Available online at www.sciencedirect.com
Chemical Geology 249 (2008) 1 – 35
www.elsevier.com/locate/chemgeo
Plešovice zircon — A new natural reference material for
U–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, Norway
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 Republic
d
NERC Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK
e
Department of Geosciences, Boise State University, Boise, ID 83702, USA
f
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 5S7
h
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, Austria
j
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
b
Received 13 August 2007; received in revised form 16 November 2007; accepted 20 November 2007
Editor: R.L. Rudnick
Abstract
Matrix-matched calibration by natural zircon standards and analysis of natural materials as a reference are the principle methods
for achieving accurate results in microbeam U–Pb dating and Hf isotopic analysis. We describe a new potential zircon reference
material for laser ablation ICP-MS that was extracted from a potassic granulite facies rock collected in the southern part of the
Bohemian Massif (Plešovice, Czech Republic).
Data from different techniques (ID-TIMS, SIMS and LA ICP-MS) and several laboratories suggest that this zircon has a
concordant U–Pb age with a weighted mean 206Pb/238U date of 337.13 ± 0.37 Ma (ID-TIMS, 95% confidence limits, including
tracer calibration uncertainty) and U–Pb age homogeneity on the scale used in LA ICP-MS dating. Inhomogeneities in trace
element composition due to primary growth zoning prevent its use as a calibration standard for trace element analysis. The content
of U varies from 465 ppm in pristine parts of the grains to ~ 3000 ppm in actinide-rich sectors that correspond to pyramidal faces
with 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
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 (N 0.9 wt.% Hf) is
homogenous within and between the grains with a mean 176Hf/177Hf value of 0.282482 ± 0.000013 (2SD). The age and Hf isotopic
homogeneity of the Plešovice zircon together with its relatively high U and Pb contents make it an ideal calibration and reference
material for laser ablation ICP-MS measurements, especially when using low laser energies and/or small diameters of laser beam
required 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 Uand Th-decay is the most precise and accurate technique
for establishing the age of high-temperature events in
magmatic and metamorphic rocks. The method is also
widely applied to dating of detrital minerals in
sedimentary provenance studies. Recent introduction
of new techniques, such as U–Pb zircon (ZrSiO4) dating
by laser ablation ICP-MS (e.g., Košler and Sylvester,
2003 and reference therein), requires development of
reference materials, both for matrix-matched age
calibration and for quality control purposes. The
requirements for such zircon reference materials are
(i) homogeneity and concordance of radiogenic Pb/U
ratios, (ii) low common Pb content, (iii) moderate U
content (tens to hundreds ppm), (iv) crystalline (nonmetamict) structure, (v) size suitable for repeated laser
ablation analyses (grains several mm to cm in diameter)
and (vi) availability to the scientific community.
Previous attempts to produce chemically homogeneous
synthetic zircon material (e.g., Hanchar et al., 2001)
have failed because Pb does not readily enter the
structure of zircon and also because of the strain
imposed on the crystal lattice.
Zircon reference material for in-situ Hf isotopic analysis by laser ablation ICP-MS should have (i) homogeneous Hf isotopic composition, both within and between
individual grains, (ii) moderate Hf content (low % level)
and preferably homogeneous Hf concentration, and
(iii) low Lu/Hf and Yb/Hf values and it should also
occur as mm–cm sized grains and be available in sufficient
quantity.
There are several natural zircon samples (e.g., 91500,
Temora, Mud Tank, GJ-1, SL13) that have been
proposed as potential calibration and reference materials
for in-situ U–Pb isotopic analysis but only a few meet
the criteria for a “good” reference material and they are
often not available in quantities needed for laser ablation
ICP-MS analysis. From these the “91500” zircon
(Wiedenbeck et al., 1995) has been most often used as
a 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. Because
of its limited amount and extensive use in microanalysis,
the supply of the 91500 zircon reference material has
been almost exhausted (Woodhead and Hergt, 2005).
This study presents new isotopic data for a natural
zircon extracted from a high-temperature potassic
granulite from the southern Bohemian Massif (locality
Plešovice [read Pleschovitze] in the Czech Republic)
that appears to be a suitable reference material for laser
ablation ICP-MS U–Pb dating and Hf isotopic measurements. This zircon meets most of the criteria for a
calibration and reference material and it can be obtained
on request from Department of Earth Science at the
University of Bergen (http://www.geo.uib.no/ceia).
2. Sample and geological setting
The studied zircon comes from a potassic granulite
that was first described by Vrána (1989) and recently also
by Janoušek et al. (2007) from the Plešovice quarry
situated in the eastern part of the Blanský les granulite
body, ca. 5 km NNE of the town of Český Krumlov
(Fig. 1) in the southern Bohemian Massif, Czech
Republic. The potassic granulite forms up to 2 m thick
foliated layers in the northern part of the present-day's
fourth level of the quarry (Fig. 2; N: 48°52′17″, E: 14°
20′28″). The layers are oriented concordantly to the
dominant metamorphic foliation in the surrounding
felsic granulites. This foliation formed as a result of
isothermal decompression that followed the peak
granulite 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 to
as hyperpotassic (up to 13 wt.% K2O), granulite in the
APQ diagram for plutonic rocks reflects its alkalifeldspar syenitic to alkali-feldspar granitic character
(Vrána, 1989; Janoušek et al., 2007). The granulite is
made up mostly of K-feldspar (up to 93%) and garnet
relatively rich in pyrope (~ 30 molar %), which has been
partly replaced by biotite during the retrograde stages of
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
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 after
Svojtka et al., 2002.
3
4
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
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 Autumn
2006) with marked location of the zircon bearing potassic granulite.
the metamorphic evolution. Apatite, monazite and
zircon are accessories; rutile is present in the form of
tiny exsolved needles in garnet. The content of zircon in
the granulite is up to 0.6 wt.% and it is variable on the
scale of tens of centimeters; higher accumulations of
zircon crystals were found in the biotite (originally
garnet)-rich domains.
The potassic granulite is thought to represent a noneutectic melt (Vrána, 1989; Janoušek et al., 2007),
possibly derived from the protolith of the adjacent felsic
granulites in the Blanský les massif (Janoušek et al.,
2007). The Blanský les massif represents part of the
allochthonous Gföhl unit (Fuchs and Matura, 1976;
Matte et al., 1990; Fiala et al., 1995; Vrána et al., 1995;
Franke, 2000), which forms the uppermost tectonic
member of the Moldanubian Zone, the core crystalline
unit of the Variscan orogen in Europe (Dallmeyer et al.,
1995). The Gföhl unit consists mainly of felsic
granulites, with subordinate mafic granulites, serpentinized garnet peridotites, pyroxenites and eclogites
(Fuchs and Matura, 1976; Franke, 1989; Fiala et al.,
1995). Migmatitic granitic gneisses (Gföhl gneisses) in
the lower part of the Gföhl unit probably also represent
overprinted felsic granulites (Fuchs and Matura, 1976;
Fiala et al., 1995).
The Blanský les massif contains mainly felsic garnet
granulite gneisses (ca. 80%) with subordinate mafic
pyroxene ± 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 with
estimated peak conditions of 900–1050 °C and 1.5–
2 GPa (Carswell and O'Brien, 1993; Kotková and
Harley, 1997; O'Brien and Rötzler, 2003). Following
the peak of metamorphism, there was almost isothermal
decompression to mid-crustal level pressures with an
overprint at 800–900 °C and 0.8–1.2 GPa (Cooke,
2000) and subsequent near-isobaric cooling. The retrogression of granulites is reflected in garnet breakdown
and formation of secondary-corona structures, retrogression 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 by
a number of U–Pb zircon ages at ca. 340 Ma (van
Breemen et al., 1982; Kröner et al., 1988; Aftalion et al.,
1989; Wendt et al., 1994; Kröner et al., 2000; Friedl
et al., 2003; Kotková et al., 2003). This age has often
been interpreted as corresponding to the time of
granulite HP–HT metamorphic peak, but Roberts and
Finger (1997) argued for zircon crystallization from
partial melt during the retrograde P–T path, and Kröner
et al. (2000) and Janoušek et al. (2004) proposed that the
zircons that grew under granulite peak conditions and
subsequently during the decompression are similar in
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
age. Some zircon cores from granulites of the Blanský
les gave a U–Pb age of ca. 470 Ma (Kröner et al., 2000),
consistent with a whole-rock Rb–Sr age obtained by
Janoušek et al. (2004) and interpreted by these authors
as corresponding to the age of the granulite protolith.
The zircons from potassic granulite in the Plešovice
quarry 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 mineral
phases of the potassic granulite as up to 0.5 cm (rarely
larger) equant or prismatic (Fig. 3), pale pink to brown
idiomorphic crystals. The external shape of the crystals
corresponds to zircons from peralkaline granites and
syenites in the classification of Pupin (1980). Mineral
inclusions 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 the
Plešovice quarry was crushed down to a grain size of
5
b 7 mm and gravimetric separation in a water-filled
sluice box was used to obtain a heavy mineral fraction
containing almost exclusively zircon. Approximately
250 kg of the rock material yielded ca. 500 g of good
quality zircon crystals between 1 and 6 mm in size.
To ensure thorough characterization of the studied
zircon, the chemical and isotopic analyses were conducted using a range of different techniques in several
laboratories (ID-TIMS: Massachusetts Institute of Technology (MIT), University of Geneva (UNIGE), NERC
Isotope Geosciences Laboratory (NIGL), Boise State
University (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 am Main (JWG) and
Memorial University of Newfoundland (MUN); MC
ICP-MS: University of Bergen, J.W. Goethe University of
Frankfurt am Main and NERC Isotope Geosciences
Laboratory (NIGL); Raman spectroscopy: University of
Vienna). Where possible, the measurements were reproduced by similar techniques in different laboratories.
Fig. 3. a) Large, short prismatic crystal of the Plešovice zircon in K-feldspar matrix of the host potassic granulite; b) typical crystal shapes of the
Plešovice zircons with prevailing equant morphology (top) and less common prismatic morphology (bottom).
6
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
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 the
references 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 for
isotopic analyses in solution (ID-TIMS U–Pb dating
and Hf isotopic analyses by MC ICP-MS — see
below). For solid sample analyses by ”in situ” techniques, the zircons were mounted in 1 in. epoxy resin
blocks, ground down to expose their internal textures,
and polished to obtain flat surfaces suitable for electron
microanalysis, cathodoluminescence (CL) and backscattered electron (BSE) imaging, ion probe (SIMS)
and laser ablation (LA) ICP-MS isotopic measurements. Sample mounts were coated with carbon
and gold prior to electron microbeam and ion probe
analyses, respectively.
3.1. Trace element concentration measurements
Trace element contents in the Plešovice zircon were
acquired at University of Bergen using a ThermoFinnigan Element 2 sector field ICP-MS coupled to a
213 NdYAG laser (New Wave Research UP-213). The
laser was fired at a repetition rate of 5 Hz, using 10 J/
cm2 laser energy, spot size of 53 μm and He as a sample
carrier gas. Synthetic silicate glass NIST-610 was used
to calibrate the trace element concentration data, repeat
measurements of NIST-612 and BCR-2 silicate glasses
were carried out for quality control purposes; average
signal intensity for NIST-610 was 2.2 × 107 cps on the
mass 29Si. Data for the gas blank were acquired for 45 s
followed by 120 s of laser ablation signal. Si was used as
internal standard to correct for differences in the ablation
yields between zircon and glass standards, timeresolved signal data were processed using the Glitter
software package.
3.2. Backscattered electron and cathodoluminiscence
imaging, Raman spectroscopy
The CL image presented in Fig. 4 was acquired using
a Premier American Technologies ELM-3R “cold
cathode” luminoscope operating in regulated mode at
12 kV and 0.7 mA. The zircon crystals studied with
colour CL were mounted in epoxy and polished to
reveal the crystal interiors. The CL images were
recorded using a KAPPA DX-30C Peltier cooled
charge-coupled device (CCD) digital camera interfaced
to an Olympus BX-50 microscope. Zircon crystals for
Raman spectroscopy were prepared as uncovered,
doubly polished thin sections (thickness ∼ 30 µm)
attached to a glass slide suitable for optical microscopy
in transmitted light. This preparation makes possible to
check the internal zoning of crystals, as zones that differ
in birefringence are easily recognized in the crosspolarized light mode. Backscattered electron (BSE)
images were acquired using a JEOL 8900 RL electron
microprobe, and cathodoluminescence (CL) images
were obtained in a “hot-cathode” system HC1-LM (for
details cf. Götze, 2000).
Raman spectra were obtained using a Renishaw RM
1000 system. This notch filter-based spectrometer was
equipped with Leica DMLM optical microscope and
Peltier-cooled, Si-based CCD (charge-coupled device)
detector. Spectra were excited with the 632.8 nm
emission of a He–Ne laser (8 mW). With the Leica
50× objective (numerical aperture 0.55), the lateral
resolution was ca. 3 μm. The spectral resolution was
determined at 2.2 cm− 1 and the wavenumber accuracy
was ca. ± 1 cm− 1 (calibrated with the Rayleigh line and
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
Ne lamp emissions). The impact of the electron beam
during electron microprobe analysis may cause partial
annealing of the radiation damage (e.g., Nasdala et al.,
2003). To avoid any analytical artifacts, Raman measurements have therefore always been done before electron probe analysis.
