plešovice zircon a new natural reference material for pb and ......plešovice zircon — a new...

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Chemical Geology 24

Plešovice zircon — A new natural reference material forU–Pb and Hf isotopic microanalysis

Jiří Sláma a,b,c,⁎, Jan Košler a, Daniel J. Condon d, James L. Crowley e, Axel Gerdes f,John M. Hanchar g, Matthew S.A. Horstwood d, George A. Morris h, Lutz Nasdala i,

Nicholas Norberg i, Urs Schaltegger j, Blair Schoene j,Michael N. Tubrett k, Martin J. Whitehouse l

a Centre for Geobiology and Department of Earth Science, University of Bergen, Allegaten 41, N-5007 Bergen, Norwayb Institute of Geology, Academy of Sciences of the Czech Republic, v.v.i., Rozvojová 135, Prague 6, 165 02, Czech Republic

c Department of Petrology and Structural Geology, Charles University in Prague, Albertov 6, Prague 2, 128 43, Czech Republicd NERC Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK

e Department of Geosciences, Boise State University, Boise, ID 83702, USAf Institute of Geosciences, Johann Wolfgang Goethe University, Altenhöferallee 1, D-60438 Frankfurt am Main, Germany

g Department of Earth Sciences, Memorial University of Newfoundland, St. John's, NL, Canada A1C 5S7h Department of Geology and Geochemistry, University of Stockholm, Svante Arrhenius väg 8C, Stockholm, SE-106 91, Sweden

i Institute for Mineralogy and Crystallography, University of Vienna, Althanstrasse 14, Vienna, A-109, Austriaj Department of Mineralogy, University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland

k Microanalytical Facility-INCO Innovation Center, Memorial University of Newfoundland, 230 Elizabeth Avenue, St. John's, NL,Canada A1C 5S7

l Laboratory for Isotope Geology, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden

Received 13 August 2007; received in revised form 16 November 2007; accepted 20 November 2007

.L. Rudnick
Editor: R
Abstract

Matrix-matched calibration by natural zircon standards and analysis of natural materials as a reference are the principle methodsfor achieving accurate results in microbeam U–Pb dating and Hf isotopic analysis. We describe a new potential zircon referencematerial for laser ablation ICP-MS that was extracted from a potassic granulite facies rock collected in the southern part of theBohemian Massif (Plešovice, Czech Republic).

Data from different techniques (ID-TIMS, SIMS and LA ICP-MS) and several laboratories suggest that this zircon has aconcordant U–Pb age with a weighted mean 206Pb/238U date of 337.13±0.37 Ma (ID-TIMS, 95% confidence limits, includingtracer calibration uncertainty) and U–Pb age homogeneity on the scale used in LA ICP-MS dating. Inhomogeneities in traceelement composition due to primary growth zoning prevent its use as a calibration standard for trace element analysis. The contentof U varies from 465 ppm in pristine parts of the grains to ~3000 ppm in actinide-rich sectors that correspond to pyramidal faceswith a high degree of metamictization (present in ca. 30% of the grains). These domains are easily recognized from high intensities

⁎ Corresponding author. Centre for Geobiology and Department of Earth Science, University of Bergen, Allegaten 41, N-5007 Bergen, Norway.Tel.: +47 555 83529; fax: +47 555 83660.

E-mail address: [email protected] (J. Sláma).

0009-2541/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.chemgeo.2007.11.005

http://dx.doi.org/10.1016/j.chemgeo.2007.11.005

mailto:[email protected]

2 J. Sláma et al. / Chemical Geology 249 (2008) 1–35

on BSE images and should be avoided during the analysis. Hf isotopic composition of the Plešovice zircon (N0.9 wt.% Hf) ishomogenous within and between the grains with a mean 176Hf/177Hf value of 0.282482±0.000013 (2SD). The age and Hf isotopichomogeneity of the Plešovice zircon together with its relatively high U and Pb contents make it an ideal calibration and referencematerial for laser ablation ICP-MS measurements, especially when using low laser energies and/or small diameters of laser beamrequired for improved spatial resolution.© 2007 Elsevier B.V. All rights reserved.

Keywords: Zircon reference material; Laser ablation ICP-MS; Plešovice; U–Pb dating; Hf isotopes; Bohemian Massif

1. Introduction

Isotopic dating of accessory minerals by means of U-and Th-decay is the most precise and accurate techniquefor establishing the age of high-temperature events inmagmatic and metamorphic rocks. The method is alsowidely applied to dating of detrital minerals insedimentary provenance studies. Recent introductionof new techniques, such as U–Pb zircon (ZrSiO4) datingby laser ablation ICP-MS (e.g., Košler and Sylvester,2003 and reference therein), requires development ofreference materials, both for matrix-matched agecalibration and for quality control purposes. Therequirements for such zircon reference materials are(i) homogeneity and concordance of radiogenic Pb/Uratios, (ii) low common Pb content, (iii) moderate Ucontent (tens to hundreds ppm), (iv) crystalline (non-metamict) structure, (v) size suitable for repeated laserablation analyses (grains several mm to cm in diameter)and (vi) availability to the scientific community.Previous attempts to produce chemically homogeneoussynthetic zircon material (e.g., Hanchar et al., 2001)have failed because Pb does not readily enter thestructure of zircon and also because of the strainimposed on the crystal lattice.

Zircon reference material for in-situ Hf isotopic anal-ysis by laser ablation ICP-MS should have (i) homo-geneousHf isotopic composition, bothwithin and betweenindividual grains, (ii) moderate Hf content (low % level)and preferably homogeneous Hf concentration, and(iii) low Lu/Hf and Yb/Hf values and it should alsooccur asmm–cm sized grains and be available in sufficientquantity.

There are several natural zircon samples (e.g., 91500,Temora, Mud Tank, GJ-1, SL13) that have beenproposed as potential calibration and reference materialsfor in-situ U–Pb isotopic analysis but only a few meetthe criteria for a “good” reference material and they areoften not available in quantities needed for laser ablationICP-MS analysis. From these the “91500” zircon(Wiedenbeck et al., 1995) has been most often used asa reference material for in-situ analysis of Hf isotopes

but the recent studies (Griffin et al., 2006; 2007; Corfu,2007) have discussed its isotopic heterogeneity. Becauseof its limited amount and extensive use in microanalysis,the supply of the 91500 zircon reference material hasbeen almost exhausted (Woodhead and Hergt, 2005).

This study presents new isotopic data for a naturalzircon extracted from a high-temperature potassicgranulite from the southern Bohemian Massif (localityPlešovice [read Pleschovitze] in the Czech Republic)that appears to be a suitable reference material for laserablation ICP-MS U–Pb dating and Hf isotopic measure-ments. This zircon meets most of the criteria for acalibration and reference material and it can be obtainedon request from Department of Earth Science at theUniversity of Bergen (http://www.geo.uib.no/ceia).

2. Sample and geological setting

The studied zircon comes from a potassic granulitethat was first described byVrána (1989) and recently alsoby Janoušek et al. (2007) from the Plešovice quarrysituated in the eastern part of the Blanský les granulitebody, ca. 5 km NNE of the town of Český Krumlov(Fig. 1) in the southern Bohemian Massif, CzechRepublic. The potassic granulite forms up to 2 m thickfoliated layers in the northern part of the present-day'sfourth level of the quarry (Fig. 2; N: 48°52′17″, E: 14°20′28″). The layers are oriented concordantly to thedominant metamorphic foliation in the surroundingfelsic granulites. This foliation formed as a result ofisothermal decompression that followed the peakgranulite facies conditions dated in this area at ca.340 Ma (van Breemen et al., 1982; Wendt et al., 1994;Kröner et al., 2000).

Classification of the potassic, sometimes referred toas hyperpotassic (up to 13 wt.% K2O), granulite in theAPQ diagram for plutonic rocks reflects its alkali-feldspar syenitic to alkali-feldspar granitic character(Vrána, 1989; Janoušek et al., 2007). The granulite ismade up mostly of K-feldspar (up to 93%) and garnetrelatively rich in pyrope (~30 molar %), which has beenpartly replaced by biotite during the retrograde stages of

Fig. 1. Schematic map of the European Variscides (inserted) and Bohemian Massif showing the position of the Blanský les granulite and the sampling location in the Plešovice quarry. Modified afterSvojtka et al., 2002.

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Fig. 2. Outline geological map of the eastern part of the Blanský les massif (after Kodym et al., 1981) showing the Plešovice quarry (as in Autumn2006) with marked location of the zircon bearing potassic granulite.


the metamorphic evolution. Apatite, monazite andzircon are accessories; rutile is present in the form oftiny exsolved needles in garnet. The content of zircon inthe granulite is up to 0.6 wt.% and it is variable on thescale of tens of centimeters; higher accumulations ofzircon crystals were found in the biotite (originallygarnet)-rich domains.

The potassic granulite is thought to represent a non-eutectic melt (Vrána, 1989; Janoušek et al., 2007),possibly derived from the protolith of the adjacent felsicgranulites in the Blanský les massif (Janoušek et al.,2007). The Blanský les massif represents part of theallochthonous Gföhl unit (Fuchs and Matura, 1976;Matte et al., 1990; Fiala et al., 1995; Vrána et al., 1995;Franke, 2000), which forms the uppermost tectonicmember of the Moldanubian Zone, the core crystallineunit of the Variscan orogen in Europe (Dallmeyer et al.,1995). The Gföhl unit consists mainly of felsicgranulites, with subordinate mafic granulites, serpenti-nized garnet peridotites, pyroxenites and eclogites(Fuchs and Matura, 1976; Franke, 1989; Fiala et al.,1995). Migmatitic granitic gneisses (Gföhl gneisses) inthe lower part of the Gföhl unit probably also representoverprinted felsic granulites (Fuchs and Matura, 1976;Fiala et al., 1995).

The Blanský les massif contains mainly felsic garnetgranulite gneisses (ca. 80%) with subordinate maficpyroxene±garnet granulites (ca. 10%), melanocratic

biotite–garnet granulites (ca. 5%) and ultramafic rocks,such as are serpentinized peridotites and eclogites (ca.5%; Fiala et al., 1987). All these rocks underwent HP–HT metamorphism during the Variscan orogeny withestimated peak conditions of 900–1050 °C and 1.5–2 GPa (Carswell and O'Brien, 1993; Kotková andHarley, 1997; O'Brien and Rötzler, 2003). Followingthe peak of metamorphism, there was almost isothermaldecompression to mid-crustal level pressures with anoverprint at 800–900 °C and 0.8–1.2 GPa (Cooke,2000) and subsequent near-isobaric cooling. The retro-gression of granulites is reflected in garnet breakdownand formation of secondary-corona structures, retro-gression of garnet to biotite and kyanite to sillimanite(Owen and Dostal, 1996; O'Brien and Rötzler, 2003;Sláma et al., 2007).

The age of granulite metamorphism is constrained bya number of U–Pb zircon ages at ca. 340 Ma (vanBreemen et al., 1982; Kröner et al., 1988; Aftalion et al.,1989; Wendt et al., 1994; Kröner et al., 2000; Friedlet al., 2003; Kotková et al., 2003). This age has oftenbeen interpreted as corresponding to the time ofgranulite HP–HT metamorphic peak, but Roberts andFinger (1997) argued for zircon crystallization frompartial melt during the retrograde P–T path, and Kröneret al. (2000) and Janoušek et al. (2004) proposed that thezircons that grew under granulite peak conditions andsubsequently during the decompression are similar in

5J. Sláma et al. / Chemical Geology 249 (2008) 1–35

age. Some zircon cores from granulites of the Blanskýles gave a U–Pb age of ca. 470 Ma (Kröner et al., 2000),consistent with a whole-rock Rb–Sr age obtained byJanoušek et al. (2004) and interpreted by these authorsas corresponding to the age of the granulite protolith.The zircons from potassic granulite in the Plešovicequarry were previously dated by Aftalion et al. (1989)and gave a U–Pb age of 338±1 Ma.

The studied zircon is included in major mineralphases of the potassic granulite as up to 0.5 cm (rarelylarger) equant or prismatic (Fig. 3), pale pink to brownidiomorphic crystals. The external shape of the crystalscorresponds to zircons from peralkaline granites andsyenites in the classification of Pupin (1980). Mineralinclusions in zircon comprise K-feldspar and apatite(Fig. 4), rarely also quartz and garnet.

3. Sample preparation and analytical methods

A sample of potassic granulite collected from thePlešovice quarry was crushed down to a grain size of

Fig. 3. a) Large, short prismatic crystal of the Plešovice zircon in K-feldspaPlešovice zircons with prevailing equant morphology (top) and less common

b7 mm and gravimetric separation in a water-filledsluice box was used to obtain a heavy mineral fractioncontaining almost exclusively zircon. Approximately250 kg of the rock material yielded ca. 500 g of goodquality zircon crystals between 1 and 6 mm in size.

To ensure thorough characterization of the studiedzircon, the chemical and isotopic analyses were con-ducted using a range of different techniques in severallaboratories (ID-TIMS: Massachusetts Institute of Tech-nology (MIT), University of Geneva (UNIGE), NERCIsotope Geosciences Laboratory (NIGL), Boise StateUniversity (BSU) and ETH Zürich (ETHZ); SIMS:Swedish Museum of Natural History in Stockholm(NORDSIM); LA ICP-MS: University of Bergen (UoB),J.W. Goethe University of Frankfurt amMain (JWG) andMemorial University of Newfoundland (MUN); MCICP-MS: University of Bergen, J.W. GoetheUniversity ofFrankfurt am Main and NERC Isotope GeosciencesLaboratory (NIGL); Raman spectroscopy: University ofVienna). Where possible, the measurements were repro-duced by similar techniques in different laboratories.

r matrix of the host potassic granulite; b) typical crystal shapes of theprismatic morphology (bottom).

Fig. 4. Cathodoluminescence photomicrograph of Plešovice zircon crystal revealing concentric growth zoning and inclusion of a small apatite crystal(yellow in CL) and two inclusions of potassium feldspar (blue in CL). Field of view is ~2.5 mm in the horizontal direction. (For interpretation of thereferences to colour in this figure legend, the reader is referred to the web version of this article.)


Loose zircon grains or their fragments were used forisotopic analyses in solution (ID-TIMS U–Pb datingand Hf isotopic analyses by MC ICP-MS — seebelow). For solid sample analyses by ”in situ” tech-niques, the zircons were mounted in 1 in. epoxy resinblocks, ground down to expose their internal textures,and polished to obtain flat surfaces suitable for electronmicroanalysis, cathodoluminescence (CL) and back-scattered electron (BSE) imaging, ion probe (SIMS)and laser ablation (LA) ICP-MS isotopic mea-surements. Sample mounts were coated with carbonand gold prior to electron microbeam and ion probeanalyses, respectively.

3.1. Trace element concentration measurements

Trace element contents in the Plešovice zircon wereacquired at University of Bergen using a Thermo-Finnigan Element 2 sector field ICP-MS coupled to a213 NdYAG laser (New Wave Research UP-213). Thelaser was fired at a repetition rate of 5 Hz, using 10 J/cm2 laser energy, spot size of 53 μm and He as a samplecarrier gas. Synthetic silicate glass NIST-610 was usedto calibrate the trace element concentration data, repeatmeasurements of NIST-612 and BCR-2 silicate glasseswere carried out for quality control purposes; averagesignal intensity for NIST-610 was 2.2×107 cps on themass 29Si. Data for the gas blank were acquired for 45 sfollowed by 120 s of laser ablation signal. Si was used asinternal standard to correct for differences in the ablationyields between zircon and glass standards, time-resolved signal data were processed using the Glittersoftware package.

3.2. Backscattered electron and cathodoluminiscenceimaging, Raman spectroscopy

The CL image presented in Fig. 4 was acquired usinga Premier American Technologies ELM-3R “coldcathode” luminoscope operating in regulated mode at12 kV and 0.7 mA. The zircon crystals studied withcolour CL were mounted in epoxy and polished toreveal the crystal interiors. The CL images wererecorded using a KAPPA DX-30C Peltier cooledcharge-coupled device (CCD) digital camera interfacedto an Olympus BX-50 microscope. Zircon crystals forRaman spectroscopy were prepared as uncovered,doubly polished thin sections (thickness ∼30 µm)attached to a glass slide suitable for optical microscopyin transmitted light. This preparation makes possible tocheck the internal zoning of crystals, as zones that differin birefringence are easily recognized in the cross-polarized light mode. Backscattered electron (BSE)images were acquired using a JEOL 8900 RL electronmicroprobe, and cathodoluminescence (CL) imageswere obtained in a “hot-cathode” system HC1-LM (fordetails cf. Götze, 2000).

Raman spectra were obtained using a Renishaw RM1000 system. This notch filter-based spectrometer wasequipped with Leica DMLM optical microscope andPeltier-cooled, Si-based CCD (charge-coupled device)detector. Spectra were excited with the 632.8 nmemission of a He–Ne laser (8 mW). With the Leica50× objective (numerical aperture 0.55), the lateralresolution was ca. 3 μm. The spectral resolution wasdetermined at 2.2 cm−1 and the wavenumber accuracywas ca. ±1 cm−1 (calibrated with the Rayleigh line and


Ne lamp emissions). The impact of the electron beamduring electron microprobe analysis may cause partialannealing of the radiation damage (e.g., Nasdala et al.,2003). To avoid any analytical artifacts, Raman mea-surements have therefore always been done before elec-tron probe analysis.

Raman bands were fitted assuming Lorentzian–Gaussian band profiles. Real band FWHM (full widthat half band maximum) values were calculated bycorrecting measured FWHMs according to

b ¼ bs �ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1� 2

sbs

� �2s

(Irmer, 1985), where b is the real (i.e. corrected) FWHM,bs is the measured FWHM, and s is the spectral res-olution of the Raman system (2.5 cm−1).

