This article was downloaded by: [Karadeniz Teknik Universitesi] On: 17 October 2012, At: 02:44 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK International Geology Review Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tigr20 Geochronological evidence and tectonic significance of Carboniferous magmatism in the southwest Trabzon area, eastern Pontides, Turkey Abdullah Kaygusuz a , Mehmet Arslan b , Wolfgang Siebel c , Ferkan Sipahi a & Nurdane Ilbeyli d a Department of Geological Engineering, Gümüşhane University, TR-29000 Gümüşhane, Turkey b Department of Geological Engineering, Karadeniz Technical University, TR-61080 Trabzon, Turkey c Institute of Geosciences, Universität Tübingen, D-72074 Tübingen, Germany d Department of Geological Engineering, Akdeniz University, TR-070058 Antalya, Turkey Version of record first published: 05 Apr 2012. To cite this article: Abdullah Kaygusuz, Mehmet Arslan, Wolfgang Siebel, Ferkan Sipahi & Nurdane Ilbeyli (2012): Geochronological evidence and tectonic significance of Carboniferous magmatism in the southwest Trabzon area, eastern Pontides, Turkey, International Geology Review, 54:15, 1776-1800 To link to this article: http://dx.doi.org/10.1080/00206814.2012.676371 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
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This article was downloaded by: [Karadeniz Teknik Universitesi]On: 17 October 2012, At: 02:44Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK
International Geology ReviewPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/tigr20
Geochronological evidence and tectonic significanceof Carboniferous magmatism in the southwest Trabzonarea, eastern Pontides, TurkeyAbdullah Kaygusuz a , Mehmet Arslan b , Wolfgang Siebel c , Ferkan Sipahi a & NurdaneIlbeyli da Department of Geological Engineering, Gümüşhane University, TR-29000 Gümüşhane,Turkeyb Department of Geological Engineering, Karadeniz Technical University, TR-61080 Trabzon,Turkeyc Institute of Geosciences, Universität Tübingen, D-72074 Tübingen, Germanyd Department of Geological Engineering, Akdeniz University, TR-070058 Antalya, Turkey
Version of record first published: 05 Apr 2012.
To cite this article: Abdullah Kaygusuz, Mehmet Arslan, Wolfgang Siebel, Ferkan Sipahi & Nurdane Ilbeyli (2012):Geochronological evidence and tectonic significance of Carboniferous magmatism in the southwest Trabzon area, easternPontides, Turkey, International Geology Review, 54:15, 1776-1800
To link to this article: http://dx.doi.org/10.1080/00206814.2012.676371
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form toanyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses shouldbe independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly inconnection with or arising out of the use of this material.
International Geology ReviewVol. 54, No. 15, November 2012, 1776–1800
Geochronological evidence and tectonic significance of Carboniferous magmatismin the southwest Trabzon area, eastern Pontides, Turkey
Abdullah Kaygusuza*, Mehmet Arslanb , Wolfgang Siebelc , Ferkan Sipahia and Nurdane Ilbeylid
aDepartment of Geological Engineering, Gümüshane University, TR-29000 Gümüshane, Turkey; bDepartment of GeologicalEngineering, Karadeniz Technical University, TR-61080 Trabzon, Turkey; cInstitute of Geosciences, Universität Tübingen, D-72074
Tübingen, Germany; dDepartment of Geological Engineering, Akdeniz University, TR-070058 Antalya, Turkey
(Accepted 12 March 2012)
The northern and southern zones of the eastern Pontides (northeast Turkey) contain numerous plutons of varying ages andcompositions. Geochemical and isotopic results on two Hercynian granitoid bodies located in the northern zone of theeastern Pontides allow a proper reconstruction of their origin for the first time. The intrusive rocks comprise four distinctbodies, two of which we investigated in detail. Based on LA–ICP–MS U–Pb zircon dating, the Derinoba and Kayadibigranites have similar 206Pb/238U versus 207Pb/235U Concordia ages of 311.1 ± 2.0 and 317.2 ± 3.5 million years for theformer and 303.8 ± 1.5 million years for the latter. Aluminium saturation index values of both granites are between 0.95 and1.35, indicating dominant peraluminous melt compositions. Both intrusions have high SiO2 (74–77 wt.%) contents and showhigh-K calc-alkaline and I- to S-type characteristics. Primitive mantle-normalized element diagrams display enrichment in K,Rb, Th, and U, and depletion in Ba, Nb, Ta, Sr, P, and Ti. Chondrite-normalized rare earth element patterns are characterizedby concave-upward shapes and pronounced negative Eu anomalies with Lacn/Ybcn = 4.6–9.7 and Eucn/Eu∗ = 0.11–0.59(Derinoba), and Lacn/Ybcn = 2.7–5.5 and Eucn/Eu∗ = 0.31–0.37 (Kayadibi). These features imply crystal-melt fractionationof plagioclase and K-feldspar without significant involvement of garnet. The Derinoba samples have initial εNd valuesbetween –6.1 and –7.1 with Nd model ages and TDM between 1.56 and 2.15 thousand million years. The Kayadibi samplesshow higher initial εNd(I) values, –4.5 to –6.2, with Nd model ages between 1.50 and 1.72 thousand million years. Thisstudy demonstrates that the Sr isotope ratios generally display negative correlation with Nd isotopes; Sr isotope ratios werelowered in some samples by hydrothermal interaction or alteration. Isotopic and petrological data suggest that both graniteswere produced by the partial melting of early Palaeozoic lower crustal rocks, with minor contribution from the mantle.Collectively, these rocks represent a late stage of Hercynian magmatism in the eastern Pontides.
The Pontide tectonic unit (Ketin 1966) includes variousintrusive and extrusive rocks, many of which are relatedto the convergence of Eurasia and Gondwana (Figure 1A).These Permo-Carboniferous rocks (Çogulu 1975; Topuzet al. 2004, 2010; Dokuz 2011) are present as basementcomplexes in a terrane formed from the Cretaceous–Palaeocene (Yılmaz et al. 2000; Boztug et al. 2006; Ilbeyli2008; Kaygusuz et al. 2008, 2009, 2010; Kaygusuz andAydınçakır 2009; Karslı et al. 2010; Sipahi 2011) to theEocene (Boztug et al. 2004; Topuz et al. 2005; Yılmaz-Sahin 2005; Arslan and Aslan 2006; Karslı et al. 2007;Eyüboglu et al. 2010, Figure 1B). Rock compositions rangefrom low-K through high-K calc-alkaline metaluminous–peraluminous granitoids to alkaline syenites (Yılmaz andBoztug 1996). Igneous activity apparently occurred in
various tectonic settings ranging from arc-collisional tosyn-collisional and post-collisional regimes (Yılmaz andBoztug 1996; Okay and Sahintürk 1997; Yılmaz et al.1997; Yegingil et al. 2002).