Raman bands were fitted assuming Lorentzian–
Gaussian band profiles. Real band FWHM (full width
at half band maximum) values were calculated by
correcting measured FWHMs according to
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
s
b ¼ bs 1 2
bs
(Irmer, 1985), where b is the real (i.e. corrected) FWHM,
bs is the measured FWHM, and s is the spectral resolution 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 without
cracks and inclusions were selected for dating. Zircon
was subjected to a modified version of the chemicalabrasion technique (CA; Mattinson, 2003; 2005). Zircon
was placed in a muffle furnace at 900 ± 20 °C for 60 h in
quartz beakers before being transferred to 300 μl Teflon
FEP microcapsules, placed in a Parr vessel, and leached
in 120 μl of 29 M HF for 12 h at 180 °C. The HF was
removed, and grains were rinsed in ultrapure H2O,
immersed in 30% HNO3, ultrasonically cleaned for an
hour, and fluxed on a hotplate at 80 °C for an hour. The
HNO3 was removed and the grains were again rinsed in
ultrapure H2O, before being loaded into 300 μl Teflon
FEP microcapsules and spiked with the EARTHTIME
mixed 205 Pb–233 U–235U tracer (ET535). Zircon was
dissolved in Parr vessels in 120 μl of 29 M HF with a
trace of 30% HNO3 at 210 °C for 48 h, dried to
fluorides, and then re-dissolved in 6 M HCl at 180 °C
overnight. U and Pb were separated using an HCl-based
anion-exchange chromatographic procedure (Krogh,
1973). Pb and U were loaded together on a single Re
filament in a silica-gel/phosphoric acid mixture (Gerstenberger and Haase, 1997) before measurement by
TIMS at the respective institutions. UNIGE and MIT
measurements are analyses of single zircon fragments
that were aliquoted in two and measured at the separate
institutions (e.g. MIT_1 is the same dissolved and
spiked solution as UNIGE_1, split in two after anion
exchange chemistry) in order to test for detector related
biases.
7
U and Pb isotopic measurements at MIT were performed on a VG Sector-54 multi-collector TIMS. Pb was
measured by peak-hopping on a Daly detector. Mass
fractionation effects were corrected for 0.25 ± 0.04/a.m.u.
U isotopic measurements were made in static Faraday
mode on 1011 Ω resistors.
Measurements at UNIGE were performed on a
Thermo Triton TIMS. Pb was measured on a MasCom
SEM detector and corrected for 0.13 ± 0.04%/a.m.u.
mass fractionation. Linearity and deadtime correction on
the SEM were monitored using repeated analyses of
NBS982, NBS983 and U500. Uranium was measured in
static Faraday mode on 1012 Ω resistors.
Measurements at NIGL were performed on a Thermo
Triton TIMS. Two Pb analyses were measured on a
MasCom SEM detector and corrected for 0.16 ± 0.04%/
a.m.u. mass fractionation. The rest of the Pb analyses
were done in a multidynamic Faraday-SEM mode, peak
hopping mass 204 and 205 in the SEM, which corrects
for the SEM gain in real time. These data were corrected
for mass fractionation of 0.12 ± 0.04%/a.m.u. Linearity
and deadtime correction on the SEM were monitored
using repeated analyses of NBS982 and U500. Uranium was measured in static Faraday mode on 1011 Ω
resistors.
Measurements at BSU were made on a GV IsoprobeT TIMS. One Pb analysis was measured on a Daly
detector corrected for 0.22 ± 0.04%/a.m.u. mass fractionation. The other analyses were performed using a twosequence Faraday–Daly routine, peak hopping masses
204 and 205 in the Daly, which corrects for the Daly
gain in real time. Linearity and deadtime correction on
the SEM were monitored using repeated analyses of
NBS982, NBS981 and U500. Uranium was run in static
Faraday mode on 1011 Ω resistors.
U was run as the oxide and corrected for isobaric
interferences with an 18O/16O of 0.00205, which was
confirmed by measuring 272(UO2)/270(UO2) on large ion
beams at NIGL, MIT and UNIGE. U mass fractionation
from all laboratories was calculated in real time using the
ET535 tracer solution. U–Pb dates and uncertainties were
calculated 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 initial 230Th disequilibrium using a Th/U[magma] of 4 ± 1
applying the algorithms of Crowley et al. (2007), resulting in an increase in the 206Pb/238U dates of ~100 kyr
and uncertainties in calculated Th/U for zircons of
~0.002. Common Pb in the analyses was attributed to
blank and subtracted based on the isotopic composition
and associated uncertainties analyzed over time in each
laboratory. Because of the radiogenic character of these
8
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
zircons, the reduced data are insensitive to reasonable
variations in the composition of this correction. U blanks
are difficult to precisely measure, but are b 0.1 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 hightemperature annealing followed by a HF leaching step
was used (Mattinson, 2005). Annealing was performed
by loading several zircon grains and fragments in quartz
crucibles and placing them into a furnace at 900 °C
for approximately 60 h. Subsequently, for the leaching
(chemical abrasion) step, zircons were transferred to
3 ml screw-top Savillex vials with ca. 120 μl concentrated HF. Loosely capped Savillex vials were arranged
into a Teflon par vessel with 1 ml concentrated HF, and
placed in an oven at 180°C for 12–15 h. After the partial
dissolution step, the leachate was completely pipetted
out and the remaining zircons were fluxed for several
hours in 6 N HCl (on a hotplate at a temperature of ca.
80 °C), rinsed in ultrapure H2O and then placed back on
the hot plate for an additional 30 min in 4 N HNO3 for a
“clean-up” step. The acid solution was removed and the
fraction was again rinsed several times in ultra-pure
water and acetone in an ultrasonic bath. Zircons were
weighed and loaded for dissolution into pre-cleaned
miniaturized Teflon vessel. After adding a mixed
205
Pb–235U spike zircons were dissolved in 63 μl concentrated HF with a trace of 7 N HNO3 at 180 °C for
5 days, evaporated and re-dissolved overnight in 36 μl
3 N HCl at 180 °C. Pb and U were separated by anion
exchange chromatography in 40 μl micro-columns,
using minimal amounts of ultra-pure HCl, and finally
dried down with 3 μl 0.2 N or 0.06 N H3PO4.
Isotopic analysis was performed on a MAT262 mass
spectrometer equipped with an ETP electron multiplier
backed by a digital ion counting system which was
calibrated by repeated analyses of the NBS 982 and
U500 standards. Mass fractionation effects were corrected for 0.09 ± 0.05%/a.m.u. Both lead and uranium
were loaded with 1 μl of silica gel-phosphoric acid
mixture on outgassed single Re-filaments, and Pb as
well as U (as UO2+) isotopes measured sequentially on
the electron multiplier. Total procedural common Pb
amounts were measured at 1.9 to 11.6 pg and were
attributed solely to laboratory contamination. The
uncertainties of blank lead isotopic composition, mass
fractionation correction, and tracer calibration were
taken into account and propagated to the uncertainties of
each individual isotopic ratio and age. The algorithms of
Ludwig (1980) were used to calculate ages and their
uncertainties.
3.3.3. SIMS U–Pb dating (Swedish Museum of Natural
History in Stockholm)
High spatial resolution U–Pb data were generated
using a Cameca IMS1270 large-format ion microprobe
at the Nordsim facility, Swedish Museum of Natural
History. Detailed analytical methods have been
described previously in Whitehouse et al. (1997 and
1999). In all cases, a defocused O2− primary beam was
used to project the image of a 150 µm aperture onto the
sample, generating elliptical, flat-bottomed craters of
nominal c. 15 µm (long axis). Complete U–Pb analyses
at a mass resolution (M/ΔM) of c. 5000 were performed
using a peak switching routine, with a single ioncounting electron multiplier (EM) as the detection
device. An energy window of 60 eV was used
throughout, with adjustments for possible sample
charging made by scanning the sample high voltage
using the 90Zr216O peak. Precise mass calibration was
maintained by using an automatic routine in the Cameca
CIPS software to scan over large peaks and extrapolate
the mass to B-field curve for peaks between these
reference points (e.g., Pb-isotopes were calibrated by
centring the 94Zr216O peak at nominal mass 204 and the
177
Hf16O2 peak at nominal mass 209). Pb/U ratios,
elemental concentrations and Th/U ratios were calibrated relative to the zircon 91500 reference material
which has an age of 1065 Ma (Wiedenbeck et al., 1995).
Common Pb was monitored using the 204 Pb signal and
corrections were made using the modern terrestrial Pb
composition from the model of Stacey and Kramers
(1975), assuming that the common Pb is largely surface
contamination introduced during sample preparation.
Cathodoluminescence images of zircons analyzed by
ion microprobe were obtained using a Phillips ESEM at
Stockholm University and were used to locate ablation
sites. After analysis, SE images of craters were obtained
with a Hitachi S4300 scanning electron microscope at
the Swedish Museum of Natural History to confirm that
the intended target had been analyzed.
3.3.4. Laser ablation ICP-MS U–Pb dating (University
of Bergen)
Isotopic analysis of N 10 zircon grains by laser
ablation ICP-MS followed the technique described in
Košler et al. (2002) and Košler and Sylvester (2003). A
Thermo-Finnigan Element 2 sector field ICP-MS
coupled to a 213 NdYAG laser (New Wave Research
UP-213) at Bergen University was used to measure Pb/U
and Pb isotopic ratios in zircons. The sample introduction system was modified to enable simultaneous
nebulisation of a tracer solution and laser ablation
of the solid sample (Horn et al., 2000). Natural Tl
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
(205Tl/203Tl = 2.3871 — Dunstan et al., 1980), 209 Bi and
enriched 233U and 237Np (N 99%) were used in the tracer
solution, which was aspirated to the plasma in an argon–
helium carrier gas mixture through an Apex desolvation
nebuliser (Elemental Scientific) and a T-piece tube
attached to the back end of the plasma torch. A helium
gas line carrying the sample from the laser cell to the
plasma was also attached to the T-piece tube.
The laser was set up to produce energy density of ca
2 J/cm2 at a repetition rate of 10 Hz. The laser beam was
imaged on the surface of the sample placed in the ablation
cell, which was mounted on a computer-driven motorized
stage of a microscope. During ablation the stage was
moved at a speed of 10 μm/second beneath the stationary
laser beam to produce a linear raster (ca 20 × 200 μm) in
the sample. Typical acquisitions consisted of a 45 s
measurement of analytes in the gas blank and aspirated
solution, particularly 203Tl–205Tl–209Bi–233U–237 Np,
followed by measurement of U and Pb signals from
zircon, along with the continuous signal from the
aspirated solution, for another 150 s. The data were
acquired in time-resolved – peak jumping – pulse
counting mode with 1 point measured per peak for
masses 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 were
corrected for dead time of the electron multiplier and
processed off line in a spreadsheet-based program
(Lamdate — Košler et al., 2002). Data reduction included
correction for gas blank, laser-induced elemental fractionation of Pb and U and instrument mass bias. Minor
formation of oxides of U and Np was corrected for by
adding signal intensities at masses 249, 253 and 254 to the
intensities at masses 233, 237 and 238, respectively. No
common Pb correction was applied to the data.
3.3.5. Laser ablation ICP-MS U–Pb dating (Memorial
University of Newfoundland)
Three grains of the Plešovice zircon were analyzed.
Grain mounts containing the samples and the calibration
material (02123 in-house zircon reference material)
were ultrasonically cleaned in deionised water and
wiped with 8 N nitric acid prior the analyses.
The analyses were performed using New Wave
Research UP-213 laser coupled to a HP-4500 ICP-MS.
Ablation spot size was 40 µm in diameter and the laser
energy was set to 75%. The ICP-MS was tuned by
ablating NIST 612 glass reference material and maximizing sensitivity for the heavy mass range (Pb–U) while
maintaining low oxide formation (ThO/Th b0.5%). The
ablated sample material was transferred to the ICP-MS
using He carrier gas at 1.2 l/min.
9
Data were acquired on seven isotopes using the
instrument's time-resolved analysis data acquisition
software with one point measured per mass peak,
201
Hg (flyback), 204 Pb, 206 Pb, 207Pb, 208Pb, 232Th and
238
U. Dwell time was 10 ms for all masses except 207Pb,
which was set to 30 ms.
