Geochemical and Sr–Nd–Pb isotopic characteristics of Paleocene plagioleucitites from the Eastern Pontides (NE Turkey)

Lithos 105 (2008) 149–161

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Geochemical and Sr–Nd–Pb isotopic characteristics of Paleocene plagioleucitites fromthe Eastern Pontides (NE Turkey)

Rainer Altherr a,⁎, Gültekin Topuz b, Wolfgang Siebel c, Cüneyt Şen d, Hans-Peter Meyer a,Muharrem Satır c, Yann Lahaye e

a Institute of Mineralogy, University of Heidelberg, Im Neuenheimer Feld 236, D-69120 Heidelberg, Germanyb Istanbul Teknik Üniversitesi, Avrasya Yer Bilimleri Enstitüsü, TR-34469 Ayazağa, Istanbul, Turkeyc Institute of Geosciences, Mineralogy and Geodynamics, University of Tübingen, Wilhelmstr. 56, D-72074 Tübingen, Germanyd Karadeniz Teknik Üniversitesi, Jeoloji Mühendisliği Bölümü, TR-61080, Trabzon, Turkeye Institute of Geosciences, Mineralogy and Geochemistry, University of Frankfurt am Main, Altenhöferallee 1, D-60438 Frankfurt am Main, Germany

⁎ Corresponding author. Tel.: +49 6221 548206; fax: +E-mail address: [email protected] (R. A

0024-4937/$ – see front matter © 2008 Published by Edoi:10.1016/j.lithos.2008.03.001

A B S T R A C T

Article history:

Keywords:PlagioleucititeSr–Nd–Pb isotopesGeochemistryEastern Pontides, Turkey

Eastern Pontides, an isolated small (~1.5 km2) outcrop of plagioleucitites occursin the Aşutka thrust sheet. Field relations constrain the timing of volcanism between Maastrichtian and latePaleocene. The plagioleucitites consist of clinopyroxene, analcime (former leucite), Ti-magnetite, plagioclase,sanidine, apatite and accessory biotite. The rocks are represented by three geochemical and petrographicvarieties: Types I and II are mostly blocks within epiclastic debris and type III are lava flows. All the rocks areconsiderably altered, whereby leucite is almost totally analcimized, apart from leucite inclusions withinclinopyroxene that are remote from cracks. Furthermore, calcite and chlorite/smectite have been formed.Chemical effects of alteration are primarily reflected in an unsystematic variation of whole-rock K2O/Na2Oratios (0.12 to 1.71) and of the abundances of large-ion lithophile elements, such as Cs and K, and perhapsalso Rb. Both the high modal abundance of (former) leucite and the composition of clinopyroxene indicate anultrapotassic nature of the primary rocks. In primitive mantle-normalized element concentration diagrams,all samples are characterized by negative anomalies of Nb–Ta, Zr–Hf and Ti and a positive anomaly in Pb,testifying the orogenic nature of the volcanics. The rocks cover restricted ranges in all initial isotope ratioswith 87Sr/86Sr(i) (60 Ma) ranging from 0.70537 to 0.70568, 143Nd/144Nd(i) from 0.512529 to 0.512585, 206Pb/204Pb(i) from 18.65 to 18.83, 207Pb/204Pb(i) from 15.65 to 15.66 and 208Pb/204Pb from 38.64 to 38.88. There isno obvious relationship between the degree of analcimization and the isotopic composition. In Pb–Pbvariation diagrams, the rocks plot above the Northern Hemisphere Reference Line (NHRL). Chondrite-normalized rare earth element (REE) patterns show no significant Eu anomaly, but a strong enrichment of theLREE over the HREE with (La/Yb)cn=11.6–14.2, whereby normalized concentrations of Er to Lu are nearlysimilar. The Everek Hanları plagioleucitites represent the youngest products of Cretaceous to Paleocene arcmagmatism of the Eastern Pontides, thus documenting the last stages of the Neotethyan subduction.

© 2008 Published by Elsevier B.V.

1. Introduction

Among subduction- and collision-related volcanic rocks, leucite-bearing ultrapotassic ones are relatively rare (Bergman, 1987; Mitchelland Bergman, 1991; Mitchell, 1995a). The most important occurrencesare known from southwestern Spain (e.g. Venturelli et al., 1984; Nelsonet al.,1986; Venturelli et al.,1988;Wagner andVelde,1986,1987; Continiet al., 1993; Venturelli et al., 1991a,b; Toscani et al., 1995), Italy (e.g.Conticelli and Peccerillo, 1992; Conticelli et al., 2002; Peccerillo, 2005;Peccerillo and Martinotti, 2006), the southern Dinarides (e.g. Altherret al., 2004;Cvetković et al., 2004; Prelević et al., 2004, 2005, 2007, 2008)

49 6221 544809.ltherr).

lsevier B.V.

and western Turkey (Akal, 2003; Çoban and Flower, 2006). Based onmajor element characteristics, ultrapotassic volcanic rocks are classifiedas (I) lamproites, characterized by relatively low contents of Al2O3, CaOandNa2O, in combinationwith highMg# [=Mg/(Mg+0.9Fetot)] andK2O/Al2O3, (II) kamafugites that also have lowAl2O3 andNa2O, but higher CaOand lower SiO2 than lamproites, and (III) plagioleucitites that are rich inAl2O3 and Na2O, have relatively low values of K2O/Al2O3 and Mg# anddisplay CaO contents that are intermediate between those of lamproitesand kamafugites (Foley et al., 1987; Foley, 1992a, 1994). Orogenicultrapotassic rocks (lamproites and plagioleucitites) are stronglyenriched in incompatible trace elements and may display extreme Sr–Nd–Pb isotope compositions (Altherr et al., 2004; Prelević et al., 2007,2008). These characteristics are best explained by invoking inhomoge-neous mantle sources with spatially restricted non-peridotitic

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assemblages rich inphlogopite and/or amphibole and ‘accessory’ phases(Foley, 1992a,b, 1994; Mitchell, 1995b).

This paper deals with the petrology of plagioleucitites that occur ina small outcrop near Everek Hanları in the southern zone of theEastern Pontides. Although no isotopic age determinations are yetavailable, the age of these volcanics is constrained between lateCampanian/Maastrichtian and late Paleocene, as indicated by fieldrelations (Bektaş and Gedik, 1988; Bektaş et al., 1999). The textural andgeochemical characteristics of these volcanics will be presented andtheir possible geodynamic significance will be discussed.