About 40% of the exposed Palaeozoic basement rocksof the eastern Pontides are made up of granitoids. Despiteextensive exposure, these granitoids have received lit-tle attention so far (e.g. Yılmaz 1974; Çogulu 1975).Thus, knowledge regarding Palaeozoic geological pro-cesses in northeast Turkey is still insufficient, and precisegeochronological data are rare, thereby hampering theunderstanding of the tectonic and magmatic evolution ofthis region. We report on our systematic research of twonewly mapped intrusions, the Derinoba and Kayadibi gran-ites. New field-based observations, as well as geochemical,geochronological, and Sr–Nd–Pb isotope data from these
Figure 1. (A) Tectonic map of Turkey and surroundings (modified after Sengör et al. (2003)). (B) Distribution of plutonic and volcanicunits in the eastern Pontides (modified from Güven (1993)). (1) Palaeozoic metamorphic rocks, (2) Palaeozoic granitoids, (3) Liassic–Dogger volcanic rocks, (4) Malm–Lower Cretaceous sedimentary rocks, (5) Upper Cretaceous volcanic rocks, (6) Upper Cretaceousgranitoids, (7) Tertiary calc-alkaline volcanic rocks, (8) Tertiary alkaline volcanic rocks, (9) Eocene granitoids, (10) alluvium. NAFZ,north Anatolian fault zone; EAFZ, east Anatolian fault zone.
rocks, are presented. This study aims to gain a betterunderstanding of the regional petrogenesis and tectonicenvironment.
Geological setting and regional geology
The eastern Pontides are commonly subdivided into anorthern zone and a southern zone (Figure 2A), basedon structural and lithological features (Özsayar et al.1981; Okay and Sahintürk 1997). Pre-Late Cretaceous
sedimentary rocks are widely exposed in the southernzone, whereas Late Cretaceous and middle Eocene–lateMiocene volcanic and volcaniclastic rocks dominate thenorthern zone (Arslan et al. 1997; Sen et al. 1998; Arslanet al. 2000; Sen 2007; Temizel et al. 2012). Liassic vol-canic rocks of the eastern Pontides lie unconformably ona Palaeozoic heterogeneous crystalline basement and arecross-cut by younger granitoids of Jurassic to Palaeoceneage (Yılmaz 1972; Çogulu 1975; Okay and Sahintürk 1997;Topuz et al. 2010; Dokuz 2011) (Figure 1A). Volcanic and
Figure 2. (A) Major structures of the eastern Pontides (modified from Eyuboglu et al. (2007)). (B) Geological map of the study areawith sample locations and main settlements.
volcano-sedimentary rocks of Early and Middle Jurassicage are tholeiitic in character (Arslan et al. 1997; Sen2007). These rocks are overlain conformably by Middle–Late Jurassic–Cretaceous neritic and pelagic carbonates.The Late Cretaceous series that unconformably overliesthese carbonate rocks is made up of sedimentary rocksin the southern part and of volcanic rocks in the northernpart (Bektas et al. 1987; Robinson et al. 1995; Yılmaz andKorkmaz 1999).
Cretaceous volcanic rocks mainly belong to the tholei-itic and calc-alkaline series. Eocene volcanic rocks uncon-formably overlie the Late Cretaceous volcanic and/orsedimentary series (Güven 1993; Yılmaz and Korkmaz1999).
The altitude of the eastern Pontides (above sea level)during the Palaeocene–early Eocene era is attributed tothe collision between the Pontide arc and the Tauride–Anatolide platform (Okay and Sahintürk 1997; Boztug
et al. 2004). Eocene volcanic and volcaniclastic rocks areintruded by calc-alkaline granitoids of similar age (Arslanand Aslan 2006; Karslı et al. 2007; Eyuboglu et al. 2011).Post-Cretaceous magmatic rocks include Palaeocene plagi-oleucitites in the southern zone (Altherr et al. 2008), earlyEocene ‘adakitic’ granitoids (Topuz et al. 2005), and mid-dle to late Eocene calc-alkaline to tholeiitic, basaltic toandesitic volcanic rocks, as well as the cross-cutting gran-itoids exposed throughout the eastern Pontides (e.g. Tokel1977; Arslan et al. 1997; Karslı et al. 2007; Boztug andHarlavan 2008; Temizel and Arslan 2009; Temizel et al.2011).
The clastic input into locally developed basins is dueto post-Eocene uplift and erosion (Korkmaz et al. 1995).Towards the end of the middle Eocene, the region is largelyabove sea level. Minor volcanism and terrigeneous sedi-mentation continues to the present (Okay and Sahintürk1997). Miocene and post-Miocene volcanic history of theeastern Pontides is characterized by calc-alkaline to mildlyalkaline volcanism (Aydın 2004; Yücel et al. 2011; Temizelet al. 2012).
The study area is located in the northern zone ofthe eastern Pontides (Figure 1). Basement rocks consist-ing of Palaeozoic granites (Derinoba, Kayadibi, Sahmetlik,and Kızılagaç) have been newly mapped and are beingreported for the first time in this study (Figure 2B).The granites are unconformably overlain by Liassic vol-canics (Figure 3A) consisting of basalts, andesites, andtheir pyroclastic equivalents. These rocks are overlain
conformably by Middle–Late Jurassic–Cretaceous carbon-ates and Late Cretaceous volcanics. All these lithologiesare cut by Late Cretaceous granitoids.
Analytical techniques
A total of 15 samples were collected from the Derinobagranite and 5 samples from the Kayadibi granite (for sam-ple location, see Figure 2B). Based on the petrographicalstudies, 16 of the freshest and most representative rocksamples from the granites were selected for whole-rockmajor, trace, and rare earth element (REE) analyses. Rocksamples were crushed in steel crushers and ground in anagate mill to a grain size of <200 µm. Major, trace,and REE analyses were carried out at ACME AnalyticalLaboratories Ltd, Vancouver, Canada. Major and trace ele-ment compositions were determined by ICP-AES after0.2 g samples of rock powder were fused with 1.5 g LiBO2
and then dissolved in 100 ml 5% HNO3. REE contentswere analysed by ICP–MS after 0.25 g samples of rockpowder were dissolved via four acid digestion steps. Losson ignition was determined by the weight difference afterignition at 1000◦C. Total iron concentration was expressedas Fe2O3. Detection limits ranged from 0.01 to 0.1 wt.% formajor oxides, 0.1 to 10 ppm for trace elements, and 0.01 to0.5 ppm for REE.