The time-resolved data were processed offline using
the spreadsheet-based laser ablation data reduction
program, Lamtrace. Elemental fractionation and instrumental mass bias were corrected by normalization to the
reference zircon 02123 (Ketchum et al., 2001), which was
analyzed regularly at the beginning and end of each
analytical session under exactly the same ablation
conditions as the unknown samples. A common Pb
correction was not possible using 204Pb due to the high
background from the isobaric interference from 204Hg;
mass 204 was monitored to ensure there were no
significant amounts of common Pb present in any
particular analyses. Background and ablation data for
each analysis were collected over single runs lasting
120 s, with background measurements obtained over the
first 30 s before ablation commenced. The Plešovice
zircon data were acquired over four separate days as part
of a U–Pb study of unknown zircons. Each analytical run
consisted of 20 analyses, 4 analyses of 02123 zircon
(reference zircon), 2 Plešovice zircons, 10 unknowns and
four 02123 zircon (reference zircon) analyses at the end of
the run. Calculation of mean ages and plotting of
concordia diagrams for all U–Pb data in this study was
done 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 were
analyzed using a Thermo-Finnigan Element 2 sector
field ICP-MS coupled to a New Wave Research UP-213
ultraviolet laser system fitted with a modified teardropshaped, 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 typical
depth of the ablation crater was 15–20 µm. Data were
acquired in peak jumping mode over 810 mass scans
during 20 s background measurement followed by 32 s
sample ablation. Signal was tuned for maximum
sensitivity for Pb and U while keeping oxide production
well below 1%. A common-Pb correction based on the
interference- and background-corrected 204 Pb signal
and a model Pb composition (Stacey and Kramers,
1975) was carried out, where necessary. The necessity of
the correction was judged on whether the corrected
207
Pb/206Pb ratio lay outside of the internal errors of the
measured ratios, which was the case in about 40% of the
10
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
analyses. The measured and background corrected (e.g.,
204
Hg) 206Pb/204Pb range from 700 to about 60,000 with
18 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 different
grains (mean of gr-2 = 8400, n = 12; mean of gr-3 =
31,000; n = 12). Analyses with high common Pb are
usually characterized by elevated uncertainties for the
207
Pb/235U (Table 3c). Raw data were corrected for
background signal, common Pb, laser-induced elemental fractionation, instrumental mass discrimination, and
time-dependent elemental fractionation of Pb/U using
an in-house MS Excel spreadsheet program. Laserinduced elemental fractionation and instrumental mass
discrimination were corrected by normalization to the
reference zircon GJ-1 (Jackson et al., 2004), which was
analyzed during the analytical session under exactly the
same conditions as the samples. Prior to this normalization, the drift in elemental fractionation was corrected
for each set of isotope ratios (ca. 40) collected during the
time of each single spot analysis. The correction was
done by applying a linear regression through all
measured ratios, excluding the outliers (N ± 2SD), and
using the intercept with the y-axis as the initial ratio.
Data were acquired during 4 analytical sessions on 4
different days. The total offset of the measured driftcorrected 206Pb/238U ratio from the ”true” ID-TIMS
value of the analyzed GJ-1 grain was typically around
3–7%. Reported uncertainties (2σ) were propagated by
quadratic addition of the external reproducibility (2SD)
obtained from the zircon reference material GJ-1 (n = 12;
around 1.3% and 1.2% for the 207 Pb/ 206 Pb and
206
Pb/238U, respectively) during the individual analytical session and the within-run precision of each
analysis (2 SE). For further details on analytical protocol
and data processing for the U–Pb method see Gerdes
and Zeh (2006).
3.4. Hf isotope analysis
3.4.1. Laser ablation and solution MC ICP-MS Hf
analyses (University of Bergen)
Hf isotopic measurements were carried out on two
polished zircon grains using a New Wave Research UP213 laser attached to a Thermo-Finnigan Neptune MC
ICP-MS. The laser was fired with energy of 2 J/cm2,
laser beam diameter was 60 μm and repetition rate was
10 Hz. The laser beam was scanned across the zircon
surface to ablate a linear raster 400 μm long. Data for
gas blank were acquired for 50 s followed by 210 s of
laser ablation. The typical signal intensity was ca. 2.5 V
for 180 Hf.
The faraday cup configuration was set to enable
detection of all Hf isotopes as well as potentially
interfering ions: L4– 172 Yb, L3– 173 Yb, L2– 175 Lu,
L1–176Hf, C–177 Hf, H1–178Hf, H2–179Hf, H3–180 Hf,
H4–182W. Data were corrected for gas blank and isobaric interferences of Yb and Lu on 176Hf using 176 Yb/
173
Yb = 0.7952 (Lapen et al., 2004) and 176Lu/175Lu =
0.02669 (Debievre and Taylor, 1993). A value for 179Hf/
177
Hf = 0.7325 (Patchett and Tatsumoto, 1980) and the
exponential law were used for mass bias correction of
interfering Yb and Lu isotopes and isotopes of Hf. A
solution of Hf isotopic standard JMC 475 (20 ppb) was
Fig. 5. Images of two Plešovice zircon crystals (30 μm thick thin sections) in transmitted light, back-scattered electron (BSE), cathodoluminescence
(CL) and cross-polarized light showing the typical compositional zoning. The bright domains on the BSE images indicate high content of actinides.
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
used as a monitor of data quality over the period of laser
ablation measurements, together with analyses of the
91500 natural zircon reference sample (Wiedenbeck
et al., 1995) that was periodically measured between
sample analyses. All zircon LA MC ICP-MS analyses
were adjusted relative to the JMC 475 176Hf/177 Hf ratio
of 0.282160.
Aliquot of the Plešovice zircon solution prepared at the
J.W. Goethe University of Frankfurt am Main (see Section
3.4.2 below) was measured using instrumental (MC ICPMS) parameters similar to those used for laser ablation
analyses. The solution was aspirated to the ICP in 2%
HNO3 through a PFA nebuliser with uptake rate of
50 μl/min and a cyclone-double pass quartz spray
chamber. The instrument sensitivity was 40 V/ppm Hf
measured at mass 180 Hf. The data acquisition procedure
consisted of 90 integration cycles acquired over a
period of 4 min, followed by 5 min of washout with a
mixture of 2% HNO3–0.2 N HF. Correction for isobaric
interferences of 176 Yb and 176 Lu on 176 Hf utilized
176
Yb/ 173 Yb = 0.7952 (Lapen et al., 2004) and
176
Lu / 175 Lu = 0.02669 respectively (Debievre and
Taylor, 1993). A value of 179 Hf/177 Hf = 0.7325 (Patchett and Tatsumoto, 1980) and the exponential law were
used for mass bias correction of interfering Yb and Lu
isotopes and for correction of Hf isotopes. Data were
normalized relative to the JMC 475 standard solution
(176Hf/177 Hf = 0.282160), which was measured at the
beginning and at the end of the session.
3.4.2. Laser ablation and solution MC ICP-MS Hf
analyses (J.W. Goethe University of Frankfurt am Main)
Hafnium isotopes were analyzed in six grains of the
Plešovice zircon using a Thermo-Finnigan Neptune
multi-collector ICP-MS at Frankfurt University coupled
to the New Wave Research UP-213 laser system and
using a teardrop-shaped, low volume laser cell (for
details on laser ablation see Section 3.3.6). Data were
collected in static mode during 60 s of ablation with a
spot size of 60, 80 and 95 µm, respectively. Nitrogen
(~ 0.005 l/min) was introduced into the Ar sample carrier
gas via an Aridus nebulisation system. Typical signal
intensity was ca. 10 V for 180Hf for a spot diameter
of 60 µm. The isotopes 172Yb, 173Yb and 175 Lu were
simultaneously monitored during each analysis step to
allow for correction of isobaric interferences of Lu and
Yb isotopes on mass 176. The 176Yb and 176 Lu were
calculated using a 176Yb/173 Yb of 0.796218 (Chu et al.,
2002) and 176Lu/175 Lu of 0.02658 (JWG in-house
value). The correction for instrumental mass bias
utilized an exponential law and a 179 Hf/177Hf value of
0.7325 (Patchett and Tatsumoto, 1980) for correction of
11
Hf isotopic ratios. The mass bias of Yb isotopes
generally differs slightly from that of the Hf isotopes
with a typical offset of the βHf/βYb of ca. 1.04 to 1.06
when using the 172 Yb/173Yb value of 1.35274 from Chu
et al. (2002). This offset was determined for each
analytical session by averaging the βHf/βYb of multiple
analyses of the JMC 475 solution doped with variable
Yb amounts and all laser ablation analyses (typically
n N 50) of zircon with a 173Yb signal intensity of
N 60 mV. The mass bias behavior of Lu was assumed
to follow that of Yb. The Yb and Lu isotopic ratios were
corrected using the βHf of the individual integration
steps (n = 60) of each analysis divided by the average
offset factor of the complete analytical session. Using
instead the βHf for mass bias correction of the interfering isotopes of Yb and Lu results only in a slight
overcorrection of about 30 ppm on the 176Hf/177Hf, e.g.,
0.000009, which is within uncertainty of the individual
analysis. This is due to the relative low Lu/Hf and Yb/Hf
of Plešovice zircon. Nevertheless the procedure was
tested with Lu- and Yb-doped JMC 475 solutions with
Table 1
Trace element composition of the Plešovice zircon (laser ablation ICPMS data, Si analyzed by electron microprobe)
Y
Nb
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Hf
Pb
Th
U
Th/U
LaN/LuN
Eu/Eu⁎
Ce/Ce⁎
Pristine zircon domains
(n = 57)
Actinide-rich zircon
domains (n = 31)
Mean
Min
Max
Mean
Min
Max
293
1.5
0.32
2.7
0.34
3
4.5
1.2
14.7
5.7
61
17.1
59
10.6
81
9.8
11 167
39
78
755
0.10
0.003
0.4
2.10
139
0.17
0.18
0.93
0.13
0.97
2.1
0.26
7
2.6
28
8
27
5
38
4.6
9477
21
44
465
0.08
0.001
0
1.53
532
3.2
1.5
9.8
1.7
11.9
11.7
3.1
32
11.2
121
35
123
24
185
23
14 431
55
183
1106
0.17
0.006
0.65
2.82
455
14.7
0.45
7.2
0.71
6.9
9.2
2.3
29
10.8
112
31
100
17.4
126
15
11 760
116
312
2215
0.14
0.006
0.43
2.77
322
2.7
0.24
4.3
0.34
4
6
1.5
20
7.1
78
19.7
67
10.3
83
8.5
8980
63
188
1289
0.10
0.002
0.31
2.13
824
28
1.4
15.7
2.2
18.7
13.1
3.4
42
15.2
160
43
143
25
187
23
13 110
158
523
3084
0.17
0.010
0.58
4.27
Values are concentrations in wt. ppm. Eu/Eu⁎ = EuN/√(SmN⁎GdN),
Ce/Ce⁎ = CeN/√(LaN⁎PrN), normalisation to chondrite after Taylor
and McLennan (1985).
12
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
Fig. 6. Chondrite-normalized trace element composition of the Plešovice zircon showing differences between pristine (dark grey) and actinide-rich
zircon domains (light grey). Chondrite composition after Taylor and McLennan (1985).
Yb/Hf and Lu/Hf up to 50 times higher than that of the
Plešovice zircon. All zircon LA MC ICP-MS analyses
were adjusted relative to the JMC 475 176Hf/177Hf ratio
of 0.282160 and quoted uncertainties are quadratic
additions of the within run precision and the reproducibility 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 the
reference zircons 91500 and GJ-1 over a period of six
months yielded a 176 Hf/177 Hf ratio of 0.282298 ±
0.000026 (2σ, n = 88) and 0.282003 ± 0.000018 (2σ),
respectively. For more details on the analytical method
see Gerdes and Zeh (2006).
In addition, a reference solution was prepared by
dissolving seven grains of the Plešovice zircon in a 4:1
HF–HNO3 mixture in Parr bombs at 220 °C over 72 h.
After almost complete evaporation the sample was taken
up with 100 ml of 0.1 M HF–0.5 M HNO3. This
procedure has probably caused some Lu/Hf fractionation due to the formation of REE fluorides. As a result,
the calculated interference corrections on the mass 176
for the Plešovice zircon solution were ca. 10–15 times
lower than that of the laser ablation analyses.
A 40-ppb aliquot of the Plešovice zircon solution
was analyzed using an Aridus nebulisation system with
50 µl/min uptake rate. Data were acquired with 60
integration cycles over a period of 2 min, followed by
8 min of washout with a mixture of 2% HNO3–0.5 N HF.
Data were corrected and normalized following the
procedure of the laser ablation analyses. Due to similar
short analysis time and similar signal strength the obtained
precision was similar to that of the laser ablation analyses.
3.4.3. Solution MC ICP-MS Hf analyses (NERC Isotope
Geosciences Laboratory)
The Hf isotope measurements at the NERC Isotope
Geosciences Laboratory, UK, were conducted on
residues remaining after separation of U and Pb using
ion exchange resin. These washes were dried down and
redissolved in 2% HNO3 + 0.1 M HF and analyzed
directly (with some dilution) on a Nu Plasma HR MC
Fig. 7. Plot of the FWHM (full width at half-maximum) of the ν3(SiO4)
Raman band versus time-integrated α-fluence showing increasing
degree of metamictization in actinide-rich parts of the Plešovice zircon.
Open diamond symbols — zircon samples representing nearly
complete accumulation of the alpha-event damage (Nasdala et al.,
2001).