3.3. Zircon dating by U–Pb techniques

3.3.1. ID-TIMS U–Pb dating (MIT, UNIGE, NIGL, BSU)Several large single zircon crystals were broken into

smaller fragments and only the clearest ones withoutcracks and inclusions were selected for dating. Zirconwas subjected to a modified version of the chemical-abrasion technique (CA; Mattinson, 2003; 2005). Zirconwas placed in a muffle furnace at 900±20 °C for 60 h inquartz beakers before being transferred to 300 μl TeflonFEP microcapsules, placed in a Parr vessel, and leachedin 120 μl of 29 M HF for 12 h at 180 °C. The HF wasremoved, and grains were rinsed in ultrapure H2O,immersed in 30% HNO3, ultrasonically cleaned for anhour, and fluxed on a hotplate at 80 °C for an hour. TheHNO3 was removed and the grains were again rinsed inultrapure H2O, before being loaded into 300 μl TeflonFEP microcapsules and spiked with the EARTHTIMEmixed 205Pb–233U–235U tracer (ET535). Zircon wasdissolved in Parr vessels in 120 μl of 29 M HF with atrace of 30% HNO3 at 210 °C for 48 h, dried tofluorides, and then re-dissolved in 6 M HCl at 180 °Covernight. U and Pb were separated using an HCl-basedanion-exchange chromatographic procedure (Krogh,1973). Pb and U were loaded together on a single Refilament in a silica-gel/phosphoric acid mixture (Ger-stenberger and Haase, 1997) before measurement byTIMS at the respective institutions. UNIGE and MITmeasurements are analyses of single zircon fragmentsthat were aliquoted in two and measured at the separateinstitutions (e.g. MIT_1 is the same dissolved andspiked solution as UNIGE_1, split in two after anionexchange chemistry) in order to test for detector relatedbiases.

U and Pb isotopic measurements at MIT were per-formed on a VG Sector-54 multi-collector TIMS. Pb wasmeasured by peak-hopping on a Daly detector. Massfractionation effects were corrected for 0.25±0.04/a.m.u.U isotopic measurements were made in static Faradaymode on 1011 Ω resistors.

Measurements at UNIGE were performed on aThermo Triton TIMS. Pb was measured on a MasComSEM detector and corrected for 0.13±0.04%/a.m.u.mass fractionation. Linearity and deadtime correction onthe SEM were monitored using repeated analyses ofNBS982, NBS983 and U500. Uranium was measured instatic Faraday mode on 1012 Ω resistors.

Measurements at NIGL were performed on a ThermoTriton TIMS. Two Pb analyses were measured on aMasCom SEM detector and corrected for 0.16±0.04%/a.m.u. mass fractionation. The rest of the Pb analyseswere done in a multidynamic Faraday-SEM mode, peakhopping mass 204 and 205 in the SEM, which correctsfor the SEM gain in real time. These data were correctedfor mass fractionation of 0.12±0.04%/a.m.u. Linearityand deadtime correction on the SEM were monitoredusing repeated analyses of NBS982 and U500. Ura-nium was measured in static Faraday mode on 1011 Ωresistors.

Measurements at BSU were made on a GV Isoprobe-T TIMS. One Pb analysis was measured on a Dalydetector corrected for 0.22±0.04%/a.m.u. mass fractio-nation. The other analyses were performed using a two-sequence Faraday–Daly routine, peak hopping masses204 and 205 in the Daly, which corrects for the Dalygain in real time. Linearity and deadtime correction onthe SEM were monitored using repeated analyses ofNBS982, NBS981 and U500. Uranium was run in staticFaraday mode on 1011 Ω resistors.

U was run as the oxide and corrected for isobaricinterferences with an 18O/16O of 0.00205, which wasconfirmed by measuring 272(UO2)/

270(UO2) on large ionbeams at NIGL, MIT and UNIGE. U mass fractionationfrom all laboratories was calculated in real time using theET535 tracer solution. U–Pb dates and uncertainties werecalculated using the algorithms of Schmitz and Schoene(2007) and a 235U/205Pb ratio for ET535 of 100.18±0.05.The 206Pb/238U ratios and dates were corrected for ini-tial 230Th disequilibrium using a Th/U[magma] of 4±1applying the algorithms of Crowley et al. (2007), re-sulting in an increase in the 206Pb/238U dates of ~100 kyrand uncertainties in calculated Th/U for zircons of~0.002. Common Pb in the analyses was attributed toblank and subtracted based on the isotopic compositionand associated uncertainties analyzed over time in eachlaboratory. Because of the radiogenic character of these

http://dx.doi.org/10.1029/2006GC001492

http://dx.doi.org/10.1029/2006GC001492


zircons, the reduced data are insensitive to reasonablevariations in the composition of this correction. U blanksare difficult to precisely measure, but are b0.1 pg.

3.3.2. ID-TIMS U–Pb dating (ETHZ)In order to minimize the effects of secondary lead

loss, the chemical-abrasion technique involving high-temperature annealing followed by a HF leaching stepwas used (Mattinson, 2005). Annealing was performedby loading several zircon grains and fragments in quartzcrucibles and placing them into a furnace at 900 °Cfor approximately 60 h. Subsequently, for the leaching(chemical abrasion) step, zircons were transferred to3 ml screw-top Savillex vials with ca. 120 μl concen-trated HF. Loosely capped Savillex vials were arrangedinto a Teflon par vessel with 1 ml concentrated HF, andplaced in an oven at 180°C for 12–15 h. After the partialdissolution step, the leachate was completely pipettedout and the remaining zircons were fluxed for severalhours in 6 N HCl (on a hotplate at a temperature of ca.80 °C), rinsed in ultrapure H2O and then placed back onthe hot plate for an additional 30 min in 4 N HNO3 for a“clean-up” step. The acid solution was removed and thefraction was again rinsed several times in ultra-purewater and acetone in an ultrasonic bath. Zircons wereweighed and loaded for dissolution into pre-cleanedminiaturized Teflon vessel. After adding a mixed205Pb–235U spike zircons were dissolved in 63 μl con-centrated HF with a trace of 7 N HNO3 at 180 °C for5 days, evaporated and re-dissolved overnight in 36 μl3 N HCl at 180 °C. Pb and U were separated by anionexchange chromatography in 40 μl micro-columns,using minimal amounts of ultra-pure HCl, and finallydried down with 3 μl 0.2 N or 0.06 N H3PO4.

Isotopic analysis was performed on a MAT262 massspectrometer equipped with an ETP electron multiplierbacked by a digital ion counting system which wascalibrated by repeated analyses of the NBS 982 andU500 standards. Mass fractionation effects were cor-rected for 0.09±0.05%/a.m.u. Both lead and uraniumwere loaded with 1 μl of silica gel-phosphoric acidmixture on outgassed single Re-filaments, and Pb aswell as U (as UO2

+) isotopes measured sequentially onthe electron multiplier. Total procedural common Pbamounts were measured at 1.9 to 11.6 pg and wereattributed solely to laboratory contamination. Theuncertainties of blank lead isotopic composition, massfractionation correction, and tracer calibration weretaken into account and propagated to the uncertainties ofeach individual isotopic ratio and age. The algorithms ofLudwig (1980) were used to calculate ages and theiruncertainties.

3.3.3. SIMS U–Pb dating (Swedish Museum of NaturalHistory in Stockholm)

High spatial resolution U–Pb data were generatedusing a Cameca IMS1270 large-format ion microprobeat the Nordsim facility, Swedish Museum of NaturalHistory. Detailed analytical methods have beendescribed previously in Whitehouse et al. (1997 and1999). In all cases, a defocused O2

− primary beam wasused to project the image of a 150 µm aperture onto thesample, generating elliptical, flat-bottomed craters ofnominal c. 15 µm (long axis). Complete U–Pb analysesat a mass resolution (M/ΔM) of c. 5000 were performedusing a peak switching routine, with a single ion-counting electron multiplier (EM) as the detectiondevice. An energy window of 60 eV was usedthroughout, with adjustments for possible samplecharging made by scanning the sample high voltageusing the 90Zr2

16O peak. Precise mass calibration wasmaintained by using an automatic routine in the CamecaCIPS software to scan over large peaks and extrapolatethe mass to B-field curve for peaks between thesereference points (e.g., Pb-isotopes were calibrated bycentring the 94Zr2

16O peak at nominal mass 204 and the177Hf16O2 peak at nominal mass 209). Pb/U ratios,elemental concentrations and Th/U ratios were cali-brated relative to the zircon 91500 reference materialwhich has an age of 1065 Ma (Wiedenbeck et al., 1995).Common Pb was monitored using the 204Pb signal andcorrections were made using the modern terrestrial Pbcomposition from the model of Stacey and Kramers(1975), assuming that the common Pb is largely surfacecontamination introduced during sample preparation.

Cathodoluminescence images of zircons analyzed byion microprobe were obtained using a Phillips ESEM atStockholm University and were used to locate ablationsites. After analysis, SE images of craters were obtainedwith a Hitachi S4300 scanning electron microscope atthe Swedish Museum of Natural History to confirm thatthe intended target had been analyzed.

3.3.4. Laser ablation ICP-MS U–Pb dating (Universityof Bergen)

Isotopic analysis of N10 zircon grains by laserablation ICP-MS followed the technique described inKošler et al. (2002) and Košler and Sylvester (2003). AThermo-Finnigan Element 2 sector field ICP-MScoupled to a 213 NdYAG laser (New Wave ResearchUP-213) at Bergen University was used to measure Pb/Uand Pb isotopic ratios in zircons. The sample introduc-tion system was modified to enable simultaneousnebulisation of a tracer solution and laser ablationof the solid sample (Horn et al., 2000). Natural Tl


(205Tl/203Tl=2.3871— Dunstan et al., 1980), 209Bi andenriched 233U and 237Np (N99%) were used in the tracersolution, which was aspirated to the plasma in an argon–helium carrier gas mixture through an Apex desolvationnebuliser (Elemental Scientific) and a T-piece tubeattached to the back end of the plasma torch. A heliumgas line carrying the sample from the laser cell to theplasma was also attached to the T-piece tube.

The laser was set up to produce energy density of ca2 J/cm2 at a repetition rate of 10 Hz. The laser beam wasimaged on the surface of the sample placed in the ablationcell, which was mounted on a computer-driven motorizedstage of a microscope. During ablation the stage wasmoved at a speed of 10 μm/second beneath the stationarylaser beam to produce a linear raster (ca 20×200 μm) inthe sample. Typical acquisitions consisted of a 45 smeasurement of analytes in the gas blank and aspiratedsolution, particularly 203Tl–205Tl–209Bi–233U–237 Np,followed by measurement of U and Pb signals fromzircon, along with the continuous signal from theaspirated solution, for another 150 s. The data wereacquired in time-resolved – peak jumping – pulsecounting mode with 1 point measured per peak formasses 202 (flyback), 203 and 205 (Tl), 206 and 207 (Pb),209 (Bi), 233 (U), 237 (Np), 238 (U), 249 (233U oxide),253 (237Np oxide) and 254 (238U oxide). Raw data werecorrected for dead time of the electron multiplier andprocessed off line in a spreadsheet-based program(Lamdate—Košler et al., 2002). Data reduction includedcorrection for gas blank, laser-induced elemental fractio-nation of Pb and U and instrument mass bias. Minorformation of oxides of U and Np was corrected for byadding signal intensities at masses 249, 253 and 254 to theintensities at masses 233, 237 and 238, respectively. Nocommon Pb correction was applied to the data.

3.3.5. Laser ablation ICP-MS U–Pb dating (MemorialUniversity of Newfoundland)

Three grains of the Plešovice zircon were analyzed.Grain mounts containing the samples and the calibrationmaterial (02123 in-house zircon reference material)were ultrasonically cleaned in deionised water andwiped with 8 N nitric acid prior the analyses.

The analyses were performed using New WaveResearch UP-213 laser coupled to a HP-4500 ICP-MS.Ablation spot size was 40 µm in diameter and the laserenergy was set to 75%. The ICP-MS was tuned byablating NIST 612 glass reference material and maximiz-ing sensitivity for the heavy mass range (Pb–U) whilemaintaining low oxide formation (ThO/Th b0.5%). Theablated sample material was transferred to the ICP-MSusing He carrier gas at 1.2 l/min.

Data were acquired on seven isotopes using theinstrument's time-resolved analysis data acquisitionsoftware with one point measured per mass peak,201Hg (flyback), 204Pb, 206Pb, 207Pb, 208Pb, 232Th and238U. Dwell time was 10 ms for all masses except 207Pb,which was set to 30 ms.

The time-resolved data were processed offline usingthe spreadsheet-based laser ablation data reductionprogram, Lamtrace. Elemental fractionation and instru-mental mass bias were corrected by normalization to thereference zircon 02123 (Ketchum et al., 2001), which wasanalyzed regularly at the beginning and end of eachanalytical session under exactly the same ablationconditions as the unknown samples. A common Pbcorrection was not possible using 204Pb due to the highbackground from the isobaric interference from 204Hg;mass 204 was monitored to ensure there were nosignificant amounts of common Pb present in anyparticular analyses. Background and ablation data foreach analysis were collected over single runs lasting120 s, with background measurements obtained over thefirst 30 s before ablation commenced. The Plešovicezircon data were acquired over four separate days as partof a U–Pb study of unknown zircons. Each analytical runconsisted of 20 analyses, 4 analyses of 02123 zircon(reference zircon), 2 Plešovice zircons, 10 unknowns andfour 02123 zircon (reference zircon) analyses at the end ofthe run. Calculation of mean ages and plotting ofconcordia diagrams for all U–Pb data in this study wasdone with the Isoplot/Ex v.3 program of Ludwig (2003).

3.3.6. Laser ablation ICP-MS U–Pb dating (J.W.Goethe University of Frankfurt am Main)

Four different grains of the Plešovice zircon wereanalyzed using a Thermo-Finnigan Element 2 sectorfield ICP-MS coupled to a New Wave Research UP-213ultraviolet laser system fitted with a modified teardrop-shaped, low volume laser cell (see Horstwood et al.,2003). Laser spot sizes of 30 µm (17 spots), 40 µm(9 spots) and 60 µm (16 spots) were used. The typicaldepth of the ablation crater was 15–20 µm. Data wereacquired in peak jumping mode over 810 mass scansduring 20 s background measurement followed by 32 ssample ablation. Signal was tuned for maximumsensitivity for Pb and U while keeping oxide productionwell below 1%. A common-Pb correction based on theinterference- and background-corrected 204Pb signaland a model Pb composition (Stacey and Kramers,1975) was carried out, where necessary. The necessity ofthe correction was judged on whether the corrected207Pb/206Pb ratio lay outside of the internal errors of themeasured ratios, which was the case in about 40% of the


analyses. The measured and background corrected (e.g.,204Hg) 206Pb/204Pb range from 700 to about 60,000 with18 of 42 analyses having a 206Pb/204Pb below 10,000.The 206Pb/204Pb is very variable within each grain (e.g.,gr-2, 700–40,000) as well as between the differentgrains (mean of gr-2=8400, n=12; mean of gr-3=31,000; n=12). Analyses with high common Pb areusually characterized by elevated uncertainties for the207Pb/235U (Table 3c). Raw data were corrected forbackground signal, common Pb, laser-induced elemen-tal fractionation, instrumental mass discrimination, andtime-dependent elemental fractionation of Pb/U usingan in-house MS Excel spreadsheet program. Laser-induced elemental fractionation and instrumental massdiscrimination were corrected by normalization to thereference zircon GJ-1 (Jackson et al., 2004), which wasanalyzed during the analytical session under exactly thesame conditions as the samples. Prior to this normal-ization, the drift in elemental fractionation was correctedfor each set of isotope ratios (ca. 40) collected during thetime of each single spot analysis. The correction wasdone by applying a linear regression through allmeasured ratios, excluding the outliers (N±2SD), andusing the intercept with the y-axis as the initial ratio.Data were acquired during 4 analytical sessions on 4different days. The total offset of the measured drift-corrected 206Pb/238U ratio from the ”true” ID-TIMSvalue of the analyzed GJ-1 grain was typically around3–7%. Reported uncertainties (2σ) were propagated byquadratic addition of the external reproducibility (2SD)obtained from the zircon reference material GJ-1 (n=12;around 1.3% and 1.2% for the 207Pb/206Pb and

Fig. 5. Images of two Plešovice zircon crystals (30 μm thick thin sections) in(CL) and cross-polarized light showing the typical compositional zoning. Th

206Pb/238U, respectively) during the individual analy-tical session and the within-run precision of eachanalysis (2 SE). For further details on analytical protocoland data processing for the U–Pb method see Gerdesand Zeh (2006).

3.4. Hf isotope analysis

3.4.1. Laser ablation and solution MC ICP-MS Hfanalyses (University of Bergen)

Hf isotopic measurements were carried out on twopolished zircon grains using a New Wave Research UP-213 laser attached to a Thermo-Finnigan Neptune MCICP-MS. The laser was fired with energy of 2 J/cm2,laser beam diameter was 60 μm and repetition rate was10 Hz. The laser beam was scanned across the zirconsurface to ablate a linear raster 400 μm long. Data forgas blank were acquired for 50 s followed by 210 s oflaser ablation. The typical signal intensity was ca. 2.5 Vfor 180Hf.

The faraday cup configuration was set to enabledetection of all Hf isotopes as well as potentiallyinterfering ions: L4–172Yb, L3–173Yb, L2–175Lu,L1–176Hf, C–177Hf, H1–178Hf, H2–179Hf, H3–180Hf,H4–182W. Data were corrected for gas blank and iso-baric interferences of Yb and Lu on 176Hf using 176Yb/173Yb=0.7952 (Lapen et al., 2004) and 176Lu/175Lu=0.02669 (Debievre and Taylor, 1993). Avalue for 179Hf/177Hf=0.7325 (Patchett and Tatsumoto, 1980) and theexponential law were used for mass bias correction ofinterfering Yb and Lu isotopes and isotopes of Hf. Asolution of Hf isotopic standard JMC 475 (20 ppb) was

transmitted light, back-scattered electron (BSE), cathodoluminescencee bright domains on the BSE images indicate high content of actinides.

http://dx.doi.org/10.1029/2003GC000582

Table 1Trace element composition of the Plešovice zircon (laser ablation ICP-MS data, Si analyzed by electron microprobe)

Pristine zircon domains(n=57)

Actinide-rich zircondomains (n=31)

Mean Min Max Mean Min Max

Y 293 139 532 455 322 824Nb 1.5 0.17 3.2 14.7 2.7 28La 0.32 0.18 1.5 0.45 0.24 1.4Ce 2.7 0.93 9.8 7.2 4.3 15.7Pr 0.34 0.13 1.7 0.71 0.34 2.2Nd 3 0.97 11.9 6.9 4 18.7Sm 4.5 2.1 11.7 9.2 6 13.1Eu 1.2 0.26 3.1 2.3 1.5 3.4Gd 14.7 7 32 29 20 42Tb 5.7 2.6 11.2 10.8 7.1 15.2Dy 61 28 121 112 78 160Ho 17.1 8 35 31 19.7 43Er 59 27 123 100 67 143Tm 10.6 5 24 17.4 10.3 25Yb 81 38 185 126 83 187Lu 9.8 4.6 23 15 8.5 23Hf 11 167 9477 14 431 11 760 8980 13 110Pb 39 21 55 116 63 158Th 78 44 183 312 188 523U 755 465 1106 2215 1289 3084Th/U 0.10 0.08 0.17 0.14 0.10 0.17LaN/LuN 0.003 0.001 0.006 0.006 0.002 0.010Eu/Eu⁎ 0.4 0 0.65 0.43 0.31 0.58Ce/Ce⁎ 2.10 1.53 2.82 2.77 2.13 4.27

Values are concentrations in wt. ppm. Eu/Eu⁎=EuN/√(SmN⁎GdN),

Ce/Ce⁎=CeN/√(LaN⁎PrN), normalisation to chondrite after Taylorand McLennan (1985).


used as a monitor of data quality over the period of laserablation measurements, together with analyses of the91500 natural zircon reference sample (Wiedenbecket al., 1995) that was periodically measured betweensample analyses. All zircon LA MC ICP-MS analyseswere adjusted relative to the JMC 475 176Hf/177Hf ratioof 0.282160.