Zircon grains were extracted by heavy-liquid and mag-netic separation methods and further purified by hand-picking under a binocular microscope. Selected grains
Derinoba granite
(C)
Kayadibi graniteDacitic dike
(B)
Derinoba granite
Hamurkesen
Formation
(A)
0 1 cm
(D)
Figure 3. Field and hand specimen photographs showing the rock types of the study area. (A) Contact between Hamurkesen Formationand Derinoba granite. (B) Dacitic dike cutting Kayadibi granite. (C) Field photograph from the Derinoba granite. (D) Hand specimenfrom the Derinoba granite.
were mounted on epoxy resin and polished until halfwaythrough. Cathodoluminescence images were acquired tocheck the internal structures of individual zircon grains andto ensure a better selection of analytical positions.
U–Pb zircon dating was carried out using LA–ICP–MS at the Geologic Lab Center, China University ofGeosciences (Beijing, China). A quadrupole ICP–MS(7500a; Agilent Inc., Santa Clara, CA, USA) was con-nected with a UP-193 solid-state laser (193 nm; ElectroScientific Industries, Inc., Portland, OR, USA) and anautomatic positioning system. The laser spot size wasset to approximately 36 µm, with an energy density of8.5 J/cm2 and repetition rate of 10 Hz. Laser samplingwas according to the following procedure: 5 s pre-ablation,20 s sample-chamber flushing, and 40 s sampling abla-tion. The ablated material was carried into the ICP–MSby a high-purity He gas stream with flux of 0.8 l/min.The entire laser path was fluxed with N2 (15 l/min) andAr (1.15 l/min) to increase energy stability. U–Pb isotopefractionation effects were corrected using zircon 91500(Wiedenbeck et al. 1995) as external standard. Zircon stan-dard TEMORA (417 million years, Black et al. 2003) wasalso used as a secondary standard to monitor the devia-tion of age measurement/calculation. A total of 10 analysesof TEMORA yielded apparent 206Pb/238U ages of 417 to418 million years. Isotopic ratios and element concentra-tions of zircons were calculated using the GLITTER soft-ware (ver. 4.4, Macquarie University, Sydney, Australia).Concordia ages and diagrams were obtained usingIsoplot/Ex (3.0) (Ludwig 2003). Common lead was cor-rected following the method of Andersen (2002).
Electron microprobe analyses on polished thin sectionswere carried out at the New Mexico Institute of Miningand Technology, Socorro, NM, USA, using a CamecaSX-100 electron microprobe with three wavelength-dispersive spectrometers. Samples were examined usingbackscattered electron imagery, and selected minerals werequantitatively analysed. Elements analysed included F, Na,Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Sr, and Ba.An accelerating voltage of 15 kV and probe current of20 nA were used, except for analyses using general glasslabels (i.e. chlorite), which utilized a 10 nA probe current.Peak count numbers of 20 s were used for all elements,except for F (40 s; amph/mica), F (60 s; glass), Cl (40 s), S(30 s), Sr (60 s), and Ba (60 s). Background count numberswere one half the peak count times. A point beam of 1 µmwas used to analyse amphibole, pyroxene, epidote, Fe–Tioxide, and zircon. A slightly defocused (10 µm) beam wasused to analyse feldspar, mica, and chlorite to avoid lossescaused by sodium volatilization (Nielsen and Sigurdsson1981). Analytical results are presented in Tables 1–3.
Sr, Nd, and Pb isotope compositions were measured ona Finnigan MAT 262 multicollector mass spectrometer atthe Institute of Geosciences, Tübingen, Germany. For Sr–Nd isotope analyses, approximately 50 mg of whole-rock
powder was decomposed in 52% HF for 4 days at 140◦Con a hot plate. Digested samples were dried and redis-solved in 6 N HCl; these were dried again and redissolvedin 2.5 N HCl. Sr and Nd were separated by conventional ionexchange techniques, and their isotopic compositions weremeasured on single W and double Re filament configura-tions, respectively. The isotopic ratios were corrected forisotopic mass fractionation by normalizing to 86Sr/88Sr =0.1194 and 146Nd/144Nd = 0.7219. The reproducibility of87Sr/86Sr and 143Nd/144Nd during the period of measure-ment was checked by analyses of NBS 987 Sr and La JollaNd standards, which yielded average values of 0.710235± 0.000015 (2SD, n = 3) and 0.511840 ± 0.000008 (2SD,n = 5), respectively. Total procedural blanks were 20–50 pgfor Sr and 40–66 pg for Nd. The separation and purifi-cation of Pb were carried out on Teflon columns with a100 µm (separation) and 40 µm bed (cleaning) of Bio-Rad AG1-X8 (100–200 mesh) anion exchange resin usingan HBr–HCl ion exchange procedure. Pb was loaded withSi-gel and phosphoric acid into a Re filament and wasanalysed at about 1300◦C in a single-filament mode. A fac-tor of 1‰ per atomic mass unit for instrumental massfractionation was applied to the Pb analyses, using NBSSRM 981 as reference material. The total procedural blanksfor Pb during the measurement period were between 20 and40 pg. Sample reproducibility was estimated at ±0.02,±0.015, and ±0.03 (2σ ) for 206Pb/204Pb, 207Pb/204Pb, and208Pb/204Pb ratios, respectively.
Results
Field relations and petrography
The resulting geological map contains four separate gran-ite bodies, namely, Derinoba, Kayadibi, Sahmetlik, andKızılagaç (Figure 2B). These intrusions form nearly NE–SW-elongated bodies in varying dimensions occupyingthe highest peaks in the region. Generally, these arebounded by the pre-Jurassic volcanic and pyroclasticrocks to the east. Liassic volcanic and pyroclastic rocks(Hamurkesen Formation) unconformably overlie the gran-ite bodies (Figure 3A). In the west, granite bodies thrustover Late Cretaceous volcanic and pyroclastic rocks (Çatakand Kızılkaya Formations).
The Derinoba granite, located about 65 km southwestof Trabzon, forms an E–W-elongated body, with the longaxis extending from northeast to southwest (Figure 2B).This granite body covers an area of approximately 13 km2.In the east, the granite is unconformably overlain byLower Jurassic volcanic and pyroclastic rocks, whereasin the west, the granite thrusts over Late Cretaceous vol-canic and pyroclastic rocks together with their cover rocks(Figure 2B). The Derinoba granite is generally unde-formed, but strongly altered and weathered. Rocks oftenhave a brick red to pink colour, except for strongly chlori-tized zones that are greenish.
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International Geology Review 1781
Tabl
e1.
Mic
ropr
obe
anal
yses
ofpl
agio
clas
esfr
omth
eD
erin
oba
and
Kay
adib
igra
nite
s.