2. Geological setting

The Eastern Pontides are generally regarded as a well-preservedCretaceous magmatic arc, resulting from the north-vergent subduc-

Fig. 1. Generalized geological map of the Bayburt region (modified after MTA, 2002). Insstratigraphic position (arrows).

tion of the northern branch of Neotethys along the Izmir–Ankara–Erzincan suture (IAES) (Şengör and Yılmaz, 1981; Okay and Şahintürk,1997; Okay and Tüysüz,1999; Boztuğ and Harvalan, 2008; Fig. 1 inset).The IAES separates the Sakarya zone of the Eurasian plate to the northfrom the Anatolide–Tauride block of Gondwana to the south. In theEastern Pontides, the collision is constrained to have occurred in thePaleocene to early Eocene (e.g. Okay and Şahintürk, 1997; Okay andTüysüz, 1999). In the northern part of the Eastern Pontides, lateCretaceous and post-collisional Eocene volcanic rocks with coevalgranitoids predominate (Boztuğ and Harvalan, 2008; Kaygusuz et al.,2008). Furthermore, there are Neogene alkaline volcanics (Aydın et al.,in press), erroneously assumed to be late Cretaceous or Eocene in age(Korkmaz et al., 1993; Şen et al., 1998). The southern part of theEastern Pontides consists of a multi-phase tectonic collage comprisingmainly plutonic, metamorphic and sedimentary rocks of pre-late

et shows the Sakarya zone and the locations of the main plagioleucitites of similar

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Cretaceous age, and including an ophiolitic mélange emplaced duringCenomanian–Turonian time (Okay and Şahintürk, 1997). In theSenonian, this southern part was in a fore-arc position, as documentedby a thick volcanoclastic flyschoid sequencewith (1) pelagic limestoneintercalations and (2) isolated ridges with shallow-marine sandstonesand rudist-bearing limestones (e.g. Okay and Şahintürk, 1997).Magmatic activity in the southern part of the Eastern Pontides isrestricted to post-collisional Eocene volcanics (basaltic to andesiticrocks of calcalkaline to tholeitic affinity) and granitoids, except for thePaleocene plagioleucitites described in this paper (e.g. Tokel, 1977;Arslan et al., 1997; Arslan and Aliyazıcıoğlu, 2001; Topuz et al., 2005;Boztuğ et al., 2006; Boztuğ and Harvalan, 2008; Karslı et al., 2007).

The Everek Hanları plagioleucitites (EHP) occur in a small area(~1.5 km2) near Maden village to the SE of Bayburt, and form part ofthe Aşutka thrust sheet in the Eastern Pontides (Figs. 1 and 2). Thestratigraphically lower parts of these volcanics are dominated byepiclastic debris, while the upper part consists of lava flows. Thevolcanic rocks rest on rudist-bearing reefal limestones dated as UpperCampanian to Maastrichtian (Özer and Fenerci, 1993; Fenerci, 1994;Yılmaz et al., 2003). These limestones transgressively overlie anophiolitic mélange, emplaced during Cenomanian–Turonian time. Allthese units are unconformably overlain by the Sipikör Formation, anUpper Paleocene to Ypresian flyschoid sequence of conglomerates,sandstones and shales (Okay et al., 1997). The actual areal coverage ofthe EHP is concealed by this flysch. Boulders of the older units arefrequently encountered in the basal horizons of the Sipikör formation,

Fig. 2. Geological map of the Everek Hanları volcanics (modifi

constraining the age of volcanism between Maastrichtian and UpperPaleocene.

The epiclastic volcanic deposits of the EHP are strongly altered anddisplay a reddish colour. Sometimes a sedimentary layering is visible.The clasts are poorly sorted. Greyish blocks (up to 40 cm) ofplagioleucitite are common. Most of these blocks have a porphyritictexture with phenocrysts (up to 1.5 cm) of greenish clinopyroxene andpinkish to white analcimized leucite within a grey groundmass. Theepiclastic deposits are overlain bymassive lava flows of plagioleucititewith phenocrysts of clinopyroxene and plagioclase, but not of leucite.Analcimized leucite is, however, an abundant groundmass phase.

Similar plagioleucitites with a comparable tectonic and strati-graphic position are reported from Gümüşhacıköy near Amasya(Tüysüz, 1996) and Ankara (Çapan, 1984) (Fig. 1, inset). For the latteroccurrence, K–Ar dating on biotite yielded ages of 60–65 Ma (Çapan,1984) that are in agreement with the stratigraphic constraints on theEHP.

3. Analytical techniques

Mineral analyses were carried out at the Institute of Mineralogy atHeidelberg using a CAMECA SX51 electron microprobe equipped withfive wavelength-dispersive spectrometers and an additional Si–Lidetector (Oxford Instruments). Standard operating conditions were15 kV accelerating voltage, 20 nA beam current and a beam diameterof ~1 μm. Counting times were usually 10 s, except for Mg, Ca and Al

ed after Bektaş and Gedik, 1988) with sample locations.

Table 1Selected microprobe analyses of clinopyroxene in leucite-bearing volcanic rocks from Everek Hanları

Sample # 8A 8A 8A 8A 20 20 20 4B 4B 4B 18 18

Rock type I I I I II II II III III III III III

Area Core Rim Matrix Matrix Core Rim Matrix Core Rim Matrix Core Matrix

Analysis # 3 53 57 58 87 111 90 146 147 149 139 133

SiO2 51.65 48.92 50.60 47.89 50.35 46.44 47.00 49.57 48.19 50.45 49.76 50.52TiO2 0.36 1.09 0.64 1.45 0.57 1.40 1.23 0.84 1.05 0.74 0.73 0.72Al2O3 2.63 4.60 2.93 4.76 3.49 6.59 6.20 4.62 5.87 2.86 4.09 2.42Cr2O3 0.28 0.03 0.00 0.00 0.22 0.00 0.01 0.02 0.02 0.05 0.03 0.04Fe2O3 3.21 3.02 2.53 3.98 4.88 5.27 5.09 3.47 4.35 2.66 4.07 2.56FeO 3.15 7.02 6.86 7.76 1.61 3.79 5.28 5.26 4.01 7.41 4.04 8.60MnO 0.13 0.30 0.30 0.40 0.25 0.17 0.31 0.29 0.26 0.45 0.37 0.52MgO 15.32 11.68 13.02 10.34 14.73 12.04 11.56 13.33 13.05 12.96 13.78 11.68CaO 23.43 22.20 22.05 21.94 23.49 23.18 22.44 21.98 22.66 21.21 22.60 21.55Na2O 0.32 0.62 0.51 0.93 0.53 0.36 0.50 0.55 0.42 0.57 0.48 0.74K2O 0.00 0.01 0.03 0.04 0.02 0.01 0.01 0.00 0.02 0.07 0.00 0.02Total 100.48 99.47 99.47 99.04 100.13 99.24 99.64 99.94 99.89 99.43 99.95 99.38

