks. Abbreviations: hbl = hornblende; pl = plagioclase; ksp = alkali feldspar; bt = biotite.

576 NURDANE ILBEYLI

melting conditions (e.g., pressure, temperature, H2Ocontent, and oxygen fugacity) cause compositionaldiversity among crustal magmas (e.g., Wolf and Wyl-lie, 1994; Gardien et al., 1995; Patiño Douce andBeard, 1995, 1996; Patiño Douce, 1996; Singh andJohannes, 1996; Thompson, 1996; Patiño Douce

and McCarthy, 1998). The chondrite-normalizedREE diagrams (Fig. 6) suggest that garnet was notstable in the source, whereas the negative Eu (Fig.6) and Sr (Fig. 5B) anomalies reveal that plagioclasewas stable in the source of the Eastern Pontideintrusive rocks. A similar mechanism (partial

FIG. 9. A–C. Partial melting of felsic pelites, metagreywackes, and amphibolites obtained in experimental studies(Patino Douce, 1999) and compositions of samples from the Eastern Pontide plutons.

SEBINKARAHISAR GRANITOIDS 577

melting from mafic lower crust) was also suggestedfor the origin of arc-related Torul pluton by Kay-gusuz et al. (in press) in the Eastern Pontides.

Tectonic implications

The Eastern Pontide intrusive rocks displayenrichment in the LIL elements (e.g. K, Rb, Ba, Th)and depletion in the HFS elements (e.g., Nb) (Fig.7). These features could be derived from theirsubduction-related setting (e.g., Rogers andHawkesworth, 1989). To characterize the tectonicenvironment for granitic rocks, Pearce et al. (1984)introduced a geochemical method: Nb-Y and espe-cially Rb-(Y+Nb) diagrams have been used todiscriminate among their tectonic settings. The

latter plot is also an indicator of protolith andprocess, which are partly functions of tectonic set-ting (Arculus, 1987; Twist and Harmer, 1987).Therefore intrusive samples (>5% of modal quartz)are plotted on the tectonic discrimination diagramsof Pearce et al. (1984) (Fig. 10). In the Nb versus Ydiagram (Fig. 10A), all intrusive rocks fall into theWPG (within-plate granite) field. In the Rb against(Y+Nb) discrimination diagram (Fig. 10B), most ofthe intrusive samples plot along the border of thesyn-COLG, VAG, and WPG fields. Bearing in mindthat results from tectonic discrimination diagramsare ambigious inasmuch as trace element features ofmagmas are mainly dependent on protolith composi-tion (e.g., Roberts and Clemens, 1993; Anthony,

FIG. 10. Tectonic discrimination diagrams of the Asarcik (Saplica, Catakhan), Eskine, and Saydere intrusive rocks(Pearce et al., 1984; samples >5% modal quartz are plotted). A. Nb versus Y diagram. B. Rb versus (Y+Nb) diagram.

578 NURDANE ILBEYLI

2005). Although the intrusive samples plot in theWPG field (Fig. 10), they conform with the defini-tion of I-type granites (e.g., amphibole as maficphases, titanite and magnetite as accessory phases,calc-alkaline; A/CNK < 1.1) (Chappell and White,1974) (Fig. 3B and Table 1). In addition, the miner-alogic and chemical compositions of the intrusiverocks are not consistent with continental rift settings(Eby, 1992). Furthermore, most samples have low

Rb/Zr values (<1.1), indicating a pre-collisional orvolcanic-arc nature (Harris et al., 1986). The intru-sive samples have high Th/Yb and La/Yb ratios thatare also consistent with a continental-arc origin(Condie, 1989).

The Early/Late Cretaceous to Early Paleocenearc magmatism in the Eastern Pontides was formedas a result of the northward subduction of the north-ern branch of the Neo-Tethyan Ocean beneath the

FIG. 11. A. Rb/Zr versus Nb diagram. B. Rb/Zr versus Y diagram (Brown et al., 1984) for the Asarcik (Saplica,Catakhan), Eskine, and Saydere intrusive rocks.

SEBINKARAHISAR GRANITOIDS 579

Eurasian plate along the Izmir–Ankara–Erzincansuture zone (Sengör and Yilmaz, 1981; Okay andSahintürk, 1997). The Late Cretaceous to EarlyPaleocene ages (Oyman et al., 1995) of the Asarcik(ASC), Eskine (ESK), and Saydere (SAY) plutonssuggest that these plutons were produced from thissubduction tectonic regime. These plutons wereprobably derived from the normal and mature stages(Fig. 11) of the above-mentioned magmatism. Thesimilar mechanism was also suggested by Boztug etal. (2006, 2007) and Boztug and Harvalan (2008) forthe Eastern Pontide granitoids.

Conclusions

The Asarcik (Saplica, Catakhan), Eskine, andSaydere plutons in the Eastern Pontides are mainlymetaluminous, high-K, and calc-alkaline, and haveI-type characteristics. These plutonic rocks rangefrom monzonite to granite. All these intrusive rocksare enriched in LILE and depleted in HFSE, show-ing features of arc-related intrusive rocks. Thegeochemical data indicate that they were generatedby partial melting of mafic lower crustal sources.These plutons are related to subduction of the north-ern branch of the Neo-Tethyan Ocean beneath theEurasian plate during Cretaceous–Paleocene times,and probably formed during normal to mature stagesof a subduction setting.

Acknowledgments

Prof. Dr. Ismet Ozgenc is thanked for his help inthe fieldwork. Special thanks are due to Prof. Dr.John Winchester.

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