Characteristics of the amphibolites from Nigde ... · PDF fileCharacteristics of the amphibolites from Nigde metamorphics ... Keywords: amphibolites, metamorphism, ... characteristics

241

Geochemical Journal, Vol. 41, pp. 241 to 257, 2007

*Corresponding author (e-mail: [email protected])

Copyright © 2007 by The Geochemical Society of Japan.

Characteristics of the amphibolites from Nigde metamorphics (Central Turkey),deduced from whole rock and mineral chemistry

KERIM KOCAK,1* HUSEYIN KURT,1 VEYSEL ZEDEF2 and ERIC C. FERRÉ3

1Department of Geology Engineering, Engineering Faculty, Selcuk University, Kampus 42075 Konya, Turkey2Department of Mining Engineering, Engineering Faculty, Selcuk University, Kampus 42075 Konya, Turkey

3Department of Geology, Southern Illinois University, Carbondale, IL 62901-4324, U.S.A.

(Received October 16, 2006; Accepted April 5, 2007)

Whole rock and mineral chemistry of amphibolites are presented for the lower (Gumusler Formation) and higher parts(Kaleboynu Formation) of the Nigde Massif with the aim to constrain protolith genesis and metamorphic P–T-conditions.The amphibolites, associated with a series of supracrustal metasediments, as thin layers and discontinuous pod/smalllenses, are of igneous origin with composition of subalkaline and tholeiitic basalts. Based on immobile elements contentand ratios, amphibolites from both formations are thought to have formed mostly by fractional crystallisation of pyroxene± spinel, amphibole, plagioclase as well as apatite and titanite; coupled with minor crustal contamination. Contaminationis particularly clear for the Gumusler Formation formed in a back-arc basin (Paleothetys) during magmatic ascent throughthe thickened Central Anatolian crust. The basic rocks could have been metamorphosed later at 7.5–3 ± 0.6 kb and 850–420°C, with the temperature gradient ranging from 35 to 122°C/km at different depths in the Neo-Tethyan subductionzone, and exhumed from depths of approximately 20 km via regional extension.

Keywords: amphibolites, metamorphism, MORB magmas, Nigde massif, geochemistry

two major tectonic zones. Each zone has distinctpressure-temperature-time and tectonic evolutions(Whitney et al., 2001). The four blocks are the Kırsehir(north-west), Akdag (north-east), Nigde (south) andAksaray (west) massifs. The northern zone, characterisedby the Kır sehir and Akda g massifs, consists ofmetasedimentary rocks cut by granitoids and gabbros (Fig.1b). These two massifs have undergone metamorphismand deformation in relation with final closure of the north-ern Neotethys during Late Cretaceous times along theI zmir-Ankara-Erzincan suture in the north (Fig. 1b).These northern massifs, thrust and folded during colli-sion, were subsequently slowly exhumed by erosion. Thenorthern CACC metamorphic rocks experienced clock-wise pressure-temperature (P–T) paths at moderate con-ditions (7–8 kbar, 650–750°C) followed by local low-P-high-T (LP–HT) overprint. The Aksaray massif is repre-sentative of the hot, shallow mid-crust that was part of aLate Cretaceous–early Tertiary arc. It consists of intru-sive units with rare metapelitic rocks that have recordedlow-P regional metamorphism overprinted by LP–HTcontact metamorphism (<4 kbar, Kocak 1993; Kocak andLeake, 1994). In contrast to the northern tectonic zone,the southern CACC (Nigde Massif; Figs. 1b and c),evolved as a metamorphic core complex in a wrench-dominated setting (Whitney and Dilek, 1998). The tec-tonic evolution of the Nigde massif as a core complex is

INTRODUCTION

Turkey accounts for a significant segment of theAlpine-Himalayan orogen. It consists of continentalblocks divided by suture zones, as a result from the clo-sure of different branches of the Neo-Tethyan ocean dur-ing the late Cretaceous-Eocene (Sengör and Yilmaz, 1981)(Fig. 1a, inset map). With the closure of Paleo-Tethysduring the middle Jurassic, only two oceans were left inTurkey: the multibranched northern, and the simplersouthern, branches of Neo-Tethys (Sengör and Yilmaz,1981). Sengör and Yilmaz (1981) assumed that the north-ern branches of Neo-Tethys contained the I zmir-Ankara-Erzincan, and the Inner Tauride oceans, and that theseseparated the Anatolide-Tauride platform from Eurasia.By contrast, the southern branch separated the platformand fragment from the main body of Gondwanaland.

The Central Anatolian Crystalline Complex (CACC,Goncuoglu et al., 1991), one of these continental blockssituated north of the Tauride-Anatolide Platform (TAP)and south of the I zmir-Ankara-Erzincan suture, wasformed by rifting from the northern margin of Gondwana.The CACC comprises of four tectonic blocks that form

242 K. Kocak et al.

due to its position adjacent to the Inner-Tauride suture,the site of closure of a Mesozoic (Neo-Tethyan) seawaywhere continental fragments collided. During protractedorogenesis, the Nigde massif experienced two cycles ofburial and exhumation: (i) Late Cretaceous subsidenceand burial of sedimentary rocks to form the basementgneiss followed by Late Cretaceous to Middle Eoceneunroofing of the basement by transtension and erosion toproduce locally derived conglomerates (deposited at theedge of a marine basin along the Ecemis Fault zone); (ii)re-burial of the basement and cover sediments, resultingin folding, shearing, and metamorphism of the sedimen-tary cover in Late Eocene through Oligocene times fol-lowed by final exhumation in the Middle Miocene (9–12Ma) along strike-slip and normal faults (Umhoefer et al.,2003).

In the CACC, amphibolites commonly occur in vari-ous forms ranging from lenticular bodies to layers, andappear to be derived from sedimentary (Kırsehir block,Erkan, 1980) or igneous (Aksaray block, Kocak, 2002)protoliths. Although amphibolites occur almost through-out the Nigde Massif, in association with metaclastic andmetacarbonate schists/gneisses, no detailed study has yetfocussed on these units. The present study aims at deter-mining the geochemical characteristics of theamphibolites from two of the oldest formations (Gumuslerand Kalkanlıdag), within the Nigde Massif, and to dis-cuss their origin (igneous or sedimentary) as well as theP–T-conditions of metamorphism.

GEOLOGICAL SETTING

The Nigde Massif consists of migmatitic gneiss,sillimanite-biotite-muscovite-gneiss, biotite-gneiss, withinterlayered calcsilicate, amphibolite, quartzite and mar-ble at the bottom (Gumusler Formation); it continues fur-ther up with thinly bedded metaclastic, metabasic andmetacarbonate schist (Kalkanlıdag Formation); and endsup towards the top with marble, minor amphibolite,quartzite, fine-grained schist, and meta-ultramafic rocks(Asıgedigi Formation, Fig. 1c). These rocks are intrudedby the Sineksizyayla metagabbro, and by aplitic, micro-pegmatitic and pegmatitic dykes of the Uckapılı granite,which are associated with Sb–Hg–W deposits (Akcay etal., 1995). This complex of igneous and metamorphicrocks is unconformably overlain by Pliocene tuffs.

