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Age and origin of granitic rocks of the eastern Vardar Zone, Greece: new constraints on the evolution of the Internal Hellenides

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Age and origin of granitic rocks of the eastern Vardar Zone, Greece: new constraints on the evolution of the Internal Hellenides
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   Journal of the Geological Society , London , Vol. 162 , 2005, pp. 857–870. Printed in Great Britain.857 Age and srcin of granitic rocks of the eastern Vardar Zone, Greece: newconstraints on the evolution of the Internal Hellenides B. ANDERS 1,2 , T. REISCHMANN 1,2 , U. POLLER  2 & D. KOSTOPOULOS 31  Institut fu¨ r Geowissenschaften, Johannes Gutenberg-Universita¨ t Mainz, Becherweg 21, 55099 Mainz, Germany(e-mail: banders@mail.uni-mainz.de) 2  Max-Planck-Institut fu¨ r Chemie, Abt. Geochemie, Postfach 3060, 55020 Mainz, Germany 3  Department of Mineralogy and Petrology, National and Kapodistrian University of Athens, Panepistimioupoli Zographou, Athens, 15784, Greece Abstract: The Vardar Zone is an integral part of the Internal Hellenides and has long been regarded as anophiolite-decorated suture zone separating two distinct continental blocks, namely the Pelagonian Zone to thewest and the Serbo-Macedonian Massif to the east. Several bodies of granites, gneisses and volcanic rocks areassociated with the ophiolitic rocks and can provide additional constraints on the evolution of the suture.Single-zircon and monazite dating of felsic rocks yields accurate ages for the processes of accretion of thesuture. The igneous formation ages obtained range from 155 to 164 Ma, suggesting an important magmatic phase in the Late Jurassic. The chemical and isotopic composition of these rocks is in accord with their formation in a volcanic-arc setting at an active continental margin. Older continental material incorporated inthe Vardar Zone is documented by 319 Ma gneisses and by inherited zircons of mainly Mid-Palaeozoic ages.The Late Jurassic magmatic event overprinted such gneisses, as is evident in monazite ages of 158 Ma. The prevalence of Late Jurassic subduction-related igneous rocks indicates that arc formation and accretionorogeny were the most important processes during the evolution of this part of the Internal Hellenides. Keywords: Vardar Zone, Late Jurassic, Greece, monazite, absolute age. The Hellenides constitute an integral part of the main Alpine– Himalayan orogenic belt and formed when Apulia and Europecollided in Late Cretaceous to Tertiary times. Traditionally, theHellenides are subdivided into several tectonostratigraphic units(Jacobshagen 1986, and references therein). These units, fromeast to west, are the Rhodope Massif, the Serbo-MacedonianMassif, the Vardar Zone, the Pelagonian Zone (Internal Helle-nides) and the External Hellenides (Fig. 1a). Sandwiched  between the Pelagonian Zone and the Serbo-Macedonian Mas-sif, the Vardar Zone is an elongated NNW–SSE-trending belt(Fig. 1a). It is characterized by numerous ophiolitic bodies and regarded as a suture zone (e.g. Mercier  et al  . 1975; Brown &Robertson 2004). At present, there are no definitive answersconcerning the presence of rocks of both Pelagonian and Serbo-Macedonian srcin within the Vardar Zone and this is also thecase for the age and srcin of the basement of the Vardar Zone.The answer to both questions could help to improve reconstruc-tions of the Late Palaeozoic to Mesozoic history of this region,which is characterized by a mosaic of continental fragmentswith ocean basins between. As the Pelagonian Zone and theSerbo-Macedonian Massif consist of basement of distinctlydifferent age, the dating of remnants of basement blocks fromthe Vardar Zone would give a clear indication as to their  provenance.In Greece, the Vardar Zone is divided into three units (Fig.1b), which, from east to west, are the Peonias, Paikon and Almopias Subzones (Mercier 1966). The Almopias Subzoneconsists of ophiolites, and metavolcanic and metasedimentaryrocks. It is interpreted as a former ocean basin that subducted eastwards underneath the Serbo-Macedonian Massif to form thePaikon volcanic arc in Mid- to Late Jurassic times. During theLate Jurassic, ophiolites from this ocean were obducted west-wards onto the Pelagonian Zone (Mercier  et al  . 