Number of cations based on 6 oxygen anions and 4 cationsSi 1.896 1.846 1.901 1.830 1.857 1.752 1.773 1.846 1.796 1.900 1.850 1.916Al(IV) 0.104 0.154 0.099 0.170 0.143 0.248 0.227 0.154 0.204 0.100 0.150 0.084Al(VI) 0.010 0.051 0.031 0.044 0.009 0.045 0.049 0.049 0.054 0.027 0.029 0.024Ti 0.010 0.031 0.018 0.042 0.016 0.040 0.035 0.024 0.029 0.021 0.020 0.021Cr 0.008 0.001 0.000 0.000 0.006 0.000 0.000 0.001 0.001 0.001 0.001 0.001Fe3+ 0.089 0.086 0.071 0.114 0.135 0.150 0.145 0.097 0.122 0.075 0.114 0.073Fe2+ 0.097 0.222 0.216 0.248 0.050 0.120 0.167 0.164 0.125 0.233 0.126 0.273Mn 0.004 0.009 0.009 0.013 0.008 0.005 0.010 0.009 0.008 0.014 0.012 0.017Mg 0.839 0.657 0.729 0.589 0.810 0.677 0.650 0.740 0.725 0.728 0.764 0.660Ca 0.922 0.898 0.887 0.880 0.928 0.937 0.907 0.877 0.905 0.856 0.900 0.875Na 0.023 0.045 0.037 0.069 0.038 0.026 0.037 0.039 0.030 0.042 0.035 0.055K 0.000 0.000 0.002 0.002 0.001 0.000 0.000 0.000 0.001 0.003 0.000 0.001Mg# 81.9 68.1 71.8 61.9 81.4 71.5 67.6 73.9 74.6 70.2 76.1 65.6

Mg#=100·Mg/(Mg+Fe2++Fe3+).

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(20 s) and Ti (30 s) in oxides, and Ba (30 s) and Sr (30 s) in feldspars.Analcime and feldspars were analyzed with a defocused beam (10 μm)in order to minimize loss of alkalis. Natural and synthetic oxide and

Fig. 3. Compositional variation of feldspars in Or–Ab–An triangle

silicate standards were used for calibration. The PAP algorithm(Pouchou and Pichoir, 1984, 1985) was applied to raw data. Detectionlimits for silicates were 0.040 wt.% SiO2, 0.063 wt.% TiO2, 0.045 wt.%

from selected samples of the Everek Hanları plagioleucitites.

Table 2Selected microprobe analyses of biotite from Everek Hanları

Sample # 23 23 18 11 13 13 4A

Rock type II II III III III III III

Analysis # 81 84 131 52 69 73 102

SiO2 40.67 41.34 40.19 34.96 38.20 39.53 40.40TiO2 0.06 0.04 2.96 6.20 4.35 3.38 3.24Al2O3 11.85 12.20 11.70 15.22 12.61 11.80 11.38Cr2O3 0.03 0.01 0.00 0.00 0.00 0.00 0.05FeOtot 12.06 12.06 11.30 14.30 15.61 12.19 11.73MnO 0.24 0.31 0.22 0.16 0.39 0.24 0.16MgO 20.18 19.75 18.85 15.12 15.57 18.90 19.00CaO 0.03 0.04 0.02 0.02 0.13 0.04 0.02Na2O 0.30 0.34 0.40 0.62 0.44 0.69 0.54K2O 9.88 9.67 9.86 8.97 8.96 9.26 9.48Total 95.30 95.76 95.50 95.57 96.26 96.02 96.00

Number of cations based on 6 oxygen anionsSi 2.994 3.018 2.948 2.614 2.837 2.895 2.949Al(IV) 1.006 0.982 1.011 1.341 1.104 1.019 0.979Al(VI) 0.022 0.068 0.000 0.000 0.000 0.000 0.000Ti 0.003 0.002 0.163 0.348 0.243 0.186 0.178Cr 0.002 0.001 0.000 0.000 0.000 0.000 0.003Fe2+ 0.743 0.736 0.693 0.894 0.969 0.747 0.716Mn 0.015 0.019 0.014 0.010 0.024 0.015 0.010Mg 2.215 2.149 2.062 1.685 1.724 2.063 2.067Ca 0.003 0.003 0.002 0.002 0.010 0.003 0.001Na 0.042 0.048 0.057 0.089 0.064 0.098 0.077K 0.928 0.901 0.923 0.856 0.848 0.865 0.883Total 7.972 7.929 7.873 7.840 7.824 7.891 7.862Mg# 74.9 74.5 74.8 65.3 64.0 73.4 74.3

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Al2O3, 0.121 wt.% Fe2O3, 0.070 wt.% Cr2O3; 0.074 wt.% MgO, 0.106 wt.%NiO, 0.080 wt.% MnO, 0.039 wt.% CaO, 0.028 wt.% Na2O and 0.031 wt.%K2O.

Major andminor oxides were determined by XRF (modernized SRS300 wavelength-dispersive spectrometer; Bruker AXS) at the Instituteof Mineralogy at Heidelberg. Lithium borate fusion disks were used.Calibration was performed with international reference samples. Theaccuracy is mostly below ±0.30%, while the analytical precision is±0.10%. Trace elements were determined by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-ICP-MS,Merchantek LUV213 coupled with ThermoFinnigan Element2) at theInstitute of Geosciences, University of Frankfurt/M. For the measure-ments, 10 mg of sample powder were melted on a platinum beltheated to ~2000 °C. The melted sample was quenched into glass withcompressed air. The melting time was held short to avoid theevaporation of alkaline elements. For each sample, two differentglasses were produced to check the reproducibility of the analyses.Calibration was performed against NIST612 (a synthetic glass withknown trace element compositions). Si concentration (also knownfrom XRF analyses) was measured together with the trace elements asan internal standard.