Metapelitic rocks in the Nigde Massif record twometamorphic events: an early, regional medium-pressure,high-temperature event associated with burial and heat-ing during collision between the Tauride and Anatolideblocks (in Early Cenozoic), and a later low-pressure, high-temperature event likely related to shallow intrusion ofthe Uckapılı granite (Whitney and Dilek, 1998, 2000;Whitney et al., 2003). The highest recorded metamorphic

KB

AB

Nigdemetamorphiccore complex

AB

Gumusler Formation

Kaleboynu Formation

urbanizationarea

contact

fault

location of the samples

EXPLANATIONS Alluvium

Uckapili granite

Sineksizyayla metagabbro

Asigedigi FormationDominantly marble, minor calcsilicatequartzite, amphibolite, metaultramafic

Çamardı

Gumusler

Nigde Massif

Nigde

Himmetli2

Ecem

is F

ault

Zone

schist, marble, calc-silicate, amphibolite, quartzite

High grade core: migmatitic gneiss/schist, marble,calc-silicate, amphibolite, quartzite

Al

1,2

Qua

tern

ary

Upp

er C

reta

ceou

sU

pper

Pal

aeoz

oic

Sillu

rian

-Dev

onia

n

Fig. 1. Simplified location map a) and geological map b) ofthe CACC. c) Geological map of the Nigde massif (modifiedfrom Atabey, 1989a, b; Atabey et al., 1990; Kocak, 1993; Kocakand Leake, 1994). AB: Akdag Block, KB: Kırsehir Block, AsB:Aksaray Block, NB: Nigde Block.

Nigde amphibolites, Turkey 243

conditions are 5–6 kbar at >700°C. The later event is docu-mented by low-pressure assemblages, such as andalusite-cordierite, in the contact aureole of the Uckapılı pluton(Goncuoglu, 1986). In summary, the Nigde Massif is char-acterised by clockwise P–T paths at moderate P–T, fol-lowed by widespread LP–HT metamorphism.

The Nigde Massif has successively undergone twoductile, and three brittle deformation phases (Goncuoglu,1977). Peak metamorphism conditions prevailed duringthe first phase of deformation produced by overturnedfolding. Refolding occurred during the second deforma-tion phase and is marked by open folding. Pre-deformation grains are rounded titanite and iron ores. The

earliest deformation phase is associated with developmentof green-blue coloured hornblende, diopside, plagioclaseand titanite, followed by crystallisation of light yellow-coloured diopside, plagioclase, and blue-green colouredamphiboles. The high-temperature fabric ofmetasedimentary rocks is defined by biotite sheets,migmatitic layering, and by a biotite-sillimanite minerallineation in the high-grade core of the massif (Whitneyet al., 2003). The development of shear zones and faultzones characterises the latest ductile deformation, asso-ciated with growth of water- and CO2-bearing phases aswell as retrograde metamorphism after post-tectonicgrowth of green-blue amphiboles, scapolites, epidote/

K6-1b K6-8 K6-10 K15-1 K15-2 K15-3 K15-9 K15-12 K15-11 K15-10 K15-18

SiO2 54.20 55.60 59.06 58.79 56.10 57.24 57.73 56.63 57.22 56.02 57.88Al2O3 28.76 27.61 25.61 26.21 27.36 26.74 26.60 27.15 26.98 27.23 26.69K2O 0.02 0.04 0.10 0.07 0.05 0.03 0.04 0.03 0.05 0.04 0.03Na2O 5.09 5.78 7.27 7.09 5.97 6.53 6.71 6.21 6.63 6.19 6.70CaO 11.17 10.11 7.46 7.93 9.71 8.87 8.41 9.32 9.06 9.60 8.57FeO 0.05 0.10 0.10 0.04 0.03 0.17 0.07 0.13 0.16 0.17 0.18Total 99.29 99.25 99.60 100.12 99.22 99.58 99.56 99.49 100.10 99.24 100.03

Si 7.92 8.05 8.31 8.26 8.09 8.17 8.20 8.12 8.13 8.08 8.20Al 4.96 4.71 4.25 4.34 4.65 4.50 4.46 4.59 4.52 4.63 4.46K 0.00 0.01 0.02 0.01 0.01 0.00 0.01 0.01 0.01 0.01 0.01Na 1.44 1.62 1.98 1.93 1.67 1.81 1.85 1.73 1.83 1.73 1.84Ca 1.75 1.57 1.13 1.20 1.50 1.36 1.28 1.43 1.38 1.48 1.30

or 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00ab 0.45 0.51 0.63 0.62 0.52 0.57 0.59 0.55 0.57 0.54 0.58an 0.55 0.49 0.36 0.38 0.47 0.43 0.41 0.45 0.43 0.46 0.41

K2-pl-8 K2-pl-13 K2-pl-15 K3-pl-12 K3-pl-18 K4-pl-1 K4-pl-9 K4-pl-8 K4-pl-7 K4-pl-10

SiO2 55.88 57.64 58.17 56.59 56.03 56.56 59.31 58.35 58.62 58.58Al2O3 27.70 26.41 26.12 27.43 27.43 27.44 25.64 26.19 26.01 26.26K2O 0.02 0.05 0.08 0.09 0.04 0.02 0.04 0.04 0.04 0.03Na2O 5.96 6.79 6.95 6.18 5.96 6.05 7.41 7.03 7.16 6.92CaO 9.98 8.42 7.97 9.69 9.63 9.70 7.37 7.95 7.90 8.10FeO 0.08 0.21 0.11 0.08 0.06 0.06 0.12 0.06 0.08 0.11Total 99.61 99.52 99.38 100.05 99.14 99.82 99.89 99.62 99.81 99.99

Si 8.05 8.20 8.25 8.08 8.09 8.10 8.32 8.25 8.26 8.26Al 4.70 4.43 4.37 4.62 4.67 4.63 4.24 4.36 4.32 4.36K 0.00 0.01 0.01 0.02 0.01 0.00 0.01 0.01 0.01 0.00Na 1.66 1.87 1.91 1.71 1.67 1.68 2.01 1.93 1.96 1.89Ca 1.54 1.28 1.21 1.48 1.49 1.49 1.11 1.21 1.19 1.22

or 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00ab 0.52 0.59 0.61 0.53 0.53 0.53 0.64 0.61 0.62 0.61an 0.48 0.41 0.39 0.46 0.47 0.47 0.35 0.38 0.38 0.39

Table 1. Selected chemical analyses of the feldspar (a), and amphiboles (b) in Gumusler amphibolites, with mini-mum crystallisation temperature (Holland and Blundy, 1994) and pressures (Schmidt, 1992)

(a)

244 K. Kocak et al.

K6-1b K6-10b K6-12 K15-1 K15-2 K15-3 K15-9b K15-12 K15-11 K15-10 K15-18

SiO2 42.93 43.46 42.78 46.95 48.47 49.34 49.68 49.16 48.01 46.50 48.83TiO2 1.25 1.70 1.01 0.54 0.48 0.45 0.37 0.48 0.62 0.45 0.47Al2O3 12.42 12.08 13.40 9.67 8.60 7.20 6.74 7.53 8.39 10.32 7.35Cr2O3 0.05 0.09 0.05 0.01 0.00 0.00 0.03 0.04 0.08 0.02 0.03Fe2O3 2.40 1.61 3.50 6.55 5.37 5.86 7.12 6.68 5.42 5.44 6.51FeO 11.37 12.35 10.67 6.11 6.87 6.13 4.79 5.38 6.63 6.95 5.49MnO 0.25 0.22 0.22 0.16 0.17 0.20 0.19 0.19 0.18 0.18 0.17MgO 11.73 11.57 11.64 14.24 14.60 15.18 15.56 15.24 14.62 13.94 15.35CaO 12.06 12.04 11.99 11.58 11.79 11.73 11.38 11.40 11.63 11.66 11.66Na2O 1.96 1.92 2.13 1.37 1.15 0.93 0.96 1.18 1.23 1.53 1.07K2O 0.73 0.78 0.70 0.39 0.30 0.24 0.22 0.28 0.29 0.46 0.26Total 97.17 97.82 98.07 97.57 97.78 97.26 97.04 97.54 97.10 97.45 97.20