1975; Be´bien et al  . 1994; Brown & Robertson 1994, 2003, 2004; Sharp &Robertson 1994). During the Cretaceous, however, an ocean basin existed in this area, either as a remnant ocean that had escaped Jurassic obduction or as a small Cretaceous pull-apart basin (Sharp & Robertson 1994). Final closure of the ocean isassumed to have occurred during the Tertiary, accompanied bythrusting of ophiolites eastwards onto the Paikon Subzone (Sharp& Robertson 1994; Brown & Robertson 2004). A differentinterpretation of the Paikon Subzone as a tectonic window(Godfriaux & Ricou 1991; Ricou & Godfriaux 1991, 1995;Ferrie`re et al  . 2001) is highly controversial (e.g. Mercier &Verge´ly 1994). The Guevgueli ophiolite in the western part of the Peonias Subzone is considered to have formed in an ensialic back-arc basin opening behind (to the east of) the Paikon arc(Be´bien 1982; Brown & Robertson 2003). It was then thrustwestwards onto the Paikon Subzone (Mercier  et al  . 1975; Brown& Robertson 1994). Evidence for subduction activity in theeastern Vardar Zone was reported from the Paikon and theeastern Peonias Subzones by Baroz et al  . (1987) and Michard  et al  . (1994), respectively, where they found high-Si phengite-and glaucophane-bearing rocks. The Guevgueli ophiolite is itself intruded by a granite pluton, namely the Fanos granite (Borsi et al  . 1966; Mercier 1966; Be´bien 1982; Christofides et al  .1990). Sparse and small outcrops of gneisses and granitic rocksare to be found east of the Guevgueli ophiolite; they have beeninterpreted as remnants of older, pre-back-arc-rift basementrocks of assumed Serbo-Macedonian origin (Zachariadou &Dimitriadis 1994; Fig. 2). These are the Pigi block around Pigivillage, consisting predominantly of migmatites with subordinateorthogneisses, the Karathodoro block on the eastern side of Axios river, also consisting predominantly of felsic metamorphic  rocks, and the anatectic Platania cordierite granite near Plataniavillage (Zachariadou & Dimitriadis 1994).The southeastern part of the Peonias Subzone comprisesophiolites together with igneous and sedimentary rocks of theChortiatis Magmatic Suite (Kockel et al  . 1977). These ophiolitesof the so-called Innermost Hellenic Ophiolite Belt are considered to have been emplaced in a wrench zone (Be´bien et al  . 1986).The Chortiatis Magmatic Suite forms a NW–SE-trending belt,extending from Mt. Chortiatis, ESE of Thessaloniki, to Sithonia(Fig. 1b) (Kockel et al  . 1977; Schu¨nemann 1985; Mussallam &Jung 1986 a ). It is a highly deformed series of rocks interpreted to have formed in an immature volcanic-arc environment (Kockel et al  . 1977; Mussallam & Jung 1986 a ).In this study we focused our attention on igneous rocks fromthe Peonias Subzone (Fig. 2). The aim was to date the pre-existing basement and correlate it, if possible, with one of theneighbouring zones, i.e. the Serbo-Macedonian Massif to the eastor the Pelagonian Zone to the west of the Vardar Zone, so as tolocate precisely the Vardar suture. Another aim was to better constrain the age and srcin of magmatic activity in this area. Toachieve this we used zircon geochronology to date the intrusionevent(s) and concentrated on felsic rocks in which zircon is avery common accessory mineral. Additionally, monazite wasanalysed to constrain the metamorphic history. Analytical methods Whole-rock samples were analysed by XRF on fused glass discs for major elements and on powder pellets for trace elements using a Philipsinstrument at the Institut fu¨r Geowissenschaften, Universita¨t Mainz.Whole-rock laser-ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) measurements of REE on fused glass droplets were performed on a ThermoFinnigan Element2 at the Max-Planck-Institut fu¨r Chemie, Mainz. Sample preparation