Table 2a
ID-TIMS U–Pb and Pb–Pb data for the Plešovice zircon
Atomic ratios
UNIGE_1
UNIGE_2
UNIGE_4
UNIGE_5
MIT_1
MIT_2
MIT_4
MIT_5
NIGL_A.1
NIGL_A.2
NIGL_A.3
NIGL_A.5
NIGL_B.3
NIGL_B.4
NIGL_B.5
NIGL_B.8
NIGL_1
NIGL_9
NIGL_10
BSU_z10
BSU_z11
BSU_z12
BSU_z13
BSU_z14
ZURICH_1
ZURICH_2
ZURICH_3
SEM
SEM
SEM
SEM
Daly
Daly
Daly
Daly
Faraday-SEM
Faraday-SEM
Faraday-SEM
Faraday-SEM
Faraday-SEM
SEM
SEM
Faraday-SEM
Faraday-SEM
Faraday-SEM
Faraday-SEM
Faraday-Daly
Faraday-Daly
Faraday-Daly
Faraday-Daly
Daly
SEM
SEM
SEM
847 1.12 0.09 56822
240 3.91 0.08 16177
348 1.71 0.08 23404
897 0.99 0.08 60249
958 0.99 0.09 64540
209 4.48 0.08 14132
366 1.62 0.08 24726
703 1.27 0.08 47484
250 6.27 0.09 16863
198 6.22 0.1
13317
1327 2.80 0.1
89204
809 3.76 0.12 54013
1086 3.08 0.12 72632
292 1.20 0.11 19551
238 1.21 0.16 15803
902 1.52 0.04 61699
68 13.39 0.13
4531
778 0.86 0.1
52287
1343 1.14 0.1
90264
3204 1.01 0.15 212721
3055 0.75 0.14 202913
897 0.99 0.1
60357
633 1.29 0.12 42415
436 0.72 0.1
29391
4426 11.60 0.09 26096
1478 3.60 0.09 27963
97 2.68 0.09
2485
Sample
Th/
U
(e)
206
Apparent ages (Ma)
204
Pb/
(f)
Pb
208
206
Pb/
Pb
207
235
Pb/
U Err
(%)
(h)
(g)
(g)
0.029
0.026
0.026
0.026
0.029
0.026
0.026
0.026
0.028
0.032
0.032
0.039
0.037
0.036
0.049
0.014
0.042
0.032
0.033
0.046
0.046
0.031
0.037
0.030
0.029
0.029
0.029
0.394065
0.394211
0.394127
0.393991
0.393926
0.394423
0.393983
0.393947
0.393979
0.394161
0.394372
0.394244
0.394331
0.394216
0.393936
0.394093
0.394228
0.392655
0.394425
0.393640
0.393663
0.393913
0.393721
0.393949
0.394000
0.393900
0.394600
0.09
0.10
0.09
0.09
0.09
0.11
0.09
0.09
0.09
0.10
0.10
0.10
0.11
0.11
0.09
0.10
0.10
0.09
0.12
0.11
0.09
0.09
0.09
0.09
0.41
0.38
0.36
206
238
Pb/
(g)
U Err
(%)
(h)
0.053691
0.053706
0.053695
0.053684
0.053696
0.053716
0.053673
0.053699
0.053700
0.053710
0.053717
0.053714
0.053706
0.053715
0.053684
0.053684
0.053721
0.053529
0.053745
0.053644
0.053650
0.053672
0.053655
0.053659
0.053620
0.053640
0.053650
0.05
0.06
0.05
0.05
0.06
0.08
0.06
0.05
0.06
0.07
0.07
0.07
0.09
0.08
0.05
0.07
0.06
0.06
0.10
0.09
0.06
0.05
0.05
0.05
0.35
0.30
0.24
207
206
Pb/
(f)
Pb Err
(%)
(h)
0.053247
0.053252
0.053252
0.053244
0.053224
0.053272
0.053254
0.053224
0.053227
0.053242
0.053263
0.053248
0.053268
0.053244
0.053237
0.053258
0.053239
0.053217
0.053242
0.053236
0.053233
0.053246
0.053237
0.053263
0.053290
0.053270
0.053300
0.04
0.05
0.04
0.04
0.04
0.05
0.05
0.04
0.04
0.05
0.04
0.04
0.04
0.05
0.04
0.04
0.05
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.21
0.11
0.25
Corr.
coef.
0.955
0.918
0.956
0.949
0.946
0.915
0.916
0.958
0.939
0.925
0.942
0.940
0.943
0.932
0.938
0.942
0.927
0.942
0.952
0.949
0.945
0.953
0.954
0.960
0.910
0.970
0.900
207
Pb/235U ±
206
Pb/238U ±
207
Pb/206Pb ±
(i)
(j)
(i)
(j)
(i)
(j)
337.33
337.44
337.38
337.28
337.23
337.60
337.27
337.25
337.27
337.40
337.56
337.46
337.53
337.44
337.24
337.36
337.45
336.31
337.60
337.02
337.04
337.22
337.08
337.25
336.70
336.80
336.90
0.25
0.28
0.25
0.25
0.26
0.32
0.27
0.25
0.27
0.29
0.28
0.29
0.32
0.32
0.26
0.29
0.29
0.27
0.35
0.33
0.26
0.25
0.25
0.25
0.83
0.70
0.60
337.14
337.24
337.17
337.10
337.17
337.29
337.03
337.19
337.20
337.26
337.30
337.28
337.24
337.29
337.10
337.10
337.33
336.15
337.48
336.86
336.89
337.03
336.92
336.95
337.30
337.20
337.70
0.17
0.20
0.16
0.17
0.18
0.27
0.19
0.16
0.19
0.23
0.23
0.24
0.29
0.28
0.18
0.24
0.21
0.21
0.33
0.30
0.20
0.17
0.17
0.16
0.70
0.70
0.70
339.4
339.5
339.5
339.2
338.4
340.4
339.6
338.4
338.5
339.1
340.0
339.4
340.2
339.2
338.9
339.8
339.0
338.1
339.1
338.9
338.8
339.3
338.9
340.0
341.1
340.2
343.6
0.9
1.1
1.0
0.9
0.9
1.1
1.1
0.9
1.0
1.0
0.9
0.9
0.9
1.0
1.0
0.9
1.1
0.9
0.9
0.9
0.9
0.9
0.9
0.9
2.4
1.3
2.9
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
(a)
Pb analyses
mode
(b)
Pb⁎/ Pbc
Pbc (pg)
(c)
(d)
(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
14
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
Fig. 8. ID-TIMS U–Pb dates of Plešovice zircon; a) Massachusetts Institute of Technology b) University of Geneva c) NERC Isotope Geosciences
Laboratory 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.
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
Fig. 8 (continued ).
15
16
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
ICP-MS using a DSN-100 desolvating nebuliser and
PFA-50 nebuliser tip to aspirate the sample into the ICP.
These washes still contained all the Zr, Hf, and REEs
from the crystal aliquot and therefore required an on-line
correction for isobaric interferences. They were run at an
11× dilution in HNO3–HF mixture (thereby reducing
matrix loading of the plasma) using an acquisition
routine that allowed for assessment of the accuracy
between an Yb correction utilizing a Hf mass bias,
versus an Yb correction utilizing an Yb mass bias (using
172
Yb/173 Yb = 1.35368). The low REE concentrations
caused the uncertainty on the data using an Yb mass bias
to be inflated but the results were still within
uncertainties of the data using Hf mass bias for all
corrections. As such, all the reported data utilized the
179
Hf/177 Hf ratios for mass bias correction.
Yb and Lu interference corrections were conducted
using measurement of the 173 Yb and 175Lu peaks
assuming true 176Yb/173 Yb and 176Lu/175Lu ratios of
0.79488 (determined prior to the analytical session
using Yb-doped JMC 475 Hf standard) and 0.02653
(Patchett, 1983) respectively. All data were normalized
to JMC 475 176 Hf/177Hf = 0.282160 and equivalent
aliquots of the 91500 zircon were also measured to
allow assessment of accuracy, giving an average of
0.282296 ± 12 (2σ). Calculation of the uncertainty of
176
Hf/177 Hf values of six analyses of four different sized
dissolutions of the Plešovice zircon was done by
propagation of the uncertainty on the JMC 475 standard
solution (35 ppm, 2σ) measured during the analytical
session.
Initial εHf values for all laser ablation and solution
analyses were calculated assuming an age of 337 Ma
and using a 176Lu decay constant of 1.8648 ⁎ 10− 11
(Scherer et al., 2001) and chondritic Hf composition
( 176 Hf/ 177 Hf = 0.282772) and 176 Lu/ 177 Hf ratio of
0.0332 from Blichert-Toft and Albarède (1997).
4. Results and discussion
A range of zircon images, showing typical internal
textures, is presented in Fig. 5. Zircon crystals often
have a well-defined zoning that is apparent in backscattered electron (BSE) and cathodoluminescence (CL)
images as well as in cross-polarized light. Idiomorphic
crystals have usually oscillatory, and less often sector
zoning, sometimes with apparently “featureless” (in CL
and BSE) inner parts of the grains. Approximately 30%
of the studied grains contain domains that are spatially
related to the growth of pyramidal crystal faces; they
typically 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, and
their surfaces are coated with a brownish material
(Fig. 5), which was in some cases determined to contain
Fe oxides/hydroxides; radial cracks are especially
abundant around the high intensity BSE patches.
Apart from the secondary crack fillings, there are
frequent primary inclusions (apatite, K-feldspar, garnet,
and quartz); these are easily recognizable in reflected
light on polished sample surfaces and can be avoided
during the analysis.
4.1. Trace element concentration
The trace element concentration data (Table 1 and
Fig. 6) show a large variation between different zones in
the Plešovice zircon crystals. The high-BSE intensity
domains (dark in CL) with low interference colours in
cross-polarized light are significantly enriched in all
analyzed elements (Table 1 and Fig. 6). Concentrations
of most trace elements are 2 to 4 times higher
(concentration of Nb is ca. 10 times higher) in these
domains compared to the low-BSE intensity zones in the
studied zircon. The content of U and radiogenic Pb
varies between 465–1106 ppm and 21–55 ppm, respectively for pristine, low-BSE intensity parts of the zircon,
and 1289–3084 ppm and 63–158 ppm, respectively for
domains with high-BSE intensities. The Th/U ratio has a
uniform value of ca. 0.1 for both the trace element rich
and trace element poor zones (Table 1). The low Th/U
values are sometimes regarded as being typical of zircon
that crystallized in metamorphic rocks (Hoskin and
Schaltegger, 2003 and references therein) but it has been
demonstrated that the Th/U ratios also reflect the
composition of the source from which the zircon
crystallized and therefore can vary considerably irrespective of the zircon origin (Kelly and Harley, 2005).
The presence of abundant apatite suggests that the
partitioning of U and Th could have been controlled by
Table 2b
Summary of ID-TIMS U–Pb and Pb–Pb data for the Plešovice zircon
Laboratory
Tracer
206
± (2σ)
MSWD
n
MIT
UNIGE
NIGL a
BSU
ET535 All
ETHZ
ET535
ET535
ET535
ET535
ET535
Zurich
337.16
337.16
337.24
336.95
337.13
337.40
0.08
0.09
0.07
0.08
0.20/0.37 b
0.40
0.36
0.98
0.82
0.40
10.40
0.57
4
4
11
5
–
3
a
b
Pb/238U
NIGL_9 not included in weighted mean calculation.
Without/with tracer calibration uncertainty.