Si 6.36 6.41 6.27 6.73 6.92 7.05 7.08 6.99 6.90 6.69 6.98Al 1.64 1.59 1.73 1.27 1.08 0.95 0.92 1.01 1.10 1.31 1.02Al 0.53 0.51 0.58 0.36 0.36 0.26 0.21 0.26 0.32 0.44 0.22Cr 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00Ti 0.14 0.19 0.11 0.06 0.05 0.05 0.04 0.05 0.07 0.05 0.05Fe3+ 0.30 0.20 0.43 0.79 0.64 0.70 0.85 0.79 0.65 0.65 0.78Mg 2.59 2.54 2.54 3.04 3.11 3.23 3.30 3.23 3.13 2.99 3.27Fe2+ 1.41 1.52 1.31 0.73 0.82 0.73 0.57 0.64 0.80 0.84 0.66Mn 0.03 0.03 0.03 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02Ca 1.91 1.90 1.88 1.78 1.80 1.80 1.74 1.74 1.79 1.80 1.79Na 0.09 0.10 0.12 0.22 0.20 0.20 0.26 0.26 0.21 0.20 0.21Na 0.48 0.45 0.49 0.16 0.12 0.05 0.00 0.06 0.14 0.23 0.08K 0.14 0.15 0.13 0.07 0.05 0.04 0.04 0.05 0.05 0.08 0.05

T [°C] 716 774 732 711 688 625 420 650 699 728 675

P (±0.6) 5.72 5.42 6.33 3.45 2.66 1.67 1.33 1.88 2.55 3.94 1.78

Table 1. (continued)

(b)

clinozoizite, biotite, garnet and titanite (Goncuoglu,1977).

The amphibolite occur as discontinuous pods, smalllenses and thin layers (some millimetres to several deci-metres thick), parallel to the main foliation commonlyshowing a sharp contact with gneisses and marbles. Theamphibolite is dark green, fine- to medium-grained, andis typically nematoblastic and foliated. The amount ofdeformation is responsible for macroscopic fabric shownby amphibolites, and lead to evolution from massive tofoliated fabrics by crystallographic preferred orientationof grains such as hornblende and plagioclase. Aplite veinscommonly cut through the amphibolites and theirmetasedimentary host-rock. The Gumusler amphibolitesexhibit evidence of migmatization with hornblende-richselvages, quartz- and feldspars-rich neosomes, presentsboth as veins and irregular patches (Kocak et al., 2006).The most migmatized part of the massif is the structur-ally deepest region, i.e., the northwestern part of the high-grade core and the vicinity of the Uckapılı granite (Fig.1c). The Kaleboynu amphibolites, compared with theGumusler amphibolites, display less metaclastics andmetacarbonates intercalations, and lack migmatitic struc-

tures. These amphibolites host garnet and are cut by thinquartzite veins/lenses.

ANALYTICAL METHODS

Mineral chemical analyses were carried out on a JEOLJSM35 Electron Microprobe running Link QX2000 en-ergy dispersive analytical software, and are given in Ta-bles 1 and 2. The operating conditions were 15 kV asacceleration voltage and 15 nA as specimen current. Fer-ric iron estimations were done using stoichiometric con-straints for ideal phases (Droop, 1987). Whole rock analy-ses for major and trace elements were carried out withInductively-Coupled Plasma Emission Spectrometer frompulps after 0.2 g rock-powder were fused with 1.5 g LiBO2and then dissolved in 100 mm3 5% HNO3 at ACME Ana-lytical Laboratories Ltd., Vancouver, Canada. The REEcontents were determined by Inductively-Coupled PlasmaMass Spectrometry from pulps after 0.25 g rock-powderwas dissolved with 4 acid digestions at ACME (Canada).Analytical uncertainties vary from 0.1% to 0.04% formajor elements; from 0.1 to 0.5% for trace elements; andfrom 0.01 to 0.5 ppm for rare earth elements.


K2-hb-5 K2-hb-11 K2-hb-13 K3-hb-13c K3-hb-19 K4-hb-1b K4-hb-8 K4-hb-7 K4-hb-6 K4-hb-9b

SiO2 40.43 41.34 40.62 46.61 46.93 43.42 44.10 43.75 44.93 43.33TiO2 1.51 1.56 1.59 0.99 0.66 1.55 1.60 0.70 0.98 1.51Al2O3 14.52 13.96 14.74 9.77 9.49 12.40 11.54 12.89 10.97 12.28Cr2O3 0.02 0.08 0.08 0.09 0.06 0.19 0.06 0.10 0.03 0.03Fe2O3 1.93 1.75 1.60 2.89 3.39 2.49 2.57 3.96 3.14 2.66FeO 12.90 12.95 13.10 9.80 8.73 11.11 10.90 9.90 9.95 11.07MnO 0.24 0.19 0.21 0.18 0.18 0.21 0.21 0.20 0.20 0.18MgO 10.40 10.70 10.45 13.62 14.24 11.70 12.27 12.21 12.86 11.96CaO 12.15 12.18 12.11 12.22 12.33 12.03 11.87 12.00 11.97 12.00Na2O 2.31 2.33 2.49 1.60 1.56 1.82 2.07 2.23 1.90 2.15K2O 0.92 0.70 0.87 0.36 0.26 0.46 0.44 0.41 0.40 0.41Total 97.31 97.74 97.84 98.11 97.82 97.37 97.63 98.35 97.31 97.58

Si 6.06 6.15 6.05 6.73 6.77 6.39 6.47 6.35 6.57 6.37Al 1.94 1.85 1.95 1.27 1.23 1.61 1.53 1.65 1.43 1.63Al 0.62 0.59 0.64 0.40 0.38 0.54 0.46 0.56 0.46 0.50Cr 0.00 0.01 0.01 0.01 0.01 0.02 0.01 0.01 0.00 0.00Ti 0.17 0.17 0.18 0.11 0.07 0.17 0.18 0.08 0.11 0.17Fe3+ 0.24 0.22 0.20 0.35 0.41 0.31 0.31 0.48 0.38 0.33Mg 2.32 2.37 2.32 2.93 3.06 2.57 2.68 2.64 2.80 2.62Fe2+ 1.62 1.61 1.63 1.18 1.05 1.37 1.34 1.20 1.22 1.36Mn 0.03 0.02 0.03 0.02 0.02 0.03 0.03 0.02 0.02 0.02Ca 1.95 1.94 1.93 1.89 1.90 1.90 1.87 1.87 1.88 1.89Na 0.05 0.06 0.07 0.11 0.10 0.10 0.13 0.13 0.12 0.11Na 0.62 0.61 0.65 0.34 0.34 0.42 0.45 0.50 0.42 0.50K 0.18 0.13 0.16 0.07 0.05 0.09 0.08 0.08 0.07 0.08

T [°C] 850 779 812 748 751 762 739 730 728 752

P (±0.6) 7.38 6.89 7.48 3.58 3.36 5.64 4.97 5.87 4.54 5.55

Table 1. (continued)

(b)

PETROGRAPHY AND MINERAL CHEMISTRY

The Gumusler amphibolites consist of plagioclase (55–70%), hornblende (25–30%), quartz (5–20%), diopside(0–5%) with accessory ilmenite, titanite, epidote and apa-tite (Figs. 2a and b). The amphibole grains showcrystallographic preferred orientation, and are altered tochlorite along their cleavage planes. The plagioclase in-cludes abundant epidote and quartz inclusions (Fig. 2a).The plagioclase shows a slight normal zonation fromoligoclase to labradorite (Fig. 3a; Table 1). Compositionof the amphiboles varies from ferrotschermakite throughtschermakite to magnesio-hornblende, with minor actino-lite and tremolite (Fig. 3b; Table 2). They are character-ised by a large variation in AlIV (0.16–1.95 a.p.f.u.) andXMg (0.43–0.10), and high Na content up to 0.72 a.p.f.u.Hornblende contains inclusions of epidote and quartz(Figs. 2a and b), and is commonly rimmed by actinolite.Diopside also can form inclusions in hornblende. Quartzhas undulatory extinction and some deformation lamel-lae. Titanite forms in Gumusler and Kaleboynu samples,with characteristic rhombic shape. Epidote developsmostly as inclusion in hornblende and plagioclase, but

also as xenoblast-hipidioblast crystals in both Gumuslerand Kaleboynu units.