Pla
gioc
lase
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kty
pes
Der
inob
agr
anit
esK
ayad
ibig
rani
tes
Sam
ples
T13
8-3
cT
138-
4r
T13
8-5
cT
138-
6r
T13
8-11
cT
138-
12r
T13
5-1
rT
135-
2c
T13
5-7
rT
135-
8c
T13
5-9
rT
135-
10c
M16
-3c
M16
-4c
M16
-5c
M16
-6r
M16
-9c
M16
-10
cS
iO2
68.0
968
.16
68.8
868
.98
65.7
468
.49
68.4
867
.26
67.5
165
.73
67.4
967
.41
67.5
666
.80
66.3
368
.21
67.3
067
.51
Al 2
O3
20.7
419
.83
20.3
120
.41
22.3
721
.09
20.0
221
.41
20.3
021
.39
19.5
620
.27
20.6
720
.68
21.0
520
.97
21.1
720
.80
FeO
T0.
060.
090.
140.
030.
280.
050.
040.
230.
050.
250.
060.
140.
050.
140.
080.
090.
110.
08C
aO0.
770.
270.
300.
140.
620.
870.
190.
280.
410.
550.
200.
270.
561.
160.
660.
841.
230.
65N
a 2O
11.3
211
.16
11.7
111
.60
10.2
511
.46
11.6
210
.97
11.2
510
.51
11.2
411
.36
11.4
011
.07
10.8
211
.34
11.1
511
.25
K2O
0.10
0.11
0.10
0.11
1.18
0.31
0.14
0.90
0.27
1.08
0.13
0.40
0.23
0.28
0.60
0.16
0.17
0.23
BaO
0.02
0.06
0.07
0.00
0.03
0.02
0.00
0.09
0.00
0.00
0.00
0.10
0.00
0.02
0.03
0.05
0.03
0.05
SrO
0.03
0.02
0.01
0.02
0.06
0.07
0.05
0.02
0.00
0.05
0.00
0.04
0.03
0.04
0.03
0.02
0.00
0.05
Tota
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99.7
101.
510
1.3
100.
510
2.4
100.
510
1.2
99.8
99.5
98.7
100.
010
0.5
100.
299
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1.7
101.
210
0.6
Cat
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sis
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xyge
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952.
992.
972.
972.
882.
942.
982.
922.
962.
912.
992.
962.
952.
932.
922.
942.
922.
94A
l1.
061.
021.
031.
041.
151.
071.
031.
101.
051.
111.
021.
051.
061.
071.
091.
071.
081.
07Fe
2+0.
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000.
010.
000.
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010.
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010.
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030.
050.
030.
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060.
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950.
950.
980.
970.
870.
950.
980.
920.
960.
900.
960.
970.
960.
940.
920.
950.
940.
95K
0.01
0.01
0.01
0.01
0.07
0.02
0.01
0.05
0.01
0.06
0.01
0.02
0.01
0.02
0.03
0.01
0.01
0.01
Ba
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
Sr
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
Tota
l5.
004.
995.
014.
995.
015.
025.
005.
025.
005.
024.
995.
015.
015.
015.
015.
015.
015.
01A
n3.
581.
301.
400.
653.
003.
970.
871.
301.
952.
610.
961.
252.
615.
403.
143.
915.
713.
04A
b95
.84
98.0
898
.06
98.7
690
.17
94.3
798
.33
93.6
396
.54
91.2
298
.32
96.5
396
.11
93.0
593
.44
95.2
393
.35
95.6
8O
r0.
580.
620.
530.
596.
831.
660.
805.
081.
516.
170.
722.
221.
281.
553.
430.
860.
941.
28
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Tabl
e2.
Mic
ropr
obe
anal
yses
ofK
-fel
dspa
rsfr
omth
eD
erin
oba
and
Kay
adib
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K-f
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par
Roc
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2+0.
000.
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0.00
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Sr
0.00
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8
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e:Fe
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Table 3. Microprobe analyses of biotites from the Derinoba and Kayadibi granites.
The Kayadibi granites, as well as the two other stocksreferred to as Sahmetlik and Kızılagaç, form small ellip-tical bodies. Each of these bodies has an outcrop area ofapproximately 1 km2 (Figure 2A), overlain unconformablyby Lower Jurassic volcanic and pyroclastic rocks in theeast and thrust over Late Cretaceous volcanic and pyroclas-tic rocks in the west (Figure 2A). All granites mentionedare cut by Late Cretaceous granites and dacitic dikes anddomes (Figure 3B).
Studied samples (i.e. obtained from Derinoba andKayadibi) are medium- to coarse-grained monzogran-ites, share several common petrographic features, andare described together. These samples are composed ofequigranular K-feldspar, quartz, plagioclase, biotite, acces-sory zircon, apatite, allanite, magnetite, and secondaryphases of sericite, chlorite, epidote, clay minerals, carbon-ates, and white mica (Figures 3C and 3D).
Plagioclase forms subhedral to euhedral, normally andreversely zoned prismatic crystals. In some samples, itis altered into sericite and clay minerals and partly intoepidote. Representative mineral analyses of plagioclasecrystals are provided in Table 1. Composition in all samplesis pure albite and varies from An1 to An4 in the Derinobagranite, whereas in the Kayadibi granite, it is slightly lessrich in sodium and ranges from An3 to An6. K-feldspar
forms anhedral, rarely subhedral crystals of orthoclase andperthitic orthoclase. Large K-feldspar oikocrysts containinclusions of abundant plagioclase, biotite, and opaqueminerals. Representative mineral analyses of K-feldsparare presented in Table 2. Compositions range from Or94
to Or99 in the Derinoba granite and Or96 to Or97 in theKayadibi granite (Table 2).
Biotite is euhedral to subhedral, is reddish-brown incolour, and forms small prismatic crystals and lamel-las. In most samples, biotite is strongly chloritizedor partially replaced by prehnite and/or pumpellyite.Biotite sheets are frequently deformed around secondaryprehnite/pumpellyite grains. Primary inclusions in biotiteare magnetite, apatite, and zircon. Representative biotiteanalyses are provided in Table 3. The Mg-number (Mg/Mg+ Fe2+) varies from 0.40 to 0.46 in the Derinoba graniteand from 0.45 to 0.47 in the Kayadibi granite (Table 3).TiO2 contents are relatively high (3.25–4.74 wt.%).
Quartz is anhedral in shape and generally shows undu-lose extinction. It locally forms large grains but also fillsthe interstitial spaces left behind from early-crystallizedplagioclase and mafic minerals.
Apatite is the most common accessory mineral andoccurs as small prismatic and acicular crystals. Allaniteforms euhedral, reddish crystals in all samples. Zircon is
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observed as short euhedral and prismatic crystals. Opaqueminerals are mostly titaniferous magnetites that occur asphenocrysts and microphenocrysts.