Aliquot of the Plešovice zircon solution prepared at theJ.W.GoetheUniversity of Frankfurt amMain (see Section3.4.2 below) was measured using instrumental (MC ICP-MS) parameters similar to those used for laser ablationanalyses. The solution was aspirated to the ICP in 2%HNO3 through a PFA nebuliser with uptake rate of50 μl/min and a cyclone-double pass quartz spraychamber. The instrument sensitivity was 40 V/ppm Hfmeasured at mass 180Hf. The data acquisition procedureconsisted of 90 integration cycles acquired over aperiod of 4 min, followed by 5 min of washout with amixture of 2%HNO3–0.2 N HF. Correction for isobaricinterferences of 176Yb and 176Lu on 176Hf utilized176Yb/173Yb = 0.7952 (Lapen et al., 2004) and176Lu / 175Lu=0.02669 respectively (Debievre andTaylor, 1993). A value of 179Hf/177Hf=0.7325 (Patch-ett and Tatsumoto, 1980) and the exponential law wereused for mass bias correction of interfering Yb and Luisotopes and for correction of Hf isotopes. Data werenormalized relative to the JMC 475 standard solution(176Hf/177Hf=0.282160), which was measured at thebeginning and at the end of the session.

3.4.2. Laser ablation and solution MC ICP-MS Hfanalyses (J.W. Goethe University of Frankfurt am Main)

Hafnium isotopes were analyzed in six grains of thePlešovice zircon using a Thermo-Finnigan Neptunemulti-collector ICP-MS at Frankfurt University coupledto the New Wave Research UP-213 laser system andusing a teardrop-shaped, low volume laser cell (fordetails on laser ablation see Section 3.3.6). Data werecollected in static mode during 60 s of ablation with aspot size of 60, 80 and 95 µm, respectively. Nitrogen(~0.005 l/min) was introduced into the Ar sample carriergas via an Aridus nebulisation system. Typical signalintensity was ca. 10 V for 180Hf for a spot diameterof 60 µm. The isotopes 172Yb, 173Yb and 175Lu weresimultaneously monitored during each analysis step toallow for correction of isobaric interferences of Lu andYb isotopes on mass 176. The 176Yb and 176Lu werecalculated using a 176Yb/173Yb of 0.796218 (Chu et al.,2002) and 176Lu/175Lu of 0.02658 (JWG in-housevalue). The correction for instrumental mass biasutilized an exponential law and a 179Hf/177Hf value of0.7325 (Patchett and Tatsumoto, 1980) for correction of

Hf isotopic ratios. The mass bias of Yb isotopesgenerally differs slightly from that of the Hf isotopeswith a typical offset of the βHf/βYb of ca. 1.04 to 1.06when using the 172Yb/173Yb value of 1.35274 from Chuet al. (2002). This offset was determined for eachanalytical session by averaging the βHf/βYb of multipleanalyses of the JMC 475 solution doped with variableYb amounts and all laser ablation analyses (typicallynN50) of zircon with a 173Yb signal intensity ofN60 mV. The mass bias behavior of Lu was assumedto follow that of Yb. The Yb and Lu isotopic ratios werecorrected using the βHf of the individual integrationsteps (n=60) of each analysis divided by the averageoffset factor of the complete analytical session. Usinginstead the βHf for mass bias correction of the inter-fering isotopes of Yb and Lu results only in a slightovercorrection of about 30 ppm on the 176Hf/177Hf, e.g.,0.000009, which is within uncertainty of the individualanalysis. This is due to the relative low Lu/Hf and Yb/Hfof Plešovice zircon. Nevertheless the procedure wastested with Lu- and Yb-doped JMC 475 solutions with

http://dx.doi.org/10.1029/2003GC000582

Fig. 6. Chondrite-normalized trace element composition of the Plešovice zircon showing differences between pristine (dark grey) and actinide-richzircon domains (light grey). Chondrite composition after Taylor and McLennan (1985).

Fig. 7. Plot of the FWHM (full width at half-maximum) of the ν3(SiO4)Raman band versus time-integrated α-fluence showing increasingdegree of metamictization in actinide-rich parts of the Plešovice zircon.Open diamond symbols — zircon samples representing nearlycomplete accumulation of the alpha-event damage (Nasdala et al.,2001).


Yb/Hf and Lu/Hf up to 50 times higher than that of thePlešovice zircon. All zircon LA MC ICP-MS analyseswere adjusted relative to the JMC 475 176Hf/177Hf ratioof 0.282160 and quoted uncertainties are quadraticadditions of the within run precision and the reprodu-cibility of the 30-ppb JMC 475 solution (2SD=30–35 ppm, n=8 per day; each 6 min analysis time).Multiple laser ablation MC ICP-MS analyses of thereference zircons 91500 and GJ-1 over a period of sixmonths yielded a 176Hf/177Hf ratio of 0.282298±0.000026 (2σ, n=88) and 0.282003±0.000018 (2σ),respectively. For more details on the analytical methodsee Gerdes and Zeh (2006).

In addition, a reference solution was prepared bydissolving seven grains of the Plešovice zircon in a 4:1HF–HNO3 mixture in Parr bombs at 220 °C over 72 h.After almost complete evaporation the sample was takenup with 100 ml of 0.1 M HF–0.5 M HNO3. Thisprocedure has probably caused some Lu/Hf fractiona-tion due to the formation of REE fluorides. As a result,the calculated interference corrections on the mass 176for the Plešovice zircon solution were ca. 10–15 timeslower than that of the laser ablation analyses.

A 40-ppb aliquot of the Plešovice zircon solutionwas analyzed using an Aridus nebulisation system with50 µl/min uptake rate. Data were acquired with 60integration cycles over a period of 2 min, followed by8 min of washout with a mixture of 2% HNO3–0.5 N HF.Data were corrected and normalized following theprocedure of the laser ablation analyses. Due to similarshort analysis time and similar signal strength the obtainedprecision was similar to that of the laser ablation analyses.

3.4.3. Solution MC ICP-MS Hf analyses (NERC IsotopeGeosciences Laboratory)

The Hf isotope measurements at the NERC IsotopeGeosciences Laboratory, UK, were conducted onresidues remaining after separation of U and Pb usingion exchange resin. These washes were dried down andredissolved in 2% HNO3+0.1 M HF and analyzeddirectly (with some dilution) on a Nu Plasma HR MC

Table 2aID-TIMS U–Pb and Pb–Pb data for the Plešovice zircon

Atomic ratios Apparent ages (Ma)

Sample Pb analysesmode

Pb⁎/Pbc

Pbc Th/U

206Pb/204Pb 208Pb/206Pb 207Pb/235U Err 206Pb/238U Err 207Pb/206Pb Err Corr.coef.

207Pb/235U ± 206Pb/238U ± 207Pb/206Pb ±(pg) (%) (%) (%)

(a) (b) (c) (d) (e) (f) (g) (g) (h) (g) (h) (f) (h) (i) (j) (i) (j) (i) (j)

UNIGE_1 SEM 847 1.12 0.09 56822 0.029 0.394065 0.09 0.053691 0.05 0.053247 0.04 0.955 337.33 0.25 337.14 0.17 339.4 0.9UNIGE_2 SEM 240 3.91 0.08 16177 0.026 0.394211 0.10 0.053706 0.06 0.053252 0.05 0.918 337.44 0.28 337.24 0.20 339.5 1.1UNIGE_4 SEM 348 1.71 0.08 23404 0.026 0.394127 0.09 0.053695 0.05 0.053252 0.04 0.956 337.38 0.25 337.17 0.16 339.5 1.0UNIGE_5 SEM 897 0.99 0.08 60249 0.026 0.393991 0.09 0.053684 0.05 0.053244 0.04 0.949 337.28 0.25 337.10 0.17 339.2 0.9MIT_1 Daly 958 0.99 0.09 64540 0.029 0.393926 0.09 0.053696 0.06 0.053224 0.04 0.946 337.23 0.26 337.17 0.18 338.4 0.9MIT_2 Daly 209 4.48 0.08 14132 0.026 0.394423 0.11 0.053716 0.08 0.053272 0.05 0.915 337.60 0.32 337.29 0.27 340.4 1.1MIT_4 Daly 366 1.62 0.08 24726 0.026 0.393983 0.09 0.053673 0.06 0.053254 0.05 0.916 337.27 0.27 337.03 0.19 339.6 1.1MIT_5 Daly 703 1.27 0.08 47484 0.026 0.393947 0.09 0.053699 0.05 0.053224 0.04 0.958 337.25 0.25 337.19 0.16 338.4 0.9NIGL_A.1 Faraday-SEM 250 6.27 0.09 16863 0.028 0.393979 0.09 0.053700 0.06 0.053227 0.04 0.939 337.27 0.27 337.20 0.19 338.5 1.0NIGL_A.2 Faraday-SEM 198 6.22 0.1 13317 0.032 0.394161 0.10 0.053710 0.07 0.053242 0.05 0.925 337.40 0.29 337.26 0.23 339.1 1.0NIGL_A.3 Faraday-SEM 1327 2.80 0.1 89204 0.032 0.394372 0.10 0.053717 0.07 0.053263 0.04 0.942 337.56 0.28 337.30 0.23 340.0 0.9NIGL_A.5 Faraday-SEM 809 3.76 0.12 54013 0.039 0.394244 0.10 0.053714 0.07 0.053248 0.04 0.940 337.46 0.29 337.28 0.24 339.4 0.9NIGL_B.3 Faraday-SEM 1086 3.08 0.12 72632 0.037 0.394331 0.11 0.053706 0.09 0.053268 0.04 0.943 337.53 0.32 337.24 0.29 340.2 0.9NIGL_B.4 SEM 292 1.20 0.11 19551 0.036 0.394216 0.11 0.053715 0.08 0.053244 0.05 0.932 337.44 0.32 337.29 0.28 339.2 1.0NIGL_B.5 SEM 238 1.21 0.16 15803 0.049 0.393936 0.09 0.053684 0.05 0.053237 0.04 0.938 337.24 0.26 337.10 0.18 338.9 1.0NIGL_B.8 Faraday-SEM 902 1.52 0.04 61699 0.014 0.394093 0.10 0.053684 0.07 0.053258 0.04 0.942 337.36 0.29 337.10 0.24 339.8 0.9NIGL_1 Faraday-SEM 68 13.39 0.13 4531 0.042 0.394228 0.10 0.053721 0.06 0.053239 0.05 0.927 337.45 0.29 337.33 0.21 339.0 1.1NIGL_9 Faraday-SEM 778 0.86 0.1 52287 0.032 0.392655 0.09 0.053529 0.06 0.053217 0.04 0.942 336.31 0.27 336.15 0.21 338.1 0.9NIGL_10 Faraday-SEM 1343 1.14 0.1 90264 0.033 0.394425 0.12 0.053745 0.10 0.053242 0.04 0.952 337.60 0.35 337.48 0.33 339.1 0.9BSU_z10 Faraday-Daly 3204 1.01 0.15 212721 0.046 0.393640 0.11 0.053644 0.09 0.053236 0.04 0.949 337.02 0.33 336.86 0.30 338.9 0.9BSU_z11 Faraday-Daly 3055 0.75 0.14 202913 0.046 0.393663 0.09 0.053650 0.06 0.053233 0.04 0.945 337.04 0.26 336.89 0.20 338.8 0.9BSU_z12 Faraday-Daly 897 0.99 0.1 60357 0.031 0.393913 0.09 0.053672 0.05 0.053246 0.04 0.953 337.22 0.25 337.03 0.17 339.3 0.9BSU_z13 Faraday-Daly 633 1.29 0.12 42415 0.037 0.393721 0.09 0.053655 0.05 0.053237 0.04 0.954 337.08 0.25 336.92 0.17 338.9 0.9BSU_z14 Daly 436 0.72 0.1 29391 0.030 0.393949 0.09 0.053659 0.05 0.053263 0.04 0.960 337.25 0.25 336.95 0.16 340.0 0.9ZURICH_1 SEM 4426 11.60 0.09 26096 0.029 0.394000 0.41 0.053620 0.35 0.053290 0.21 0.910 336.70 0.83 337.30 0.70 341.1 2.4ZURICH_2 SEM 1478 3.60 0.09 27963 0.029 0.393900 0.38 0.053640 0.30 0.053270 0.11 0.970 336.80 0.70 337.20 0.70 340.2 1.3ZURICH_3 SEM 97 2.68 0.09 2485 0.029 0.394600 0.36 0.053650 0.24 0.053300 0.25 0.900 336.90 0.60 337.70 0.70 343.6 2.9

(a) XXX_1, 2 etc. are labels for fractions composed of single zircon fragments, XXX_A.1, A.2 are labels for single zircon fragments from the same crystal.(b) See Section 3.3.1 for details.(c) Ratio of radiogenic Pb to common Pb.(d) Total weight of common Pb.(e) Model Th/U ratio calculated from radiogenic 208Pb/206Pb ratio and 207Pb/206Pb age.(f) Measured ratio corrected for spike and fractionation only. Mass fractionation corrections were based on analysis of NBS-981.(g) Corrected for fractionation, spike, and blank. All common Pb was assumed to be procedural blank. 206Pb/238U ratio corrected for initial disequilibrium in 230Th/238U using Th/U [magma]=4±1.(h) Errors are 2 sigma, propagated using the algorithms of Schmitz and Schoene (2007) and Crowley et al. (2007).(i) Calculations are based on the decay constants of Jaffey et al. (1971). 206Pb/238U date corrected for initial disequilibrium in 230Th/238U using Th/U [magma]=4±1.(j) Errors are 2 sigma. 13

J.Slám

aet

al./Chem

icalGeology

249(2008)

1–35

http://dx.doi.org/10.1029/2006GC001492

Fig. 8. ID-TIMS U–Pb dates of Plešovice zircon; a) Massachusetts Institute of Technology b) University of Geneva c) NERC Isotope GeosciencesLaboratory d) Boise State University and e) ETH Zürich; f) summary of the ID-TIMS dates from the labs using the ET535 spike (MIT, UNIGE,NIGL, BSU). On the left are concordia plots with decay constant uncertainties and on the right are 206Pb/238U dates. Uncertainties are 2σ.


Fig. 8 (continued ).


Table 2bSummary of ID-TIMS U–Pb and Pb–Pb data for the Plešovice zircon

Laboratory Tracer 206Pb/238U ± (2σ) MSWD n

MIT ET535 337.16 0.08 0.36 4UNIGE ET535 337.16 0.09 0.98 4NIGL a ET535 337.24 0.07 0.82 11BSU ET535 336.95 0.08 0.40 5ET535 All ET535 337.13 0.20/0.37 b 10.40 –ETHZ Zurich 337.40 0.40 0.57 3a NIGL_9 not included in weighted mean calculation.b Without/with tracer calibration uncertainty.


ICP-MS using a DSN-100 desolvating nebuliser andPFA-50 nebuliser tip to aspirate the sample into the ICP.These washes still contained all the Zr, Hf, and REEsfrom the crystal aliquot and therefore required an on-linecorrection for isobaric interferences. They were run at an11× dilution in HNO3–HF mixture (thereby reducingmatrix loading of the plasma) using an acquisitionroutine that allowed for assessment of the accuracybetween an Yb correction utilizing a Hf mass bias,versus an Yb correction utilizing an Yb mass bias (using172Yb/173Yb=1.35368). The low REE concentrationscaused the uncertainty on the data using an Yb mass biasto be inflated but the results were still withinuncertainties of the data using Hf mass bias for allcorrections. As such, all the reported data utilized the179Hf/177Hf ratios for mass bias correction.

Yb and Lu interference corrections were conductedusing measurement of the 173Yb and 175Lu peaksassuming true 176Yb/173Yb and 176Lu/175Lu ratios of0.79488 (determined prior to the analytical sessionusing Yb-doped JMC 475 Hf standard) and 0.02653(Patchett, 1983) respectively. All data were normalizedto JMC 475 176Hf/177Hf=0.282160 and equivalentaliquots of the 91500 zircon were also measured toallow assessment of accuracy, giving an average of0.282296±12 (2σ). Calculation of the uncertainty of176Hf/177Hf values of six analyses of four different sizeddissolutions of the Plešovice zircon was done bypropagation of the uncertainty on the JMC 475 standardsolution (35 ppm, 2σ) measured during the analyticalsession.

Initial εHf values for all laser ablation and solutionanalyses were calculated assuming an age of 337 Maand using a 176Lu decay constant of 1.8648⁎10−11

(Scherer et al., 2001) and chondritic Hf composition(176Hf/177Hf=0.282772) and 176Lu/177Hf ratio of0.0332 from Blichert-Toft and Albarède (1997).

4. Results and discussion

A range of zircon images, showing typical internaltextures, is presented in Fig. 5. Zircon crystals oftenhave a well-defined zoning that is apparent in back-scattered electron (BSE) and cathodoluminescence (CL)images as well as in cross-polarized light. Idiomorphiccrystals have usually oscillatory, and less often sectorzoning, sometimes with apparently “featureless” (in CLand BSE) inner parts of the grains. Approximately 30%of the studied grains contain domains that are spatiallyrelated to the growth of pyramidal crystal faces; theytypically show high BSE intensities (dark in CL; Fig. 5).These domains have also significantly lowered birefrin-

gence (Fig. 5), suggesting strong loss of crystallinity.Fractures are present in majority of zircon crystals, andtheir surfaces are coated with a brownish material(Fig. 5), which was in some cases determined to containFe oxides/hydroxides; radial cracks are especiallyabundant around the high intensity BSE patches.Apart from the secondary crack fillings, there arefrequent primary inclusions (apatite, K-feldspar, garnet,and quartz); these are easily recognizable in reflectedlight on polished sample surfaces and can be avoidedduring the analysis.