followed the procedure of Gumann et al  . (2003). For whole-rock Sr- and Nd-isotope composition analyses, powders from five samples were dissolved and the Sr and REEchromatographically separated using 5 ml cation-exchange resin columns,following standard procedures (White & Patchett 1984), including asecond clean-up step for Sr using 1 ml resin columns. Nd was collected from the REE fraction with HDHP-coated Teflon columns. Sr was loaded with TaF 2 on W filaments, whereas Re filaments in double configurationwere used for Nd measurements. Isotopes were measured with a FinniganMAT261 thermal ionization mass spectrometer (TIMS) in multicollector mode. Mass fractionations were corrected to 146  Nd  = 144  Nd  ¼ 0 : 7219 and  86 Sr  = 88 Sr  ¼ 0 : 1194. International standards were also measured over the period of measurements. For La Jolla, the measured  143  Nd/ 144  Nd ratiowas 0.511819 Æ 9 ( n ¼ 16), whereas for NIST SRM 987 (formerly NBS987) an 87 Sr/ 86 Sr ratio of 0.710234 Æ 12 ( n ¼ 16) was obtained.The conventional U–Pb zircon dating is based on the low-contamina- Thessaloniki Serbo-MacedonianMassif  Oreokastro RhodopeMassif  22°24°41°40° PelagonianZone  V a r d a r  Z o n e 050 km25 SithoniaF.Y.R.O.M.  A  S P a  S P e  S N N RM ( a ) VPZEH ACM GREECE ( b ) 200 km OphiolitesChortiatis Magmatic SuiteFanos granite A SAlmopias SubzonePa SPaikon SubzonePe SPeonias SubzoneGuevgueliophiolite SM K UK UV U V UVertiskos UnitK UKerdilion Unit Athos Fig. 1. ( a ) Simplified map of thetectonostratigraphic zones of Greecemodified after the IGME geological map of Greece (IGME 1983), scale 1:500000. RM,Rhodope Massif; SM, Serbo-MacedonianMassif; V, Vardar Zone; PZ, PelagonianZone; ACM, Attico-Cycladic Massif; EH,External Hellenides. ( b ) Simplified map of the Vardar Zone, modified after Kockel et al  . (1977) and Mussallam & Jung (1986 b ).F.Y.R.O.M., Former Yugoslav Republic of Macedonia. Kerdilion Unit of Athos after F.Himmerkus (pers. comm.). The boxindicates the study area (Fig. 2). Fig. 2. Simplified map of the study area, modified after the IGMEgeological map of Greece, sheet Skra (IGME 1982), scale 1:50000, and sheet Evzoni (IGME 1993), scale 1:50000. Numbers mark the samplelocations: 1, Skra mylonites Pl32 and Pl33; 2, Fanos granites Pl35 and Pl36; 3, Fanos granite P5; 4, Pigi orthogneisses P1 and P2; 5, MikroDassos rhyolite P6; 6, Platania granites PLT-1 and PLT-2.B. ANDERS ET AL .858  tion dissolution method of Krogh (1973). Zircon separation followed standard procedures, with handpicking as a last step to avoid zircons withvisible inclusions. Before dissolution, the zircons were washed in 7NHNO 3 and a mixed  205 Pb–  235 U spike was added. After dissolution withHF, chemical separation of U and Pb with HBr chemistry followed, using20 ì  l columns with anion-exchange resin. Pb and U were loaded onsingle Re filaments with silica gel and analysed with a Finnigan MAT261TIMS using an electron multiplier detector. Procedural blanks were , 40 pg Pb; the fractionation factor was determined by repeated measure-ments of NBS 981 under the same conditions as for the samples. After correction for fractionation (3‰ per  ˜ a.m.u.), blank and common Pb(values from Stacey & Kramers 1975), ages were calculated with Isoplot(Ludwig 2003). All TIMS analyses were carried out at the Max-Planck-Institut fu¨r Chemie, Mainz.Geochronological analyses of zircons by secondary ionization massspectrometry (SIMS), using sensitive high-resolution ion microprobe(SHRIMP), were performed on zircon grains of five samples. The method has been described in detail by, for example, Compston et al  . (1984),Williams (1998) and Compston (1999). Zircons of four samples (P2, P6,Pl33 and PLT-1) were dated using SHRIMP II at the Australian NationalUniversity (ANU), Canberra. Zircon standard FC1 (age 1099 Ma; Paces& Miller 1993) was used for calibration of the Pb–U ratios and referencezircon SL13 was used for calibration of the U concentrations. Sample P5was dated using SHRIMP II at the Centre of Isotopic Research, St.Petersburg. There, the TEMORA reference zircon (age 416.75 Ma; Black  et al  . 