Kaleboynu amphibolites are composed of hornblende(52–58%), plagioclase (42–45%) with accessory epidote,titanite, garnet, sericite, quartz and opaques in anematoblastic microstructure (Figs. 2c and d). TheKaleboynu amphibolites differ from their Gumusler coun-terpart by a lesser amount of plagioclase and quartz, andhigher hornblende contents, as well as presence of garnetand lack of diopside. Lineation in the samples is createdby alignment of hornblende and plagioclase grains (Fig.2c). The plagioclase has Na-rich composition, varyingfrom albite to andesine, and is partly sericitised. Garnetand opaques often occur as inclusions within theplagioclase without sericite crystals. The poikiloblasticamphiboles have inclusions of plagioclase, epidote andtitanite. These amphiboles have restricted XMg composi-tion (0.52–0.66), but variable Si composition (6.4–7.8).Their compositions vary from tschermakite throughmagnesiohornblende and actinolite. Both Gumusler (Fig.2a) and Kaleboynu amphiboles contain inclusions ofepidote and quartz and are rimmed by actinolite.

Both amphibolites also display some retrogression,

246 K. Kocak et al.

39b 38b

1-Pl-1c 1-Pl-1r 1-Pl-2c 1-Pl-2r 2-Pl-1c 2-Pl-1r 2-Pl-2c 2-Pl-2r 3-Pl-1c 3-Pl-1r 3-Pl-2r

SiO2 57.34 58.96 63.35 67.50 56.67 56.09 56.78 60.09 56.91 61.87 58.52Al2O3 26.62 26.16 22.81 20.58 27.51 27.80 26.75 25.17 27.21 24.04 26.14K2O 0.04 0.05 0.08 0.05 0.04 0.06 0.02 0.04 0.06 0.07 0.05Na2O 6.32 6.96 9.14 10.81 6.05 5.84 6.26 7.57 6.09 8.44 6.94CaO 8.96 7.86 4.34 1.40 9.56 10.00 9.05 6.79 9.32 5.61 8.10FeO 0.09 0.11 0.08 0.21 0.11 0.22 0.08 0.18 0.10 0.20 0.20Total 99.37 100.10 99.80 100.55 99.94 100.01 98.95 99.84 99.69 100.23 99.94

Si 10.33 10.51 11.22 11.76 10.18 10.09 10.28 10.71 10.23 10.96 10.47Al 5.65 5.49 4.76 4.22 5.82 5.89 5.71 5.29 5.76 5.01 5.51K 0.01 0.01 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.01Na 2.21 2.41 3.14 3.65 2.11 2.04 2.20 2.62 2.12 2.90 2.41Ca 1.73 1.50 0.82 0.26 1.84 1.93 1.76 1.30 1.80 1.06 1.55

Ab 0.56 0.61 0.79 0.93 0.53 0.51 0.56 0.67 0.54 0.73 0.61An 0.44 0.38 0.21 0.07 0.47 0.49 0.44 0.33 0.46 0.27 0.39Or 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

39b 38b

1-1c 1-1r 1-2c 1-2r 2-1c 2-1r 2-2c 2-2r 3-1c 3-1r 3-2r

SiO2 44.31 47.09 47.30 44.98 43.87 46.38 46.11 46.67 44.97 48.94 52.44TiO2 1.29 1.05 1.11 1.20 1.43 1.12 1.14 1.06 1.24 0.68 0.11Al2O3 10.92 8.25 8.16 10.07 11.32 8.76 9.06 8.85 10.18 6.41 2.63Cr2O3 0.01 0.02 0.03 0.04 0.03 0.07 0.01 0.08 0.09 0.03 0.02Fe2O3 5.16 6.13 6.25 5.27 5.79 5.95 5.51 6.63 3.99 5.06 2.88FeO 13.26 11.94 11.88 13.06 13.13 12.23 12.47 11.35 15.31 13.32 14.74MnO 0.22 0.30 0.30 0.26 0.25 0.27 0.23 0.25 0.27 0.24 0.29MgO 9.71 11.11 11.12 10.00 9.62 10.88 10.88 11.19 9.19 11.46 12.79CaO 11.39 11.32 11.28 11.40 11.37 11.31 11.47 11.46 11.81 11.77 12.47Na2O 1.37 1.11 1.09 1.28 1.60 1.29 1.31 1.04 1.09 0.79 0.23K2O 0.53 0.36 0.31 0.40 0.48 0.40 0.38 0.35 0.51 0.22 0.08Total 98.18 98.68 98.81 97.96 98.89 98.66 98.56 98.92 98.64 98.92 98.65

Si 6.56 6.88 6.89 6.66 6.47 6.79 6.76 6.79 6.67 7.13 7.62Al 1.44 1.12 1.11 1.34 1.53 1.21 1.24 1.21 1.33 0.87 0.38Al 0.47 0.29 0.29 0.42 0.43 0.30 0.33 0.31 0.44 0.23 0.07Cr 0.00 0.00 0.00 0.01 0.00 0.01 0.00 0.01 0.01 0.00 0.00Ti 0.14 0.12 0.12 0.13 0.16 0.12 0.13 0.12 0.14 0.07 0.01Fe3+ 0.58 0.67 0.69 0.59 0.64 0.66 0.61 0.73 0.45 0.55 0.32Mg 2.14 2.42 2.42 2.21 2.12 2.38 2.38 2.43 2.03 2.49 2.77Fe2+ 1.64 1.46 1.45 1.62 1.62 1.50 1.53 1.38 1.90 1.62 1.79Mn 0.03 0.04 0.04 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.04Ca 1.81 1.77 1.76 1.81 1.80 1.78 1.80 1.79 1.88 1.84 1.94Na 0.19 0.23 0.24 0.19 0.20 0.23 0.20 0.21 0.13 0.16 0.06Na 0.20 0.09 0.07 0.18 0.25 0.14 0.17 0.08 0.19 0.06 0.01K 0.10 0.07 0.06 0.08 0.09 0.08 0.07 0.06 0.10 0.04 0.02T [°C] 716 774 732 711 688

P (±0.6) 5.72 5.42 6.33 3.45 2.66

Table 2. Selected chemical analyses of the feldspar (a), and amphiboles (b) in Kaleboynu amphibolites, with minimumcrystallisation temperature (Holland and Blundy, 1994) and pressures (Schmidt, 1992). c: core, m: middle, r: rim.

(a)

(b)


which is manifested by development of small equantgrained actinolite crystals around large porphyroblasticor poikiloblastic hornblende in Gumusler amphibolites;and of chlorite and sericite after hornblendes andplagioclase, respectively in both groups. In addition,albite-rich plagioclase and epidote crystals also appearin some samples.

The amphibolites have the required mineral assem-blage to use the aluminium hornblende geobarometer(Schmidt, 1992). They yield a pressure of between ~1.3and 7.5 ± 0.6 kb, but mostly >5 kb (Table 1) for theGumusler amphibolites, and 2.7 and 6.3 ± 0.6 kb for theKaleboynu amphibolites (Table 2). Therefore the maxi-mum possible pressure for hornblende crystallisationstage was 8 kbar, which implies an overburden thicknessof <25 km. The hornblende-plagioclase geothermometer(Holland and Blundy, 1994) offers an independent ap-proach of evaluating magmatic temperature. Using rimchemical composition of plagioclase and hornblendes thatare in contact with each other, minimum crystallisationtemperature of the amphiboles are determined as 420–850°C (Table 2), with an average of 733°C for theGumusler amphibolites, and as much as 690–770°C withan average of 724 for 5 kbar pressure for the Kaleboynu

amphibolites, mostly within the sillimanite, and to a mi-nor extent, in the andalusite stability fields (Fig. 3c).