Sr, Nd and Pb isotope analyses were performed at the Institute ofGeosciences, University of Tübingen. Rock powders were dissolved in52% HF for four days at 140 °C on a hot plate. Digested samples weredried and redissolved in 6 N HCl, dried again and redissolved in 2.5 NHCl (for Sr and Nd separation) or 2.5 N HBr (for Pb separation). Sr andlight rare earth elements were isolated on quartz columns byconventional ion exchange chromatography with a 5 ml resin bed ofBio Rad AG 50W-X12, 200–400 mesh. Nd was separated from otherrare earth elements on quartz columns using 1.7 ml Teflon powdercoated with HDEHP, di(2-ethylhexyl)orthophosphoric acid, as cationexchange medium. Separation and purification of Pb were carried outon Teflon columns with a 100 μl (separation) and 40 μl bed (cleaning)of Bio Rad AG1-X8 (100–200mesh) anion exchange resin using a HBr–HCl ion exchange procedure. All isotopic measurements weremade bythermal ionizationmass spectrometry using a FinniganMAT 262massspectrometer. Sr was loaded with a Ta–HF activator on pre-conditioned W filaments and was measured in single-filamentmode. Nd was loaded as phosphate on pre-conditioned Re filamentsand measurements were performed in a Re double filament config-uration. 87Sr/86Sr isotope ratios were normalized to 86Sr/88Sr=0.1194and 143Nd/144Nd isotope ratios to 146Nd/144Nd=0.7219. The La JollaNd-Standard yielded a value of 0.511833±09 (reference value0.511850) and the NBS 987 Sr standard yielded 87Sr/86Sr ratios of0.710235±09 (reference value 0.710248). Pb was loaded with a Si-gelonto a Re filament andmeasured at ~1300 °C in single-filament mode.A factor of 1‰ per mass unit for instrumental mass fractionation wasapplied to the Pb analyses, using NBS SRM 981 as reference material.Total procedural blanks (chemistry and loading) were 88 pg for Nd,1043 pg for Sr and 30 pg for Pb isotope measurements.

4. Petrography and mineral chemistry

The EHP include three types that are characterized by differenttextures and chemical compositions. Rocks of types I and II occur inthe lower part of the volcanic formation, either in form of boulders oras rare massive flows. Rocks of type I have porphyritic textures, withphenocrysts of olivine (completely altered into smectite and calcite),clinopyroxene and subordinate leucite (completely analcimized). Thegroundmass consists of microcrystalline clinopyroxene, Ti-magnetite,analcime (leucite), sanidine, plagioclase, apatite and altered glass.

Type-II rocks are characterized by porphyritic to glomeroporphyri-tic textures, with phenocrysts of clinopyroxene and analcimizedleucite in a fine-grained groundmass of clinopyroxene, Ti-magnetite,plagioclase, sanidine, analcime (leucite) and accessory biotite. Sec-ondary phases include calcite and smectite/chlorite. Clinopyroxene

phenocrysts contain inclusions of Ti-magnetite, leucite (partly fresh)and former glass, and commonly display oscillatory and sector zoning.Leucite (analcime) phenocrysts often have fine-grained rims ofsanidine, most probably due to peritectic reaction between leuciteand melt.

Rocks of type III are relatively fine-grained and occur as massiveflows in the upper part of the volcanic formation. Rare phenocrysts ofclinopyroxene, Ti-magnetite and plagioclase are embedded in agroundmass of sanidine, plagioclase, leucite (analcime), Ti-magnetiteand accessory biotite. Plagioclase phenocrysts often have a cloudyappearance, caused by secondary analcime and chlorite. Alongfractures, clinopyroxene phenocrysts are partially replaced by chlor-ite/smectite and calcite.

Clinopyroxene compositions (phenocrysts and groundmass) aresimilar in all rock types and show considerable variations. Mg#[100·Mg/(Mg+Fetot)] ranges from 81.9 to 51.8, Si from 1.94 to 1.66cations per formula unit (cpfu), Altot from 0.072 to 0.384 and Na from0.021 to 0.075 cpfu (Table 1). Phenocrysts are always zoned with coresrich in Si andMg but low in Al, Ti and Na, overgrown bymarginal zonesthat are low in Si and Mg but high in Ti and Al. The boundary betweencore and marginal zones is in most cases abrupt and step-like. Thecomposition of groundmass clinopyroxene is also highly variable withrespect to Si and Al; Mg# values are similar to or lower than those ofphenocryst rims. Ti–Al relationships are similar to those of clinopyrox-ene in plagioleucitites from the Roman and Campanian province, asgiven by Prelević et al. (2005) and Çoban and Flower (2006).

Leucite is generally analcimized, except for leucite inclusions inclinopyroxene that are remote from cracks. Preserved leucite grainshave variable Na/(Na+K) values between 0.014 and 0.101. Composi-tions of coexisting feldspars (sanidine/anorthoclase and plagioclase)in all rock types are shown in Fig. 3. The absence of a miscibility gapbetween Ab and Or suggests a relatively low PH2O during feldsparcrystallization (babout 0.3 GPa) (Yoder et al., 1957; Tuttle and Bowen,1958). Sanidine/anorthoclase may contain considerable amounts ofBa (≤0.095 cpfu), while plagioclase is often relatively rich in Sr(≤0.098 cpfu). Accessory biotite in the groundmass of type-II rocks has

Table 3Whole-rock compositions of the Everek Hanları plagioleucitites, Eastern Pontides, NE Turkey

Sample 8A 14 7 20 22 23 4A 4B 11 12 13 18

Type I I II II II II III III III III III III

SiO2 46.90 48.62 46.71 46.68 46.07 49.98 52.73 51.4 52.09 53.00 53.23 53.57TiO2 0.91 0.82 0.91 0.95 0.89 0.94 0.76 0.78 0.72 0.74 0.72 0.72Al2O3 13.87 13.65 16.51 16.42 16.20 16.38 18.66 17.83 18.73 19.19 19.05 19.10Fe2O3