4.1. Trace element concentration

The trace element concentration data (Table 1 andFig. 6) show a large variation between different zones inthe Plešovice zircon crystals. The high-BSE intensitydomains (dark in CL) with low interference colours incross-polarized light are significantly enriched in allanalyzed elements (Table 1 and Fig. 6). Concentrationsof most trace elements are 2 to 4 times higher(concentration of Nb is ca. 10 times higher) in thesedomains compared to the low-BSE intensity zones in thestudied zircon. The content of U and radiogenic Pbvaries between 465–1106 ppm and 21–55 ppm, respec-tively for pristine, low-BSE intensity parts of the zircon,and 1289–3084 ppm and 63–158 ppm, respectively fordomains with high-BSE intensities. The Th/U ratio has auniform value of ca. 0.1 for both the trace element richand trace element poor zones (Table 1). The low Th/Uvalues are sometimes regarded as being typical of zirconthat crystallized in metamorphic rocks (Hoskin andSchaltegger, 2003 and references therein) but it has beendemonstrated that the Th/U ratios also reflect thecomposition of the source from which the zirconcrystallized and therefore can vary considerably irre-spective of the zircon origin (Kelly and Harley, 2005).The presence of abundant apatite suggests that thepartitioning of U and Th could have been controlled by

Table 3aLaser ablation U–Pb data for the Plešovice zircon (University of Bergen)

Analysis Atomic ratios Apparent ages (Ma)207Pb/235U 1σ 206Pb/238U 1σ 207Pb/235U 1σ 206Pb/238U 1σ

(abs) (abs) (abs) (abs)

UoB-LA1 0.40348 0.01614 0.05316 0.00095 344.2 13.8 333.9 6.0UoB-LA2 0.38827 0.01785 0.05180 0.00084 333.1 15.3 325.6 5.3UoB-LA3 0.39307 0.01521 0.05238 0.00088 336.6 13.0 329.1 5.5UoB-LA4 0.37946 0.01656 0.05242 0.00074 326.6 14.3 329.4 4.6UoB-LA5 0.39746 0.01395 0.05340 0.00087 339.8 11.9 335.3 5.4UoB-LA6 0.40264 0.01527 0.05322 0.00093 343.6 13.0 334.3 5.8UoB-LA7 0.40897 0.01839 0.05251 0.00095 348.1 15.7 329.9 6.0UoB-LA8 0.40031 0.02011 0.05295 0.00078 341.9 17.2 332.6 4.9UoB-LA9 0.39511 0.03086 0.05421 0.00126 338.1 26.4 340.3 7.9UoB-LA10 0.39279 0.01885 0.05321 0.00097 336.4 16.1 334.2 6.1UoB-LA11 0.39938 0.01322 0.05407 0.00085 341.2 11.3 339.5 5.3UoB-LA12 0.40230 0.01668 0.05377 0.00085 343.3 14.2 337.6 5.3UoB-LA13 0.39045 0.01897 0.05542 0.00099 334.7 16.3 347.7 6.2UoB-LA14 0.39298 0.02071 0.05259 0.00120 336.5 17.7 330.4 7.5UoB-LA15 0.39620 0.02544 0.05311 0.00159 338.9 21.8 333.6 10.0UoB-LA16 0.40467 0.02097 0.05313 0.00143 345.0 17.9 333.7 9.0UoB-LA17 0.40713 0.02376 0.05290 0.00167 346.8 20.2 332.3 10.5UoB-LA18 0.41446 0.02604 0.05408 0.00151 352.1 22.1 339.5 9.5UoB-LA19 0.41404 0.01598 0.05477 0.00116 351.8 13.6 343.8 7.3UoB-LA20 0.40806 0.02208 0.05523 0.00096 347.5 18.8 346.5 6.0UoB-LA21 0.38277 0.02179 0.05454 0.00103 329.1 18.7 342.3 6.5UoB-LA22 0.40741 0.01865 0.05386 0.00092 347.0 15.9 338.2 5.7UoB-LA23 0.39308 0.02211 0.05433 0.00143 336.6 18.9 341.0 9.0UoB-LA24 0.39632 0.02876 0.05298 0.00162 339.0 24.6 332.8 10.2UoB-LA25 0.40068 0.02293 0.05439 0.00117 342.1 19.6 341.4 7.3UoB-LA26 0.37569 0.02439 0.05510 0.00117 323.9 21.0 345.7 7.3UoB-LA27 0.40829 0.02525 0.05489 0.00139 347.6 21.5 344.5 8.7UoB-LA28 0.39824 0.02108 0.05428 0.00107 340.4 18.0 340.8 6.7UoB-LA29 0.41707 0.01631 0.05454 0.00103 354.0 13.8 342.3 6.4UoB-LA30 0.38071 0.02293 0.05364 0.00135 327.6 19.7 336.8 8.5UoB-LA31 0.39095 0.02238 0.05470 0.00122 335.1 19.2 343.3 7.7UoB-LA32 0.41691 0.01459 0.05518 0.00092 353.8 12.4 346.2 5.8UoB-LA33 0.40391 0.02435 0.05332 0.00116 344.5 20.8 334.9 7.3UoB-LA34 0.41454 0.02176 0.05504 0.00127 352.1 18.5 345.4 7.9UoB-LA35 0.37680 0.01339 0.05348 0.00103 324.7 11.5 335.9 6.4UoB-LA36 0.37982 0.01411 0.05565 0.00098 326.9 12.1 349.1 6.2UoB-LA37 0.37067 0.01838 0.05400 0.00099 320.1 15.9 339.0 6.2UoB-LA38 0.41703 0.02803 0.05522 0.00129 353.9 23.8 346.5 8.1UoB-LA39 0.40623 0.02970 0.05426 0.00126 346.2 25.3 340.6 7.9UoB-LA40 0.36095 0.01778 0.05354 0.00081 312.9 15.4 336.2 5.1UoB-LA41 0.41656 0.01924 0.05388 0.00107 353.6 16.3 338.3 6.7UoB-LA42 0.40198 0.01385 0.05459 0.00123 343.1 11.8 342.6 7.7UoB-LA43 0.43123 0.01746 0.05447 0.00129 364.0 14.7 341.9 8.1UoB-LA44 0.39371 0.01871 0.05335 0.00105 337.1 16.0 335.0 6.6UoB-LA45 0.38890 0.01922 0.05330 0.00112 333.6 16.5 334.7 7.0UoB-LA46 0.37012 0.01724 0.05270 0.00109 319.7 14.9 331.1 6.9UoB-LA47 0.38928 0.01647 0.05165 0.00112 333.8 14.1 324.6 7.1UoB-LA48 0.37774 0.01864 0.05228 0.00092 325.4 16.1 328.5 5.8UoB-LA49 0.39338 0.03413 0.05093 0.00131 336.8 29.2 320.2 8.2UoB-LA50 0.41838 0.01464 0.05301 0.00063 354.9 12.4 333.0 3.9UoB-LA51 0.37390 0.01371 0.05408 0.00055 322.5 11.8 339.5 3.5UoB-LA52 0.36756 0.01625 0.05485 0.00069 317.8 14.1 344.2 4.3UoB-LA53 0.38137 0.01398 0.05436 0.00060 328.0 12.0 341.2 3.8UoB-LA54 0.38115 0.01605 0.05383 0.00075 327.9 13.8 338.0 4.7

(continued on next page)


Table 3a (continued)

Analysis Atomic ratios Apparent ages (Ma)207Pb/235U 1σ 206Pb/238U 1σ 207Pb/235U 1σ 206Pb/238U 1σ

(abs) (abs) (abs) (abs)

UoB-LA55 0.37463 0.01221 0.05457 0.00067 323.1 10.5 342.5 4.2UoB-LA56 0.41708 0.01355 0.05540 0.00053 354.0 11.5 347.6 3.3UoB-LA57 0.41763 0.01257 0.05408 0.00063 354.4 10.7 339.5 3.9UoB-LA58 0.39342 0.01189 0.05568 0.00065 336.9 10.2 349.3 4.1UoB-LA59 0.39234 0.01243 0.05356 0.00080 336.1 10.6 336.3 5.0UoB-LA60 0.39958 0.01161 0.05465 0.00088 341.3 9.9 343.0 5.5UoB-LA61 0.39309 0.01419 0.05289 0.00085 336.6 12.1 332.2 5.3


concurrent growth of zircon and apatite during theircrystallization from parental magma. This assumption isconsistent with the Th/U ratio being almost constanteven in the high-BSE intensity domains of the grainsthat contain ca. 3 times more of U and Th compared tothe low-BSE intensity domains. The well developednetwork of cracks around the trace element rich zones isconsistent with the damage induced by the decay of Uand Th and associated volume changes of the zircon.The REE show typical “magmatic” steep chondrite-normalized patterns enriched in HREE relative toLREE, negative Eu and a positive Ce anomaly that aresimilar in domains with high (LaN/LuN~0.006, Eu/Eu⁎~0.43, Ce/Ce⁎~2.77) and low (LaN/LuN~0.003,Eu/Eu⁎~0.40, Ce/Ce⁎~2.10) BSE intensities in thestudied zircon grains. The large variations in traceelement contents, both between and within the Plešovicezircon grains suggest a disequilibrium growth (Janoušeket al., 2007) and preclude the use of this zircon as areference material for trace element microanalysis.

4.2. Structural study by Raman spectroscopy

Study of Raman spectra of the Plešovice zircon,especially with emphasis on the bright-BSE domains,has been conducted to characterize its structural proper-ties and homogeneity. Nasdala et al. (2006) have shownthat within zircon single-crystals, heterogeneity of theBSE intensity is most likely due to structural hetero-geneity (i.e., electron channeling contrast caused byheterogeneous radiation damage). The presumption thatthe zircon grains are heterogeneously radiation-damagedis also supported by the range of interference coloursobserved in the cross-polarized light mode (Fig. 5) andfracture patterns that are typical of heterogeneousvolume swelling upon damage accumulation (Lee andTromp, 1995).

The degree of radiation damage was determinedaccording to Nasdala et al. (1995) from the FWHM ofthe ν3(SiO4) Raman band (B1g mode; Raman shift about

1000 cm−1). Determined FWHMs vary in the range 7–30 cm−1, which characterizes the corresponding micro-areas to be moderately to highly damaged. The range ofthe determined degrees of damage corresponds verywell with internal variations of actinide (U and Th)concentrations (see Table 1 and Fig. 6).

To evaluate the degree of storage of the self-irradiation damage, the calculated self-irradiationdoses were compared with the structural damage thatis presently observed. For this, time-integrated alphafluences Dα (i.e., the number of α-decay events pergram) were calculated from

Da ¼ 8 � cU � NA � 0:9928M238 � 106

� ek238t � 1� �þ 7

� cU � NA � 0:0072M235 � 106

� ek235t � 1� �þ 6

� cTh � NA

M232 � 106� ek232t � 1� �

(Murakami et al., 1991; Nasdala et al., 2001), where cUand cTh are the present actinide concentrations (in ppm),NA is Avogadro's number, M238, M235, and M232 are themolecular weights of the parent isotopes, λ238, λ235, andλ232 are the respective decay constants (Firestone andShirley, 1996), and t is the integration time (assumed tobe ca. 337 Ma, i.e. the isotopic age of the zircon). Theabove equation is based on the assumption of naturalisotopic composition of uranium.

The plot of Raman band FWHMs (quantifying thepresent damage) versus time-integrated alpha fluences(Fig. 7) shows that data pairs for studied zircon samplesplot close to the trend defined by zircon samples that arebelieved to represent nearly complete accumulation of thealpha-event damage (Nasdala et al., 2001). As the alphadoses were calculated assuming a damage accumulationperiod of 337 million years, this suggests that thePlešovice zircon has stored the majority of radiationdamage since crystal growth. This, in turn, suggests that


the Plešovice zircon cannot have experienced majorthermal annealing of the radiation damage after itsmagmatic growth.

Fig. 9. Laser ablation ICP-MS U–Pb ages obtained at: a) University of BeUniversity of Frankfurt am Main. On the left are concordia plots and on the rbars on the 206Pb/238U plots are 1σ; Concordia age ellipses (gray filled) are 2σb, c) which is a result of different data reduction procedures used by individ

Post-growth alteration processes, however, areindicated by the observation that internal fractures andcracks are filled/coated with a brown substance, most

rgen, b) Memorial University of Newfoundland and c) J.W. Goetheight are 206Pb/238U dates. Error ellipses in the concordia plots and error. Note the differences in uncertainties of individual data between a) andual laboratories (see Sections 3.3.4–3.3.6 for details).


likely formed by iron oxides/hydroxides (Fig. 5). Thesefractures typically occur in less radiation-damagedinternal regions; they have been generated by volumeexpansion as a result of heterogeneous metamictization

Table 3bLaser ablation U–Pb data for the Plešovice zircon (Memorial University of

Analysis Atomic ratios

207Pb/235U 1σ 206Pb/238U 1σ(abs) (a

MUN-LA1 0.38080 0.00740 0.05220 0.MUN-LA2 0.38480 0.00834 0.05270 0.MUN-LA3 0.38540 0.00621 0.05400 0.MUN-LA4 0.38560 0.00918 0.05420 0.MUN-LA5 0.38580 0.00443 0.05360 0.MUN-LA6 0.38670 0.00436 0.05320 0.MUN-LA7 0.38670 0.01209 0.05440 0.MUN-LA 8 0.38690 0.00492 0.05300 0.MUN-LA9 0.38694 0.00830 0.05370 0.MUN-LA10 0.38840 0.00898 0.05410 0.MUN-LA11 0.38860 0.00503 0.05270 0.MUN-LA12 0.38860 0.00806 0.05380 0.MUN-LA13 0.38870 0.00693 0.05320 0.MUN-LA14 0.38870 0.00768 0.05370 0.MUN-LA15 0.38900 0.00674 0.05330 0.MUN-LA16 0.38930 0.00510 0.05290 0.MUN-LA17 0.38990 0.00630 0.05360 0.MUN-LA18 0.39130 0.00755 0.05350 0.MUN-LA19 0.39140 0.00785 0.05380 0.MUN-LA20 0.39150 0.00541 0.05320 0.MUN-LA21 0.39180 0.00471 0.05350 0.MUN-LA22 0.39180 0.00426 0.05330 0.MUN-LA23 0.39220 0.00717 0.05390 0.MUN-LA24 0.39230 0.00830 0.05410 0.MUN-LA25 0.39240 0.00707 0.05390 0.MUN-LA26 0.39370 0.00502 0.05230 0.MUN-LA27 0.39380 0.00809 0.05400 0.MUN-LA28 0.39380 0.00607 0.05240 0.MUN-LA29 0.39390 0.00700 0.05380 0.MUN-LA30 0.39440 0.00373 0.05320 0.MUN-LA31 0.39450 0.00664 0.05290 0.MUN-LA32 0.39470 0.00913 0.05330 0.MUN-LA33 0.39480 0.00587 0.05390 0.MUN-LA34 0.39490 0.00690 0.05320 0.MUN-LA35 0.39530 0.00760 0.05330 0.MUN-LA36 0.39540 0.00642 0.05300 0.MUN-LA37 0.39570 0.00433 0.05410 0.MUN-LA38 0.39590 0.00793 0.05280 0.MUN-LA39 0.39760 0.00586 0.05390 0.MUN-LA40 0.39770 0.00619 0.05330 0.MUN-LA41 0.39800 0.00799 0.05370 0.MUN-LA42 0.39900 0.00669 0.05410 0.MUN-LA43 0.39960 0.00612 0.05430 0.MUN-LA44 0.40180 0.00512 0.05380 0.MUN-LA45 0.40190 0.00682 0.05420 0.MUN-LA46 0.40290 0.01076 0.05350 0.MUN-LA47 0.40320 0.00821 0.05370 0.MUN-LA48 0.40580 0.00846 0.05440 0.