2003) was used for calibration of the Pb–U ratios and referencezircon 91500 for calibration of the U concentrations (Wiedenbeck  et al  .1995). Data reduction and age calculations were performed using SQUID(Ludwig 2001). The measured isotopic ratios were corrected for commonPb, based on the measured  204 Pb. For each spot analysed, the isotopiccomposition of the common Pb component was assumed to resemble thevalues given by Stacey & Kramers (1975) according to the individual ageobtained. Concordia diagrams were drawn with Isoplot (Ludwig 2003).Ages were calculated with the built-in concordia age function of SQUID(Ludwig 2001) and include the error of the standard. All ages are givenat the 95% confidence level; the MSWD and the probability giveninclude both concordance and equivalence.Monazites from one sample were dated with an electron microprobe.Monazites were identified in thin section by their very bright back-scattered electron (BSE) images and verified by energy-dispersivespectrometry (EDS). Measurements were carried out on a JEOL JXA8900 RL (Institut fu¨r Geowissenschaften, Universita¨t Mainz) equipped with five wavelength-dispersive spectrometers. Measurement conditionswere acceleration voltage 15 kV, probe current 100 nA, and spot size5 ì  m. Analysed lines were Pb  M  â , U  M  â and Th  M  Æ . Measurement timeson peak position were 400 s for Pb, 120 s for U and 70 s for Th. Toevaluate monazite purity and the quality of spot analysis the mostcommon elements occurring in monazites (Si, Ca, Nd, Er, Al, P, Ce, Dy,Y, La, Gd, Eu, Sm, Pr) were also analysed. Totals were in the range of 100–102 wt%. Chemical U–Th–Pb ages were calculated by the method described by Montel et al  . (1996). Errors were based on countingstatistics. Errors on ages of individual spots were calculated by error  propagation of the U, Th and Pb errors. Systematic errors of the method are not included because of lack of an international monazite standard.Ages were calculated as weighted averages using Isoplot (Ludwig 2003).Additionally, monazite F5 from the Gfoehl granite of the BohemianMassif with a known age of 341 Æ 2 Ma (Finger  et al  . 2003) wasanalysed to check the quality of the results. An age of 334 Æ 4 Ma wasobtained as a weighted average of 25 spots on three monazite grainsand therefore a good external reproducibility was achieved with adeviation , 3%. Sample description and geochemistry The samples of the present study were collected from the eastern Vardar Zone. Sample description is arranged from west to east. It starts withrocks from the easternmost Paikon Subzone and continues into thePeonias Subzone. Sample locations are shown in Figure 2 and approx-imate GPS coordinates are included in Table 1.The westernmost samples are grey mylonitic gneisses sampled from alarge shear zone SW of Skra village (Fig. 2, location 1; samples Pl32 and Pl33). Sample Pl33 (Skra mylonite) is a strongly sheared, very fine-grained rock. It consists mainly of quartz, K-feldspar and white mica.Cube-shaped holes indicate a previously existing, now completelyremoved mineral that might have been pyrite. Pl32 is a coarser-grained grey mylonite taken from the same shear zone. Like Pl33, it consistsmainly of quartz, feldspar and white mica; plagioclase can also bedistinguished under the microscope.The major intrusion in the study area is the Fanos granite. This reddishgranite was sampled at two localities, one west of Fanos village (Fig. 2,location 2) and the other west of Plagia village (Fig. 2, location 3). Atthe former locality, the granite consists of coarse-grained and fine- tomedium-grained varieties, both of which were sampled (Pl35, Pl36). Atthe latter locality a medium-grained sample (P5) was taken. Despite thedifference in grain size, the modal and geochemical composition is verymuch the same, with similar contents of quartz, K-feldspar, plagioclaseand biotite.Good outcrops of migmatites and orthogneisses can be found west of Pigi village. Samples P1 and P2 (Pigi orthogneiss), located  c . 