Whole-rock chemistry
Major, trace, and REE analyses of representative sam-ples from the Derinoba and Kayadibi granites are givenin Table 4. In the classification diagram of Debon and LeFort (1982), all samples are plotted in the granite field(Figure 4A). In the Rb–Sr–Ba ternary diagram (Tarney andJones 1994), samples are plotted in the field of low Ba–Srgranitoids (not shown here).
Both granites span a narrow compositional range(Table 4, Figure 4A). SiO2 ranges from 75 to 77 wt.%in the Derinoba granite and from 74 to 75 wt.% in theKayadibi granite (Table 4). K2O/Na2O ratios vary between0.98 and 1.45 (Derinoba) and 1.18 and 1.43 (Kayadibi).The aluminium saturation index (ASI) (molar Al2O3/(CaO+ Na2O + K2O)) values of samples from the Derinobaand Kayadibi granites are between 0.95 and 1.35, withan average of 1.14. These figures indicate that the gran-ites are dominantly peraluminous (Table 4, Figure 4B).Both granites show subalkaline affinity and belong to thehigh-K calc-alkaline series (Figure 5A). In the SiO2 ver-sus ASI diagram (Figure 5B), the samples are plotted inthe I- to S-type granite fields. Some altered samples fromthe Derinoba granite portray elevated ASI values. Harkerplots of selected major and trace elements (Figure 5C–5R) show systematic variations in element concentration.The rocks define trends without a compositional gap. CaO,MgO, Fe2O3(T), TiO2, P2O5, Ba, Sr, Th, Ni, and Y con-tents decrease with increasing SiO2 content, whereas K2O,Al2O3, Zr, and Nb increase with increasing SiO2 content;Na2O and Pb are nearly constant (Figure 5C–5R).
In the primitive mantle-normalized trace element dia-grams (Figure 6A–6C), all samples from the Kayadibi andDerinoba granites display marked negative anomalies inBa, Nb, Ta, Sr, P, and Ti, but positive anomalies in Kand partly Pb, which indicate fractionation of plagioclase,K-feldspar, biotite, apatite, and Fe–Ti oxides.
Chondrite-normalized REE patterns of the Kayadibiand Derinoba granite samples (Figure 6D–6F) are gener-ally characterized by concave-upward shapes (Lacn/Ybcn
= 2.7–9.7) and pronounced negative Eu anomalies(Eucn/Eu∗) of 0.11–0.59, whereas the largest Eu-anomaliesappear in the Derinoba granite (Table 4). Comparedwith other Palaeozoic granitoids of the eastern Pontides(Figure 6C and 6F), the trace and REE patterns of theDerinoba and Kayadibi granites resemble those of theGümüshane pluton (Topuz et al. 2010). However, theDerinoba and Kayadibi granites differ from the Gümüshanepluton in terms of the stronger negative Eu anomalies(Figure 6F).
In the (Zr + Nb + Ce + Y) versus FeO∗/MgO tec-tonic discrimination diagram of Whalen et al. (1987), theDerinoba and Kayadibi granites fall within the I-type gran-ite field (Figure 7A). Furthermore, the tectonic discrimina-tion diagram of Batchelor and Bowden (1985) (Figure 7B)suggests a syn- to post-collisional geochemical signaturefor both granites.
Sr–Nd–Pb isotopes
Sr, Nd, and Pb isotope data for the Kayadibi and Derinobagranites are given in Tables 5 and 6 and plotted in Figure 8.Initial Sr, Nd, and Pb isotope ratios are calculated usingRb, Sr, Sm, Nd, U, Th, and Pb concentration data obtainedfrom ICP–AES and MS analyses, with the assumed graniteages of 303 million years (Kayadibi) and 317–311 millionyears (Derinoba) (see below). Samples from the Kayadibiand Derinoba granites show a relatively wide range of ini-tial 87Sr/86Sr ratios (0.6974–0.7079) and a narrow range ofεNd(I) values (–4.6 to –7.1). The corresponding Nd modelages (TDM) of the granites are in the range 1.50–2.15 thou-sand million years. Extremely low (87Sr/86Sr)(I) ratios(0.6974–0.7003) are found in samples, showing evidencefor alteration, which may suggest that the Rb–Sr systemis more severely influenced by hydrothermal alteration orweathering than the Sm–Nd isotope system.
No correlation exists between εNd(I) and (87Sr/86Sr)(I)
but the Derinoba samples display lower εNd(I) val-ues (–7.1 to –6.1) and higher (87Sr/86Sr)(I) ratios(0.7003–0.7079) than the Kayadibi samples [εNd(I) =–4.6 to –6.2, (87Sr/86Sr)(I) = 0.6974–0.703] (Figure 8A).In the SiO2 versus (87Sr/86Sr)(I) and (143Nd/144Nd)(I) dia-grams (Figures 8B and 8C), the samples define nearlyhorizontal trends, indicating fractional crystallization.A slightly positive correlation, however, is shown in the(143Nd/144Nd)(I) versus Nd plot (Figure 8D).
In Figure 8A, the Derinoba and Kayadibi granitesare compared with other Palaeozoic granites from theeastern Pontides. As shown in this plot, the studied sam-ples have similar εNd(I) and (87Sr/86Sr)(I) ratios to thosefrom Gümüshane pluton but lower (87Sr/86Sr)(I) ratios thanthose of the Köse pluton. The Köse samples show a nega-tive correlation between εNd(I) and (87Sr/86Sr)(I), whereasthe Kayadibi, Derinoba, and Gümüshane samples show noobvious correlation between these two parameters.
Samples from the Kayadibi and Derinoba granites havesimilar (207Pb/204Pb)(I) = 15.55–15.62, but have vari-able (206Pb/204Pb)(I) = 17.29–18.0 and (208Pb/204Pb)(I) =36.38–37.67 isotopic compositions (Table 6, Figures 8Eand 8F). In the (207Pb/204Pb)(I) versus (206Pb/204Pb)(I)
diagram (Figure 8E), the samples are plotted to the leftof the geochron and above the Northern HemisphereReference Line (Hart 1984). In the (206Pb/204Pb)(I) versus(207Pb/204Pb)(I) diagram (Figure 8F), the studied samples
Figure 4. (A) Chemical nomenclature diagram (Debon and Le Fort 1982) for samples from the Derinoba and Kayadibi granites. (B)A/CNK (Al2O3/CaO + Na2O + K2O) versus A/NK (Na2O + K2O) molar diagram showing the range in alumina saturation index (ASI)of Derinoba and Kayadibi granites.
form subparallel trends to the orogen curve (Zartman andDoe 1981).