(Chakoumakos et al., 1987; Lee and Tromp, 1995). Theformation of minerals at these fractures is significantlyyounger than the zircon grains because (i) suchfractures are only formed after a certain time-period,

Newfoundland)

Apparent ages (Ma)

207Pb/235U 1σ 206Pb/238U 1σbs) (abs) (abs)

00052 328.0 6.0 328.0 3.000066 331.0 7.0 331.0 4.000081 331.0 5.0 339.0 5.000061 331.0 7.0 340.0 4.000049 331.0 3.0 336.0 3.000073 332.0 3.0 334.0 5.000067 332.0 9.0 342.0 4.000032 332.0 4.0 333.0 2.000072 332.0 6.0 337.6 4.600081 333.0 6.0 339.0 5.000068 333.0 3.0 331.0 4.000094 333.0 6.0 338.0 6.000053 333.0 5.0 334.0 3.000034 333.0 5.0 337.0 2.000082 334.0 5.0 335.0 5.000058 334.0 4.0 332.0 4.000049 334.0 4.0 337.0 3.000034 335.0 5.0 336.0 2.000045 335.0 5.0 338.0 3.000036 335.0 3.0 334.0 2.000052 336.0 4.0 336.0 4.000034 336.0 3.0 335.0 2.000081 336.0 5.0 338.0 4.000063 336.0 6.0 340.0 4.000063 336.0 5.0 338.0 4.000047 337.0 4.0 328.0 2.000081 337.0 6.0 339.0 5.000045 337.0 4.0 330.0 3.000063 337.0 5.0 338.0 4.000059 338.0 3.0 334.0 3.000051 338.0 5.0 332.0 3.000065 338.0 7.0 335.0 4.000057 338.0 4.0 339.0 4.000058 338.0 5.0 334.0 3.000069 338.0 5.0 335.0 4.000045 338.0 4.0 333.0 3.000031 339.0 4.0 340.0 2.000093 339.0 6.0 332.0 6.000078 340.0 4.0 338.0 5.000055 340.0 5.0 335.0 4.000083 340.0 6.0 337.0 5.000039 341.0 5.0 340.0 3.000082 341.0 4.0 341.0 5.000040 343.0 4.0 338.0 3.000055 343.0 5.0 340.0 3.000055 344.0 8.0 336.0 3.000064 344.0 6.0 337.0 4.000123 346.0 6.0 342.0 8.0


when damage accumulation (and, thus, volume swel-ling) in the higher-actinide regions had reached asufficient level and (ii) there are virtually no newlygenerated but unfilled cracks. The formation of thesefracture fillers must have been connected with a low-temperature fluid (i.e., well below 200 °C). Thisconclusion is supported by the consideration that anyalteration process at more elevated temperature should

Table 3cLaser ablation U–Pb data for Plešovice zircon (J.W. Goethe University of F

Analysis a Atomic ratios207Pb/235U 1σ 206Pb/238U

(abs)

JWG-LA1 (gr-1) 0.39323 0.00433 0.05380JWG-LA2 (gr-1) 0.39460 0.00338 0.05369JWG-LA3 (gr-1) 0.39634 0.00368 0.05390JWG-LA4 (gr-1) 0.38993 0.00363 0.05328JWG-LA5 (gr-1) 0.40024 0.00408 0.05434JWG-LA6 (gr-1) 0.39578 0.00360 0.05366JWG-LA7 (gr-1) 0.39237 0.00337 0.05373JWG-LA8 (gr-1) 0.39962 0.00325 0.05449JWG-LA9 (gr-1) 0.39690 0.00351 0.05400JWG-LA10 (gr-1) 0.39161 0.00354 0.05376JWG-LA11 (gr-1) 0.39213 0.00360 0.05338JWG-LA12 (gr-2) 0.39784 0.00863 0.05335JWG-LA13 (gr-2) 0.38189 0.00834 0.05316JWG-LA14 (gr-2) 0.39632 0.00591 0.05290JWG-LA15 (gr-2) 0.39482 0.00646 0.05348JWG-LA16 (gr-2) 0.40473 0.00943 0.05443JWG-LA17 (gr-2) 0.39942 0.00636 0.05421JWG-LA18 (gr-2) 0.37682 0.01050 0.05349JWG-LA19 (gr-2) 0.40184 0.02018 0.05420JWG-LA20 (gr-2) 0.39688 0.00713 0.05431JWG-LA21 (gr-2) 0.38879 0.00907 0.05284JWG-LA22 (gr-2) 0.39168 0.00611 0.05336JWG-LA23 (gr-2) 0.40074 0.00742 0.05417JWG-LA24 (gr-3) 0.39492 0.00427 0.05372JWG-LA25 (gr-3) 0.39475 0.00432 0.05368JWG-LA26 (gr-3) 0.39398 0.00530 0.05375JWG-LA27 (gr-3) 0.39779 0.00434 0.05380JWG-LA28 (gr-3) 0.39149 0.00491 0.05345JWG-LA29 (gr-3) 0.39094 0.00537 0.05461JWG-LA30 (gr-3) 0.39373 0.00505 0.05350JWG-LA31 (gr-3) 0.39689 0.00456 0.05411JWG-LA32 (gr-3) 0.39222 0.00405 0.05372JWG-LA33 (gr-3) 0.40175 0.00425 0.05435JWG-LA34 (gr-3) 0.39298 0.00410 0.05342JWG-LA35 (gr-3) 0.39369 0.00446 0.05363JWG-LA36 (gr-4) 0.38270 0.00591 0.05221JWG-LA37 (gr-4) 0.39361 0.00607 0.05372JWG-LA38 (gr-4) 0.39371 0.00672 0.05360JWG-LA39 (gr-4) 0.40152 0.00645 0.05504JWG-LA40 (gr-4) 0.40555 0.00573 0.05461JWG-LA41 (gr-4) 0.39883 0.00616 0.05415JWG-LA42 (gr-4) 0.39182 0.00558 0.05313

a gr indicates individual zircon grains analyzed during the LA ICP-MS an

have resulted in notable annealing of the radiationdamage, which is not observed.

4.3. U–Pb dating

The new U–Pb age data obtained by ID-TIMS (MIT,UNIGE, NIGL, BSU and ETHZ) and LA ICP-MS(UoB, MUN, JWG) from randomly selected grains and

rankfurt am Main)

Apparent ages (Ma)

1σ 207Pb/235U 1σ 206Pb/238U 1σ(abs) (abs) (abs)

0.00038 336.7 3.7 337.8 2.30.00035 337.7 2.9 337.1 2.10.00040 339.0 3.2 338.4 2.50.00039 334.3 3.1 334.6 2.40.00041 341.8 3.5 341.1 2.50.00039 338.6 3.1 336.9 2.40.00038 336.1 2.9 337.4 2.30.00038 341.4 2.8 342.0 2.30.00037 339.4 3.0 339.0 2.30.00038 335.5 3.0 337.6 2.30.00037 335.9 3.1 335.2 2.20.00073 340.1 7.4 335.1 4.40.00064 328.4 6.2 333.9 3.90.00064 339.0 4.3 332.3 3.90.00063 337.9 4.7 335.9 3.80.00066 345.1 6.9 341.6 4.10.00069 341.2 4.6 340.3 4.20.00069 324.7 7.8 335.9 4.20.00068 343.0 14.8 340.2 4.20.00064 339.4 5.2 340.9 3.90.00066 333.5 6.7 331.9 4.00.00064 335.6 4.5 335.1 3.90.00065 342.2 5.4 340.1 4.00.00050 338.0 3.1 337.3 3.10.00050 337.8 3.2 337.1 3.00.00051 337.3 3.9 337.5 3.10.00051 340.0 3.2 337.8 3.20.00051 335.5 3.6 335.7 3.10.00056 335.1 3.9 342.8 3.40.00049 337.1 3.7 336.0 3.00.00047 339.4 3.3 339.7 2.90.00050 336.0 3.0 337.3 3.10.00050 342.9 3.1 341.2 3.10.00048 336.5 3.0 335.5 2.90.00049 337.1 3.3 336.8 3.00.00068 329.0 4.4 328.1 4.20.00065 337.0 4.4 337.3 4.00.00066 337.1 4.9 336.6 4.00.00072 342.7 4.7 345.4 4.40.00061 345.7 4.2 342.8 3.70.00067 340.8 4.5 340.0 4.10.00062 335.7 4.1 333.7 3.8

alytical session.

Table 4Ion-microprobe U–Th–Pb data for the Plešovice zircon (Swedish Museum of Natural History in Stockholm)

Concentrations Atomic ratios Apparent ages (Ma)

Sample/ U Pb Th/Ucalc

206Pb/204Pb f206207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ Disc. 207Pb/235Ucorr 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ

spot # (ppm) (ppm) (%) (%) (%) (%) (%) (abs) (abs) (abs)(a) (b) (c) (c) (c) (d) (e)

NS-10-1 921 55 0.108 100 526 0.02 0.40134 0.90 0.05501 0.76 0.05292 0.50 345.4 2.6 345.2 2.5 325.2 11.2NS-10-2 772 45 0.085 106 275 0.02 0.39487 0.91 0.05384 0.74 0.05320 0.53 338.0 2.5 338.0 2.4 337.2 11.9NS-1-1 945 55 0.087 897 2.09 0.40239 1.57 0.05372 0.75 0.05433 1.38 336.8 2.7 337.3 2.5 384.6 30.8NS-11-1 544 32 0.085 55 142 0.03 0.39967 1.00 0.05439 0.80 0.05329 0.60 341.4 2.7 341.4 2.6 341.3 13.5NS-12-1 830 50 0.096 58 758 (0.00) 0.40621 1.05 0.05530 0.74 0.05328 0.75 347.0 2.5 347.0 2.5 340.6 16.8NS-13-1 930 55 0.109 72 744 0.03 0.39522 1.01 0.05435 0.74 0.05274 0.68 341.4 2.5 341.2 2.5 317.4 15.5NS-14-1a 598 36 0.100 52 465 0.04 0.40922 1.03 0.05639 0.81 0.05264 0.63 2.51 354.0 2.8 353.6 2.8 313.1 14.3NS-15-1 831 50 0.102 230 388 (0.01) 0.40376 1.02 0.05532 0.74 0.05293 0.69 347.3 2.5 347.1 2.5 326.0 15.6NS-15-2 846 50 0.101 87 747 (0.02) 0.40124 1.01 0.05484 0.74 0.05306 0.69 344.3 2.5 344.2 2.5 331.5 15.6NS-15-3 784 46 0.090 38 615 0.05 0.39682 1.06 0.05432 0.74 0.05298 0.76 341.1 2.5 341.0 2.5 328.1 17.1NS-15-4 1032 61 0.096 60 608 0.03 0.39463 1.04 0.05426 0.80 0.05275 0.67 340.8 2.7 340.6 2.7 318.1 15.1NS-15-5 1144 67 0.094 271 698 (0.01) 0.39665 0.98 0.05425 0.75 0.05303 0.63 340.6 2.5 340.5 2.5 330.2 14.3NS-15-6 1148 67 0.093 71 755 0.03 0.39836 0.98 0.05434 0.74 0.05317 0.64 341.2 2.5 341.1 2.4 336.0 14.4NS-15-7 618 35 0.096 145 497 (0.01) 0.38273 1.15 0.05280 0.74 0.05257 0.88 331.9 2.4 331.7 2.4 310.2 19.9NS-16-1 596 35 0.100 93 202 (0.02) 0.39488 1.20 0.05449 0.75 0.05256 0.94 342.4 2.5 342.0 2.5 309.7 21.2NS-17-1 881 53 0.111 84 964 (0.02) 0.40735 1.05 0.05507 0.75 0.05365 0.74 345.4 2.6 345.5 2.5 356.5 16.5NS-18-1 1391 81 0.138 202 441 (0.01) 0.39237 1.02 0.05338 0.74 0.05331 0.71 335.2 2.4 335.2 2.4 342.2 15.9NS-19-1 1013 59 0.110 16 449 0.11 0.39430 1.09 0.05355 0.76 0.05341 0.78 336.2 2.5 336.3 2.5 346.1 17.5NS-20-1 941 55 0.099 31 354 0.06 0.39857 1.06 0.05431 0.74 0.05323 0.76 340.9 2.5 340.9 2.5 338.6 17.2NS-2-1 771 45 0.112 62 557 0.03 0.38973 1.07 0.05459 0.74 0.05178 0.78 9.85 343.3 2.5 342.6 2.5 275.6 17.8NS-2-2 704 42 0.090 154 445 (0.01) 0.40886 1.02 0.05540 0.74 0.05353 0.71 347.5 2.5 347.6 2.5 351.1 15.9NS-21-1 937 55 0.102 207 163 (0.01) 0.39285 1.03 0.05362 0.74 0.05314 0.72 336.7 2.5 336.7 2.4 334.8 16.3NS-22-1 1128 64 0.095 1606 1.16 0.38532 1.52 0.05248 0.74 0.05325 1.33 329.6 2.5 329.7 2.4 339.4 29.8NS-22-2 1003 59 0.117 451 177 (0.00) 0.39289 1.05 0.05387 0.74 0.05290 0.75 338.4 2.5 338.2 2.4 324.3 16.9NS-22-3 892 52 0.106 65 887 (0.03) 0.39194 1.07 0.05388 0.74 0.05275 0.76 338.5 2.5 338.3 2.5 318.3 17.3NS-22-4 791 46 0.095 61 190 (0.03) 0.39528 1.08 0.05392 0.74 0.05316 0.79 338.6 2.5 338.6 2.4 335.8 17.8NS-22-5 769 45 0.090 27 678 0.07 0.40170 1.16 0.05430 0.75 0.05366 0.88 340.7 2.5 340.8 2.5 356.7 19.6NS-22-6 831 48 0.102 1793 1.04 0.39476 1.52 0.05373 0.75 0.05328 1.33 337.4 2.5 337.4 2.5 340.8 29.7NS-22-7 952 56 0.108 67 626 (0.03) 0.39790 1.07 0.05458 0.74 0.05288 0.77 342.8 2.5 342.6 2.5 323.4 17.4NS-22-8 680 39 0.098 93 935 (0.02) 0.38998 1.25 0.05327 0.74 0.05310 1.00 334.6 2.5 334.6 2.4 332.9 22.6

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NS-23-1 818 49 0.095 200 958 (0.01) 0.40832 1.05 0.05529 0.74 0.05356 0.74 346.8 2.5 346.9 2.5 352.8 16.7NS-24-1 923 55 0.110 141 245 (0.01) 0.39691 1.03 0.05462 0.75 0.05270 0.71 343.1 2.5 342.8 2.5 315.9 16.0NS-25-1 824 49 0.106 123 166 (0.02) 0.39853 1.07 0.05448 0.74 0.05305 0.78 342.1 2.5 342.0 2.5 331.0 17.5NS-26-1 1107 66 0.156 154 761 (0.01) 0.39849 1.00 0.05451 0.74 0.05302 0.68 342.3 2.5 342.1 2.5 329.7 15.3NS-27-1 1106 67 0.172 237 888 (0.01) 0.39824 1.11 0.05494 0.75 0.05257 0.82 345.1 2.6 344.8 2.5 310.3 18.6NS-28-1 961 57 0.113 109 294 (0.02) 0.39643 1.05 0.05433 0.74 0.05292 0.74 341.2 2.5 341.0 2.5 325.5 16.6NS-29-1 832 48 0.117 201 074 (0.01) 0.39442 1.09 0.05338 0.74 0.05359 0.80 335.1 2.5 335.3 2.4 353.8 17.9NS-30-1 869 51 0.100 207 815 (0.01) 0.39564 1.07 0.05405 0.74 0.05309 0.78 339.4 2.5 339.3 2.4 332.8 17.5NS-3-1 928 56 0.103 137 298 (0.01) 0.41122 0.93 0.05576 0.74 0.05349 0.56 349.8 2.6 349.8 2.5 349.7 12.6NS-31-1 879 51 0.108 122 944 (0.02) 0.39104 1.18 0.05354 0.74 0.05297 0.93 336.3 2.4 336.2 2.4 327.4 20.9NS-32-1 1118 67 0.155 180 290 (0.01) 0.39949 1.30 0.05435 0.74 0.05331 1.07 341.2 2.5 341.2 2.5 341.9 24.0NS-33-1 984 58 0.105 81 145 (0.02) 0.39966 1.08 0.05447 0.74 0.05322 0.79 341.9 2.5 341.9 2.5 338.2 17.8NS-33-2 890 52 0.097 179 112 (0.01) 0.39879 1.02 0.05399 0.74 0.05357 0.71 338.8 2.5 339.0 2.4 353.0 16.0NS-33-3 624 36 0.102 44 594 0.04 0.39168 1.24 0.05390 0.74 0.05270 1.00 338.7 2.5 338.4 2.4 315.9 22.5NS-33-4 932 55 0.145 2680 0.70 0.38433 1.34 0.05374 0.75 0.05186 1.11 0.42 338.0 2.5 337.5 2.5 279.4 25.2NS-33-5 1096 65 0.150 41 489 0.05 0.39491 1.00 0.05380 0.74 0.05324 0.67 337.8 2.5 337.8 2.4 338.8 15.0NS-33-6 1375 82 0.138 88 805 0.02 0.40007 1.00 0.05460 0.74 0.05314 0.67 342.8 2.5 342.7 2.5 334.7 15.2NS-33-7 1138 67 0.144 188 164 (0.01) 0.39577 0.98 0.05360 0.74 0.05355 0.65 336.4 2.5 336.6 2.4 352.2 14.6NS-33-8 753 43 0.109 26 041 0.07 0.38601 1.16 0.05302 0.74 0.05280 0.89 333.2 2.4 333.0 2.4 320.4 20.1NS-4-1 606 36 0.092 46 468 0.04 0.40132 1.00 0.05490 0.78 0.05302 0.63 344.7 2.6 344.5 2.6 329.6 14.1NS-4-2 828 49 0.097 36 317 0.05 0.40331 0.91 0.05473 0.74 0.05344 0.54 343.5 2.5 343.5 2.5 347.6 12.1NS-4-3 1102 66 0.096 26 891 0.07 0.40779 0.91 0.05502 0.74 0.05375 0.52 345.1 2.5 345.3 2.5 360.7 11.7NS-4-4 781 47 0.117 94 966 0.02 0.40738 0.93 0.05587 0.74 0.05289 0.56 350.7 2.6 350.4 2.5 324.0 12.7NS-4-5 783 47 0.102 74 241 0.03 0.40787 0.93 0.05600 0.74 0.05283 0.56 0.22 351.5 2.6 351.2 2.5 321.3 12.7NS-4-6 548 33 0.088 76 351 (0.02) 0.41406 0.99 0.05630 0.74 0.05334 0.66 353.2 2.6 353.1 2.5 343.2 14.8NS-5-1 704 41 0.098 88 278 (0.02) 0.39494 1.06 0.05429 0.76 0.05276 0.73 341.0 2.6 340.8 2.5 318.6 16.6NS-6-1 563 34 0.091 58 758 (0.03) 0.40550 1.12 0.05518 0.74 0.05330 0.83 346.3 2.5 346.2 2.5 341.5 18.7NS-7-1 1233 75 0.152 108 451 (0.02) 0.40280 0.94 0.05511 0.74 0.05301 0.58 346.0 2.5 345.8 2.5 329.4 13.1NS-8-1 746 44 0.087 100 778 (0.02) 0.40304 1.03 0.05460 0.75 0.05354 0.71 342.6 2.5 342.7 2.5 351.9 16.0NS-9-1 1094 65 0.089 79 675 0.02 0.40435 0.88 0.05514 0.78 0.05318 0.42 346.1 2.6 346.0 2.6 336.5 9.4NS-9-2 811 48 0.087 93 847 0.02 0.40709 0.90 0.05469 0.75 0.05399 0.50 −0.33 342.9 2.5 343.2 2.5 370.6 11.2

(a) Calculated from measured ThO intensity.(b) Percentage of common Pb detected, calculated from measured 204Pb and assuming 0 Ma, Stacey and Kramers (1975) average terrestrial Pb. Figures in parentheses indicate, where no common Pbcorrections have been applied.(c) Corrected for common lead.(d) Degree of discordance (%); not reported for analyses, which are concordant within 2σ error limits.(e) Ages calculated by projecting from an assumed common Pb composition onto Concordia (Ludwig, 2003).

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grain fragments suggest a homogeneous age that is nowmore precisely determined, but still in good agreementwith the previously reported U–Pb age of 338±1 Ma forzircons from the same rock (Aftalion et al., 1989; ID-TIMS).