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
17
Table 3a
Laser ablation U–Pb data for the Plešovice zircon (University of Bergen)
Analysis
Atomic ratios
207
235
Pb/
UoB-LA1
UoB-LA2
UoB-LA3
UoB-LA4
UoB-LA5
UoB-LA6
UoB-LA7
UoB-LA8
UoB-LA9
UoB-LA10
UoB-LA11
UoB-LA12
UoB-LA13
UoB-LA14
UoB-LA15
UoB-LA16
UoB-LA17
UoB-LA18
UoB-LA19
UoB-LA20
UoB-LA21
UoB-LA22
UoB-LA23
UoB-LA24
UoB-LA25
UoB-LA26
UoB-LA27
UoB-LA28
UoB-LA29
UoB-LA30
UoB-LA31
UoB-LA32
UoB-LA33
UoB-LA34
UoB-LA35
UoB-LA36
UoB-LA37
UoB-LA38
UoB-LA39
UoB-LA40
UoB-LA41
UoB-LA42
UoB-LA43
UoB-LA44
UoB-LA45
UoB-LA46
UoB-LA47
UoB-LA48
UoB-LA49
UoB-LA50
UoB-LA51
UoB-LA52
UoB-LA53
UoB-LA54
0.40348
0.38827
0.39307
0.37946
0.39746
0.40264
0.40897
0.40031
0.39511
0.39279
0.39938
0.40230
0.39045
0.39298
0.39620
0.40467
0.40713
0.41446
0.41404
0.40806
0.38277
0.40741
0.39308
0.39632
0.40068
0.37569
0.40829
0.39824
0.41707
0.38071
0.39095
0.41691
0.40391
0.41454
0.37680
0.37982
0.37067
0.41703
0.40623
0.36095
0.41656
0.40198
0.43123
0.39371
0.38890
0.37012
0.38928
0.37774
0.39338
0.41838
0.37390
0.36756
0.38137
0.38115
U
Apparent ages (Ma)
1σ
(abs)
206
238
0.01614
0.01785
0.01521
0.01656
0.01395
0.01527
0.01839
0.02011
0.03086
0.01885
0.01322
0.01668
0.01897
0.02071
0.02544
0.02097
0.02376
0.02604
0.01598
0.02208
0.02179
0.01865
0.02211
0.02876
0.02293
0.02439
0.02525
0.02108
0.01631
0.02293
0.02238
0.01459
0.02435
0.02176
0.01339
0.01411
0.01838
0.02803
0.02970
0.01778
0.01924
0.01385
0.01746
0.01871
0.01922
0.01724
0.01647
0.01864
0.03413
0.01464
0.01371
0.01625
0.01398
0.01605
0.05316
0.05180
0.05238
0.05242
0.05340
0.05322
0.05251
0.05295
0.05421
0.05321
0.05407
0.05377
0.05542
0.05259
0.05311
0.05313
0.05290
0.05408
0.05477
0.05523
0.05454
0.05386
0.05433
0.05298
0.05439
0.05510
0.05489
0.05428
0.05454
0.05364
0.05470
0.05518
0.05332
0.05504
0.05348
0.05565
0.05400
0.05522
0.05426
0.05354
0.05388
0.05459
0.05447
0.05335
0.05330
0.05270
0.05165
0.05228
0.05093
0.05301
0.05408
0.05485
0.05436
0.05383
Pb/
U
1σ
(abs)
207
Pb/235U
1σ
(abs)
206
Pb/238U
1σ
(abs)
0.00095
0.00084
0.00088
0.00074
0.00087
0.00093
0.00095
0.00078
0.00126
0.00097
0.00085
0.00085
0.00099
0.00120
0.00159
0.00143
0.00167
0.00151
0.00116
0.00096
0.00103
0.00092
0.00143
0.00162
0.00117
0.00117
0.00139
0.00107
0.00103
0.00135
0.00122
0.00092
0.00116
0.00127
0.00103
0.00098
0.00099
0.00129
0.00126
0.00081
0.00107
0.00123
0.00129
0.00105
0.00112
0.00109
0.00112
0.00092
0.00131
0.00063
0.00055
0.00069
0.00060
0.00075
344.2
333.1
336.6
326.6
339.8
343.6
348.1
341.9
338.1
336.4
341.2
343.3
334.7
336.5
338.9
345.0
346.8
352.1
351.8
347.5
329.1
347.0
336.6
339.0
342.1
323.9
347.6
340.4
354.0
327.6
335.1
353.8
344.5
352.1
324.7
326.9
320.1
353.9
346.2
312.9
353.6
343.1
364.0
337.1
333.6
319.7
333.8
325.4
336.8
354.9
322.5
317.8
328.0
327.9
13.8
15.3
13.0
14.3
11.9
13.0
15.7
17.2
26.4
16.1
11.3
14.2
16.3
17.7
21.8
17.9
20.2
22.1
13.6
18.8
18.7
15.9
18.9
24.6
19.6
21.0
21.5
18.0
13.8
19.7
19.2
12.4
20.8
18.5
11.5
12.1
15.9
23.8
25.3
15.4
16.3
11.8
14.7
16.0
16.5
14.9
14.1
16.1
29.2
12.4
11.8
14.1
12.0
13.8
333.9
325.6
329.1
329.4
335.3
334.3
329.9
332.6
340.3
334.2
339.5
337.6
347.7
330.4
333.6
333.7
332.3
339.5
343.8
346.5
342.3
338.2
341.0
332.8
341.4
345.7
344.5
340.8
342.3
336.8
343.3
346.2
334.9
345.4
335.9
349.1
339.0
346.5
340.6
336.2
338.3
342.6
341.9
335.0
334.7
331.1
324.6
328.5
320.2
333.0
339.5
344.2
341.2
338.0
6.0
5.3
5.5
4.6
5.4
5.8
6.0
4.9
7.9
6.1
5.3
5.3
6.2
7.5
10.0
9.0
10.5
9.5
7.3
6.0
6.5
5.7
9.0
10.2
7.3
7.3
8.7
6.7
6.4
8.5
7.7
5.8
7.3
7.9
6.4
6.2
6.2
8.1
7.9
5.1
6.7
7.7
8.1
6.6
7.0
6.9
7.1
5.8
8.2
3.9
3.5
4.3
3.8
4.7
(continued on next page)
18
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
Table 3a (continued)
Analysis
Atomic ratios
207
235
Pb/
UoB-LA55
UoB-LA56
UoB-LA57
UoB-LA58
UoB-LA59
UoB-LA60
UoB-LA61
0.37463
0.41708
0.41763
0.39342
0.39234
0.39958
0.39309
U
Apparent ages (Ma)
1σ
(abs)
206
238
0.01221
0.01355
0.01257
0.01189
0.01243
0.01161
0.01419
0.05457
0.05540
0.05408
0.05568
0.05356
0.05465
0.05289
Pb/
U
1σ
(abs)
207
Pb/235U
1σ
(abs)
206
Pb/238U
0.00067
0.00053
0.00063
0.00065
0.00080
0.00088
0.00085
323.1
354.0
354.4
336.9
336.1
341.3
336.6
10.5
11.5
10.7
10.2
10.6
9.9
12.1
342.5
347.6
339.5
349.3
336.3
343.0
332.2
1σ
(abs)
4.2
3.3
3.9
4.1
5.0
5.5
5.3
concurrent growth of zircon and apatite during their
crystallization from parental magma. This assumption is
consistent with the Th/U ratio being almost constant
even in the high-BSE intensity domains of the grains
that contain ca. 3 times more of U and Th compared to
the low-BSE intensity domains. The well developed
network of cracks around the trace element rich zones is
consistent with the damage induced by the decay of U
and Th and associated volume changes of the zircon.
The REE show typical “magmatic” steep chondritenormalized patterns enriched in HREE relative to
LREE, negative Eu and a positive Ce anomaly that are
similar 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 the
studied zircon grains. The large variations in trace
element contents, both between and within the Plešovice
zircon grains suggest a disequilibrium growth (Janoušek
et al., 2007) and preclude the use of this zircon as a
reference material for trace element microanalysis.
1000 cm− 1). Determined FWHMs vary in the range 7–
30 cm− 1, which characterizes the corresponding microareas to be moderately to highly damaged. The range of
the determined degrees of damage corresponds very
well with internal variations of actinide (U and Th)
concentrations (see Table 1 and Fig. 6).
To evaluate the degree of storage of the selfirradiation damage, the calculated self-irradiation
doses were compared with the structural damage that
is presently observed. For this, time-integrated alpha
fluences Dα (i.e., the number of α-decay events per
gram) were calculated from
4.2. Structural study by Raman spectroscopy
(Murakami et al., 1991; Nasdala et al., 2001), where cU
and cTh are the present actinide concentrations (in ppm),
NA is Avogadro's number, M238, M235, and M232 are the
molecular weights of the parent isotopes, λ238, λ235, and
λ232 are the respective decay constants (Firestone and
Shirley, 1996), and t is the integration time (assumed to
be ca. 337 Ma, i.e. the isotopic age of the zircon). The
above equation is based on the assumption of natural
isotopic composition of uranium.
The plot of Raman band FWHMs (quantifying the
present damage) versus time-integrated alpha fluences
(Fig. 7) shows that data pairs for studied zircon samples
plot close to the trend defined by zircon samples that are
believed to represent nearly complete accumulation of the
alpha-event damage (Nasdala et al., 2001). As the alpha
doses were calculated assuming a damage accumulation
period of 337 million years, this suggests that the
Plešovice zircon has stored the majority of radiation
damage since crystal growth. This, in turn, suggests that
Study of Raman spectra of the Plešovice zircon,
especially with emphasis on the bright-BSE domains,
has been conducted to characterize its structural properties and homogeneity. Nasdala et al. (2006) have shown
that within zircon single-crystals, heterogeneity of the
BSE intensity is most likely due to structural heterogeneity (i.e., electron channeling contrast caused by
heterogeneous radiation damage). The presumption that
the zircon grains are heterogeneously radiation-damaged
is also supported by the range of interference colours
observed in the cross-polarized light mode (Fig. 5) and
fracture patterns that are typical of heterogeneous
volume swelling upon damage accumulation (Lee and
Tromp, 1995).
The degree of radiation damage was determined
according to Nasdala et al. (1995) from the FWHM of
the ν3(SiO4) Raman band (B1g mode; Raman shift about
cU NA 0:9928 k238 t
e
1 þ7
6
M238 10
cU NA 0:0072 k235 t
e
1 þ6
6
M235 10
cTh NA k232 t
e
1
6
M232 10
Da ¼ 8 J. Sláma et al. / Chemical Geology 249 (2008) 1–35
the Plešovice zircon cannot have experienced major
thermal annealing of the radiation damage after its
magmatic growth.
19
Post-growth alteration processes, however, are
indicated by the observation that internal fractures and
cracks are filled/coated with a brown substance, most
Fig. 9. Laser ablation ICP-MS U–Pb ages obtained at: a) University of Bergen, b) Memorial University of Newfoundland and c) J.W. Goethe
University of Frankfurt am Main. On the left are concordia plots and on the right are 206Pb/238U dates. Error ellipses in the concordia plots and error
bars on the 206Pb/238U plots are 1σ; Concordia age ellipses (gray filled) are 2σ. Note the differences in uncertainties of individual data between a) and
b, c) which is a result of different data reduction procedures used by individual laboratories (see Sections 3.3.4–3.3.6 for details).