tot 10.54 10.02 10.50 10.57 10.26 9.47 7.41 8.17 7.10 7.44 7.13 6.95MnO 0.16 0.20 0.19 0.23 0.20 0.26 0.14 0.14 0.17 0.14 0.19 0.14MgO 7.55 7.46 4.95 4.82 4.82 4.50 2.87 3.70 3.32 2.84 2.72 2.99CaO 8.60 10.36 6.98 7.41 6.56 7.03 4.47 4.98 2.74 2.67 3.95 3.65Na2O 4.10 4.04 6.86 7.09 7.26 3.37 4.95 4.93 3.88 4.47 5.23 4.20K2O 2.59 1.71 1.08 0.92 0.88 4.77 4.66 3.91 6.62 6.20 4.39 5.90P2O5 0.55 0.58 0.83 0.84 0.79 0.58 0.51 0.51 0.44 0.45 0.45 0.43LOI 4.08 3.05 5.15 4.94 5.43 2.71 4.31 3.43 3.60 3.79 3.08 2.99Total 99.85 100.51 100.67 100.87 99.36 99.99 101.47 99.78 99.41 100.93 100.14 100.64Li 41 20 n.a. 39 49 48 n.a. 33 55 n.a. n.a. 57B 33 10 n.a. 17 40 51 n.a. 68 58 n.a. n.a. 82Sc 34 35.1 n.a. 13 15 22 n.a. 13 12 n.a. n.a. 11V 321 223 n.a. 301 328 269 n.a. 201 185 n.a. n.a. 188Cr 127 107 n.a. 10 13 26 n.a. 11 7 n.a. n.a. 7Co 46 32 n.a. 32 36 27 n.a. 22 17 n.a. n.a. 18Ni 55 63 n.a. 22 21 20 n.a. 13 9 n.a. n.a. 10Cu 50 71 n.a. 69 97 140 n.a. 93 67 n.a. n.a. 49Zn 118 11 n.a. 72 113 96 n.a. 81 79 n.a. n.a. 83Ga 36 88 n.a. 49 57 38 n.a. 46 40 n.a. n.a. 46Cs 9.08 4.78 n.a. 15.9 24.2 5.47 n.a. 6.04 8.65 n.a. n.a. 8.55Rb 46 10 n.a. 28 24 47 n.a. 49 111 n.a. n.a. 84Ba 1149 3083 n.a. 1198 2040 1270 n.a. 1420 1279 n.a. n.a. 1592Th 10.6 13.9 n.a. 11.7 16.0 13.9 n.a. 14.0 13.2 n.a. n.a. 14.5U 4.3 2.7 n.a. 3.0 4.2 4.5 n.a. 5.8 5.9 n.a. n.a. 5.8Sr 631 850 n.a. 763 956 871 n.a. 944 757 n.a. n.a. 973Y 25 27 n.a. 26 31 27 n.a. 19 22 n.a. n.a. 23Pb 22.8 5.4 n.a. 7.4 22.0 20.0 n.a. 17.1 18.5 n.a. n.a. 18.3Nb 11.6 9.0 n.a. 11.7 14.7 14.5 n.a. 18.6 16.5 n.a. n.a. 16.3Ta 0.62 0.63 n.a. 0.60 0.80 0.84 n.a. 1.01 0.93 n.a. n.a. 0.92Zr 130 147 n.a. 141 170 166 n.a. 152 161 n.a. n.a. 165Hf 3.25 3.70 n.a. 3.18 3.77 4.08 n.a. 3.39 3.65 n.a. n.a. 3.77La 38.44 38.4 n.a. 43.03 54.03 42.22 n.a. 38.38 37.29 n.a. n.a. 40.83Ce 83.46 59.6 n.a. 91.04 109.74 86.58 n.a. 77.1 77.19 n.a. n.a. 82.12Nd 41.44 35.61 n.a. 45.33 53.87 42.64 n.a. 32.22 32.02 n.a. n.a. 34.72Sm 9.26 8.24 n.a. 9.71 11.53 9.40 n.a. 6.48 6.49 n.a. n.a. 6.95Eu 2.70 2.15 n.a. 2.77 3.26 2.70 n.a. 1.96 1.93 n.a. n.a. 2.13Gd 7.76 7.52 n.a. 8.10 9.50 7.92 n.a. 5.41 5.50 n.a. n.a. 5.86Tb 0.99 0.95 n.a. 1.00 1.20 1.01 n.a. 0.69 0.72 n.a. n.a. 0.75Dy 5.20 5.21 n.a. 5.27 6.39 5.49 n.a. 3.71 4.02 n.a. n.a. 4.19Ho 0.90 0.96 n.a. 0.93 1.14 1.00 n.a. 0.69 0.77 n.a. n.a. 0.80Er 2.32 2.55 n.a. 2.36 2.94 2.61 n.a. 1.92 2.16 n.a. n.a. 2.25Tm 0.31 0.35 n.a. 0.32 0.39 0.36 n.a. 0.26 0.31 n.a. n.a. 0.32Yb 2.06 2.23 n.a. 2.08 2.60 2.43 n.a. 1.83 2.17 n.a. n.a. 2.22Lu 0.28 0.33 n.a. 0.28 0.36 0.33 n.a. 0.26 0.32 n.a. n.a. 0.32K2O/Na2O 0.63 0.42 0.16 0.13 0.12 1.42 0.94 0.79 1.71 1.39 0.84 1.40Mg# 61.2 62.1 50.9 50.0 50.8 51.1 46.0 49.9 50.7 45.6 45.6 48.6(La/Yb)cn 12.61 11.62 – 13.92 14.01 11.69 – 14.15 11.60 – – 12.41Eu/Eu⁎ 0.97 0.83 – 0.95 0.95 0.96 – 1.01 0.99 – – 1.02

Mg#=100×molar MgO/(MgO+0.9 FeOtot). Oxides are given in wt.%, trace elements in μg/g.

Table 4Sr–Nd–Pb isotope ratios of plagioleucitites from Everek Hanları, Eastern Pontides

Sample 87Rb/86Sr 87Sr/86Sr 87Sr/86Sr(i) 143Nd/144Nd 143Nd/144Nd(i) εNd(i) 206Pb/204Pb 206Pb/204Pb(i) 207Pb/204Pb 207Pb/204Pb(i) 208Pb/204Pb 208Pb/204Pb(i)

Type I8A 0.211 0.705700 (09) 0.70552 0.512638 (07) 0.512585 0.5 18.941 18.83 15.665 15.66 38.969 38.8814 0.034 0.705401 (10) 0.70537 0.512622 (09) 0.512567 0.1 18.948 18.65 15.664 15.65 38.972 38.46