The new dating of four (MIT and UNIGE), eleven(NIGL), five (BSU) and three (ETHZ) Plešovice zirconfragments yielded 206Pb/238U and 207Pb/235U dates thatagree within the decay constant uncertainties (Table 2a,Fig. 8). The weighted mean 206Pb/238U dates aresummarized in Table 2b for each laboratory. A weightedmean ET535 206Pb/238U date was calculated based uponall MIT, UNIGE, NIGL and BSU data points (excludingNIGL_9 which is an outlier) at 337.13±0.06 Ma(±0.23 Ma including tracer calibration uncertainties;MSWD=1.9, n=23). A weighted mean 206Pb/238U datewas calculated based upon the ETHZ analyses at 337.40±0.40Ma (including ETHZ tracer calibration uncertainties;MSWD=0.57, n=3; Fig. 8e). A weighted mean of theages obtained by different labs using the ET535 spikegives a 206Pb/238U date of 337.13±0.37 Ma (with tracercalibration uncertainty of 0.05%; mean value of theweighted means is identical within the analyticaluncertainty with the value of 337.13±0.25, 2SD), withan MSWD of 10.4 (Fig. 8f). This is our best estimate forthe age of the Plešovice zircon, and the variability of thefragments represented in this study, measured with theET535 tracer. The high MSWD is a result of either a)systematic measurement uncertainty due to interlabora-tory bias or, b) actual age variations in the grains mea-sured, given that the fragments dated in each lab comefrom different large grains.

Laser ablation ICP-MS U–Pb dates obtained in threedifferent laboratories are concordant and identical within

Fig. 10. Ion-microprobe U–Pb ages of the Plešovice zircon obtained at Nordsleft is concordia plot and on the right are 206Pb/238U dates. Error ellipses in

the limits of analytical precision. They are also statis-tically indistinguishable from the 337.13±0.37 Ma ID-TIMS weighted mean 206Pb/238U date. The respectivecalculated laser ablation ICP-MS concordia ages fromUoB, MUN and JWG are as follows: 338±1 Ma (2σ, 61analyses; Table 3a and Fig. 9a), 336±1 Ma (2σ, 48analyses; Table 3b and Fig. 9b) and 338±1 Ma (2σ, 42analyses; Table 3c and Fig. 9c). Despite the lowerprecision of dates obtained by LA ICP-MS compared tothe ID-TIMS dates, the data are useful in that they showage homogeneity on the scale of tens of microns both forindividual grains and for a multi-grain sub-sample of thezircon fraction separated from the potassic granulite. Theactinide-rich domains that occur in some of the Plešovicegrains (some with U concentrations N3000 ppm) weretested for radiogenic Pb loss. Our LA ICP-MS data andadditional SHRIMP analyses (Curtin University ofTechnology, Perth) suggest that, regardless of strongradiation damage in the actinide-rich domains, there wasno significant Pb-loss. However, from a practicalstandpoint, it is preferred to avoid such zones duringlaser ablation ICP-MS analyses as (i) the high U signalmight exceed the dynamic range of some (e.g. SEM)detection devices, (ii) corrections for detector dead-timetend to be less accurate for very high signal intensitiesand can lead to inaccurate ages, (iii) the high concentra-tion of U ions can lead to unexpected space charge/matrix effects and (iv) ablation rates in the radiation-damaged zones and pristine zircon might be different,potentially leading to significant differences in theplasma load between pristine and radiation-damagedzircons.

SIMSU–Pb analyses of the Plešovice zircon yielded aweighted mean 206Pb/238U date of 341.4±1.3 Ma (61

im facility (Swedish Museum of Natural History in Stockholm). On thethe concordia plots and error bars on the 206Pb/238U plots are 1σ.


analyses from 33 individual grains; Table 4, Fig. 10).While the multiple analyses of grains NS-22 and NS-33yield ages identical to the ID-TIMS and laser ablationICP-MSmeasurements (Fig. 11), some analyses are olderto significantly older (cf. Table 4), resulting in the meanage obtained by SIMSbeing somewhat older compared tothe ages obtained by other techniques. The data show nonotable correlation between the type of zircon zoning, Uconcentration, position of the analyzed spot within thegrains and the obtained age (e.g., zircon NS-15 yieldsyounger ages towards the rim of the grain but zirconNS-4shows an opposite trend with ages increasing towards thegrain rim, cf. Fig. 11). Other grains (zircons NS-22 andNS-33 in Fig. 11) yielded more uniform ages of ca. 338±3 Ma. A possible explanation of the variations in SIMSU–Pb ages is a uranium and lead decoupling in some

Fig. 11. Cathodoluminescence images of four Plešovice zircon crystals withcorrespond to Table 4.

parts of the zircon at a scale of the volume analyzed bySIMS (about 300 of μm3). No similar variations wereobserved by laser ablation ICP-MS measurements or ID-TIMS analyses of fragments of the zircon grains. A moredetailed SIMS and structural study of the Plešovice zirconis needed to fully explain the cause of the observed agevariations but the present data suggest that at this stage ofcharacterization, the Plešovice zircon is not an ideal agereference material for high spatial resolution (SIMS)measurements.

4.4. Hf isotopic composition

Concentration of Hf in the Plešovice zircon variesbetween 0.9–1.44 wt.% (Table 1) and the estimatedaccuracy of trace element and Hf determinations in this

marked position of analyzed spots by ion microprobe. The analyses


study is ca. 5–10% (2 sigma). The laser ablation MCICP-MS data suggest a homogenous Hf isotopiccomposition (Fig. 12) within and between individualzircon grains with 176Hf/177Hf values of 0.282482±0.000012 (178Hf/177Hf=1.46723±0.00002; 2SD, UoB)and 0.282481 ± 0.000014 (178Hf/177Hf = 1.46719 ±0.00010; 2SD, JWG; cf. Table 5a) and with a mean176Hf/177Hf value for the pooled data set of 0.282481±0.000014 (2SD, 61 analyses from 8 grains, Fig. 12).

MC-ICP-MS analyses of solution prepared by dis-solution of seven zircon grains yielded similar Hf isotopiccompositions of 0.282483±0.000012 (178Hf/177Hf=1.46722±0.00001; 2SD, UoB) and 0.282486±0.000008(178Hf/177Hf=1.46722±0.00003; 2SD, JWG; cf. Table5b) Another 6 analyses conducted on 4 different solutions(washes from U–Pb columns, NIGL) also gave a homo-genous Hf isotopic composition with mean 176Hf/177Hfvalue of 0.282480±0.000013 (178Hf/177Hf=1.46730±0.00002; 2SD, Table 5b). The mean 176Hf/177Hf value forall zircon analyses in solution mode is 0.282484±0.000008 (2SD, 26 analyses, Fig. 13). As there are nosignificant differences in Hf isotopic compositionobtained by laser ablation and solution techniques, norare there significant differences between results from thethree laboratories, the mean value of 176Hf/177Hf of0.282482±0.000013 (2SD) calculated from all 87analyses (solution and laser ablation) is considered as abest estimate of the Hf isotopic composition for thePlešovice zircon.

In spite of the consistency of the laser ablation andsolution Hf isotopic data obtained from the threelaboratories, there is a small (but statistically insignif-icant) difference in laser ablation Hf isotopic measure-ments conducted at the JWG and data reported fromUoB. Hf isotopic composition of the Plešovice zirconmeasured at the JWG shows somewhat larger variation

Fig. 12. Hf isotopic composition of the Plešovice zircon sample obtained by lwith 2SD uncertainty for all analyses is shown as gray shaded area. Differen

of the 176Hf/177Hf data within and between individualgrains (cf. Fig. 12). This could suggest some minorheterogeneity of the Hf isotope composition within andbetween the grains. However, without additional solu-tion mode data supporting this, it appears at presentmore likely that these variations are at the limit of theanalytical precision and probably represent only ananalytical artifact. It should be highlighted here thatdifferent parameters and approaches were used forinterference corrections (see Chu et al., 2002; Wood-head et al., 2004) between the three laboratories. The179Hf/177Hf ratio of Patchett and Tatsumoto (1980) wasused for mass bias correction of Hf as well as ofinterfering isotopes of Yb and Lu isotopes in samplesanalyzed at the UoB and in the NIGL. Analyses from theJWG used the 179Hf/177Hf ratio for correction of Hfisotopic ratios and a daily correction factor to accountfor the differences between the Hf and the Yb andLu mass bias, respectively. This approach uses the172Yb/173Yb ratio of Chu et al. (2002) as externalreference. None of the laboratories involved in thisstudy relies on the Yb isotopic ratio measured duringindividual analyses when correcting the Yb and Luisotopic ratios for mass bias. Low Yb/Hf in zirconand low signal intensity of Yb can result in largeruncertainties and scatter of the 176Hf/177Hf ratios. Forcomparison, the Hf isotopic data from the 91500 andPlešovice zircons were corrected for mass bias usingboth approaches (cf. Fig. 14). The 91500 zircon Hf datacorrected with 179Hf/177Hf ratio yield more consistentHf isotopic composition with lower analytical uncer-tainty and better external reproducibility compared tothe same data processed with 179Hf/177Hf correction ofHf isotopes and 172Yb/173Yb correction of Yb and Luisotopes. The mean 176Hf/177Hf value of 91500 zircon(0.282277±0.000043, Fig. 14a) calculated using the

aser ablation MC ICP-MS analyses. The mean 176Hf/177Hf compositiont symbols indicate individual zircon grains.

Table 5aLaser ablation MC ICP-MS measurements of Hf isotopic composition in the Plešovice zircon

Analysis Lu/Hf Yb/Hf 176Hf/177Hf 2σ 178Hf/177Hf 180Hf/177Hf εHf337 2σ

UoB Hf2/1 0.0005 0.0116 0.282482 0.000014 1.467237 1.886714 −2.8 0.5UoB Hf2/2 0.0007 0.0162 0.282482 0.000013 1.467224 1.886720 −2.8 0.5UoB Hf2/3 0.0010 0.0217 0.282491 0.000013 1.467221 1.886688 −2.6 0.5UoB Hf2/4 0.0009 0.0208 0.282484 0.000013 1.467217 1.886709 −2.8 0.5UoB Hf2/5 0.0006 0.0128 0.282480 0.000014 1.467237 1.886754 −2.9 0.5UoB Hf2/6 0.0006 0.0127 0.282473 0.000013 1.467238 1.886749 −3.1 0.5UoB Hf2/7 0.0008 0.0170 0.282481 0.000013 1.467245 1.886691 −2.9 0.5UoB Hf2/8 0.0008 0.0180 0.282476 0.000013 1.467221 1.886712 −3.0 0.5UoB Hf2/9 0.0008 0.0188 0.282479 0.000013 1.467231 1.886704 −2.9 0.5UoB Hf2/10 0.0007 0.0182 0.282494 0.000013 1.467238 1.886701 −2.4 0.5UoB Hf2/11 0.0005 0.0122 0.282478 0.000013 1.467236 1.886691 −3.0 0.5UoB Hf3/1 0.0007 0.0154 0.282490 0.000014 1.467225 1.886678 −2.5 0.5UoB Hf3/2 0.0011 0.0225 0.282485 0.000013 1.467235 1.886684 −2.7 0.5UoB Hf3/3 0.0011 0.0229 0.282471 0.000013 1.467209 1.886696 −3.2 0.5UoB Hf3/4 0.0011 0.0235 0.282482 0.000014 1.467208 1.886710 −2.9 0.5UoB Hf3/5 0.0011 0.0245 0.282486 0.000014 1.467237 1.886723 −2.7 0.5JWG Hf4/1 0.0009 0.0077 0.282480 0.000013 1.467142 1.886556 −2.9 0.5JWG Hf4/2 0.0007 0.0066 0.282481 0.000011 1.467168 1.886552 −2.9 0.4JWG Hf4/3 0.0010 0.0085 0.282481 0.000011 1.467121 1.886555 −2.9 0.4JWG Hf4/4 0.0010 0.0090 0.282471 0.000011 1.467183 1.886584 −3.3 0.4JWG Hf4/5 0.0009 0.0082 0.282477 0.000011 1.467146 1.886554 −3.0 0.4JWG Hf4/6 0.0010 0.0075 0.282485 0.000014 1.467240 1.886711 −2.8 0.5JWG Hf4/7 0.0009 0.0074 0.282482 0.000017 1.467291 1.886665 −2.9 0.6JWG Hf5/1 0.0007 0.0057 0.282480 0.000014 1.467126 1.886535 −2.9 0.5JWG Hf5/2 0.0005 0.0044 0.282482 0.000013 1.467141 1.886617 −2.8 0.5JWG Hf5/3 0.0004 0.0038 0.282472 0.000014 1.467157 1.886636 −3.2 0.5JWG Hf5/4 0.0005 0.0050 0.282473 0.000012 1.467169 1.886634 −3.1 0.4JWG Hf5/5 0.0008 0.0073 0.282472 0.000012 1.467164 1.886656 −3.2 0.4JWG Hf5/6 0.0008 0.0072 0.282470 0.000010 1.467190 1.886651 −3.2 0.4JWG Hf6/1 0.0006 0.0048 0.282472 0.000014 1.467181 1.886578 −3.2 0.5JWG Hf6/2 0.0006 0.0056 0.282481 0.000011 1.467146 1.886566 −2.9 0.4JWG Hf6/3 0.0006 0.0052 0.282483 0.000011 1.467188 1.886656 −2.8 0.4JWG Hf6/4 0.0009 0.0080 0.282474 0.000014 1.467266 1.886788 −3.1 0.5JWG Hf6/5 0.0008 0.0075 0.282475 0.000013 1.467256 1.886724 −3.1 0.5JWG Hf7/1 0.0006 0.0052 0.282486 0.000011 1.467211 1.886619 −2.7 0.4JWG Hf7/2 0.0004 0.0043 0.282484 0.000011 1.467177 1.886564 −2.8 0.4JWG Hf7/3 0.0005 0.0044 0.282478 0.000013 1.467169 1.886658 −3.0 0.5JWG Hf7/4 0.0004 0.0040 0.282482 0.000011 1.467195 1.886606 −2.9 0.4JWG Hf7/5 0.0007 0.0065 0.282493 0.000013 1.467162 1.886729 −2.4 0.5JWG Hf7/6 0.0012 0.0108 0.282485 0.000015 1.467093 1.886618 −2.8 0.5JWG Hf7/7 0.0004 0.0039 0.282490 0.000013 1.467093 1.886840 −2.5 0.5JWG Hf8/1 0.0010 0.0094 0.282488 0.000013 1.467218 1.886661 −2.6 0.5JWG Hf8/2 0.0009 0.0077 0.282494 0.000013 1.467115 1.886609 −2.4 0.4JWG Hf8/3 0.0009 0.0074 0.282486 0.000015 1.467139 1.886628 −2.7 0.5JWG Hf8/4 0.0008 0.0080 0.282481 0.000015 1.467166 1.886618 −2.9 0.5JWG Hf8/5 0.0011 0.0099 0.282481 0.000015 1.467286 1.886798 −2.9 0.5JWG Hf8/6 0.0011 0.0096 0.282481 0.000015 1.467250 1.886777 −2.9 0.5JWG Hf8/7 0.0011 0.0098 0.282482 0.000016 1.467285 1.886789 −2.9 0.6JWG Hf8/8 0.0010 0.0075 0.282495 0.000013 1.467252 1.886790 −2.4 0.5JWG Hf8/9 0.0012 0.0116 0.282485 0.000015 1.467227 1.886815 −2.7 0.5JWG Hf8/10 0.0013 0.0123 0.282493 0.000017 1.467211 1.886720 −2.5 0.6JWG Hf8/11 0.0012 0.0116 0.282495 0.000015 1.467258 1.886811 −2.4 0.5JWG Hf9/1 0.0013 0.0123 0.282477 0.000017 1.467265 1.886753 −3.0 0.6JWG Hf9/2 0.0009 0.0085 0.282482 0.000013 1.467212 1.886615 −2.8 0.5JWG Hf9/3 0.0007 0.0070 0.282467 0.000013 1.467234 1.886594 −3.4 0.5JWG Hf9/4 0.0006 0.0063 0.282478 0.000014 1.467140 1.886688 −3.0 0.5JWG Hf9/5 0.0008 0.0073 0.282471 0.000013 1.467165 1.886674 −3.2 0.4

(continued on next page)


Table 5a (continued)

Analysis Lu/Hf Yb/Hf 176Hf/177Hf 2σ 178Hf/177Hf 180Hf/177Hf εHf337 2σ

JWG Hf9/6 0.0008 0.0075 0.282467 0.000012 1.467193 1.886642 −3.4 0.4JWG Hf9/7 0.0009 0.0080 0.282477 0.000013 1.467233 1.886768 −3.0 0.5JWG Hf9/8 0.0009 0.0069 0.282484 0.000012 1.467224 1.886675 −2.8 0.4JWG Hf9/9 0.0009 0.0073 0.282472 0.000011 1.467143 1.886654 −3.2 0.4

Analyses names indicate where the measurements were done: UoB— University of Bergen, JWG— J.W. Goethe University of Frankfurt am Main.εHf337 calculated as an initial value for the age 337 Ma obtained by U–Pb dating of Plešovice zircon.


first approach is closer to value of 0.282284±0.000060of Wiedenbeck et al. (1995) compared to the datacalculated using the second approach (0.282315±0.000095, Fig. 14b). Wu et al. (2006) compiled allavailable data for the 91500 zircon and reported a mean176Hf/177Hf value of 0.282303±0.000021. Similarly,the 179Hf/177Hf-corrected data from the Plešovice zirconshow less variation and a lower mean 176Hf/177Hf valuecompared to the data where the 179Hf/177Hf and172Yb/173Yb ratios were used for mass bias correctionof Hf and Yb–Lu isotopes, respectively (Fig. 14c,d). Inconclusion, the two mass bias correction proceduresyield results that, within their analytical uncertainties,