20
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
likely formed by iron oxides/hydroxides (Fig. 5). These
fractures typically occur in less radiation-damaged
internal regions; they have been generated by volume
expansion as a result of heterogeneous metamictization
(Chakoumakos et al., 1987; Lee and Tromp, 1995). The
formation of minerals at these fractures is significantly
younger than the zircon grains because (i) such
fractures are only formed after a certain time-period,
Table 3b
Laser ablation U–Pb data for the Plešovice zircon (Memorial University of Newfoundland)
Analysis
Atomic ratios
Pb/235U
MUN-LA1
MUN-LA2
MUN-LA3
MUN-LA4
MUN-LA5
MUN-LA6
MUN-LA7
MUN-LA 8
MUN-LA9
MUN-LA10
MUN-LA11
MUN-LA12
MUN-LA13
MUN-LA14
MUN-LA15
MUN-LA16
MUN-LA17
MUN-LA18
MUN-LA19
MUN-LA20
MUN-LA21
MUN-LA22
MUN-LA23
MUN-LA24
MUN-LA25
MUN-LA26
MUN-LA27
MUN-LA28
MUN-LA29
MUN-LA30
MUN-LA31
MUN-LA32
MUN-LA33
MUN-LA34
MUN-LA35
MUN-LA36
MUN-LA37
MUN-LA38
MUN-LA39
MUN-LA40
MUN-LA41
MUN-LA42
MUN-LA43
MUN-LA44
MUN-LA45
MUN-LA46
MUN-LA47
MUN-LA48
Apparent ages (Ma)
207
1σ
(abs)
206
Pb/238U
1σ
(abs)
207
Pb/235U
1σ
(abs)
206
Pb/238U
1σ
(abs)
0.38080
0.38480
0.38540
0.38560
0.38580
0.38670
0.38670
0.38690
0.38694
0.38840
0.38860
0.38860
0.38870
0.38870
0.38900
0.38930
0.38990
0.39130
0.39140
0.39150
0.39180
0.39180
0.39220
0.39230
0.39240
0.39370
0.39380
0.39380
0.39390
0.39440
0.39450
0.39470
0.39480
0.39490
0.39530
0.39540
0.39570
0.39590
0.39760
0.39770
0.39800
0.39900
0.39960
0.40180
0.40190
0.40290
0.40320
0.40580
0.00740
0.00834
0.00621
0.00918
0.00443
0.00436
0.01209
0.00492
0.00830
0.00898
0.00503
0.00806
0.00693
0.00768
0.00674
0.00510
0.00630
0.00755
0.00785
0.00541
0.00471
0.00426
0.00717
0.00830
0.00707
0.00502
0.00809
0.00607
0.00700
0.00373
0.00664
0.00913
0.00587
0.00690
0.00760
0.00642
0.00433
0.00793
0.00586
0.00619
0.00799
0.00669
0.00612
0.00512
0.00682
0.01076
0.00821
0.00846
0.05220
0.05270
0.05400
0.05420
0.05360
0.05320
0.05440
0.05300
0.05370
0.05410
0.05270
0.05380
0.05320
0.05370
0.05330
0.05290
0.05360
0.05350
0.05380
0.05320
0.05350
0.05330
0.05390
0.05410
0.05390
0.05230
0.05400
0.05240
0.05380
0.05320
0.05290
0.05330
0.05390
0.05320
0.05330
0.05300
0.05410
0.05280
0.05390
0.05330
0.05370
0.05410
0.05430
0.05380
0.05420
0.05350
0.05370
0.05440
0.00052
0.00066
0.00081
0.00061
0.00049
0.00073
0.00067
0.00032
0.00072
0.00081
0.00068
0.00094
0.00053
0.00034
0.00082
0.00058
0.00049
0.00034
0.00045
0.00036
0.00052
0.00034
0.00081
0.00063
0.00063
0.00047
0.00081
0.00045
0.00063
0.00059
0.00051
0.00065
0.00057
0.00058
0.00069
0.00045
0.00031
0.00093
0.00078
0.00055
0.00083
0.00039
0.00082
0.00040
0.00055
0.00055
0.00064
0.00123
328.0
331.0
331.0
331.0
331.0
332.0
332.0
332.0
332.0
333.0
333.0
333.0
333.0
333.0
334.0
334.0
334.0
335.0
335.0
335.0
336.0
336.0
336.0
336.0
336.0
337.0
337.0
337.0
337.0
338.0
338.0
338.0
338.0
338.0
338.0
338.0
339.0
339.0
340.0
340.0
340.0
341.0
341.0
343.0
343.0
344.0
344.0
346.0
6.0
7.0
5.0
7.0
3.0
3.0
9.0
4.0
6.0
6.0
3.0
6.0
5.0
5.0
5.0
4.0
4.0
5.0
5.0
3.0
4.0
3.0
5.0
6.0
5.0
4.0
6.0
4.0
5.0
3.0
5.0
7.0
4.0
5.0
5.0
4.0
4.0
6.0
4.0
5.0
6.0
5.0
4.0
4.0
5.0
8.0
6.0
6.0
328.0
331.0
339.0
340.0
336.0
334.0
342.0
333.0
337.6
339.0
331.0
338.0
334.0
337.0
335.0
332.0
337.0
336.0
338.0
334.0
336.0
335.0
338.0
340.0
338.0
328.0
339.0
330.0
338.0
334.0
332.0
335.0
339.0
334.0
335.0
333.0
340.0
332.0
338.0
335.0
337.0
340.0
341.0
338.0
340.0
336.0
337.0
342.0
3.0
4.0
5.0
4.0
3.0
5.0
4.0
2.0
4.6
5.0
4.0
6.0
3.0
2.0
5.0
4.0
3.0
2.0
3.0
2.0
4.0
2.0
4.0
4.0
4.0
2.0
5.0
3.0
4.0
3.0
3.0
4.0
4.0
3.0
4.0
3.0
2.0
6.0
5.0
4.0
5.0
3.0
5.0
3.0
3.0
3.0
4.0
8.0
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
when damage accumulation (and, thus, volume swelling) in the higher-actinide regions had reached a
sufficient level and (ii) there are virtually no newly
generated but unfilled cracks. The formation of these
fracture fillers must have been connected with a lowtemperature fluid (i.e., well below 200 °C). This
conclusion is supported by the consideration that any
alteration process at more elevated temperature should
21
have resulted in notable annealing of the radiation
damage, 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
Table 3c
Laser ablation U–Pb data for Plešovice zircon (J.W. Goethe University of Frankfurt am Main)
Analysis a
Atomic ratios
207
235
Pb/
JWG-LA1 (gr-1)
JWG-LA2 (gr-1)
JWG-LA3 (gr-1)
JWG-LA4 (gr-1)
JWG-LA5 (gr-1)
JWG-LA6 (gr-1)
JWG-LA7 (gr-1)
JWG-LA8 (gr-1)
JWG-LA9 (gr-1)
JWG-LA10 (gr-1)
JWG-LA11 (gr-1)
JWG-LA12 (gr-2)
JWG-LA13 (gr-2)
JWG-LA14 (gr-2)
JWG-LA15 (gr-2)
JWG-LA16 (gr-2)
JWG-LA17 (gr-2)
JWG-LA18 (gr-2)
JWG-LA19 (gr-2)
JWG-LA20 (gr-2)
JWG-LA21 (gr-2)
JWG-LA22 (gr-2)
JWG-LA23 (gr-2)
JWG-LA24 (gr-3)
JWG-LA25 (gr-3)
JWG-LA26 (gr-3)
JWG-LA27 (gr-3)
JWG-LA28 (gr-3)
JWG-LA29 (gr-3)
JWG-LA30 (gr-3)
JWG-LA31 (gr-3)
JWG-LA32 (gr-3)
JWG-LA33 (gr-3)
JWG-LA34 (gr-3)
JWG-LA35 (gr-3)
JWG-LA36 (gr-4)
JWG-LA37 (gr-4)
JWG-LA38 (gr-4)
JWG-LA39 (gr-4)
JWG-LA40 (gr-4)
JWG-LA41 (gr-4)
JWG-LA42 (gr-4)
a
0.39323
0.39460
0.39634
0.38993
0.40024
0.39578
0.39237
0.39962
0.39690
0.39161
0.39213
0.39784
0.38189
0.39632
0.39482
0.40473
0.39942
0.37682
0.40184
0.39688
0.38879
0.39168
0.40074
0.39492
0.39475
0.39398
0.39779
0.39149
0.39094
0.39373
0.39689
0.39222
0.40175
0.39298
0.39369
0.38270
0.39361
0.39371
0.40152
0.40555
0.39883
0.39182
U
Apparent ages (Ma)
1σ
(abs)
206
238
0.00433
0.00338
0.00368
0.00363
0.00408
0.00360
0.00337
0.00325
0.00351
0.00354
0.00360
0.00863
0.00834
0.00591
0.00646
0.00943
0.00636
0.01050
0.02018
0.00713
0.00907
0.00611
0.00742
0.00427
0.00432
0.00530
0.00434
0.00491
0.00537
0.00505
0.00456
0.00405
0.00425
0.00410
0.00446
0.00591
0.00607
0.00672
0.00645
0.00573
0.00616
0.00558
0.05380
0.05369
0.05390
0.05328
0.05434
0.05366
0.05373
0.05449
0.05400
0.05376
0.05338
0.05335
0.05316
0.05290
0.05348
0.05443
0.05421
0.05349
0.05420
0.05431
0.05284
0.05336
0.05417
0.05372
0.05368
0.05375
0.05380
0.05345
0.05461
0.05350
0.05411
0.05372
0.05435
0.05342
0.05363
0.05221
0.05372
0.05360
0.05504
0.05461
0.05415
0.05313
Pb/
U
1σ
(abs)
207
1σ
(abs)
206
1σ
(abs)
0.00038
0.00035
0.00040
0.00039
0.00041
0.00039
0.00038
0.00038
0.00037
0.00038
0.00037
0.00073
0.00064
0.00064
0.00063
0.00066
0.00069
0.00069
0.00068
0.00064
0.00066
0.00064
0.00065
0.00050
0.00050
0.00051
0.00051
0.00051
0.00056
0.00049
0.00047
0.00050
0.00050
0.00048
0.00049
0.00068
0.00065
0.00066
0.00072
0.00061
0.00067
0.00062
336.7
337.7
339.0
334.3
341.8
338.6
336.1
341.4
339.4
335.5
335.9
340.1
328.4
339.0
337.9
345.1
341.2
324.7
343.0
339.4
333.5
335.6
342.2
338.0
337.8
337.3
340.0
335.5
335.1
337.1
339.4
336.0
342.9
336.5
337.1
329.0
337.0
337.1
342.7
345.7
340.8
335.7
3.7
2.9
3.2
3.1
3.5
3.1
2.9
2.8
3.0
3.0
3.1
7.4
6.2
4.3
4.7
6.9
4.6
7.8
14.8
5.2
6.7
4.5
5.4
3.1
3.2
3.9
3.2
3.6
3.9
3.7
3.3
3.0
3.1
3.0
3.3
4.4
4.4
4.9
4.7
4.2
4.5
4.1
337.8
337.1
338.4
334.6
341.1
336.9
337.4
342.0
339.0
337.6
335.2
335.1
333.9
332.3
335.9
341.6
340.3
335.9
340.2
340.9
331.9
335.1
340.1
337.3
337.1
337.5
337.8
335.7
342.8
336.0
339.7
337.3
341.2
335.5
336.8
328.1
337.3
336.6
345.4
342.8
340.0
333.7
2.3
2.1
2.5
2.4
2.5
2.4
2.3
2.3
2.3
2.3
2.2
4.4
3.9
3.9
3.8
4.1
4.2
4.2
4.2
3.9
4.0
3.9
4.0
3.1
3.0
3.1
3.2
3.1
3.4
3.0
2.9
3.1
3.1
2.9
3.0
4.2
4.0
4.0
4.4
3.7
4.1
3.8
gr indicates individual zircon grains analyzed during the LA ICP-MS analytical session.
Pb/235U
Pb/238U
22
Table 4
Ion-microprobe U–Th–Pb data for the Plešovice zircon (Swedish Museum of Natural History in Stockholm)
Concentrations
NS-10-1
NS-10-2
NS-1-1
NS-11-1
NS-12-1
NS-13-1
NS-14-1a
NS-15-1
NS-15-2
NS-15-3
NS-15-4
NS-15-5
NS-15-6
NS-15-7
NS-16-1
NS-17-1
NS-18-1
NS-19-1
NS-20-1
NS-2-1
NS-2-2
NS-21-1
NS-22-1
NS-22-2
NS-22-3
NS-22-4
NS-22-5
NS-22-6
NS-22-7
NS-22-8
U
(ppm)
921
772
945
544
830
930
598
831
846
784
1032
1144
1148
618
596
881
1391
1013
941
771
704
937
1128
1003
892
791
769
831
952
680
Pb
(ppm)
55
45
55
32
50
55
36
50
50
46
61
67
67
35
35
53
81
59
55
45
42
55
64
59
52
46
45
48
56
39
Atomic ratios
Th/U
calc
(a)
206
Pb/204Pb
0.108
0.085
0.087
0.085
0.096
0.109
0.100
0.102
0.101
0.090
0.096
0.094
0.093
0.096
0.100
0.111
0.138
0.110
0.099
0.112
0.090
0.102
0.095
0.117
0.106
0.095
0.090
0.102
0.108
0.098
100 526
106 275
897
55 142
58 758
72 744
52 465
230 388
87 747
38 615
60 608
271 698
71 755
145 497
93 202
84 964
202 441
16 449
31 354
62 557
154 445
207 163
1606
451 177
65 887
61 190
27 678
1793
67 626
93 935
Pb/235U
f206
(%)
(b)
207
0.02
0.02
2.09
0.03
(0.00)
0.03
0.04
(0.01)
(0.02)
0.05
0.03
(0.01)
0.03
(0.01)
(0.02)
(0.02)
(0.01)
0.11
0.06
0.03
(0.01)
(0.01)
1.16
(0.00)
(0.03)
(0.03)
0.07
1.04
(0.03)
(0.02)
0.40134
0.39487
0.40239
0.39967
0.40621
0.39522
0.40922
0.40376
0.40124
0.39682
0.39463
0.39665
0.39836
0.38273
0.39488
0.40735
0.39237
0.39430
0.39857
0.38973
0.40886
0.39285
0.38532
0.39289
0.39194
0.39528
0.40170
0.39476
0.39790
0.38998
1σ
(%)
(c)
Apparent ages (Ma)
206
Pb/238U
1σ
(%)
(c)
0.90
0.91
1.57
1.00
1.05
1.01
1.03
1.02
1.01
1.06
1.04
0.98
0.98
1.15
1.20
1.05
1.02
1.09
1.06
1.07
1.02
1.03
1.52
1.05
1.07
1.08
1.16
1.52
1.07
1.25
0.05501
0.05384
0.05372
0.05439
0.05530
0.05435
0.05639
0.05532
0.05484
0.05432
0.05426
0.05425
0.05434
0.05280
0.05449
0.05507
0.05338
0.05355
0.05431
0.05459
0.05540
0.05362
0.05248
0.05387
0.05388
0.05392
0.05430
0.05373
0.05458
0.05327
207
Pb/206Pb
1σ
(%)
(c)
0.76
0.74
0.75
0.80
0.74
0.74
0.81
0.74
0.74
0.74
0.80
0.75
0.74
0.74
0.75
0.75
0.74
0.76
0.74
0.74
0.74
0.74
0.74
0.74
0.74
0.74
0.75
0.75
0.74
0.74
0.05292
0.05320
0.05433
0.05329
0.05328
0.05274
0.05264
0.05293
0.05306
0.05298
0.05275
0.05303
0.05317
0.05257
0.05256
0.05365
0.05331
0.05341
0.05323
0.05178
0.05353
0.05314
0.05325
0.05290
0.05275
0.05316
0.05366
0.05328
0.05288
0.05310
0.50
0.53
1.38
0.60
0.75
0.68
0.63
0.69
0.69
0.76
0.67
0.63
0.64
0.88
0.94
0.74
0.71
0.78
0.76
0.78
0.71
0.72
1.33
0.75
0.76
0.79
0.88
1.33
0.77
1.00
Disc.