200 mapart, were collected in this vicinity (Fig. 2, location 4). Both are slightlydeformed, medium-grained orthogneisses with centimetre-sized pink K-feldspar crystals. The orthogneisses consist mainly of quartz and feldspar with additional biotite, an opaque phase and minor white mica and epidote. Some of the biotites show incipient alteration to chlorite.Evidence for fluid infiltration can be seen in sample P2, where moreleucocratic domains occur and are accompanied by patches of dark minerals. In places mafic dykes crosscut the orthogneisses and themigmatites.The Mikro Dassos rhyolite (P6) is exposed near the village of MikroDassos (Fig. 2, location 5). It is a light grey, porphyritic volcanic tosubvolcanic rock, which shows almost no deformation. The main phenocryst assemblage is quartz and sericitized feldspar together withchlorite pseudomorphs replacing biotite phenocrysts, minor epidote and an opaque phase. The fine-grained matrix consists mainly of quartz and feldspar. Only one remnant of biotite was positively identified and itcannot be ruled out that it is a xenocryst. Dark green to black xenoliths1–6 cm in size occur in the rhyolite. Moreover, xenoliths of quartz and feldspar 0.5–3 mm in size can be identified under the microscope bytheir coarser grain size as compared with the fine-grained matrix.The easternmost sample of this study is the Platania granite. Twosamples (PLT-1 and PLT-2), located  c . 20 m apart, were collected near Platania village (Fig. 2, location 6). Sample PLT-1 is a reddish coloured,medium- to coarse-grained granite. Centimetre-sized layers of differentgrain size define a weak deformation foliation. K-feldspar dominates thecoarser layers whereas the finer layers are rich in dark minerals. Quartz,feldspar, white mica and biotite are all major constituents. The biotiteshows incipient alteration to chlorite. PLT-2 is a grey, fine-grained rock that occurs as xenolithic rafts within PLT-1.With regard to their geochemical characteristics all samples show afelsic composition with SiO 2 contents . 70 wt% (Table 1). On the Ab– An–Or classification diagram (O’Connor 1965) they classify as granites(Fig. 3a). The Mikro Dassos rhyolite P6, shown for comparison, plots inthe trondhjemite field. This is ascribed to its low K  2 O content, which isdue to the replacement of biotite by chlorite. We therefore continue toclassify this sample as a rhyolite. All samples have molecular A/NK and A/CNK ratios between 1.04 and 1.91 and classify as peraluminous (Table1). K  2 O contents are in the range of 3–5 wt% with two exceptions. TheMikro Dassos rhyolite (P6), as already mentioned, has a low K  2 O contentof only 0.6 wt%, and one Skra mylonite (Pl33) has a very high K  2 Oconcentration of about 7 wt%. Na 2 O concentrations give a similar  picture, only this time the Skra mylonite (Pl33) has a rather lowconcentration of 0.55 wt% whereas the Mikro Dassos rhyolite contains asmuch as 5.4 wt%. Because secondary alteration processes can lead tosevere shifts in sodium and/or potassium contents, the chemical index of alteration (CIA; Nesbitt & Young 1982, 1989) was calculated to evaluatethe possible influence of weathering and alteration. For the Fanos granite,the Pigi orthogneiss, the Mikro Dassos rhyolite and one of the Plataniagranites (PLT-1) the CIA values range from 50.9 to 54.1 and thereforethese samples still qualify as fresh granites (CIA for average fresh graniteGRANITIC ROCKS OF THE VARDAR ZONE 859  Table 1. Major and trace element analyses Sample: P1 P2 P5 P6 PL32 PL33 PL35 PL36 PLT-1 PLT-2Location: Pigi Pigi Fanos M. Dassos Skra Skra Fanos Fanos Platania PlataniaGPS 41 8 00.85 9  N 41 8 00.91 9  N 41 8 04.85 9  N 41 8 04.29 9  N 41 8 05.35 9  N 41 8 04.92 9  N 41 8 05.03 9  N 41 8 05.03 9  N 41 8 04.30 9  N 41 8 04.30 9  Ncoordinates: 22 8 29.30 9 E 22 8 29.22 9 E 22 8 29.23 9 E 22 8 33.74 9 E 22 8 11.03 9 E 22 8 22.58 9 E 22 8 27.88 9 E 22 8 27.88 9 E 22 8 36.30 9 E 22 8 36.30 9 ERock type: gneiss gneiss granite rhyolite mylonite mylonite granite granite granite granite  Major elements (wt%) SiO 2 72.14 73.32 