Type II20 0.106 0.705746 (09) 0.70566 0.512580 (09) 0.512529 −0.6 18.901 18.66 15.665 15.65 38.963 38.6522 0.073 0.705739 (10) 0.70568 0.512590 (09) 0.512539 −0.4 18.896 18.78 15.658 15.65 38.946 38.8023 0.156 0.705506 (10) 0.70537 0.512622 (05) 0.512569 0.2 18.966 18.83 15.669 15.66 38.999 38.86

Type III4B 0.150 0.705516 (08) 0.70539 0.512615 (10) 0.512567 0.1 18.961 18.76 15.664 15.65 38.978 38.8211 0.424 0.705807 (10) 0.70545 0.512610 (09) 0.512562 0.0 18.966 18.77 15.665 15.66 38.981 38.8418 0.250 0.705722 (08) 0.70551 0.512619 (07) 0.512571 0.2 18.960 18.77 15.666 15.66 38.961 38.80

Uncertainties for the 87Sr/86Sr and 143Nd/144Nd ratios are 2σm errors in the last two digits (in parentheses). Uncertainties for Pb isotope ratios are b0.1%, and ratios are corrected for0.1% mass fractionation per mass unit. Initial values are calculated for an assumed age of 60 Ma. εNd(i) values are calculated relative to CHUR with present-day values of 143Nd/144Nd=0.512638 and 147Sm/144Nd=0.1967 (Jacobsen and Wasserburg, 1980).

154 R. Altherr et al. / Lithos 105 (2008) 149–161

155R. Altherr et al. / Lithos 105 (2008) 149–161

high Mg# (74.9–73.9) and is low in Ti (b0.003 cpfu) and AlVI (0.021–0.069 cpfu); Na/(Na+K) values range from 0.03 to 0.05. Biotite in type-III rocks has variable Mg# (75.3–64.0), relatively high Ti (0.139–0.348 cpfu) and high Na/(Na+K) values (0.080–0.117) (Table 2).

Ti-magnetite from type-I and type-II rocks are compositionallysimilar, with relatively low Ti and Fe2+, but high Fe3+ and Al contents(Type I:Mg0.27–0.00Fe2+0.82–1.20Mn0.01–0.12Al0.05–0.36Fe3+1.51–1.25Ti012–0.32O4;type II: Mg0.29–0.01Fe2+0.82–1.26Mn0.01–0.10 Al0.07–0.33Fe3+1.40–1.27Ti013–0.32O4).In contrast, Ti-magnetite of type-III rocks is richer inTi andFe2+ andpoorerin Fe3+ and Al (Mg0.04–0.00Fe 2+

1.39–1.68 Mn0.01–0.05Al0.04–0.11Fe3+1.04–0.52Ti0.44–0.69O4).

5. Bulk-rock chemistry and Sr–Nd–Pb isotopic compositions

Bulk-rock chemical and isotopic compositions of selected samplesare given in Tables 3 and 4, respectively. Bulk-rock K2O/Na2O ratiosshow a considerable scatter (0.12–1.71) and do not represent primaryvalues due to analcimization of leucite. The lowest values are found inthe strongly altered type-I and type-II rocks. Analcimitization of leuciteresults in an increase in Na2O but a decrease in K2O. According to Foleyet al. (1987), fresh ultrapotassic rocks are characterized byMgON3.0 wt.%, K2ON3.0 wt.% and K2O/Na2ON2.0. Since modalabundances of primary leucite in the EHP are between 20 to 40 vol.%,these rocks originally were ultrapotassic. In a CaO versus Al2O3

diagram (Fig. 4) that is used to classify ultrapotassic rocks, the bulk-rock analyses plot into the plagioleucitite field, as defined by Foley(1994).

Variation diagrams of selected major and trace elements versusSiO2 are presented in Fig. 5. There is an overall decrease in TiO2, FeOtot,V and Y with increasing silica, and an increase in K2O and Rb. Otherelements either display different trends in the three rock types (e.g.Al2O3, MgO, CaO, Na2O, P2O5, Sc, Cr, Ni, Zr) or do not show anysystematic variations (e.g. Ba, Sr). MgO contents and the abundancesof Cr and Ni systematically decrease from type I to type III.

In primitive mantle-normalized element concentration diagrams,all samples are characterized by negative anomalies of Rb, Nb–Ta, Zr–Hf and Ti, accompanied by a positive anomaly in Pb of variablemagnitude (Fig. 6a, c, e). The large-ion lithophile elements (LILE) Cs,Rb, Ba and K are decoupled and show unsystematic inter-samplevariations. Ba/Th and Ba/La ratios are high (91–222 and 30–80,respectively) and in primitive mantle-normalized element abundancepatterns (Fig. 6a, c, e) the samples do not display negative Baanomalies. Chondrite-normalized rare earth element (REE) patternsshow no significant Eu anomaly (Eu/Eu⁎=1.02–0.83) and a strongenrichment of the LREE over the HREE [(La/Yb)cn=11.62–14.15],

Fig. 4. Variation of CaOwith Al2O3 in plagioleucitites from Everek Hanları. Fields labeledGroups I, II and III (separated by thick lines) correspond to lamproites senso stricto fromcontinental settings with mild extension, kamafugites from continental rift zones andother settings, and plagioleucitites from active orogenic areas, respectively, assuggested by Foley et al. (1987) and Foley (1994).

whereby normalized concentrations of Er to Lu are nearly similar(Fig. 6b, d, f).

Measured and calculated initial (60 Ma) Sr, Nd and Pb isotopiccompositions of selected samples are listed in Table 4 and plotted inFigs. 7 and 9. The rocks cover restricted ranges in all initial isotoperatios, whereby isotopic values are not related to rock type. 87Sr/86Sr(i)ranges from 0.70537 to 0.70568 and 143Nd/144Nd(i) from 0.512529 to0.512585. In a Sr–Nd plot, the data points do not define a linear trend.206Pb/204Pb(i) ratios show a restricted variation from 18.65 to 18.83.207Pb/204Pb(i) and 208Pb/204Pb(i) ratios are relatively low (15.65–15.66and 38.64–38.88, respectively). In Pb–Pb diagrams (Fig. 7), thesamples plot well above the Northern Hemisphere Reference Line(NHRL; Hart, 1984) with almost constant Δ7/4 values (+12.3 to +13.7)and somewhat variable, but generally high Δ8/4 values (+28.5 to+52.0).