(%)
(d)
2.51
9.85
207
Pb/235Ucorr
1σ
(abs)
206
Pb/238U
1σ
(abs)
207
Pb/206Pb
1σ
(abs)
2.6
2.5
2.7
2.7
2.5
2.5
2.8
2.5
2.5
2.5
2.7
2.5
2.5
2.4
2.5
2.6
2.4
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
345.2
338.0
337.3
341.4
347.0
341.2
353.6
347.1
344.2
341.0
340.6
340.5
341.1
331.7
342.0
345.5
335.2
336.3
340.9
342.6
347.6
336.7
329.7
338.2
338.3
338.6
340.8
337.4
342.6
334.6
2.5
2.4
2.5
2.6
2.5
2.5
2.8
2.5
2.5
2.5
2.7
2.5
2.4
2.4
2.5
2.5
2.4
2.5
2.5
2.5
2.5
2.4
2.4
2.4
2.5
2.4
2.5
2.5
2.5
2.4
325.2
337.2
384.6
341.3
340.6
317.4
313.1
326.0
331.5
328.1
318.1
330.2
336.0
310.2
309.7
356.5
342.2
346.1
338.6
275.6
351.1
334.8
339.4
324.3
318.3
335.8
356.7
340.8
323.4
332.9
11.2
11.9
30.8
13.5
16.8
15.5
14.3
15.6
15.6
17.1
15.1
14.3
14.4
19.9
21.2
16.5
15.9
17.5
17.2
17.8
15.9
16.3
29.8
16.9
17.3
17.8
19.6
29.7
17.4
22.6
(e)
345.4
338.0
336.8
341.4
347.0
341.4
354.0
347.3
344.3
341.1
340.8
340.6
341.2
331.9
342.4
345.4
335.2
336.2
340.9
343.3
347.5
336.7
329.6
338.4
338.5
338.6
340.7
337.4
342.8
334.6
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
Sample/
spot #
818
923
824
1107
1106
961
832
869
928
879
1118
984
890
624
932
1096
1375
1138
753
606
828
1102
781
783
548
704
563
1233
746
1094
811
49
55
49
66
67
57
48
51
56
51
67
58
52
36
55
65
82
67
43
36
49
66
47
47
33
41
34
75
44
65
48
0.095
0.110
0.106
0.156
0.172
0.113
0.117
0.100
0.103
0.108
0.155
0.105
0.097
0.102
0.145
0.150
0.138
0.144
0.109
0.092
0.097
0.096
0.117
0.102
0.088
0.098
0.091
0.152
0.087
0.089
0.087
200 958
141 245
123 166
154 761
237 888
109 294
201 074
207 815
137 298
122 944
180 290
81 145
179 112
44 594
2680
41 489
88 805
188 164
26 041
46 468
36 317
26 891
94 966
74 241
76 351
88 278
58 758
108 451
100 778
79 675
93 847
(0.01)
(0.01)
(0.02)
(0.01)
(0.01)
(0.02)
(0.01)
(0.01)
(0.01)
(0.02)
(0.01)
(0.02)
(0.01)
0.04
0.70
0.05
0.02
(0.01)
0.07
0.04
0.05
0.07
0.02
0.03
(0.02)
(0.02)
(0.03)
(0.02)
(0.02)
0.02
0.02
0.40832
0.39691
0.39853
0.39849
0.39824
0.39643
0.39442
0.39564
0.41122
0.39104
0.39949
0.39966
0.39879
0.39168
0.38433
0.39491
0.40007
0.39577
0.38601
0.40132
0.40331
0.40779
0.40738
0.40787
0.41406
0.39494
0.40550
0.40280
0.40304
0.40435
0.40709
1.05
1.03
1.07
1.00
1.11
1.05
1.09
1.07
0.93
1.18
1.30
1.08
1.02
1.24
1.34
1.00
1.00
0.98
1.16
1.00
0.91
0.91
0.93
0.93
0.99
1.06
1.12
0.94
1.03
0.88
0.90
0.05529
0.05462
0.05448
0.05451
0.05494
0.05433
0.05338
0.05405
0.05576
0.05354
0.05435
0.05447
0.05399
0.05390
0.05374
0.05380
0.05460
0.05360
0.05302
0.05490
0.05473
0.05502
0.05587
0.05600
0.05630
0.05429
0.05518
0.05511
0.05460
0.05514
0.05469
0.74
0.75
0.74
0.74
0.75
0.74
0.74
0.74
0.74
0.74
0.74
0.74
0.74
0.74
0.75
0.74
0.74
0.74
0.74
0.78
0.74
0.74
0.74
0.74
0.74
0.76
0.74
0.74
0.75
0.78
0.75
0.05356
0.05270
0.05305
0.05302
0.05257
0.05292
0.05359
0.05309
0.05349
0.05297
0.05331
0.05322
0.05357
0.05270
0.05186
0.05324
0.05314
0.05355
0.05280
0.05302
0.05344
0.05375
0.05289
0.05283
0.05334
0.05276
0.05330
0.05301
0.05354
0.05318
0.05399
0.74
0.71
0.78
0.68
0.82
0.74
0.80
0.78
0.56
0.93
1.07
0.79
0.71
1.00
1.11
0.67
0.67
0.65
0.89
0.63
0.54
0.52
0.56
0.56
0.66
0.73
0.83
0.58
0.71
0.42
0.50
0.42
0.22
−0.33
346.8
343.1
342.1
342.3
345.1
341.2
335.1
339.4
349.8
336.3
341.2
341.9
338.8
338.7
338.0
337.8
342.8
336.4
333.2
344.7
343.5
345.1
350.7
351.5
353.2
341.0
346.3
346.0
342.6
346.1
342.9
2.5
2.5
2.5
2.5
2.6
2.5
2.5
2.5
2.6
2.4
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.4
2.6
2.5
2.5
2.6
2.6
2.6
2.6
2.5
2.5
2.5
2.6
2.5
346.9
342.8
342.0
342.1
344.8
341.0
335.3
339.3
349.8
336.2
341.2
341.9
339.0
338.4
337.5
337.8
342.7
336.6
333.0
344.5
343.5
345.3
350.4
351.2
353.1
340.8
346.2
345.8
342.7
346.0
343.2
2.5
2.5
2.5
2.5
2.5
2.5
2.4
2.4
2.5
2.4
2.5
2.5
2.4
2.4
2.5
2.4
2.5
2.4
2.4
2.6
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.6
2.5
352.8
315.9
331.0
329.7
310.3
325.5
353.8
332.8
349.7
327.4
341.9
338.2
353.0
315.9
279.4
338.8
334.7
352.2
320.4
329.6
347.6
360.7
324.0
321.3
343.2
318.6
341.5
329.4
351.9
336.5
370.6
16.7
16.0
17.5
15.3
18.6
16.6
17.9
17.5
12.6
20.9
24.0
17.8
16.0
22.5
25.2
15.0
15.2
14.6
20.1
14.1
12.1
11.7
12.7
12.7
14.8
16.6
18.7
13.1
16.0
9.4
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 Pb
corrections 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).
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
NS-23-1
NS-24-1
NS-25-1
NS-26-1
NS-27-1
NS-28-1
NS-29-1
NS-30-1
NS-3-1
NS-31-1
NS-32-1
NS-33-1
NS-33-2
NS-33-3
NS-33-4
NS-33-5
NS-33-6
NS-33-7
NS-33-8
NS-4-1
NS-4-2
NS-4-3
NS-4-4
NS-4-5
NS-4-6
NS-5-1
NS-6-1
NS-7-1
NS-8-1
NS-9-1
NS-9-2
23
24
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
grain fragments suggest a homogeneous age that is now
more precisely determined, but still in good agreement
with the previously reported U–Pb age of 338 ± 1 Ma for
zircons from the same rock (Aftalion et al., 1989; IDTIMS).
The new dating of four (MIT and UNIGE), eleven
(NIGL), five (BSU) and three (ETHZ) Plešovice zircon
fragments yielded 206Pb/238U and 207Pb/235U dates that
agree within the decay constant uncertainties (Table 2a,
Fig. 8). The weighted mean 206 Pb/238 U dates are
summarized in Table 2b for each laboratory. A weighted
mean ET535 206Pb/238U date was calculated based upon
all MIT, UNIGE, NIGL and BSU data points (excluding
NIGL_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 date
was calculated based upon the ETHZ analyses at 337.40 ±
0.40 Ma (including ETHZ tracer calibration uncertainties;
MSWD = 0.57, n = 3; Fig. 8e). A weighted mean of the
ages obtained by different labs using the ET535 spike
gives a 206Pb/238U date of 337.13 ± 0.37 Ma (with tracer
calibration uncertainty of 0.05%; mean value of the
weighted means is identical within the analytical
uncertainty with the value of 337.13 ± 0.25, 2SD), with
an MSWD of 10.4 (Fig. 8f). This is our best estimate for
the age of the Plešovice zircon, and the variability of the
fragments represented in this study, measured with the
ET535 tracer. The high MSWD is a result of either a)
systematic measurement uncertainty due to interlaboratory bias or, b) actual age variations in the grains measured, given that the fragments dated in each lab come
from different large grains.
Laser ablation ICP-MS U–Pb dates obtained in three
different laboratories are concordant and identical within
the limits of analytical precision. They are also statistically indistinguishable from the 337.13 ± 0.37 Ma IDTIMS weighted mean 206Pb/238U date. The respective
calculated laser ablation ICP-MS concordia ages from
UoB, MUN and JWG are as follows: 338 ± 1 Ma (2σ, 61
analyses; Table 3a and Fig. 9a), 336 ± 1 Ma (2σ, 48
analyses; Table 3b and Fig. 9b) and 338 ± 1 Ma (2σ, 42
analyses; Table 3c and Fig. 9c). Despite the lower
precision of dates obtained by LA ICP-MS compared to
the ID-TIMS dates, the data are useful in that they show
age homogeneity on the scale of tens of microns both for
individual grains and for a multi-grain sub-sample of the
zircon fraction separated from the potassic granulite. The
actinide-rich domains that occur in some of the Plešovice
grains (some with U concentrations N 3000 ppm) were
tested for radiogenic Pb loss. Our LA ICP-MS data and
additional SHRIMP analyses (Curtin University of
Technology, Perth) suggest that, regardless of strong
radiation damage in the actinide-rich domains, there was
no significant Pb-loss. However, from a practical
standpoint, it is preferred to avoid such zones during
laser ablation ICP-MS analyses as (i) the high U signal
might exceed the dynamic range of some (e.g. SEM)
detection devices, (ii) corrections for detector dead-time
tend to be less accurate for very high signal intensities
and can lead to inaccurate ages, (iii) the high concentration of U ions can lead to unexpected space charge/
matrix effects and (iv) ablation rates in the radiationdamaged zones and pristine zircon might be different,
potentially leading to significant differences in the
plasma load between pristine and radiation-damaged
zircons.
SIMS U–Pb analyses of the Plešovice zircon yielded a
weighted mean 206Pb/238U date of 341.4 ± 1.3 Ma (61
Fig. 10. Ion-microprobe U–Pb ages of the Plešovice zircon obtained at Nordsim facility (Swedish Museum of Natural History in Stockholm). On the
left is concordia plot and on the right are 206Pb/238U dates. Error ellipses in the concordia plots and error bars on the 206Pb/238U plots are 1σ.
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
analyses from 33 individual grains; Table 4, Fig. 10).
While the multiple analyses of grains NS-22 and NS-33
yield ages identical to the ID-TIMS and laser ablation
ICP-MS measurements (Fig. 11), some analyses are older
to significantly older (cf. Table 4), resulting in the mean
age obtained by SIMS being somewhat older compared to
the ages obtained by other techniques. The data show no
notable correlation between the type of zircon zoning, U
concentration, position of the analyzed spot within the
grains and the obtained age (e.g., zircon NS-15 yields
younger ages towards the rim of the grain but zircon NS-4
shows an opposite trend with ages increasing towards the
grain rim, cf. Fig. 11). Other grains (zircons NS-22 and
NS-33 in Fig. 11) yielded more uniform ages of ca. 338 ±
3 Ma. A possible explanation of the variations in SIMS
U–Pb ages is a uranium and lead decoupling in some
25
parts of the zircon at a scale of the volume analyzed by
SIMS (about 300 of μm3). No similar variations were
observed by laser ablation ICP-MS measurements or IDTIMS analyses of fragments of the zircon grains. A more
detailed SIMS and structural study of the Plešovice zircon
is needed to fully explain the cause of the observed age
variations but the present data suggest that at this stage of
characterization, the Plešovice zircon is not an ideal age
reference material for high spatial resolution (SIMS)
measurements.
4.4. Hf isotopic composition
Concentration of Hf in the Plešovice zircon varies
between 0.9–1.44 wt.% (Table 1) and the estimated
accuracy of trace element and Hf determinations in this
Fig. 11. Cathodoluminescence images of four Plešovice zircon crystals with marked position of analyzed spots by ion microprobe. The analyses
correspond to Table 4.