75.76 71.47 73.07 74.52 75.72 77.8 74.77 76.73TiO 2 0.38 0.28 0.15 0.30 0.22 0.23 0.13 0.1 0.06 0.59Al 2 O 3 14.88 14.13 13.22 14.60 14.11 13.04 13.06 12.3 13.78 10.92Fe 2 O 3T 2.10 2.24 1.23 2.07 2.14 1.19 0.86 0.7 0.43 3.53MnO b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d.MgO 0.47 0.48 0.23 0.63 1.18 1.19 0.07 0.04 0.10 1.02CaO 0.81 1.00 0.88 1.95 b.d. b.d. 0.58 0.4 0.56 0.60 Na 2 O 3.68 3.01 3.39 5.41 2.63 0.55 3.40 3.6 3.11 1.35K  2 O 4.75 4.79 5.15 0.55 4.14 7.05 5.08 4.4 5.97 3.22P 2 O 5 0.22 0.19 0.05 0.07 0.01 0.01 0.01 0.01 0.17 0.04LOI 0.95 0.69 0.33 0.81 1.76 1.47 0.32 0.2 0.34 1.16Total 100.41 100.16 100.42 97.87 99.27 99.28 99.24 99.6 99.3 99.20A/NK 1.33 1.39 1.19 1.54 1.60 1.53 1.18 1.14 1.19 1.91A/CNK 1.17 1.18 1.04 1.12 1.60 1.53 1.08 1.06 1.09 1.61 Trace elements (ppm) Zn 54 42 14 13 56 39 8 6 3 52Ga 21 20 15 12 16 14 14 13 12 13Rb 155 153 250 24 136 160 232 221 177 94Sr 183 175 213 312 15 31 168 85 91 78Y 13 10 11 14 31 18 8 7 15 16Zr 167 141 121 162 214 203 98 42 53 222 Nb 10 9 32 5 11 9 29 29 5 10Ba 851 754 387 183 1136 1766 297 103 321 878Pb 29 27 31 6 4 4 23 18 33 22Th 16 13 46 14 18 12 39 30 3 13U 4 2 11 3 6 4 10 7 1 2  REE (ppm) La 25.83 31.37 22.93 34.24 5.07Ce 62.41 61.29 46.48 67.94 10.34Pr 6.71 5.39 4.88 7.17 1.26 Nd 23.99 16.41 17.33 25.87 4.62Sm 4.23 2.18 3.05 4.20 1.20Eu 0.64 0.38 0.61 0.48 0.23Gd 2.86 1.56 2.60 3.15 1.25Tb 0.34 0.21 0.37 0.39 0.27Dy 1.49 1.30 2.19 2.34 1.94Ho 0.23 0.28 0.45 0.53 0.40Er 0.55 0.97 1.40 1.79 1.23Tm 0.07 0.17 0.22 0.31 0.20Yb 0.43 1.34 1.68 2.40 1.48Lu 0.06 0.22 0.27 0.40 0.22 Major elements and trace elements were determined by XRF. Compatible trace elements such as Sc, Ni and Co are below 10 ppm and not shown in the table. REE weredetermined by LA-ICP-MS. b.d., below detection limit; LOI, loss on ignition; A/NK, molecular ratio of Al 2 O 3 /(Na 2 O þ K  2 O); A/CNK, molecular ratio of Al 2 O 3 /(CaO þ  Na 2 O þ K  2 O). ( a ) Or  An granite   g   r  a  n  o  d   i  o  r   i   t  e   t  o  n  a   l   i   t  e trond-hjemite  Ab 103050709050707050 ( b )  Al 2 O 3404060608080 CaOK 2 O typical fresh granitetypical tonaliteLegend for (a) and (b):Skra mylonites (Pl32, Pl33)Fanos granite (P5, Pl35, Pl36)pre-existing basement(P1, P2, PLT-1, PLT-2)Mikro Dassos rhyolite (P6) +Na2O Fig. 3. Geochemical classification of theanalysed rocks. ( a ) Classification withnormative Ab– An–Or after O’Connor (1965) modified by Barker (1979, bold lines). ( b ) A–CN–K diagram after Nesbitt& Young (1989); the long arrow indicatesthe weathering trend.B. ANDERS ET AL .860  is 45–55; Nesbitt & Young 1982). This could indicate that at least part of the high sodium and low potassium concentration of the Mikro Dassosrhyolite is a primary feature. Nevertheless, it only rules out thedisturbance of the alkali content by alteration of feldspar. The low K  2 Ocontent can readily be derived by metamorphism that leads to destructionof biotite. By contrast, alteration is evident for the Skra mylonites and one of the Platania granites (PLT-2). For these rocks higher CIA values of 60.4–61.6 were obtained. The samples are also plotted on the A–CN–K diagram of Nesbitt & Young (1989; Fig. 3b) where it can be seen thatmost plot close to the average granite except for the Skra mylonites and the Platania granite PLT-2, which are shifted in the direction of alteration.Therefore, in using classification diagrams that are based on potassiumcontent it has to be kept in mind that the Skra mylonites are shifted tohigher potassium concentrations by an unknown amount. This alterationwill also affect classifications using Rb. On the Nb–Y trace elementdiscrimination diagram of different tectonic environments for graniticrocks (Pearce et al  . 1984), all samples plot in the field of syncollisional(syn-COLG) or volcanic-arc granites (VAG; Fig. 4a). Using the Rb–(Y þ  Nb) classification scheme (Fig. 4b), the Fanos granite plots along or slightly below the line that separates the syn-COLG from the VAG field,as noted by previous workers (Christofides et al  . 