6. Discussion

6.1. Geochemical impact of hydrothermal alteration

The formation of secondary analcime, chlorite, smectite and calciteat the expense of leucite, plagioclase, olivine and glass indicatesconsiderable hydrothermal alteration of the investigated volcanicrocks. Analcimization of leucite is a common phenomenon inultrapotassic rocks worldwide (e.g. Mitchell et al., 1987; Venturelliet al., 1991a; Putnis et al., 1994, 2007; Carlson et al., 1996; Araujo et al.,2001; Prelević et al., 2004; Putnis et al., 2007). In the Everek Hanlarıplagioleucitites, the observed decoupling of LILE, as indicated byconsiderable depletions of K and Rb, but not of Ba, enrichments in Naand possibly also in Cs (Fig. 6a, c, e), and highly variable K2O/Na2Oratios, is related to hydrothermal alteration. While both type-Isamples are strongly altered and have low K2O/Na2O ratios (b0.63),sample 23 among type-II rocks and samples 11, 12 and 18 among type-III rocks appear to be the least altered ones and are characterized byK2O/Na2O ratios between 1.39 and 1.71 (Table 3).

Samples 14 (type-I) and 20 (type-II) with low K2O/Na2O ratios arecharacterized by relatively low abundances of Pb (Table 3) and highCe/Pb ratios (11.0 and 12.3), in conjunction with ‘initial’ 206Pb/204Pbratios of ~18.66 that are significantly lower than those of the othersamples (18.76–18.83; Table 4 and Fig. 7d). Since present-day Pbisotopic ratios of all samples are very similar, it is well possible that thecalculated ‘initial’ Pb isotope values of samples 14 and 20 are anartefact of a Pb loss from the system. On the other hand, the restrictedranges of initial Sr and Nd isotopic ratios suggest that the budgets ofthese two elements were not significantly affected during alteration,in particular that no Sr was introduced from outside the system.Seawater 87Sr/86Sr in the Paleocene was near to 0.7076 (e.g. Burkeet al., 1982), so any alteration involving seawater should have changedoriginal Sr isotopic ratios towards higher values. The coherent andsystematic behavior of all other trace elements, in particular the HFSEand REE (Fig. 6), suggests that they are virtually unaffected byhydrothermal alteration.

6.2. Magma genesis

The four samples characterized by relatively high K2O/Na2O ratios(samples 11, 12, 18 and 23) should have chemical compositions thatcan be used to deduce their petrogenesis. Primitive mantle-normal-ized element concentration patterns of these samples reveal a numberof characteristic signatures that are typical for magmas generatedalong converging plate margins, i.e. negative anomalies of Nb–Ta, Zr–Hf and Ti and positive Pb anomalies (Fig. 6). Furthermore, low ratios ofNb/U (2.7–3.9) and Ce/Pb (3.6–5.0) also suggest a subduction-relatednature of the Everek Hanları plagioleucitites. Moreover, in the Th/Ybversus Ta/Yb discriminant diagram of Pearce (1982), all investigatedsamples plot in the field of arc volcanics (Fig. 8a).

Fig. 5. Harker diagrams of (a) TiO2, (b) Al2O3, (c) Fe2O3 (total iron), (d) MgO, (e) CaO, (f) Na2O, (g) K2O, (h) P2O5, (i) Sc, (j) Ba, (k) V, (l) Cr, (m) Ni, (n) Rb, (o) Sr, (p) Y, (q) Zr, and (r) Nb ofthe Everek Hanları plagioleucitites.

156 R. Altherr et al. / Lithos 105 (2008) 149–161

Fig. 6. (a), (c), (e) Primitive mantle-normalized element abundance patterns of plagioleucitites from Everek Hanları. For normalizing values and sequence of elements, see Sun andMcDonough (1989). All samples are characterized by negative anomalies of Nb–Ta, Zr–Hf and Ti, and positive anomalies of Pb. (b), (d), (f) Chondrite-normalized rare earth elementdiagrams. Normalizing values were taken from Boynton (1984).

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Mg# values as well as Ni and Cr contents (Table 3) indicate that theEHP crystallized from fractionatedmagmas. The chondrite-normalizedREEpatterns (Fig. 6) are very similar to those ofMacedonian lamproites(Altherr et al., 2004) or Italian plagioleucitites (Peccerillo, 2005) andsuggest fractionation of the original melts from a garnet-bearingmantle residue. Since the rocks have high CaO contents, the magmasshould be derived from a clinopyroxene-bearing, fertile mantle.

Orogenic ultrapotassic volcanic rocks containing both leucite andplagioclase (i.e. plagioleucitites) are relatively rare. The two mostimportant recent examples are the innermost volcanic islands of theSunda–Banda Arc (e.g. Tambora, Sangeang Api, Muriah, Batu Tara) andthe volcanic provinces developed on the Italian peninsula in responseto subduction of the Adriatic and Ionian plates. Both settings have incommon that large amounts of continental materials have beensubducted, either in the form of sediments or as continental crust.Indeed, the chemical and isotopic signatures of the K-rich magmasin these arcs have been interpreted to reflect the involvement of

continent-derived materials in the magma sources (e.g. Hutchison,1982; Stolz et al., 1988, 1990; van Bergen et al., 1992; Serri et al., 1993;Hoogewerff et al., 1997; Peccerillo, 1999, 2001; Turner and Foden,2001; Peccerillo, 2002; Elburg et al., 2004; Peccerillo, 2005; Peccerilloand Martinotti, 2006). In Italy, Pliocene–Quaternary plagioleucititesare known from the Roman and Campaninan provinces (Peccerillo,2005; Peccerillo and Martinotti, 2006). It is worth to note, that theleast altered EHP samples exhibit striking chemical and Sr–Nd–Pbisotopic similarities to the volcanics from the Campanian province,while both are isotopically different from the plagioleucitites of theRoman province (Figs. 8b, c and 9).

Mediterranean Cenozoic lamproitic and plagioleucititic magma-tism is generally characterized by highly variable Nd–Sr isotopic ratiosat almost constant Pb isotopic composition (Altherr et al., 2004;Peccerillo, 2005; Prelević et al., 2005; Peccerillo and Martinotti, 2006;Prelević et al., 2007; Prelević et al., 2008). The EHP fit into this isotopicscheme, being isotopically similar to plagioleucitites from the

Fig. 7. Variation of initial 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of Everek Hanları plagioleucitites. (a) and (b) Nd and Sr isotope ratios. (c) and (d) 207Pb/206Pb(i) versus 206Pb/204Pb(i) and 208Pb/206Pb(i) versus 206Pb/204Pb(i) plot high above the Northern Hemisphere Reference Line (NHRL) of Hart (1984).