GEOCHEMISTRY

Amphibolites are characterised by high Cr/Th (>100)and low Th/La (~0.15) ratios, which differ from those ofsedimentary rocks (Taylor and McLennan, 1985) but aretypical of magmatic suites (Rollinson, 1996). High Zr/Tiratio and low Ni contents (Figs. 4a and b) also support anigneous origin (Table 3). Similarly, amphibolites from theAksaray Block were also suggested to be derived froman igneous protolith on the basis of geochemical data andpreserved volcanic microstructure (Kocak, 1993, 2002;Kocak and Leake, 1994).

These rocks have undergone polymetamorphic events,and it is likely that they experienced considerable ele-ment mobility, particularly involving the alkali and largeion lithophile (LIL) elements, e.g., K, Rb, Ba. Charac-terisation and discrimination of the amphibolites into dif-ferent suites and assignment to particular environmentalsettings has been the basis of trace elements discrimina-tion, usually considered comparatively stable during al-teration for instance the high-field-strength (HFS) ele-

Ep

Pl

Hb

0 2 mm 0 2 mm

a c

Hb

Hb

PlPl

pl

hb

b d

0 2 mm 0 2 mm

Hb

Hb

Pl

Fig. 2. Plane-polarized light photomicrographs of typical minerals located in the Gumusler (a–b), Kaleboynu (c–d) amphibolites:a) Polysynthetic twinning in plagioclase, and xenoblast epidote (ep) crystals. b) Plagioclase inclusion (pl) within hornblende(hb) crystals. c) Lineation developed by alingment of hornblende. d) Polysynthetic twinning in plagioclase.

248 K. Kocak et al.

ments and rare earth elements (REE; e.g., Floyd and Win-chester 1978, 1983). All amphibolites exhibit good lin-ear consistency between pairs of stable incompatible ele-ments, and smooth normalised patterns for the REE, or asequence of incompatible elements. This likely resultsfrom original igneous fractionation processes. Under some

circumstances, for example the widespreadcarbonatisation of metabasites, the REE and HFS elementscan also be mobilised and/or abundances diluted (e.g.,Hynes, 1980; Humphris, 1984; Rice-Birchall and Floyd,1988), although this seems only to have significantly af-fected one high-CaO Gumusler samples (K1).

Fig. 3. Chemical composition of the feldspars (a) and amphiboles (b), Leake et al. (1997). (c) P–T diagram of the Gumusleramphibolites. P–T grid of metamorphism conditions for the Gumusler (filled diamond) and Kaleboynu (open triangle) amphibolites.The arrow indicates a retrograde trend corresponding to exhumation of high-grade amphibolites (sample k15). Geotherms shownafter Cloos (1993): CS, cold subduction (6°C/km); WS, warm subduction (10°C/km); NG, normal geotherm (25°C/km); MOR,geotherm near spreading center and active volcanic arc (60°C/km). P–T field of metamorphism of oceanic plutonic rocks shownas in Silantyev (1995). Stability fields of the Al2SiO5 polymorphs are included for reference (Holdaway, 1971). Filled diamondsand open triangles represent Gumusler and Kaleboynu amphibolites, respectively.

AnAb

Or

Ab An

twofeldspars

Anortoclase

Plagioclase

sanidine

Albite Oligoclase Andesine Labradorite Bytownite Anorthite

Intrusion ofUckapili granite

0

2

4

6

8

10

200 400 600 800 1000

ToC

P(k

b)

P-T conditons of metamorphismof MOR-plutonic rocks

MOR

CSWS

NG

8.0 7.5 7.0 6.5 6.0

0.8

0.6

0.4

0.2

Ca<0.5

Si

ferro-actinolite ferrohornblende ferro-

tschermakite

actinolite

tremolite magnesio-hornblende

tschermakite

a

cb

Mg/

Mg+

Fe2+


Coherent variation of Zr/Ti and Zr/Y ratios (Figs. 4aand c) suggests co-genetic occurrence of amphibolites,which have a composition corresponding to subalkalinebasalts (Fig. 4d) with SiO2 ranging between 46 and 51%.Most samples are characterised by moderate to high Al2O3(10.6–17.6 wt.%), and CaO (9.1–14.5 wt.%) contents, andlow CaO/Al2O3 ratio. The MgO and Fe2O3 contents arevariable and range from 4.5 to 12.4, and from 7.0 to 17.5wt.%, respectively.

Both amphibolites exhibit a distinct correlation ofmajor and trace elements with differentiation (Fig. 5a).Elongated variation trends show that the rocks of each

unit might represent a cogenetic suite and were modifiedlargely by mafic fractionation that produced a typical Fe-enrichment trend for the amphibolites. The linearcovariance for Zr and Y (Y vs. Zr, Fig. 4c) indicates thatthis suite was formed predominantly through plagioclase-olivine fractionation. Decreasing Cr contents relative toZr (used as a fractionation index) in all samples, also sug-gests that pyroxene ± spinel were important phases dur-ing primary fractionation. Similarly, the existence of apositive correlation between Zr and TiO2 and P2O5 indi-cates effective ilmenite and apatite fractionation, respec-tively. Ba, Sr, Rb and other LIL elements are compara-

SedimentarySedimentary

IgneousIgneous

0 50 100 150 0.5 1.0 1.5 2.0 2.5 3.0

100

10

1

0.1

0.01

0.001

1000

100

10

1

Ni ppm TiO2 wt%

Zr/

Ti

Ni p

pm0

20

40

60

0 100 200 300

Y p

pm

Zr/Y=2 Zr/Y=4

0.001

0.010

0.100

0.01 0.10 1.00 10.00

Zr/

Ti

Rhyodacite

Dacite Trachyandesite

Andesite

Subalkaline basalt

Alkalibasalt

Zr ppm Nb/Y

a b

c d

Fig. 4. Discrimination diagrams used to denote the original rock of the Nigde amphibolites (a–b); a) Ni–Zr/TiO2, b) TiO2–Ni todistinguish between para- and ortho-amphibolites (Winchester et al., 1980). c) Zr–Y diagram, d) nomenclature of the amphibolites(Winchester and Floyd, 1977). Filled diamonds and open triangles represent Gumusler and Kaleboynu amphibolites, respec-tively.

250 K. Kocak et al.

tively enriched and their abundances do not characteriseany regular trend with Zr, hence indicating the post-magmatic mobility of these elements.

On the primitive mantle-normalised diagrams (Fig.5b), large ion lithophile elements (e.g., Rb, Ba) appearrather scattered confirming alteration/metamorphic proc-

esses whereas REE (e.g., Sm, Lu) and high field strengthelements (HFSE, e.g., Zr, Ti) are relatively coherent, pos-sibly reflecting pre-metamorphic compositions. TheGumusler amphibolites are characterised by negative Rb,and positive U and K2O anomalies. In contrast, theKaleboynu amphibolites are typified by positive Rb, andmuch pronounced P2O5 and K2O anomalies. Positive Sr,and negative Nb anomalies are also characteristic for bothgroup amphibolites in the diagram.

The comparison of chemical data for the Paleozoicmetabasic rocks of the Nigde area with modern lavas fromknown tectonic settings helps constrain the paleotectonicaffinities of these rocks, source character and petrogeneticprocesses. Tectonic discriminations on Ti–Y–Zr and Zr/Y vs. Zr (Pearce and Cann, 1973; Pearce and Norry, 1979)diagrams show that most samples plot in the island arcbasalt (IAB) and Mid-Ocean Ridge basalt fields (MORB,Figs. 6a and b). The Nb–Y–Zr ternary diagram also illus-trates that all amphibolites have typical normal-MORB(N-MORB) character, with slight enriched-MORB (E-MORB) tendency (Fig. 6c).