U–Pb zircon dating
LA–ICP–MS U–Pb zircon dating results are presented inTable 7 and shown in Concordia diagrams (Figure 9).Zircons are colourless to light yellow, with long prismatic,perfectly euhedral, and oscillatory zoning (Figure 10).Zircon grains are mostly fine-grained (63–125 µm) andhave aspect ratios of about 1:3. Inclusions of apatite andinternal fractures are common. All these features indicatethat zircons are of magmatic origin. Some grains are cor-roded and display altered domains. Only the uncorrodedinner parts of the grains are investigated for U–Pb isotopeanalyses. Most analyses give concordant age data. A totalof 23 spots from sample T138 (Derinoba) yield 206Pb/238Uages ranging from 301 to 317 million years, with aweighted mean age of 311.1 ± 2.0 million years (MSWD =1.4) (Table 7, Figure 9A), and 12 spots from another sam-ple of this granite (T135) give 206Pb/238U ages between310 and 325 million years, with a weighted mean age of317.2 ± 3.5 million years (MSWD = 1.7) (Figure 9B).A total of 30 spots from sample M16 (Kayadibi) provide206Pb/238U ages between 300 and 306 million years, with aweighted mean age of 303.8 ± 1.5 million years (MSWD =0.119) (Figure 9C). Thus, Lower Carboniferous ages areestablished for both granites by U–Pb zircon dating, andthese ages are interpreted as magmatic emplacement ages.
Discussion
Age constraints
In previous works, the emplacement age of granitoidsin the eastern Pontides is mainly estimated from contactrelationships, stratigraphic criteria, or biostratigraphic data.Such data, however, are often imprecise or difficult to
obtain due to rock deformation or tectonic displace-ment. Thus, an age reassessment, in the light of newgeochronological data, is essential. Early geochronologicstudies on the Gümüshane and Köse plutons, however,have given ambiguous and inconsistent results between107 and 535 million years (Delaloye et al. 1972; Çogulu1975; Moore et al. 1980; JICA 1986; Bergougnan 1987).More recently, Topuz et al. (2010) reported concor-dant U–Pb zircon and Ar–Ar biotite/hornblende ages of324 and 320 million years, respectively, for granite samplesfrom the Gümüshane pluton. Almost concurrently, Ar–Ar biotite/hornblende/K-feldspar ages between 322 and306 million years have been obtained for the Köse pluton(Dokuz 2011).
Prior to this study, knowledge about the emplacementage of the Kayadibi and Derinoba granites was insufficientfor the reconstruction of their geological history. Fromcontact relationships and stratigraphic criteria, an UpperCretaceous age has been conjectured (Güven 1993). Thenew LA–ICP–MS U–Pb zircon ages of these granites, how-ever, range from 303.8 ± 1.5 million years (MSWD =0.12) to 317.2 ± 3.5 million years (MSWD = 1.7).These ages are more or less coeval with the emplacementage of the Gümüshane and Köse plutons (Topuz et al.2010; Dokuz 2011). Hence, the Derinoba and Kayadibigranites are interpreted as members of a larger coher-ent pluton, referred to here as the eastern Pontide pluton.Remnants of this pluton either extend below the cover ofthe volcanic and volcaniclastic rocks or are now partlyeroded.
Petrogenesis of the Derinoba and Kayadibi granites
Major and trace element compositional variations in theDerinoba and Kayadibi granites suggest that fractionationplayed a major role during the crystallization of the graniticmagmas (Figure 11). Fractionation of feldspar would also
Figure 5. (A–R) Variation diagrams of SiO2 (wt.%) versus major oxides (wt.%) and trace elements (ppm) for samples from the Derinobaand Kayadibi granites. (A) K2O versus SiO2 diagram with field boundaries between medium-K, high-K, and shoshonitic series accordingto Peccerillo and Taylor (1976). (B) ASI versus SiO2 with field boundaries between I-type and S-type according to Chappell and White(1974) and peraluminous and metaluminous fields of Shand (1947). ASI (aluminium saturation index) = molar Al2O3/(Na2O + K2O +CaO). Same symbols as in Figure 4.
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0.1
1.0
10.0
100.0
1000.0
Sam
ple
/prim
itiv
e m
antle
Derinoba granite(A)
Ba U Ta La Pb Sr Nd Hf Eu Dy YbRb Th Nb K Ce Pr P Zr Sm Ti Y Lu
1
10
100
1000
Sam
ple
/chondrite
(F)
Kösepluton
Gümüşhane pluton
La Ce Pr Nd SmEu Gd Tb Dy Ho Er TmYb Lu
0.1
1.0
10.0
100.0
1000.0
Sam
ple
/prim
itiv
em
antle
Kayadibi granite(B)
Ba U Ta La Pb Sr Nd Hf Eu Dy YbRb Th Nb K Ce Pr P Zr Sm Ti Y Lu
0.1
1.0
10.0
100.0
1000.0
Sam
ple
/prim
itiv
e m
antle
Kösepluton
Gümüşhane pluton(C)
Ba U Ta La Pb Sr Nd Hf Eu Dy YbRb Th Nb K Ce Pr P Zr Sm Ti Y Lu
1
10
100
1000
Sam
ple
/chondrite
(D) Derinoba granite
(La/Yb)cn
= 4.6–9.7
La Ce Pr Nd SmEu Gd Tb Dy Ho Er TmYb Lu
La Ce Pr Nd SmEu Gd Tb Dy Ho Er TmYb Lu1
10
100
1000
Sam
ple
/chondrite
(E) Kayadibi granite
(La/Yb)cn
= 2.7–5.5
Figure 6. (A–C) Primitive mantle-normalized trace element patterns (normalizing values from Sun and McDonough 1989) for samplesfrom the Derinoba and Kayadibi granites. (D–F) Chondrite-normalized REE patterns (normalizing values from Taylor and McLennan1985). Symbols as in Figure 4.
Figure 7. (A) FeO∗/MgO versus (Zr + Nb + Ce + Y) classification diagram (Whalen et al. 1987) for the Derinoba and Kayadibigranites. (B) R1 versus R2 diagram of Batchelor and Bowden (1985). R1 = 4Si − 11(Na + K) − 2(Fe + Ti); R2 = 6Ca + 2 Mg + Al.Symbols as in Figure 4.