1990; Soldatos et al  .1993). Therefore, all samples are interpreted to have formed either in avolcanic-arc or in an active continental-margin environment. On achondrite-normalized REE plot the samples show enrichment in the lightREE (LREE) and a negative Eu anomaly, again a pattern typical for continental crust (Fig. 4c). For Platania granite PLT1 the LREE enrich-ment is only weak. A small increase in the heavy REE (HREE) can beseen for the Fanos granite (P5), Mikro Dassos rhyolite (P6), Skramylonite (Pl33) and Platania granite (PLT-1), whereas for the Pigiorthogneiss (P2) a constant decrease from LREE to HREE is displayed (Fig. 4c). Geochronological results In this section, the zircon ages are presented according to samplelocation from west to east; they are followed by the monaziteages. Analytical data are listed in Tables 2–4, and concordia ( c )( b ) Y+Nb [ppm]    R   b   [  p  p  m   ] ORGVAGWPGsyn-COLG 5005051155050010001001010.1LaCePrNdSmEuGdTbDyHoErTmYbLu   s  a  m  p   l  e   /  c   h  o  n   d  r   i   t  e Skra mylonite Pl33Fanos granite P5Pigi orthogneiss P2Mikro Dassos rhyolite P6Platania granite PLT-1 ( a ) ORGWPGVAG +syn-COLGY [ppm]    N   b   [  p  p  m   ] 50050511550500 Fig. 4. Trace element classification of the sampled rocks. ( a ) and ( b )Geotectonic environment classification after Pearce et al  . (1984). WPG,within-plate granite; ORG, ocean-ridge granite; VAG, volcanic-arcgranite; syn-COLG, syncollisional granite. Symbols are as in Figure 3.( c ) REE pattern, normalized to chondrite. T    a      b      l    e      2  .     R   e   s   u    l   t   s   o    f   c   o   n   v   e   n   t    i   o   n   a    l   s    i   n   g    l   e  -   z    i   r   c   o   n    U  –    P    b    d   a   t    i   n   g     S   a   m   p    l   e    G   r   a    i   n    M   e   a   s   u   r   e    d   r   a    t    i   o   s    (    f   r   a   c    t    i   o   n   a    t    i   o   n   c   o   r   r   e   c    t   e    d    )    R   a    d    i   o   g   e   n    i   c   r   a    t    i   o   s ,   c   o   r   r   e   c    t   e    d    f   o   r   s   p    i    k   e ,    f   r   a   c    t    i   o   n   a    t    i   o   n   a   n    d   c   o   m   m   o   n    P    b    U     t   o    t     /    P    b    r   a    d     A   p   p   a   r   e   n    t   a   g   e   s    (    M   a    )     2    0    6     P    b    /     2    0    4     P    b       Æ     2      ó     2    0    7     P    b    /     2    0    6     P    b       Æ     2      ó     2    0    7     P    b    /     2    3    5     U       Æ     2      ó     2    0    6     P    b    /     2    3    8     U       Æ     2      ó     R     2    0    7     P    b    /     2    0    6     P    b       Æ     2      ó     2    0    6     P    b    /     2    3    8     U       Æ     2      ó     2    0    7     P    b    /     2    3    5     U       Æ     2      ó     2    0    7     P    b    /     2    0    6     P    b       Æ     2      ó     P    L    T  -    1   a    2    7    2    2    0 .    1    1    0    1    7    0 .    0    0    0    1    0    0 .    4    3    2    6    0 .    0    0    5    4    0 .    0    5    5    3    0    0 .    0    0    0    2    6    0 .    3    5    0 .    0    5    6    7    4    0 .    0    0    0    6    6    1    5 .    8    3    4    7    2    3    6    5    4    4    8    2    2    6    P    L    T  -    1    b    7    1    6    3    8    0 .    0    7    4    0    4    0 .    0    0    0    6    5    0 .    3    8    2    2    0 .    0    1    6    9    0 .    0    5    1    4    5    0 .    0    0    0    5    0    0 .    2    3    0 .    0    5    3    8    8    0 .    0    0    1    9    9    1    7 .    9    3    2    3    3    3    2    9    1    3    3    6    6    8    6    P    L    T  -    1   c    1    8    9    2    0 .    1    3    1    8    8    0 .    0    0    0    1    9    0 .    2    9    7    0    0 .    0    0    9    7    0 .    0    3    9    1    9    0 .    0    0    0    4    0    0 .    2    2    0 .    0    5    4    9    7    0 .    0    0    2    2    5    2    3 .    