Chondrite normalised Rare Earth Element (REE) pat-terns of the amphibolites are presented in Fig. 6d. TheGumusler amphibolites display almost flat Heavy RareEarth Element (HREE) patterns accompanied by (Gd/Lu)Nranging from 0.9 to 1.5, some of which crosscut others,with insignificant Eu anomaly (Eu/Eu* ca. 1.10–0.97).The samples have usually fractionated LREE (La/Yb)Nca. 1.3–2.5) pattern, which is similar to that of E-MORB.

The chondrite-normalized REE spidergrams of theKaleboynu amphibolites show N-MORB geochemicalsignatures. They are characterised by slightly depletedLREE (0.47–0.68), except a sample with La/Sm: 1.3, andflat HREE patterns with variable total HREE content rang-ing between 5 and 28 times that of chondrites. The uni-form increase in total REE contents may be the result ofshallow magmatic differentiation, as suggested by theexistence of a clear correlation between total REE con-tent and Zr. Slight Eu anomaly (Eu/Eu* = 0.83) and theexistence of minor negative correlation between Zr andEu/Eu* may indicate plagioclase fractionation. Depletionin LREE may be explained by the fractionation of LREE-rich minerals such as apatite.

DISCUSSION

In spite of the limited outcrop extent of amphibolitesin the Nigde massif, their origin and tectonic significanceare key aspects to fully understand the tectonomagmaticevolution of the massif. Geochemical characteristics ofthe amphibolites indicate an igneous origin. Because ofstrong ductile shearing and metamorphism, as well as thelack of adequate field outcrop, it was not possible to dem-onstrate whether the amphibolites originally character-

0 50 100 150 50 100 150

2.0

1.6

1.2

0.8

0.4

0.0

2.0

1.0

1000

600

200

0.3

0.2

0.1

Zr ppm Zr ppm

FeO

*/M

gO

1

10

100

Sam

ple/

Pri

mit

ive

Man

tle

0.1

1

10

100

Cs Rb BaK2O Th U Nb La Ce Sr Nd Zr

P2O5

Sm EuTiO

2 Y Yb Lu

Sam

ple/

Pri

mit

ive

Man

tle

b

a

TiO

2 wt%

Cr

ppm

P2O

5 wt%

Fig. 5. a) Influence of crystal fractionation in amphibolitesrelative to Zr as a stable fractionation index. b) Primitive man-tle normalized spider diagram. Normalizing values are fromSun and McDonough (1989). Filled diamonds and open trian-gles represent Gumusler and Kaleboynu amphibolites, respec-tively.


A

B

C

D

Zr Y*3

Ti/100

A: Island arc tholeiiteB: Ocean floor basalt,

Island arc tholeiite

C: Calc-alkaline basaltD:Within-plate basalt

10 100 10001

10

20 A - Within Plate BasaltsB - Island Arc BasaltsC - Mid Ocean Ridge Basalts

A

B

Zr

Zr/

Y

AI

AII

B

CD

Zr/4 Y

Nb*2

AI-AII: within plate alkaline basaltsAII-C: within plate tholeiites

B:Enriched Mid-Ocean Ridge BasaltsD: Normal Mid-Ocean Ridge BasaltsC-D: Volcanic Arc Basalts

N-MORB

10

100

Sam

ple/

Cho

ndri

te

OIB

N-MORB

10

100

Sam

ple/

Cho

ndri

te

OIB

a b

dc

C

E-MORB

E-MORB

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Fig. 6. lncompatiblc trace element discrimination diagrams (a–c) for the amphibolites; a) Ti–Y–Zr diagram showing low-Ktholeiitic character of the samples (Pearce and Cann, 1973), b) logZr-logZr/y diagram (Pearce and Norry, 1979), c) Nb–Y–Zrdiagram (Meschede, 1986), d) chondrite normalized Rare Earth Element diagram. Normalizing values are from Boynton (1984).Rare patterns for OIB, E-MORB and N-MORB are taken from Sun and McDonough (1989). Filled diamonds and open trianglesrepresent Gumusler and Kaleboynu amphibolites, respectively.

252 K. Kocak et al.

Fig. 7. a) Ta/Yb vs. Th/Yb plot, in which the mantle array field is after Pearce (1982); SZ: subduction zone enrichment, W:within-plate enrichment. Filled diamonds and open triangles represent Gumusler and Kaleboynu amphibolites, respectively. b)Sm vs. Ce/Yb diagram. Arrow show the trends of Kaleboynu amphibolites. The effects of fractional crystallization is also shown.c) Chemical comparison of the amphibolites. island-arc tholeiite (IAT) and back-arc basin basalts (BABB), fields derived fromcompilation of arc-back-arc pairs by Woodhead et al. (1993). Typical N-MORB is from the Pacific Ocean. E-MORB, N-MORB,PM, OIB, Continental Crust (CC) and Upper Continental Crust (UCC) compositions from Sun and McDonough (1989) andTaylor and MacLennan (1985). Filled diamonds and open triangles represent Gumusler and Kaleboynu amphibolites, respec-tively.

0.0

0.1

1.0

10.00Ta/Yb

Th/

Yb

N-MORB

E-MORB

OIB

UCC

PM

0.01 0.10 1.001

10

100

1.0 10.0 100.0

Ce/

YbC.Crust

OIB

E-MORB

PM

N-MORBLow-Pfractionation

N-MORB

BAB

IAT

0.03

0.06

0.09

0.12

0 100 150

Zr ppm

V/T

i

a b

c

Sm ppm

50

to superimposed high-grade metamorphism. LIL element(e.g., Na, Rb, Ba) abundances are often highly variable,together with most major elements and ratios (e.g., FeO*/MgO, not shown), suggesting mobility of these elementsdue to metamorphism. However, characteristic magmaticinter-element relationships are frequently preserved bythose elements that are considered comparatively immo-bile during alteration, such as high field strength (HFS)

ised a series of lavas, basic volcaniclastics accumulationsor sheet-like intrusions.

The mineralogical composition of these amphibolites(e.g., plagioclase with composition mostly <% 50 An),and their minimum crystallisation temperatures (420–850°C) determined by hornblende-plagioclasegeothermometer, indicate that the mineral assemblagesformed under magmatic conditions have disappeared due


Tabl

e 3.

G

eoch

emic

al d

ata

of t

he G

umus

ler

and

Him

met

li a

mph

ibol

ites

Ele

men

tH

usey

in

K-1

k8K

-2k1

0K

-3k1

2K

-4k1

4K

-5k1

6K

-6H

K-3

7H

K-3

8AH

K-3

8BH

K-3

9AH

K-3

9BH

K-4

0BM

K-5

3M

K-4

0M

K-5

1

SiO

248

.49

47.3

146

.13

46.5

646

.99

46.9

8546

.98

48.5

950

.248

.605

47.0

151

.450

.546

.546

.847

.848

.251

.046

.050

.5T

iO2

0.45

0.67

0.89

0.96

51.

041.

11.

160.

865

0.57

0.83

51.

11.

30.

31.

91.

81.

70.

70.

31.

41.

7A

l 2O

313

.79

15.7

117

.63

16.5

6515

.515

.87

16.2

416

.385

16.5

316

.77

17.0

115

.110

.614

.013

.613

.416

.015

.116

.713

.0F

e 2O

39.

3210

.25

11.1

811

.155

11.1

311

.025

10.9

29.

948.

9610

.135

11.3

110

.710

.215

.715

.714

.99.

77.

017

.514

.5M

gO11

.68

9.78

7.88

8.48

9.08

8.8

8.52

8.48

58.

458.

175

7.9

7.8

12.4

7.2

7.5

7.1

9.9

8.5

4.5

5.8

MnO

0.14

0.14

50.

150.

150.

150.

150.

150.

115

0.08

0.11

50.

150.

00.

20.

20.

20.

20.

10.

10.

30.

2C

aO13

.22

12.2

2511

.23

11.6

612

.09

11.5

7511

.06

11.1

111

.16

11.0

6510

.97

9.1

10.6

10.4

9.8

10.3

10.6

14.5

11.8

9.5

Na 2

O0.

922.