Figure 8. (A) εNd(I) versus (87Sr/86Sr)(I) diagram for the Derinoba and Kayadibi granites. (B–D) (87Sr/86Sr)(I) and (143Nd/144Nd)(I) versusSiO2 and Nd plots, respectively. (E and F) Pb isotope correlation plots of the Derinoba and Kayadibi granites. EMI, enriched mantle typeI (Zindler and Hart 1986); HIMU,– high-µ (µ = 238U/204Pb, Lustrino and Dallai 2003); EMII, enriched mantle type II (enriched in Sr);LC,– lower crust; NHRL, Northern Hemisphere Reference Line (Hart 1984); UC, upper crust. Mantle (MORB), orogen, upper crust (UC),and lower crust (LC) evolution lines are from Zartman and Doe (1981). Symbols as in Figure 4.
result in the depletion of Ba and Sr. Negative Eu anoma-lies and a decrease in Sr with increasing silica (Figure 5L)indicate that plagioclase is an important fractionatingphase. The rocks show similar REE patterns, with a generalincrease of both light and heavy REEs with increasingSiO2 (Figure 6). The magnitude of the negative Eu anoma-lies increases with increasing SiO2 contents, suggestingfractionation of plagioclase for both granites. Fractionationof Fe–Ti oxide may be responsible for the negative anomalyin Ti. The negative anomaly in P is most probably theresult of apatite fractionation (Figure 6). Garnet may havenot been involved in magma genesis (Table 4); chondrite-normalized REE patterns show almost no fractionationbetween middle and heavy REE, and Sr/Y ratios are low(i.e. 1.2–3.7).
The Derinoba and Kayadibi granites are high-K calc-alkaline rocks, and their primitive mantle-normalized
spider diagrams are characterized by pronounced neg-ative Ba, Sr, Ti, and Nb anomalies and enrichmentin Rb, K, and La. These are typical features of syn-orogenic crustal-derived granitoids. Moderate to highRb/Sr ratios (0.5–5.2) and high K2O (3.2–4.8 wt.%) andSiO2 (74–77 wt.%) contents are consistent with the deriva-tion from a metasedimentary or felsic micaceous crustalsource (cf. Van de Flierdt et al. 2003; Jung et al. 2009).Moreover, Nb/Ta ratios vary from 5.7 to 20.5 (averagevalue = 12.7), Zr/Hf from 24.3 to 51.4 (average = 30.5),and Th/U from 2.5 to 13.8 (average = 5.40). Thesegeochemical signatures also suggest the derivation of thesemagmas from the partial melting of crustal rocks.
The ASI values indicate strongly peraluminous com-position, as expected for melts derived by partial meltingof continental crustal rocks. Hence, a derivation fromcrustal sources is apparent. The heterogeneity of the initial
Figure 9. (A–C) Concordia diagrams showing LA–ICP–MS U–Pb zircon dating results from (A and B) Derinoba granite (samplesT138 and T135) and (C) Kayadibi granite (sample M16).
(A) T138 (B) M16
100 μm100 μm
Figure 10. (A and B) Cathodoluminescence images of typical zircons from (A) Derinoba granite (sample T138) and (B) Kayadibi granite(sample M16).
Sr isotope values is also consistent with this interpreta-tion. However, the granites have undergone deformationand alteration to variable degrees. Therefore, a prudentassumption is that the measured Rb/Sr and 87Sr/86Srratios have been modified to a certain extent, at least insome samples. Extremely low (87Sr/86Sr)(I) values (e.g.
0.6974–0.7003) have been found in samples, showing signsof aqueous alteration. Therefore, these values do not pro-vide a significant geological meaning. On the other hand,Nd isotope ratios are known to be more robust duringalteration and provide less ambiguous constraints on theorigin of these rocks. Initial 143Nd/144Nd isotope values
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Sr
10
100
1000
Rb
Pl
Kf
Bi
Cpx Hb
(A)
10 100 1000 10 100 1000
Sr
10
100
1000
Ba
Pl
Kf
Bi
CpxHb (B)
Figure 11. (A and B) Variation of (A) Rb versus Sr and (B) Ba versus Sr. Fractionation vectors were calculated according to the partitioncoefficients listed in Rollinson (1993). Symbols as in Figure 4.
(0.51188–0.51201) of the studied granites are homoge-neous with negative εNd(I) values (–4.6 to –7.1), con-firming the derivation of granitic magma from crustalsources.
Experimental data on high-K calc-alkaline granitoidrocks show that such rocks can be produced by melt-ing different crustal sources (e.g. Roberts and Clemens1993). Furthermore, partial melting yields compositionaldifferences among magmas produced by melting com-mon crustal rocks, such as amphibolites, tonalitic gneisses,metagreywackes, and metapelites under variable meltingconditions (e.g. Patiño-Douce 1999). This compositionalvariation can be visualized in terms of major oxide ratios(Figures 12A–12D) or molar oxide ratios (Figures 12E–12G). The plots in Figures 12A–12F show that partialmelts derived from metapelites and metagreywackes sourcerocks have higher molar (Na2O + K2O)/(FeOT + MgO+ TiO2) and K2O/Na2O ratios as well as lower molarCaO/(MgO + FeOT) and Na2O, relative to those originatedfrom the mafic to intermediate source rocks (Figure 12).Most samples from the Derinoba and Kayadibi granitesplot in the metagreywackes field (Figure 12) and showhigh molar (Na2O + K2O)/(FeOT + MgO + TiO2) andmolar K2O/Na2O ratios but relatively low CaO/(MgO +FeOT). In the Al2O3/TiO2 versus CaO/Na2O diagram(Figure 12H), the granites show varying CaO/Na2O val-ues, which indicate the protolith composition of a mixtureof sandstone and argillaceous rocks. These features, asso-ciated with relatively low Mg-number values (9–33), sug-gest melt production from lower crustal metasedimentarysource rocks. A similar origin is suggested for granophyresfrom the Gümüshane pluton (Topuz et al. 2010).
Geodynamic implications
Hercynian plutonism in Turkey is confined spatially to thePontides, specifically to its eastern portion (Figure 1B).The subduction polarity and geotectonic evolution ofthe eastern Pontide orogenic belt are still controversial.The various models proposed for the subduction polar-ity of the eastern Pontides can be grouped into three:(i) Adamia et al. (1977) and Ustaömer and Robertson
(1996) suggested that the eastern Pontides developed by thenorthward subduction of the Palaeotethys, which was situ-ated to the south of the magmatic arc, from the Palaeozoicuntil the end of the Eocene; (ii) Sengör and Yılmaz(1981) proposed that the Palaeotethys was situated to thenorth of the Pontides, and hence southward subductionoccurred from the Palaeozoic until the Middle Jurassic,whereas northward subduction occurred subsequently fromthe Upper Cretaceous until the end of the Eocene; (iii)Dewey et al. (1973), Bektas et al. (1999), and Eyubogluet al. (2007) suggested that southward subduction contin-ued uninterruptedly from the Palaeozoic until the end ofthe Eocene.