7    2    4    8    3    2    6    4    8    4    1    1    9    4    P    L    T  -    1    d    2    9    8    4    0 .    1    0    4    9    1    0 .    0    0    0    1    1    0 .    3    0    1    0    0 .    0    0    6    2    0 .    0    3    8    4    3    0 .    0    0    0    2    1    0 .    3    0    0 .    0    5    6    8    1    0 .    0    0    0    8    8    2    3 .    8    2    4    3    1    2    6    7    5    4    8    4    3    5    P    L    T  -    1   e    1    7    9    1    0 .    1    3    3    6    3    0 .    0    0    0    1    9    0 .    2    3    4    0    0 .    0    0    3    8    0 .    0    3    2    7    2    0 .    0    0    0    1    3    0 .    2    0    0 .    0    5    1    8    7    0 .    0    0    0    9    1    2    8 .    6    2    0    8    1    2    1    3    3    2    8    0    4    1    P    L    T  -    1    f    3    3    4    3    0 .    0    9    6    6    6    0 .    0    0    0    1    5    0 .    2    0    9    1    0 .    0    0    3    4    0 .    0    2    8    6    1    0 .    0    0    0    1    4    0 .    2    9    0 .    0    5    3    0    1    0 .    0    0    0    7    2    3    2 .    3    1    8    2    1    1    9    3    3    3    2    9    3    1    P    L    T  -    1   g    5    1    0    0 .    3    4    3    7    9    0 .    0    0    0    4    4    0 .    2    0    2    0    0 .    0    0    9    5    0 .    0    2    5    9    7    0 .    0    0    0    3    0    0 .    0    6    0 .    0    5    6    4    2    0 .    0    0    7    0    1    3    4 .    2    1    6    5    2    1    8    7    8    4    6    9    3    0    1    P    L    T  -    1    h    1    1    3    2    0 .    1    7    8    3    7    0 .    0    0    0    3    3    0 .    1    7    2    2    0 .    0    1    0    9    0 .    0    2    5    6    8    0 .    0    0    0    2    4    0 .    1    0    0 .    0    4    8    6    4    0 .    0    0    3    3    0    3    5 .    2    1    6    3    2    1    6    1    9    1    3    0    1    5    2    P    L    T  -    1    i    1    0    3    1    0 .    1    9    2    6    3    0 .    0    0    0    2    7    0 .    1    1    6    5    0 .    0    0    4    2    0 .    0    1    6    9    1    0 .    0    0    0    1    2    0 .    1    3    0 .    0    4    9    9    7    0 .    0    0    2    0    6    5    4 .    7    1    0    8    1    1    1    2    4    1    9    3    9    9    P    L    T  -    2    j    8    1    1    1    8    0 .    0    7    6    9    7    0 .    0    0    0    4    0    0 .    7    2    7    9    0 .    0    1    8    6    0 .    0    8    8    8    1    0 .    0    0    0    9    1    0 .    6    0    0 .    0    5    9    4    4    0 .    0    0    0    7    7    8 .    8    5    4    9    5    5    5    5    1    1    5    3    8    2    8    P    L    T  -    2    k    2    4    6    5    3    9    0 .    0    6    2    2    5    0 .    0    0    0    0    6    0 .    5    5    6    7    0 .    0    0    5    2    0 .    0    7    1    5    2    0 .    0    0    0    4    6    0 .    9    4    0 .    0    5    6    4    5    0 .    0    0    0    1    3    1    2 .    7    4    4    5    3    4    4    9    3    4    7    0    5    P    L    T  -    2    l    1    8    9    9    1    1    4    0 .    0    6    3    8    5    0 .    0    0    0    3    0    0 .    4    7    7    8    0 .    0    0    9    1    0 .    0    6    1    5    6    0 .    0    0    0    3    0    0 .    3    1    0 .    0    5    6    2    9    0 .    0    0    0    7    6    1    4 .    6    3    8    5    2    3    9    7    6    4    6    4    3    0    P    L    T  -    2   m    1    7    3    5    7    6    0 .    0    6    2    3    2    0 .    0    0    0    0    9    0 .    4    1    0    6    0 .    0    0    6    6    0 .    0    5    5    1    3    0 .    0    0    0    4    0    0 .    6    5    0 .    0    5    4    0    2    0 .    0    0    0    4    4    1    6 .    1    3    4    6    2    3    4    9    5    3    7    2    1    8 GRANITIC ROCKS OF THE VARDAR ZONE 861
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