105

3.29

2.89

52.

52.

755

3.01

2.81

52.

622.

775

2.93

2.6

1.7

2.4

2.5

2.6

2.2

1.4

0.7

3.3

K2O

0.21

0.33

0.45

0.35

50.

260.

260.

260.

240.

220.

320.

420.

40.

40.

40.

70.

50.

30.

50.

10.

4P

2O5

0.07

0.08

0.09

0.11

50.

140.

135

0.13

0.09

50.

060.

10.

140.

20.

00.

20.

20.

20.

10.

10.

30.

1L

OI

1.6

1.25

0.9

0.95

11.

21.

41.

21

0.95

0.9

1.4

3.1

1.1

1.2

1.3

1.9

Tot

al99

.89

99.8

699

.82

99.8

599

.88

99.8

699

.83

99.8

499

.85

99.8

599

.84

99.8

499

.87

99.9

899

.97

99.9

699

.93

98.4

599

.30

99.0

0

Ni

1422

3030

3040

5037

2336

509.

326

.516

.619

.516

.342

.8C

o47

4849

4745

4546

4238

4043

42.2

48.9

53.1

47.3

47.8

40.0

Cr

840

580

320

315

310

420

530

460

390

450

510

170

1110

230

230

200

540

Sc

3844

4948

4644

4241

4041

4150

.043

.050

.046

.047

.039

.0C

u42

6487

5726

3850

4131

4457

44.3

85.8

36.8

27.5

43.9

56.5

Ga

1416

1817

1717

1817

1618

2017

.09.

820

.319

.119

.314

.2W

00

11

11

11

11

00.

90.

21.

10.

91.

31.

7Pb

63

01

11

12

32

10.

72.

30.

71.

51.

31.

1Z

n4

1627

2522

2527

2012

1824

17.0

15.0

27.0

34.0

27.0

16.0

Cs

10

00

00

00

11

10.

10.

10.

10.

20.

10.

3R

b4

710

62

22

34

56

8.6

10.2

8.6

15.2

14.0

9.7

Sr

281

392

503

353

202

201

199

265

330

272

213

203.

611

2.1

170.

913

7.5

171.

416

4.5

Ba

6310

915

589

2321

2024

2837

4639

.382

.587

.596

.275

.154

.3Z

r25

3952

5762

6772

5130

5274

53.7

16.2

107.

611

1.5

98.7

39.0

Hf

0.8

1.3

1.7

1.7

1.6

1.8

2.0

1.5

0.9

1.6

2.2

1.7

<.5

3.3

3.3

3.2

1.2

Nb

0.6

2.7

4.7

4.9

5.0

5.6

6.2

3.5

0.8

3.5

6.2

1.4

0.6

2.2

2.9

2.0

1.5

Ta

<.1

<.1

0.2

0.3

0.3

0.4

0.4

<.1

<.1

0.3

0.3

0.1

<.1

0.1

0.2

0.1

0.1

Th

<.1

<.1

1.0

1.2

1.3

0.9

0.5

0.4

0.3

0.7

1.0

<.1

0.4

<.1

0.7

0.2

0.3

U<

.1<

.10.

20.

60.

90.

60.

20.

2<

.10.

70.

8<

.10.

30.

10.

10.

1<

.1Y

14.6

17.2

19.7

22.2

24.6

26.2

27.7

22.3

16.9

21.4

25.9

28.1

8.0

47.4

44.2

44.5

17.8

La

1.1

3.75

6.4

6.35

6.3

6.05

5.8

3.85

1.9

4.1

6.3

2.0

1.8

3.7

4.5

3.5

1.9

Ce

3.9

9.6

15.3

15.5

15.7

15.3

14.9

9.95

510

.716

.46.

74.

312

.114

.211

.65.

5P

r0.

641.

305

1.97

2.04

2.11

2.06

52.

021.

420.

821.

505

2.19

1.2

0.6

2.2

2.3

2.1

0.9

Nd

3.8

7.15

10.5

10.5

510

.610

.95

11.3

7.9

4.5

8.2

11.9

7.0

2.8

12.4

12.8

11.8

4.6

Sm1.

42.

12.

82.

852.

93

3.1

2.4

1.7

2.5

3.3

2.7

0.9

4.4

4.3

4.3

1.8

Eu

0.56

0.83

51.

111.

071.

031.

081.

130.

885

0.64

0.93

1.22

1.0

0.3

1.5

1.5

1.4

0.7

Gd

1.83

2.61

3.39

3.53

3.67

3.88

4.09

3.10

52.

123.

025

3.93

4.0

1.1

6.4

6.3

5.9

2.5

Tb

0.34

0.44

50.

550.

575

0.6

0.63

0.66

0.52

50.

390.

530.

670.

70.

21.

11.

11.

00.

4D

y2.

312.

835

3.36

3.71

4.06

4.32

4.58

3.50

52.

433.

275

4.12

4.5

1.3

7.8

7.6

7.4

3.0

Ho

0.5

0.62

50.

750.

780.

810.

870.

930.

765

0.6

0.75

0.9

0.9

0.3

1.5

1.4

1.4

0.6

Er

1.53

1.83

2.13

2.28

2.43

2.60

52.

782.

265

1.75

2.24

52.

742.

80.

84.

44.

44.

51.

9T

m0.

210.

250.

290.

325

0.36

0.39

0.42

0.34

50.

270.

330.

390.

40.

20.

70.

60.

60.

3Y

b1.

571.

685

1.8

1.98

52.

172.

285

2.4

2.05

51.

712.

075

2.44

2.9

0.9

4.7

4.3

4.5

1.8

Lu

0.24

0.26

0.28

0.32

0.36

0.39

50.

430.

350.

270.

325

0.38

0.4

0.1

0.7

0.6

0.6

0.2

Gum

usle

r

254 K. Kocak et al.

elements and rare earth elements (REE) (e.g., Smith andSmith 1976; Floyd and Winchester 1978).

Both amphibolite units share a sub-alkaline (Fig. 4d)and tholeiitic character (Figs. 6a–c), and define twochemically distinct groups as Gumusler and Kaleboynuamphibolites (Fig. 6d). The (La/Yb)N values for bothGumusler and Kaleboynu amphibolites are low (0.5–2.5;0.5–1.4, respectively) and display a narrow variation,which is consistent with a generation by partial meltingof a mantle source in which garnet does not remain as aresidual phase. Hence, the magma generation depth shouldhave been at < 60–80 km, within the spinel peridotite field(Watson and McKenzie, 1991).

Existence of a Nb anomaly and a high Th/La ratio (Fig.5b), in addition to the enrichment of LREE (Fig. 6d) sug-gests an asthenospheric or primitive mantle source withcrustal contamination. This crustal component consistedof two parts: i) one linked to source enrichment and asso-ciated with a subduction zone, ii) one associated withcrustal contamination that took place via assimilation andfractional crystallisation (AFC) during magmatic ascentthrough the thickened Central Anatolian crust. The formeris unrecognisable in our samples since there is no samplewith sufficient chemical contrast(s), e.g., the MgO/MgO+ FeO ratios of which are high and which at the sametime have distinctly low SiO2 and Th compared to thewhole range of other samples. We have represented in aTa/Yb vs. Th/Yb plot the average upper continental crustvalue from Taylor and MacLennan (1985) in Fig. 7a. TheKaleboynu samples are found next to the mantle array,between the compositions of typical N-MORB and theprimitive mantle (PM), but are displaced towards higherTh/Yb ratios while Gumusler samples display an increasein the Th/Yb ratio, suggesting coupled crustal contami-nation with fractional crystallisation. The slightly nega-tive Nb anomaly could also be formed in the same way(Wilson, 1989). The variations observed in Fig. 7b forthe Kaleboynu amphibolites can be better explained interms of an evolution mostly by low-pressure fractionalcrystallisation from asthenospheric melts. Gumusler sam-ples cluster around E-MORB (excluding two LREE-depleted samples). The enrichment in LIL elements ex-hibited in the MORB-normalised diagrams (Fig. 5) couldalso be attributed to mixing with crustal melts. However,this should be considered with caution, because the origi-nal LILE contents could have been mostly modified bymetamorphism, due to the mobility of these elements. Toconclude, the different geochemical features indicate thatthe Kaleboynu amphibolites have many features similarto present-day MORB magmas and derive from a moredepleted source than the Gumusler amphibolites. In ad-dition, the Gumusler amphibolites are more affected bycrustal contamination than their Kaleboynu counterpart.The nature of this crustal material is unknown, but it could