Table 5bSolution MC ICP-MS measurements of Hf isotopic composition in the Plešo

Analysis Lu/Hf Yb/Hf 176Hf/177Hf 2σ

UoB Hf1/1 0.0001 0.0012 0.282483 0.000UoB Hf1/2 0.0001 0.0012 0.282481 0.000UoB Hf1/3 0.0001 0.0012 0.282481 0.000UoB Hf1/4 0.0001 0.0011 0.282482 0.000UoB Hf1/5 0.0001 0.0011 0.282483 0.000UoB Hf1/6 0.0001 0.0011 0.282481 0.000UoB Hf1/7 0.0001 0.0011 0.282484 0.000UoB Hf1/8 0.0001 0.0011 0.282487 0.000UoB Hf1/9 0.0001 0.0011 0.282482 0.000UoB Hf1/10 0.0001 0.0011 0.282485 0.000JWG Hf1/1 0.0001 0.0006 0.282481 0.000JWG Hf1/2 0.0001 0.0008 0.282485 0.000JWG Hf1/3 0.0001 0.0008 0.282491 0.000JWG Hf1/4 0.0001 0.0005 0.282489 0.000JWG Hf1/5 0.0001 0.0004 0.282492 0.000JWG Hf1/6 0.0001 0.0005 0.282483 0.000JWG Hf1/7 0.0001 0.0005 0.282485 0.000JWG Hf1/8 0.0001 0.0006 0.282491 0.000JWG Hf1/9 0.0001 0.0006 0.282481 0.000JWG Hf1/10 0.0001 0.0007 0.282487 0.000NIGL Z10 0.0007 0.0077 0.282478 0.000NIGL Z9/1 0.0006 0.0068 0.282485 0.000NIGL Z9/2 0.0006 0.0067 0.282479 0.000NIGL Z9/3 0.0006 0.0068 0.282481 0.000NIGL Z8 0.0015 0.0135 0.282480 0.000NIGL Z7 0.0007 0.0076 0.282478 0.000

Analyses names indicate where the measurements were done: UoB— UniverNIGL— NERC Isotope Geosciences Laboratory. εHf337 calculated as an inzircon.

agree with the recommended Hf isotopic composition.When both the Hf and REE isotopic ratios are correctedusing the 179Hf/177Hf ratios, the resulting 176Hf/177Hfvalues show significantly less scatter but the achievedanalytical precision did not allow assessing which of thetwo correction procedures can potentially provide moreaccurate Hf isotopic composition of zircon. For bettercomparison and understanding of the correction proce-dures they have to be tested on zircon grains with higherYb/Hf ratio (Woodhead and Hergt, 2005). The correc-tion of the REE isotopic ratios using the Hf mass bias isvalid probably only for zircon with low Yb/Hf. In suchzircons will the choice of the Yb mass bias correction

vice zircon178Hf/177Hf 180Hf/177Hf εHf337 2σ

013 1.467219 1.886675 −2.8 0.4012 1.467216 1.886655 −2.9 0.4012 1.467223 1.886680 −2.9 0.4013 1.467222 1.886676 −2.9 0.4012 1.467216 1.886684 −2.8 0.4013 1.467222 1.886677 −2.9 0.4013 1.467220 1.886674 −2.8 0.4012 1.467224 1.886671 −2.7 0.4012 1.467220 1.886691 −2.8 0.4012 1.467218 1.886682 −2.7 0.4009 1.467222 1.886673 −2.9 0.3008 1.467216 1.886709 −2.8 0.3010 1.467182 1.886632 −2.6 0.3009 1.467238 1.886634 −2.6 0.3008 1.467194 1.886643 −2.5 0.3010 1.467238 1.886639 −2.8 0.3007 1.467219 1.886686 −2.8 0.2010 1.467203 1.886672 −2.6 0.3009 1.467222 1.886673 −2.9 0.3008 1.467225 1.886656 −2.7 0.3012 1.467291 N/A −3.0 0.4013 1.467300 N/A −2.8 0.5011 1.467292 N/A −3.0 0.4011 1.467289 N/A −2.9 0.4018 1.467290 N/A −2.9 0.6013 1.467312 N/A −3.0 0.4

sity of Bergen, JWG— J.W. Goethe University of Frankfurt am Main,itial value for the age 337 Ma obtained by U–Pb dating of Plešovice

Fig. 13. Hf isotopic composition of the Plešovice zircon sample obtained by solution MC ICP-MS analyses. The mean 176Hf/177Hf composition with2SD uncertainty for all solution Hf analyses is shown as gray shaded area.


protocol have only little effect on the resulting Hfisotopic composition due to the insignificant contribu-tion of 176Yb to 176Hf (Wu et al., 2006).

4.5. Implications for granulite facies rocks in southernBohemian Massif

The new U–Pb zircon age data, together with theprevious petrological studies of the host potassicgranulite from Plešovice (Vrána, 1989; Janoušek et al.,2007) can be used to precisely constrain the timing ofmineral growth during granulite facies metamorphism inthe southern Bohemian Massif. Aftalion et al. (1989)reported identical ages of 338±1 Ma for zircons in thematrix of the potassic granulite and zircons that occur asinclusions in garnet. Garnet (pyrope up to 33 mol%;Vrána, 1989) in this rock is weakly zoned with pyropecomponent decreasing from core to rim, which iscompensated for by increase in almandine and spessar-tine components and it contains exsolution needles ofrutile throughout the garnet grains. The chemical andtextural evidence suggests crystallization of the garnetfrom non-eutectic melt at granulite facies conditions attemperatures exceeding 1000 °C (Vrána, 1989; Janou-šek et al., 2007). Other phases that occur both in thegranulite matrix and also as inclusions in the garnet areK-feldspar, apatite, monazite and zircon. Zircon oftenincludes K-feldspar and apatite, and rarely also garnetand quartz. The observed mineral relations point tosimultaneous crystallization of garnet, K-feldspar,apatite, monazite and zircon, the age of which hasnow been constrained to 337.13±0.37 Ma.

Similar to the previous evidence based on Sr and Ndisotopes for crustal origin of the parent magma of thegranulites in southern Bohemian Massif (Janoušek et al.,2007), the new zircon Hf isotopic data with epsilon

values between −3.4 and −2.4 also point to formation oftheir host potassic granulite from a mature continentalcrust source, such as would be expected in theMoldanubian Zone.

4.6. Comparison with other zircon reference materials

In addition to many in-house zircon referencematerials used for microanalytical techniques, severalnatural zircons have been proposed as referencematerials for in-situ U–Pb and/or Hf isotopic analyses(Tables 6 and 7). From these, the 91500 zircon has beenwell characterized for U–Pb, Hf and O isotopiccomposition, trace elements and crystal structuralproperties (Wiedenbeck et al., 1995; 2004).

Isotopic analyses by LA ICP-MS require that zirconreference material should be isotopically homogeneousand available in sufficient quantity (at least tens,preferably hundreds of grams), should contain radio-genic Pb at ppm or higher concentrations and should alsohave at least mm-scale grain size suitable for repeatanalyses by laser beam that can be up to several tens ofmicrometers in diameter. The 91500 zircon (Wiedenbecket al., 1995) possesses most of the properties required fora reference sample but its supply will soon be exhausted(Woodhead and Hergt, 2005). The alternatives includethe Temora 2 zircon (Black et al., 2004) which occurs assmall grains that are difficult to sample for LA ICP-MSanalysis (Woodhead and Hergt, 2005), the Mud Tankzircon that has rather low U and radiogenic Pb contents(Table 6) and the GJ-1 zircon (Jackson et al., 2004) thathas variable 207Pb/235U ratios within as well as betweenindividual zircon grains. From the available zirconreference samples, the Plešovice zircon has the highestcontent of U (Table 6) but this study provides noevidence for Pb loss from the actinide-rich domains in

Fig. 14. Comparison of Hf isotopic data obtained using different correction procedures for mass discrimination. a) Hf isotopic analyses of 91500 zircon. 179Hf/177Hf value of Patchett and Tatsumoto(1980) was used for mass bias correction of Hf, Yb and Lu isotopes; b) the same Hf data but with the 172Yb/173Yb ratio (Chu et al., 2002) applied for mass bias correction of Lu and Yb isotopes. The176Hf/177Hf values for 91500 after Wiedenbeck et al. (2005) and Wu et al. (2006) are also shown. c) and d) corresponding data for the Plešovice zircon. Shaded rectangles correspond to the calculatedmean 176Hf/177Hf values with 2SD uncertainty.

30J.

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1–35

Table 6Summary of natural zircon reference materials used/proposed for in-situ isotopic analysis and compilation of their U–Pb data

Reference material Age (Ma) Reference U (ppm) Pbrad (ppm) Grain size Comments

QGNGa 1850 (1) 35–1151 0.05–0.3 mm Available from rock outcrop; probable Pb lossAS3 1099 (2) 113–626 22–135 Up to 0.5 mm Available from rock outcrop; probable Pb loss91500 1065 (3) 71–86 13–16 Variable size; 238 g Almost exhausted supplyMud tank 732 (4) 6.1–36.5 0.73–4.39 mm–cm Available from rock outcropGJ-1 a, b 609 (5) 212–422 19.3–37.4 ca. 1 cm Several crystal from a gem dealerSL 13 a 572 (6) 240±20 N/A One single crystal; probable Pb lossZ6266 (Br266) 559 (7) 871–958 76.5–84.2 2–5 mm 2.5 g prepared for distributionR33 419 (8) 61–398 N/A Available from rock outcrop; probable Pb lossTemora 1 417 (9) 64–846 14.3 (aver.) Up to 0.6 mm Available from rock outcropTemora 2 417 (8) 82–320 0.05–0.3 mm Available from rock outcropPlešovice 337.1 This work 465– 3084 21–158 1–6 mm Available from rock outcrop; 500 g prepared

for distribution61.308Ab, 61.308Bb 2.5 (3) 132–242 0.064–0.131 0.49 and 0.71 g

crystalsLimited supply; very small sample

G42728Ab, G42728Bb 1 (3) 21.3–26 0.0026–0.0044 1.86 g crystals Limited supply; very small sample

References: (1) Black et al., 2003b (2) Paces and Miller 1993 (3) Wiedenbeck et al 1995 (4) Black and Gulson 1978 (5) Jackson et al., 2004 (6) Kinnyet al., 1991 (7) Stern 2001 (8) Black et al., 2004 (9) Black et al., 2003a. Other references used to compile this table: Woodhead and Hergt 2005;Schmitz et al., 2003; Stern and Amelin 2003.a Inhomogeneous Pb/U ratios.b Discordant age.


this zircon. The high concentration of U in the Plešovicezircon makes it a potentially suitable reference materialfor U–Pb dating of high-U zircons.

In addition to the U–Pb systematics, the 91500 andPlešovice zircons have also been characterized for Hfisotopes (Table 7). The 91500 zircon was reported tohave a heterogeneous Hf isotopic composition (Griffinet al., 2006, 2007), although this was recently disputed byCorfu (2007). Woodhead and Hergt (2005) proposed theTemora 2 and Mud Tank zircons as potential referencematerials for in-situ Hf isotopic measurements by LAICP-MS. While Temora 2 occurs as grains that are toosmall for repeat laser ablation sampling, the Mud Tank

Table 7Summary of natural zircon reference materials used/proposed for in-situ isot

Reference material Reference Hf (ppm) 176Hf/177Hf (±

QGNG (1) 10600±340 0.281612±0.0As3 (2)91500 (3) 5610– 29748 0.282303±0.0Mud tank (4) 0.282507±0.0GJ-1 (5)SL 13 (6)Z6266 (Br266) (7)R33 (8)Temora 1 (9)Temora 2 (8) 8310±90 0.282686±0.0Plešovice This work 8980–14431 0.282482±0.061.308A, 61.308B (3) 5350–6060 0.282977±0.0G42728A, G42728B (3)

References: (1) Black et al., 2003b (2) Paces andMiller 1993 (3) Wiedenbecket al., 1991 (7) Stern 2001 (8) Black et al., 2004 (9) Black et al., 2003a. Otheand Hergt 2005; Izuka and Hirata 2005; Nebel-Jacobsen et al., 2005; Wu et a

zircon is both homogeneous in Hf isotopic compositionand has a suitable size for laser ablation ICP-MS analysis(Table 7). The Plešovice zircon is also homogeneous inHf isotopes and it has a large range of Lu/Hf and Yb/Hfratios. Compared to Temora 2, the Plešovice zircon has alower Yb/Hf ratio which requires to make the isobaricinterference corrections using Hf (see Section 4.4).

5. Conclusions

The new ID-TIMS and laser ablation ICP-MS datingof the Plešovice zircon material gave consistent con-cordant U–Pb ages that are in average only 1Ma younger

opic analysis and compilation of their Lu–Hf data

2SD) Lu/Hf Yb/Hf

00004 0.0053

00021 0.0004–0.0217 0.0106–0.016800006 0.0003

0.0156

00008 0.0078 0.0262–0.055400013 0.0004–0.0015 0.0038–0.0245 (aver. 0.0100)00014 (1SD) 0.0126–0.0178 0.0302–0.0636

et al. 1995 (4) Black and Gulson 1978 (5) Jackson et al., 2004 (6) Kinnyr references used to compile this table: Amelin et al., 2000; Woodheadl., 2006; Griffin et al., 2006, 2007; Corfu 2007; Woodhead et al., 2004.


than the previously reported U–Pb age of zircon from thepotassic granulite by Aftalion et al. (1989). The newmeanID-TIMS U–Pb age of 337.13±0.37 Ma (2SD) isconsidered to represent the best age estimate for thePlešovice zircon.

Solution and laser ablation MC ICP-MS analyses of amultigrain sample of the Plešovice zircon suggest it hasa homogenous Hf isotopic composition. The low Lu/Hf(up to 0.001) and Yb/Hf (up to 0.025) ratios in the zirconresult in only a small influence of the choice of isobaricinterference correction procedure on the value anduncertainty of the corrected 176Hf/177Hf ratios. Themean 176Hf/177Hf value of 0.282482±0.000013 (2SD)is considered as the best estimate of the Hf isotopiccomposition of the Plešovice zircon.

Raman spectroscopy, optical and BSE imaging andtrace element analysis revealed the presence of stronglyradiation-damaged domains in ca. one third of studiedPlešovice zircon grains. These domains are rich inactinides (U and Th) and appear as bright patches onBSE images that can be easily avoided during the laserablation ICP-MS analysis. Although there has been nosignificant Pb loss found in these zones, they should beavoided during routine laser ablation ICP-MS analysisbecause of likely space charge effects and differentablation properties. On the other hand these areas could beused in U–Pb analyses of unknown zircons with similarlevel of actinides concentration. Occasional inclusions ofK-feldspar and apatite can be easily identified under anoptical microscope and avoided during the analysis.

Despite the significant variations in trace elementcontents that preclude the use of the Plešovice zircon asa reference material for in-situ trace elements analyses,the zircon is well suited as calibration and referencematerial for laser ablation ICP-MS U–Pb and Hfisotopic measurements. At this stage of characterization,the Plešovice zircon is not suitable as a referencematerial for the SIMS U–Pb isotopic dating.

Acknowledgements

We thank A.K. Kennedy for experimental assistanceon SHRIMP, F. Veselovský for assistance with mineralseparation and A. Wagner for sample preparation forRaman spectroscopy. Assistance with BSE imaging wasprovided by N. Groschopf and J. Götze acquired the CLimages. J. Sláma has been financially supported by theGrant Agency of the Academy of Sciences of the CzechRepublic (KJB300130701), Czech Science Foundation(205/05/0381) and the Charles University (264/2005/B-GEO). Two anonymous reviewers provided careful andconstructive reviews of the manuscript.

References

Aftalion, M., Bowes, D.R., Vrána, S., 1989. Early CarboniferousU–Pb zircon age of garnetiferous, perpotassic granulites, Blanský lesmassif, Czechoslovakia. Neues Jahrbuch für Mineralogie, Monat-sheftem, 4, 145–152.

Amelin, Y., Lee, D.C., Halliday, A.N., 2000. Early-middle Archaeancrustal evolution deduced from Lu–Hf and U–Pb isotopic stud-ies of single zircon grains. Geochimica et Cosmochimica Acta,64 (24), 4205–4225.

Black, L.P., Gulson, B.L., 1978. The age of the Mud Tank carbonatite,Strangways Range, Northern Territory. BMR Journal of AustralianGeology and Geophysics, 3, 227–232.

Black, L.P., Kamo, S.L., Allen, C.M., Aleinikoff, J.N., Davis, D.W.,Korsch, R.J., Foudoulis, C., 2003a. TEMORA 1: a new zirconstandard for phanerozoic U–Pb geochronology. Chemical Geology200, 155–170.

Black, L.P., Kamo, S.L., Allen, C.M., Davis, D.W., Aleinikoff, J.N.,Valley, J.W., Mundil, R., Campbell, I.H., Korsch, R.J.,Williams, I.S., Foudoulis, C., 2004. Improved Pb-206/U-218microprobe geochronology by the monitoring of a trace-element-related matrix effect; SHRIMP, ID-TIMS, ELA-ICP-MS andoxygen isotope documentation for a series of zircon standards.Chemical Geology 205, 115–140.

Black, L.P., Kamo, S.L., Williams, I.S., Mundil, R., Davis, D.W.,Korsch, R.J., Foudoulis, C., 2003b. The application of SHRIMP tophanerozoic geochronology: a critical appraisal of four zirconstandards. Chemical Geology 200, 171–188.

Blichert-Toft, J., Albarede, F., 1997. The Lu–Hf isotope geochemistryof chondrites and the evolution of the mantle–crust system. EarthPlanetary Science Letters 148, 243–258.

Carswell, D.A., O'Brien, P.J., 1993. Thermobarometry and geotec-tonic significance of high-pressure granulites: examples from theMoldanubian zone of the Bohemian Massif in Lower Austria.Journal of Petrology 34, 427–459.

Chakoumakos, B.C., Murakami, T., Lumpkin, G.R., Ewing, R.C.,1987. Alpha-decay-induced fracturing in zircon: the transition fromthe crystalline to the metamict state. Science 236, 1556–1559.

Chu, N.C., Taylor, R.N., Chavagnac, V., Nesbitt, R.W., Boella, R.M.,Milton, J.A., German, C.R., Bayon, G., Burton, K., 2002. Hfisotope ratio analysis using multi-collector inductively coupledplasma mass spectrometry: an evaluation of isobaric interferencecorrections. Journal of Analytical Atomic Spectrometry 17,1567–1574.

Cooke, R.A., 2000. High-pressure/temperature metamorphism in theSt. Leonhard Granulite Massif, Austria: evidence from intermedi-ate pyroxene-bearing granulites. International Journal of EarthSciences 89, 631–651.

Corfu, F., 2007. Comment to short-communication ‘Comment: Hf-isotope heterogeneity in zircon 91500′ by W.L. Griffin, N.J.Pearson, E.A. Belousova and A. Saeed (Chemical Geology 233(2006) 358–363). Chemical Geology 244, 350–353.

Crowley, J.L., Schoene, B., Bowring, S.A., 2007. U–Pb dating ofzircon in the Bishop Tuff at the millennial scale. Geology 35 (12),1123–1126.