Researchers are likewise debating whether the easternPontides belong to Gondwana or Eurasia (Laurussia)(Sengör et al. 1980; Sengör and Yılmaz 1981; Robertsonand Dixon 1984; Robinson et al. 1995; Okay and Sahintürk1997; Yılmaz et al. 1997; Wehrmann et al. 2010).The oceanic domain between Gondwana and Eurasia(Laurussia) is known as the Palaeotethys. The locationof the eastern Pontides during the late Palaeozoic erais contentious. Some authors have suggested that theeastern Pontides formed part of the active northern mar-gin of Gondwana (Sengör and Yılmaz 1981; Sengör 1990),whereas Okay et al. (2006) and Moix et al. (2007) pro-posed that this block was located at the southern margin ofLaurussia.
Palaeozoic low-P–high-T metamorphic rocks andgranitoids are common throughout the Sakarya zone andin the Caucasus, which form the eastward extension ofthe eastern Pontides (e.g. Hanel et al. 1992; Okay et al.2002; Nzegge et al. 2006; Somin et al. 2006; Treloar et al.2009). On the other hand, Palaeozoic metamorphism ormagmatism has not been reported in the Tauride–Anatolideblock, which has a Neo-Proterozoic crystalline basementoverlain by different sedimentary successions ranging fromMid-Cambrian to Miocene in age. The basement and partsof the overlying successions were strongly deformed andpartly metamorphosed during the Alpine orogeny (Okayet al. 2006, and references therein). Based on the differ-ences in stratigraphy, type, and age of the basement rocks,Topuz et al. (2010) suggested that the Sakarya zone and
Figure 12. (A–G) Chemical composition of the Derinoba and Kayadibi granites: outlined fields denote compositions of partial meltsobtained in experimental studies by dehydration melting of various bulk compositions. MB, metabasalts; MA, meta-andesites; MGW,metagreywackes; MP, metapelites; FP, felsic pelites; AMP, amphibolites. (H) Al2O3/TiO2 versus CaO/Na2O diagram showing the prove-nance of early Palaeozoic granites in the central-southern Jiangxi Province. Lac, Lachlan fold zone in Australia; Alps, the Alpine orogenicbelt in Europe; Her, Hercynian orogenic belt in Europe; Him, the Himalaya orogenic belt. Data sources: Vielzeuf and Holloway (1988),Patiño Douce and Johnston (1991), Rapp et al. (1991), Gardien et al. (1995), Rapp (1995), Rapp and Watson (1995), Patiño Douce andBeard (1996), Stevens et al. (1997), Skjerlie and Johnston (1996), Patiño Douce (1997), Patiño Douce and McCarthy (1998) and PatiñoDouce (1999). Symbols as in Figure 4.
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the Tauride–Anatolide block formed distinct entities dur-ing the late Palaeozoic to the early Mesozoic. Hence, theeastern Pontides were probably part of Laurussia during thePalaeozoic (Topuz et al. 2010).
The presence of Carboniferous low-P–high-T meta-morphism in the eastern Pontides is regarded as late impactof the Hercynian orogeny and as evidence of a coeval sub-duction zone during the emplacement of the CarboniferousGümüshane pluton (Topuz et al. 2010). However, neitherlow- nor high-P metamorphic rocks have been observedin the area of the Derinoba and Kayadibi granitic bodies.Thus, the present theory is that granites and metamorphicrocks were separated by thrusting after pluton emplacementor the original contact between these lithological units maybe hidden by younger cover units.
Carboniferous Derinoba and Kayadibi granites can beregarded as late-stage magmatic products of the Hercynianorogeny. Moreover, the overall geochemical and isotopicfeatures of the granites, along with the regional geology,favour an emplacement in a continental arc or syn- orpost-collisional setting. Hence, the Derinoba and Kayadibigranites, together with the Gümüshane and Köse plutons,can be interpreted as members of a larger coherent plu-ton, namely, the eastern Pontide pluton. This pluton wasgenerated by the partial melting of a variety of meta-mafic to metafelsic source rocks in the lower continentalcrust. Furthermore, the eastern Pontides are assumed tobe part of Laurussia during the Palaeozoic, and that theCarboniferous period reflects the transition from conti-nental arc setting to a syn- or post-collisional setting.Thus, the crustal melts were probably generated in a syn-or post-collisional setting, although the melting mecha-nism of the lower crust is still a matter of debate. Topuzet al. (2010) suggested that in a post-collisional setting,delamination of the subcontinental lithosphere might haveoccurred, leading to the underplating of mafic rocks. Theseunderplated magmas may have provided the heat nec-essary to melt the existent mafic into relatively felsiclower crustal rocks, resulting in the formation of meta-luminous to peraluminous granitic melts. Under a syn-or post-orogenic condition, these melts intruded into theupper crust, leading to the development of I- and S-typegranites.
Conclusions
Our study for the first time establishes the presence ofHercynian granitoids in the northern zone of the easternPontides. Among these rocks, the Derinoba and Kayadibimedium- to coarse-grained granites form a distinctive con-stituent of the pre-Liassic basement of the eastern Pontides.Based on LA–ICP–MS U–Pb zircon analyses, ages of317.2 ± 3.5 and 311.1 ± 2.0 million years (Derinoba) and303.8 ± 1.5 million years (Kayadibi) are assigned to thesebodies. These ages are coeval with the emplacement agesof the Gümüshane and Köse granites.
These bodies show a high-K calc-alkaline and I- toS-type character. Fractional crystallization processes oper-ated during the evolution of the plutonic rocks withplagioclase, K-feldspar, apatite, and magnetite as the mostimportant fractionating minerals. All rocks define a smallrange of Nd isotope ratios. Nd model ages of the granitesrange from 1.50 to 2.15 thousand million years.
These characteristics, combined with high K2O/Na2O,(Na2O + K2O)/(FeOT + MgO + TiO2), and relativelylow CaO/(MgO + FeOT) ratios, suggest that the Derinobaand Kayadibi granites were generated by the partial melt-ing of lower crustal metasedimentary protoliths in a syn- orpost-collisional setting. The Derinoba and Kayadibi intru-sions, together with the Gümüshane and Köse plutons,can be interpreted as members of a larger coherent plutoncomplex, termed the eastern Pontide pluton.
AcknowledgementsThis research was supported by the Akdeniz University ResearchFund and grant no. 109Y052 from the Turkish ResearchFoundation (TÜBITAK). We appreciate the help of Bin Chenand Elmar Reiter during isotope analyses and Lynn Heizler formicroprobe analyses. Thanks are due to W.G. Ernst and theanonymous reviewer for their comments, which helped to improvethe manuscript. We thank Emre Aydınçakır, Mürsit Öztürk, andMetin Çiftçi for their help in the field.
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