Fig. 8. (a) Th/Yb versus Ta/Yb with fields for arc and intraplate volcanics (Pearce, 1982)and position of Everek Hanları plagioleucitites. (b) Ce/Sr versus Th/Ta ratios ofCampanian, Roman and Everek Hanları plagioleucitites. (c) 87Sr/86Sr(i) versus Ba/La ofEverek Hanları plagioleucitites. For symbols see Fig. 7.

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Campanian Province (Fig. 9). In contrast to lamproites from SE Spain,the Western Alps, Tuscany–Corsica and Serbia–Macedonia, plagioleu-citites from the Campanian Province and from Everek Hanları showNd–Sr isotope ratios that are roughly similar to those of bulk Earth(Fig. 9). On the other hand, their Pb isotopic ratios are similar to thoseof Mediterranean lamproites, i.e. they plot into the fields of pelagicsediments (Ben Othman et al., 1989).

Ba abundances in the EHP are relatively high resulting in similarvalues of Ba, Th and U in primitive mantle-normalized elementvariation diagrams (Fig. 6a, c, e). This feature is also shown byplagioleucitites from the Campanian province and by lamproites fromMacedonia and southern Serbia (Altherr et al., 2004; Peccerillo, 2005;Prelević et al., 2008). On the other hand, lamproites from Spain, Italyand northern Serbia as well as plagioleucitites from the Romanprovince are all characterized by pronounced negative Ba anomalies(Altherr et al., 2004; Peccerillo, 2005; Prelević et al., 2008). A negativeBa anomaly may be caused by a Ba-rich residual phase (e.g.phlogopite) during partial melting. However, the fact that theMacedonian and some Serbian lamproites contain Cr-rich phlogopitexenocrysts with high Mg# and do not show negative Ba anomalies(Altherr et al., 2004) while the EHP are nearly phlogopite-free, clearlyargues against this hypothesis. Alternatively, the variable relative Bacontents of the Mediterranean lamproites and plagioleucitites mayresult from variable Ba contents in the mantle source. The generallyhigh Ba/La and Ba/Th ratios of the EHP suggest a significantcontribution of a sedimentary component with somewhat elevatedBa contents, such as, for example, pelagic clays.

Hf/Sm ratios of the Everek Hanları plagioleucitites range from 0.33to 0.56 and are clearly subchondritic (chondritic value=0.75) andsimilar to those of pelagic sediments in contrast to terrigeneoussediments that have Hf/SmN0.75 (e.g. Patchett et al., 1984, 2004).However, it is not to be expected that pelagic sediments withsubchondritic Hf/Sm ratio would also show unradiogenic Sr andradiogenic Nd isotopic ratios as do the Everek Hanları plagioleucitites.In a phlogopite-bearing lherzolitic mantle, most of the Pb and Rb willbe stored in phlogopite, while most of the Sr is partitioned betweenphlogopite and clinopyroxene and most of the Nd (REE) will reside inclinopyroxene.

Nb/Ta ratios of the Everek Hanları plagioleucitites (14.3–19.5) arewithin the range ofMediterranean lamproites (10.0–26.0; Prelević et al.,2008), while Zr/Hf ratios (39.7–45.1) are slightly higher (34.0–40.0 in

lamproites; Prelević et al., 2008). In general, the plagioleucitites fromEverek Hanları have relatively low Nb contents (9.0–18.6 ppm). Thesecharacteristics suggest melting in the presence of Ti-oxide (Foley et al.,

Fig. 9. Age corrected isotope diagrams for Everek Hanları plagioleucitites, Mediterra-nean lamproites (Spanish, Italian, Serbian and Macedonian) and Italian plagioleucitites(Campanian and Roman provinces). Data sources: Conticelli et al. (2002), Altherr et al.(2004), Peccerillo (2005), Prelević et al. (2005, 2007). (a) (143Nd/144Nd)i versus (87Sr/86Sr)i (b) (207Pb/204Pb)i versus (206Pb/204Pb)i (c) (208Pb/204Pb)i versus (206Pb/204Pb)i.

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2000). Such a process would also explain the very low TiO2 abundancesof these magmas (Table 3).

6.3. Geodynamic significance

Forming part of the Aşutka thrust sheet (Okay and Şahintürk,1997), the Everek Hanları volcanic rocks clearly pre-date the majorcompressive deformational event during late Paleocene–early Eocenethat has been attributed to the collision between the Pontide arc andthe Tauride microplate in the south (e.g. Okay and Şahintürk, 1997). Sofar, these volcanics represent the youngest products of the lateCretaceous to Paleocene arc of the Eastern Pontides. The anomalous

chemical compositions of these magmas, attributed to the involve-ment of a sialic component in their sources, signalize the involvementof material derived from the continental crust in their magma sources.

7. Conclusions

The Paleocene Everek Hanları plagioleucitites occurring in thesouthern part of the Eastern Pontides represent the youngest volcanicrocks that are directly related to the north-vergent subduction of thenorthern branch of Neotethys. The almost complete analcimization ofabundant leucite in these rocks has considerably changed theirprimary chemical compositions, at least the contents of K, Na andCs. Apart from the changes related to analcimization of leucite,however, the chemical and Sr–Nd–Pb isotopic budgets of thesevolcanics were probably not changed significantly.

The unusual chemical composition of the plagioleucitite magmas,i.e. their primary ultrapotassic character and their orogenic natureindicates that during the last stages of the closure of the northernbranch of Neotethys, the subduction of continental crustal material,most probably in the form of sediments, had started locally. Two otheroccurrences of Paleogene ultrapotassic plagioleucitites in the morewestern parts of the southern Pontides (Fig. 1), at Gümüşhacıköy nearAmasya (Tüysüz, 1996) and near Ankara (Çapan, 1984) have to beinterpreted in a similar way. Such a situation was comparable to thatof Plio-Quaternary magmatism in central Italy (Campanian, Romanand Tuscany provinces).

Acknowledgements

Special thanks are due to Murat Kayıkçı for cutting rock slices and toIlona Fin and Oliver Wienand for preparing high quality polished thinsections. Logistic helps of M. Burhan Sadıklar, Cemil Yılmaz, İsmet GedikandGerhardBreyare greatlyappreciated.OsmanNuriAlbayrak is thankedfor the companionship during fieldwork. Furthermore, we thank twoanonymous referees for their very constructive and helpful suggestions.

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