be similar to some of the neighbouring paragneisses, al-though no chemical analyses are available to support thishypothesis. Metasediments from the Ortakoy blocks, ad-jacent to the study area, are silica rich (61–79%) withhave intermediate negative Eu (Kocak, 1993) anomaly,which do not support such large contribution to theamphibolite magmas with low SiO2 (46–51%). Besides,the magnitude of the negative Nb anomaly in amphibolites(Fig. 5b) does not deepen with increasing SiO2 or Ce, nordoes La/Ybcn covary with Zr (not shown), as would beexpected for progressive contamination by continentalcrust. The samples are devoid of negative Ti anomalies(Fig. 5b). Thus, we argue that these data do not supportsubstantial assimilation of crust. The LILE and LREEenrichment and the negative Nb anomalies may not beassociated with crustal contamination.

Major, trace element variations show that chemicalcomposition of the amphibolites was mostly controlledby fractional crystallisation of olivine, pyroxene ± spinel,plagioclase, ilmenite and apatite. In both group samples,Zr shows slight negative Eu/Eu*, and strong positive cor-relation with Sr/Ce, confirming plagioclase fractionation.The lack of Eu anomalies (e.g., T13; Fig. 6) may be ex-plained as due to fractionation in high-oxidation condi-tions during which high Fe(Ti) magmas form with muchreduced KdEu

pl-liquid (Juster et al., 1989). Alternatively,crystallisation of sufficient pyroxene into the frameworkof plagioclase would cancel the Eu fractionation effectsof the feldspar (Patchett et al., 1994). Amphibole couldbe the possible phase of petrogenetic significance in themantle sources. The amphibolites have noticeably lowerNb/Ta (average 6 in Gumusler and 5 in Kaleboynu sam-ples) than the value of the primitive mantle or MORB(~18); such low Nb/Ta values and the relative Nb–Ta de-pletion suggest retention of these elements in theamphibole. Ionov and Hofmann (1995) also reported thathigh Nb–Ta partition coefficients for mantle amphibolewith higher Kdamph-liq for Nb than Ta.

The Gumusler and Kaleboynu samples have REE pat-terns that resemble E-MORB and N-MORB (Fig. 5b),respectively. On a few tectonomagmatic discriminationdiagrams, the samples are also found in MORB and IAB(Figs. 6a–c). In addition, on a Zr vs. V/Ti diagram, theGumusler samples also plot close to the BAB field whilethe Kaleboynu amphibolites cluster mostly in and next toN-MORB field (Fig. 7c). Both groups of samples couldhave been formed as back-arc basalt since geochemicalcharacterisation of back-arc basin basalts is usually tran-sitional between MORB and IAB due to contaminationor metasomatism with subduction zone fluids (Gale andPearce, 1982; Tarney et al., 1981). The genesis of theback-arc magmas could be related to suprasubduction ofthe mantle and/or to the partial melting of a shallow man-tle by release of lithostatic pressure. Floyd et al. (2000)


reported that the Kaleboynu amphibolites also includewithin-plate alkalic basalts in addition to tholeiitic basalts,and suggested that they formed in a rifted carbonate plat-form in where rifting had reached the stage of small ba-sins floored with ocean crust.

By assuming a Triassic age for metabasics, Floyd etal. (2000) suggested that the metabasic rocks were formedas a result of opening of Neothetys ocean. However, Ozgul(1976) suggested that the Devonian-Late Cretaceous-agedBolkardagı Unit might correspond to the cover forma-tion of the Nigde Massif. In addition, based on their fos-sil content, the precursor ages for lower part of the com-plex were suggested to range from Silurian to Devonianin Ortakoy Block (Kocak, 1993, 2000; Kocak and Leake,1994). The Kaleboynu Formation therefore should beUpper Paleozoic in age, and the development of theGumusler and Kaleboynu amphibolites should have beenassociated with the evolution of the Palaeotethys ocean,which was opened as a back-arc basin due to slab rollbackof the Rheic and Asiatic oceans (von Raumer et al., 2002;Stampfli et al., 2002), and closed finally in Turkey dur-ing the Cimmerian orogenic cycle (Eren et al., 2004). Thisis also compatible with suggestion of back-arc basin madeby Kurt et al. (2005). Although the eo-Cimmerian eventhas clearly been recognised in the Taurus, little is knownon the location of the Palaeotethys suture, most likelylargely subducted during the Alpine tectonic phases, start-ing with a major Late Cretaceous ophiolitic obduction(Lycian type) covering most of the Anatolides region.Accordingly, Whitney et al. (2003) determined 91.0 ± 2.0Ma as the timing of peak metamorphism from schist sam-ples from Nigde block by U–Pb SHRIMP, and suggestedthat high-grade metamorphic rocks were buried to 16–20km (5–6 kbar depth) at >700°C temperature, in relationwith closure of Tethyan seaways in Early Cenozoic. Widerange in conditions of regional metamorphism, whichcorrespond to 7.5–1.3 ± 0.6 kb pressure and 850–420°Ctemperature, may be a consequence of metamorphism atdifferent depths in the Neo-Tethyan subduction zone.

It is possible to estimate the depth from which theGumusler amphibolites were exhumed at approximately20 km by a regional extension in the Late Campanian toPalaeocene (Gautier et al., 2002) from Fig. 3c, thoughsome suggest tectonic denudation for unroofing (Fayonet al., 2001). High-temperature, moderate (~9 km) de-compression and cooling segment of the path between~6–3 kb in Fig. 3c may have been connected to initialslow cooling during erosional denudation. In contrast,high grade rocks cooled rapidly between 7.5–6 kb from850 to 740°C and 1.5–3 kb from 710 to 420°C. First, rapidcooling segment may indicate rapid exhumation while thelatest cooling may reflect intrusion of hot rocks, such asthe Uckapili granite, in shallow crustal levels.

CONCLUSIONS

Major, trace and rare earth element analyses show thatthe Gumusler and Kaleboynu amphibolites representtholeiit ic basaltic magmatism, derived fromasthenospheric or primitive mantle source at <60–80 km,developed mostly by fractional crystallisation of pyroxene± spinel, amphibole, plagioclase as well as apatite andtitanite crystals. The Gumusler amphibolites appears tobe more affected by crustal contamination than theKaleboynu amphibolites, with geochemical characteris-tics similar to present-day MORB magmas.

Basic magmatism in the area is suggested to devel-oped in relation with ensialic rifting of the Tauride-Anatolide Platform, which resulted in development of aback arc basin (Palaeotethys) in the area.Geothermometric studies show that they were at last meta-morphosed under variable pressure and temperatures,corresponding to 7.5–1.3 ± 0.6 kb and 850–420°C respec-tively, with the temperature gradient ranging from 35 to122°C/km, in relation with closure of Tethyan seawaysin Early Cenozoic. Alternatively, they were possibly bur-ied to ~23 km and 850°C, and exhumed to ~4 km due toregional extension.

Acknowledgments—We are grateful to Professors M. Santoshand M. Terabayashi for comments on earlier version of themanuscript. We thank H. Bas (Selcuk Univ.) for constructivesuggestions during the preparation of this paper. Our thanksalso go to Selcuk University (Konya-Turkey) Scientific Re-search Fund for their support.

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