Dallmeyer, R.D., Franke, W., Weber, K. (Eds.), 1995. Pre-PermianGeology of Central and Eastern Europe. Springer-Verlag, Berlin.

Debievre, P., Taylor, P.D.P., 1993. Table of the isotopic compositionsof the elements. International Journal of Mass Spectrometry andIon Processes 123, 149–166.

Dunstan, L.P., Gramlich, J.W., Barnes, I.L., Purdy, W.C., 1980.Absolute isotopic abundance and the atomic weight of a reference


sample of thallium. Journal of Research of the National Bureau ofStandards 85, 1–10.

Fiala, J., Fuchs, G., Wendt, J.I., 1995. Moldanubian Zone —stratigraphy. In: Dallmeyer, R.D., Franke, W., Weber, K. (Eds.),Pre-Permian Geology of Central and Eastern Europe. Springer,Berlin, pp. 417–428.

Fiala, J., Matějovská, O., Vaňková, V., 1987. Moldanubian granulitesand related rocks: petrology, geochemistry, and radioactivity.Rozpravy Československé akademie věd, řada matematických apřírodních věd 97, 1–102.

Firestone, R.B., Shirley, V.S., 1996. Table of Isotopes. Wiley, NewYork.Franke, W., 1989. Tectonostratigraphic units in the Variscan Belt of

Central Europe. Geological Society of America Special Paper 230,67–90.

Franke, W., 2000. The mid-European segment of the Variscides:tectonostratigraphic units, terrane boundaries and plate tectonicevolution. In: Franke, W., Haak, V., Oncken, O., Tanner, D. (Eds.),Orogenic Processes: Quantification and Modelling in the VariscanBelt. Geological Society, London, Special Publication, vol. 179.Geological Society, London, pp. 35–61.

Friedl, G., Cooke, R., Finger, F., McNaughton, N.J., Fletcher, A.,2003. U–Pb SHRIMP dating and trace element investigations onmultiple zoned zircons from a South-Bohemian granulite. Journalof the Czech Geological Society, 48, 51–52.

Fuchs, G., Matura, M., 1976. Zur Geologie des Kristallins dersüddlichen Böhmishe Masse. Jahre plante die GeologischeBundesanstalt 119, 1–43.

Gerdes, A., Zeh, A., 2006. Combined U–Pb and Hf isotope LA-(MC-)ICP-MS analyses of detrital zircons: comparison with SHRIMPand new constraints for the provenance and age of an Armoricanmetasediment in Central Germany. Earth and Planetary ScienceLetters 249, 47–62.

Gerstenberger, H., Haase, G., 1997. A highly effective emittersubstance for mass spectrometric Pb isotope ratio determinations.Chemical Geology 136, 309–312.

Götze, J., 2000. Cathodoluminescence microscopy and spectroscopyin applied mineralogy. Freiberger Forschungshefte C 485, 128 pp.

Griffin, W.L., Pearson, N.J., Belousova, E.A., Saeed, A., 2006.Comment: Hf-isotope heterogeneity in zircon 91500. ChemicalGeology 233, 358–363.

Griffin, W.L., Pearson, N.J., Belousova, E.A., Saeed, A., 2007. Reply to“Comment to short-communication ‘Comment: Hf-isotope hetero-geneity in zircon 91500’ by W.L. Griffin, N.J. Pearson, E.A.Belousova and A. Saeed (Chemical Geology 233 (2006) 358–363)”by F. Corfu. Chemical Geology 244, 354–356.

Hanchar, J.M., Finch, R.J., Hoskin, P.W.O., Watson, E.B., 2001.Strain-limited rare-earth element incorporation in zircon. EleventhAnnual V.M. Goldschmidt Conference, Abstract # 3712, LPIContrib No. 1088, Lunar Planet Inst, Houston (CD-ROM).

Horn, I., Rudnick, R.L., McDonough, W.F., 2000. Precise elementaland isotope ratio determination by simultaneous solution nebuliza-tion and laser ablation-ICP-MS: application to U–Pb geochronol-ogy. Chemical Geology 164, 281–301.

Horstwood, M.S.A., Foster, G.L., Parrish, R.R., Noble, S.R., Nowell,G.M., 2003. Common-Pb corrected in situ U–Pb accessorymineral geochronology by LA-MC-ICP-MS. Journal of AnalyticalAtomic Spectrometry 18, 837–846.

Hoskin, P.W.O., Schaltegger, U., 2003. The composition of zircon andigneous and metamorphic petrogenesis. In: Hanchar, J.M., J.M.,Hoskin, P.W.O. (Eds.), Zircon. Reviews in Mineralogy andGeochemistry, vol. 53. Mineralogical Society of America,Washington, DC., pp. 27–62.

Iizuka, T., Hirata, T., 2005. Improvements of precision and accuracy inin situ Hf isotope microanalysis of zircon using the laser ablation-MC-ICPMS technique. Chemical Geology, 220 (1–2), 121–137.

Irmer, G., 1985. Zum Einfluß der Apparatefunktion auf die Bestimmungvon Streuquerschnitten und Lebensdauern aus optischen Phononen-spektren. Experimentelle Technik der Physik 33, 501–506.

Jackson, S.E., Pearson, N.J., Griffin, W.L., Belousova, E.A., 2004.The application of laser ablation-inductively coupled plasma-massspectrometry to in situ U–Pb zircon geochronology. ChemicalGeology, 211, 47–69.

Jaffey, A.H., Flynn, K.F., Glendenin, L.E., Bentley,W.C., Essling, A.M.,1971. Precision measurement of half-lives and specific activities of235U and 228U. Physics Review Section C 4, 1889–1906.

Janoušek, V., Finger, F., Roberts, M., Frýda, J., Pin, Ch., Dolejš, D.,2004. Deciphering the petrogenesis of deeply buried granites:whole-rock geochemical constraints on the origin of largelyundepleted felsic granulites from the Moldanubian Zone of theBohemianMassif. Transactions of the Royal Society of Edinburgh:Earth Sciences 95, 141–159.

Janoušek, V., Krenn, E., Finger, F., Míková, J., Frýda, J., 2007.Hyperpotassic granulites from Blanský les (Moldanubian Zone,Bohemian Massif) revisited. Journal of Geosciences 52, 73–112.

Kelly, N.M., Harley, S.L., 2005. An integrated microtextural andchemical approach to zircon geochronology: refining the Archaeanhistory of the Napier Complex, east Antarctica. Contributions toMineralogy and Petrology 149, 57–84.

Ketchum, J.W.F., Jackson, S.E., Culshaw, N.G., Barr, S.M., 2001.Depositional and tectonic setting of the Paleoproterozoic LowerAillik Group, Makkovik Province, Canada: evolution of a passivemargin-foredeep sequence based on petrochemistry and U–Pb(TIMS and LAM-ICP-MS) geochronology. Precambrian Research105, 331–356.

Kinny, P.D., Compston, W., Williams, I.S., 1991. A reconnaissanceion-probe study of hafnium isotopes in zircons. Geochimica etCosmochimica Acta 55, 849–859.

Kodym, O., et al. (Ed.), 1981. Základní Geologická Mapa ČSSR1:25 000. List 32-223 Kamenný Újezd. Ústrední ústav geologický,Praha (in Czech).

Košler, J., Fonneland, H., Sylvester, P., Tubrett, M., Pedersen, R.B.,2002. U–Pb dating of detrital zircons for sediment provenancestudies — a comparison of laser ablation ICP-MS and SIMStechniques. Chemical Geology 182, 605–618.

Košler, J., Sylvester, P.J., 2003. Present trends and the future of zirconin geochronology: laser ablation ICP-MS. In: Hanchar, J.M., J.M.,Hoskin, P.W.O. (Eds.), Zircon. Reviews in Mineralogy andGeochemistry, vol. 53. Mineralogical Society of America,Washington, DC., pp. 243–275.

Kotková, J., Gerdes, A., Parrish, R.R., Novák, M., 2003. Pressure–temperature–time evolution of granulite clasts from LowerCarboniferous conglomerates — evidence for rapid exhumationat the eastern margin of the Variscan Bohemian Massif.Geophysical Research Abstracts 5, 434.

Kotková, J., Harley, S.L., 1997. Mineral controls on the traceelement and REE geochemistry of high-pressure leucogranulitesfrom the Bohemian Massif. Journal of the Czech GeologicalSociety 42, 40.

Krogh, T.E., 1973. Low-contamination method for hydrothermaldecomposition of zircon and extraction of U and Pb for isotopicage determinations. Geochimica et Cosmochimica Acta 37,485–494.

Kröner, A., O'Brien, P.J., Nemchin, A.A., Pidgeon, R.T., 2000. Zirconages for high pressure granulites from South Bohemia, Czech


Republic, and their connection to Carboniferous high temperatureprocesses. Contributions to Mineralogy and Petrology 138,127–142.

Kröner, A., Wendt, I., Liew, T.C., Compston, W., Todt, W., Fiala, J.,Vaňková, V., Vaněk, J., 1988. U–Pb zircon and Sm–Nd modelages of high-grade Moldanubian metasediments, BohemianMassif, Czechoslovakia. Contributions to Mineralogy and Petrol-ogy 99, 257–266.

Lapen, T.J., Mahlen, N.J., Johnson, C.M., Beard, B.L., 2004. Highprecision Lu and Hf isotope analyses of both spiked and unspikedsamples: a new approach. Geochemistry, Geophysics andGeosystems 5. doi:10.1029/2003GC000582, Q01010.

Lee, J.K.W., Tromp, J., 1995. Self-induced fracture generation inzircon. Journal of Geophysical Research 100, 17753–17770.

Ludwig, K.R., 1980. Calculation of uncertainties of U–Pb isotopedata. Earth and Planetary Science Letters 46 (2), 212–220.

Ludwig, K.R., 2003. Isoplot/Ex Version 3.00: a GeochronologicalToolkit for Microsoft Excel. Berkeley Geochronology Center,Berkeley, CA.

Matte, P., Maluski, H., Rajlich, P., Franke, W., 1990. Terraneboundaries in the Bohemian Massif: result of large-scale Variscanshearing. Tectonophysics 177, 151–170.

Mattinson, J.M., 2003. CA (chemical abrasion)-TIMS: high-resolutionU–Pb zircon geochronology combining high-temperature annealingof radiation damage and multi-step partial dissolution analysis. FallMeeting Suppl., Abstract V22E-06. Eos, Trans, AGU, vol. 84 (46).

Mattinson, J.M., 2005. Zircon U–Pb chemical abrasion (“CA-TIMS”)method: combined annealing and multi-step partial dissolutionanalysis for improved precision and accuracy of zircon ages.Chemical Geology 220, 47–66.

Murakami, T., Chakoumakos, B.C., Ewing, R.C., Lumpkin, G.R.,Weber, W.J., 1991. Alpha-decay event damage in zircon. AmericanMineralogist 76, 1510–1532.

Nasdala, L., Irmer, G., Wolf, D., 1995. The degree of metamictizationin zircon: a Raman spectroscopic study. European Journal ofMineralogy 7, 471–478.

Nasdala, L., Kronz, A., Hanchar, J.M., Tichomirowa, M., Davis, D.D.,Hofmeister, W., 2006. Effects of natural radiation damage on back-scattered electron images of single-crystals of minerals. AmericanMineralogist 91, 1738–1746.

Nasdala, L., Wenzel, M., Vavra, G., Irmer, G., Wenzel, T., Kober, B.,2001. Metamictisation of natural zircon: accumulation versusthermal annealing of radioactivity-induced damage. Contributionsto Mineralogy and Petrology 141, 125–144.

Nasdala, L., Zhang, M., Kempe, U., Panczer, G., Gaft, M., Andrut, M.,Plötze, M., 2003. Spectroscopic methods applied to zircon. In:Hanchar, J.M., J.M., Hoskin, P.W.O. (Eds.), Zircon. Reviews inMineralogy and Geochemistry, vol. 53. Mineralogical Society ofAmerica, Washington, DC, pp. 427–467.

Nebel-Jacobsen, Y., Scherer, E.E., Munker, C., Mezger, K., 2005.Separation of U, Pb, Lu, and Hf from single zircons for combinedU–Pb dating and Hf isotope measurements by TIMS and MC-ICPMS. Chemical Geology, 220 (1–2), 105–120.

O'Brien, P.J., Rötzler, J., 2003. High-pressure granulites: formation,recovery of peak conditions and implications for tectonics. Journalof Metamorphic Geology 21, 3–20.

Owen, J.V., Dostal, J., 1996. Contrasting corona structures in maficgranulite from the Blanský Les complex, Bohemian Massif, CzechRepublic. Canadian Mineralogist 34, 959–966.

Paces, J.B., Miller, J.D., 1993. Precise U–Pb ages of Duluth Complexand related mafic intrusions, northeastern Minnesota: geochronolo-gical insights into physical, petrogenetic, paleomagnetic and

tectonomagmatic processes associated with the 1.1 Ga midcontinentrift system. Journal of Geophysical Research 98, 13997–14013.

Patchett, P.J., 1983. Importance of the Lu–Hf isotopic system instudies of planetary chronology and chemical evolution. Geochi-mica et Cosmochimica Acta 47, 81–91.

Patchett, P.J., Tatsumoto, M., 1980. A routine high-precision methodfor Lu–Hf isotope geochemistry and chronology. Contributions toMineralogy and Petrology 75, 263–267.

Pupin, J.P., 1980. Zircon and granite petrology. Contributions toMineralogy and Petrology 73, 207–220.

Roberts, M.P., Finger, F., 1997. Do U–Pb zircon ages from granulitesreflect peak metamorphic conditions? Geology 25, 319–322.

Scherer, E.E., Münker, C., Mezger, K., 2001. Calibration of the Lu–HfClock. Science 293, 683–687.

Schmitz, M.D., Bowring, S.A., Ireland, T.R., 2003. Evaluation ofDuluth Complex anorthositic series (AS3) zircon as a U–Pbgeochronological standard, new high-precision isotope dilutionthermal ionization mass spectrometry results. Geochimica etCosmochimica Acta, 67 (19), 3665–3672.

Schmitz, M.D., Schoene, B., 2007. Derivation of isotope ratios, errorsand error correlations for U–Pb geochronology using 205Pb–235U–(233U)-spiked isotope dilution thermal ionization massspectrometric data. Geochemistry, Geophysics and Geosystems 8.doi:10.1029/2006GC001492 (G3), Q08006.

Sláma, J., Košler, J., Pedersen, R.B., 2007. Behaviour of zircon inhigh-grade metamorphic rocks— evidence from Hf isotopes, traceelements and textural studies. Contributions to Mineralogy andPetrology 154, 335–356.

Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial lead.isotope evolution by a two-stage model. Earth and PlanetaryScience Letters 26, 207–221.

Stern, R.A., 2001. A new isotopic and trace element standard forthe ion microprobe: preliminary TIMS U–Pb and electron mi-croprobe data, current research. Radiogenic Age and IsotopicStudies: Report 14. Geological Survey of Canada, Ottawa,Canada.

Stern, R.A., Amelin, Y., 2003. Assessment of errors in SIMS zirconU–Pb geochronology using a natural zircon standard and NISTSRM 610 glass. Chemical Geology, 197 (1–4), 111–142.

Svojtka, M., Košler, J., Venera, Z., 2002. Dating granulite-faciesstructures and the exhumation of lower crust in the MoldanubianZone of the BohemianMassif. International Journal of Earth Sciences91, 373–385.

Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: itsComposition and Evolution. Blackwell, Oxford. 312 pp.

van Breemen, O., Aftalion, M., Bowes, D.R., Dudek, A., Mísař, Z.,Povondra, P., Vrána, S., 1982. Geochronological studies of theBohemian Massif, Czechoslovakia, and their significance in theevolution of Central Europe. Transactions of the Royal Society ofEdinburgh, Earth Sciences 73, 89–108.

Vrána, S., 1989. Perpotassic granulites from southern Bohemia — anew rock-type derived from partial melting of crustal rocks underupper mantle conditions. Contributions to Mineralogy andPetrology 103, 510–522.

Vrána, S., Blümel, P., Petrakakis, K., 1995. Metamorphic evolution. In:Dallmeyer, R.D., Franke,W.,Weber,K. (Eds.), Pre-PermianGeologyof Central and Eastern Europe. Springer, Berlin Heidelberg NewYork, pp. 453–466.

Wendt, J.I., Kröner, A., Fiala, J., Todt, W., 1994. U–Pb zircon andSm–Nd dating of Moldanubian HP/HT granulites from southBohemia, Czech Republic. Journal of the Geological Society ofLondon 151, 83–90.


Whitehouse, M.J., Claesson, S., Sunde, T., Vestin, J., 1997. Ion-microprobeU–Pb zircon geochronology and correlation ofArchaeangneisses from the Lewisian Complex of Gruinard Bay, north-westScotland. Geochimica et Cosmochimica Acta 61, 4429–4438.

Whitehouse, M.J., Kamber, B., Moorbath, S., 1999. Age significanceof U–Th–Pb zircon data from early Archaean rocks of westGreenland—a reassessment based on combined ion-microprobeand imaging studies. Chemical Geology 160, 201–224.

Wiedenbeck, M., Alle, P., Corfu, F., Griffin, W.L., Meier, M., Oberli,F., von Quadt, A., Roddick, J.C., Spiegel, W., 1995. Three naturalzircon standards for U–Th–Pb, Lu–Hf, trace element and REEanalyses. Geostandards Newsletter 19, 1–23.

Wiedenbeck, M., Hanchar, J.M., Peck, W.H., Sylvester, P., Valley, J.,Whitehouse, M., Kronz, A., Morishita, Y., Nasdala, L., 2004.

Further characterisation of the 91500 zircon crystal. Geostandardsand Geoanalytical Research 28 (1), 9–39.

Woodhead, J.D., Hergt, J.M., 2005. A preliminary appraisal of sevennatural zircon reference materials for in situ Hf isotope determina-tion. Geostandards and Geoanalytical Research 29 (2), 183–195.

Woodhead, J., Hergt, J., Shelley, M., Eggins, S., Kemp, R., 2004.Zircon Hf-isotope analysis with an excimer laser, depth profiling,ablation of complex geometries, and concomitant age estimation.Chemical Geology 209 (1–2), 121–135.

Wu, F.Y., Yang, Y.H., Xie, L.W., Yang, J.H., Xu, P., 2006. Hfisotopic compositions of the standard zircons and baddeleyitesused in U–Pb geochronology. Chemical Geology 234 (1–2),105–126.

plešovice zircon a new natural reference material for pb and ......plešovice zircon — a new...

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