26
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
study is ca. 5–10% (2 sigma). The laser ablation MC
ICP-MS data suggest a homogenous Hf isotopic
composition (Fig. 12) within and between individual
zircon grains with 176 Hf/177Hf values of 0.282482 ±
0.000012 (178Hf/177Hf = 1.46723 ± 0.00002; 2SD, UoB)
and 0.282481 ± 0.000014 ( 178 Hf/ 177 Hf = 1.46719 ±
0.00010; 2SD, JWG; cf. Table 5a) and with a mean
176
Hf/177 Hf 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 dissolution of seven zircon grains yielded similar Hf isotopic
compositions 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. Table
5b) Another 6 analyses conducted on 4 different solutions
(washes from U–Pb columns, NIGL) also gave a homogenous Hf isotopic composition with mean 176Hf/177Hf
value of 0.282480 ± 0.000013 (178Hf/177Hf = 1.46730 ±
0.00002; 2SD, Table 5b). The mean 176Hf/177Hf value for
all zircon analyses in solution mode is 0.282484 ±
0.000008 (2SD, 26 analyses, Fig. 13). As there are no
significant differences in Hf isotopic composition
obtained by laser ablation and solution techniques, nor
are there significant differences between results from the
three laboratories, the mean value of 176Hf/177Hf of
0.282482 ± 0.000013 (2SD) calculated from all 87
analyses (solution and laser ablation) is considered as a
best estimate of the Hf isotopic composition for the
Plešovice zircon.
In spite of the consistency of the laser ablation and
solution Hf isotopic data obtained from the three
laboratories, there is a small (but statistically insignificant) difference in laser ablation Hf isotopic measurements conducted at the JWG and data reported from
UoB. Hf isotopic composition of the Plešovice zircon
measured at the JWG shows somewhat larger variation
of the 176 Hf/177Hf data within and between individual
grains (cf. Fig. 12). This could suggest some minor
heterogeneity of the Hf isotope composition within and
between the grains. However, without additional solution mode data supporting this, it appears at present
more likely that these variations are at the limit of the
analytical precision and probably represent only an
analytical artifact. It should be highlighted here that
different parameters and approaches were used for
interference corrections (see Chu et al., 2002; Woodhead et al., 2004) between the three laboratories. The
179
Hf/177Hf ratio of Patchett and Tatsumoto (1980) was
used for mass bias correction of Hf as well as of
interfering isotopes of Yb and Lu isotopes in samples
analyzed at the UoB and in the NIGL. Analyses from the
JWG used the 179Hf/177Hf ratio for correction of Hf
isotopic ratios and a daily correction factor to account
for the differences between the Hf and the Yb and
Lu mass bias, respectively. This approach uses the
172
Yb/173 Yb ratio of Chu et al. (2002) as external
reference. None of the laboratories involved in this
study relies on the Yb isotopic ratio measured during
individual analyses when correcting the Yb and Lu
isotopic ratios for mass bias. Low Yb/Hf in zircon
and low signal intensity of Yb can result in larger
uncertainties and scatter of the 176Hf/177Hf ratios. For
comparison, the Hf isotopic data from the 91500 and
Plešovice zircons were corrected for mass bias using
both approaches (cf. Fig. 14). The 91500 zircon Hf data
corrected with 179Hf/177Hf ratio yield more consistent
Hf isotopic composition with lower analytical uncertainty and better external reproducibility compared to
the same data processed with 179 Hf/177Hf correction of
Hf isotopes and 172Yb/173 Yb correction of Yb and Lu
isotopes. The mean 176 Hf/177Hf value of 91500 zircon
(0.282277 ± 0.000043, Fig. 14a) calculated using the
Fig. 12. Hf isotopic composition of the Plešovice zircon sample obtained by laser ablation MC ICP-MS analyses. The mean 176Hf/177Hf composition
with 2SD uncertainty for all analyses is shown as gray shaded area. Different symbols indicate individual zircon grains.
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
27
Table 5a
Laser ablation MC ICP-MS measurements of Hf isotopic composition in the Plešovice zircon
Analysis
Lu/Hf
Yb/Hf
176
2σ
178
180
εHf337
2σ
UoB Hf2/1
UoB Hf2/2
UoB Hf2/3
UoB Hf2/4
UoB Hf2/5
UoB Hf2/6
UoB Hf2/7
UoB Hf2/8
UoB Hf2/9
UoB Hf2/10
UoB Hf2/11
UoB Hf3/1
UoB Hf3/2
UoB Hf3/3
UoB Hf3/4
UoB Hf3/5
JWG Hf4/1
JWG Hf4/2
JWG Hf4/3
JWG Hf4/4
JWG Hf4/5
JWG Hf4/6
JWG Hf4/7
JWG Hf5/1
JWG Hf5/2
JWG Hf5/3
JWG Hf5/4
JWG Hf5/5
JWG Hf5/6
JWG Hf6/1
JWG Hf6/2
JWG Hf6/3
JWG Hf6/4
JWG Hf6/5
JWG Hf7/1
JWG Hf7/2
JWG Hf7/3
JWG Hf7/4
JWG Hf7/5
JWG Hf7/6
JWG Hf7/7
JWG Hf8/1
JWG Hf8/2
JWG Hf8/3
JWG Hf8/4
JWG Hf8/5
JWG Hf8/6
JWG Hf8/7
JWG Hf8/8
JWG Hf8/9
JWG Hf8/10
JWG Hf8/11
JWG Hf9/1
JWG Hf9/2
JWG Hf9/3
JWG Hf9/4
JWG Hf9/5
0.0005
0.0007
0.0010
0.0009
0.0006
0.0006
0.0008
0.0008
0.0008
0.0007
0.0005
0.0007
0.0011
0.0011
0.0011
0.0011
0.0009
0.0007
0.0010
0.0010
0.0009
0.0010
0.0009
0.0007
0.0005
0.0004
0.0005
0.0008
0.0008
0.0006
0.0006
0.0006
0.0009
0.0008
0.0006
0.0004
0.0005
0.0004
0.0007
0.0012
0.0004
0.0010
0.0009
0.0009
0.0008
0.0011
0.0011
0.0011
0.0010
0.0012
0.0013
0.0012
0.0013
0.0009
0.0007
0.0006
0.0008
0.0116
0.0162
0.0217
0.0208
0.0128
0.0127
0.0170
0.0180
0.0188
0.0182
0.0122
0.0154
0.0225
0.0229
0.0235
0.0245
0.0077
0.0066
0.0085
0.0090
0.0082
0.0075
0.0074
0.0057
0.0044
0.0038
0.0050
0.0073
0.0072
0.0048
0.0056
0.0052
0.0080
0.0075
0.0052
0.0043
0.0044
0.0040
0.0065
0.0108
0.0039
0.0094
0.0077
0.0074
0.0080
0.0099
0.0096
0.0098
0.0075
0.0116
0.0123
0.0116
0.0123
0.0085
0.0070
0.0063
0.0073
0.282482
0.282482
0.282491
0.282484
0.282480
0.282473
0.282481
0.282476
0.282479
0.282494
0.282478
0.282490
0.282485
0.282471
0.282482
0.282486
0.282480
0.282481
0.282481
0.282471
0.282477
0.282485
0.282482
0.282480
0.282482
0.282472
0.282473
0.282472
0.282470
0.282472
0.282481
0.282483
0.282474
0.282475
0.282486
0.282484
0.282478
0.282482
0.282493
0.282485
0.282490
0.282488
0.282494
0.282486
0.282481
0.282481
0.282481
0.282482
0.282495
0.282485
0.282493
0.282495
0.282477
0.282482
0.282467
0.282478
0.282471
0.000014
0.000013
0.000013
0.000013
0.000014
0.000013
0.000013
0.000013
0.000013
0.000013
0.000013
0.000014
0.000013
0.000013
0.000014
0.000014
0.000013
0.000011
0.000011
0.000011
0.000011
0.000014
0.000017
0.000014
0.000013
0.000014
0.000012
0.000012
0.000010
0.000014
0.000011
0.000011
0.000014
0.000013
0.000011
0.000011
0.000013
0.000011
0.000013
0.000015
0.000013
0.000013
0.000013
0.000015
0.000015
0.000015
0.000015
0.000016
0.000013
0.000015
0.000017
0.000015
0.000017
0.000013
0.000013
0.000014
0.000013
1.467237
1.467224
1.467221
1.467217
1.467237
1.467238
1.467245
1.467221
1.467231
1.467238
1.467236
1.467225
1.467235
1.467209
1.467208
1.467237
1.467142
1.467168
1.467121
1.467183
1.467146
1.467240
1.467291
1.467126
1.467141
1.467157
1.467169
1.467164
1.467190
1.467181
1.467146
1.467188
1.467266
1.467256
1.467211
1.467177
1.467169
1.467195
1.467162
1.467093
1.467093
1.467218
1.467115
1.467139
1.467166
1.467286
1.467250
1.467285
1.467252
1.467227
1.467211
1.467258
1.467265
1.467212
1.467234
1.467140
1.467165
1.886714
1.886720
1.886688
1.886709
1.886754
1.886749
1.886691
1.886712
1.886704
1.886701
1.886691
1.886678
1.886684
1.886696
1.886710
1.886723
1.886556
1.886552
1.886555
1.886584
1.886554
1.886711
1.886665
1.886535
1.886617
1.886636
1.886634
1.886656
1.886651
1.886578
1.886566
1.886656
1.886788
1.886724
1.886619
1.886564
1.886658
1.886606
1.886729
1.886618
1.886840
1.886661
1.886609
1.886628
1.886618
1.886798
1.886777
1.886789
1.886790
1.886815
1.886720
1.886811
1.886753
1.886615
1.886594
1.886688
1.886674
−2.8
−2.8
−2.6
−2.8
−2.9
−3.1
−2.9
−3.0
−2.9
−2.4
−3.0
−2.5
−2.7
−3.2
−2.9
−2.7
−2.9
−2.9
−2.9
−3.3
−3.0
−2.8
−2.9
−2.9
−2.8
−3.2
−3.1
−3.2
−3.2
−3.2
−2.9
−2.8
−3.1
−3.1
−2.7
−2.8
−3.0
−2.9
−2.4
−2.8
−2.5
−2.6
−2.4
−2.7
−2.9
−2.9
−2.9
−2.9
−2.4
−2.7
−2.5
−2.4
−3.0
−2.8
−3.4
−3.0
−3.2
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.5
0.6
0.5
0.5
0.5
0.4
0.4
0.4
0.5
0.4
0.4
0.5
0.5
0.4
0.4
0.5
0.4
0.5
0.5
0.5
0.5
0.4
0.5
0.5
0.5
0.5
0.6
0.5
0.5
0.6
0.5
0.6
0.5
0.5
0.5
0.4
Hf/177Hf
Hf/177Hf
Hf/177Hf
(continued on next page)
28
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
Table 5a (continued)
Analysis
Lu/Hf
Yb/Hf
176
2σ
178
180
εHf337
2σ
JWG Hf9/6
JWG Hf9/7
JWG Hf9/8
JWG Hf9/9
0.0008
0.0009
0.0009
0.0009
0.0075
0.0080
0.0069
0.0073
0.282467
0.282477
0.282484
0.282472
0.000012
0.000013
0.000012
0.000011
1.467193
1.467233
1.467224
1.467143
1.886642
1.886768
1.886675
1.886654
−3.4
−3.0
−2.8
−3.2
0.4
0.5
0.4
0.4
Hf/177Hf
Hf/177Hf
Hf/177Hf
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 ± 0.000060
of Wiedenbeck et al. (1995) compared to the data
calculated using the second approach (0.282315 ±
0.000095, Fig. 14b). Wu et al. (2006) compiled all
available data for the 91500 zircon and reported a mean
176
Hf/177 Hf value of 0.282303 ± 0.000021. Similarly,
the 179Hf/177 Hf-corrected data from the Plešovice zircon
show less variation and a lower mean 176Hf/177 Hf value
compared to the data where the 179 Hf/ 177 Hf and
172
Yb/173 Yb ratios were used for mass bias correction
of Hf and Yb–Lu isotopes, respectively (Fig. 14c,d). In
conclusion, the two mass bias correction procedures
yield results that, within their analytical uncertainties,
agree with the recommended Hf isotopic composition.
When both the Hf and REE isotopic ratios are corrected
using the 179Hf/177Hf ratios, the resulting 176Hf/177 Hf
values show significantly less scatter but the achieved
analytical precision did not allow assessing which of the
two correction procedures can potentially provide more
accurate Hf isotopic composition of zircon. For better
comparison and understanding of the correction procedures they have to be tested on zircon grains with higher
Yb/Hf ratio (Woodhead and Hergt, 2005). The correction of the REE isotopic ratios using the Hf mass bias is
valid probably only for zircon with low Yb/Hf. In such
zircons will the choice of the Yb mass bias correction
Table 5b
Solution MC ICP-MS measurements of Hf isotopic composition in the Plešovice zircon
Analysis
Lu/Hf
Yb/Hf
176
2σ
178
180
εHf337
2σ
UoB Hf1/1
UoB Hf1/2
UoB Hf1/3
UoB Hf1/4
UoB Hf1/5
UoB Hf1/6
UoB Hf1/7
UoB Hf1/8
UoB Hf1/9
UoB Hf1/10
JWG Hf1/1
JWG Hf1/2
JWG Hf1/3
JWG Hf1/4
JWG Hf1/5
JWG Hf1/6
JWG Hf1/7
JWG Hf1/8
JWG Hf1/9
JWG Hf1/10
NIGL Z10
NIGL Z9/1
NIGL Z9/2
NIGL Z9/3
NIGL Z8
NIGL Z7
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0007
0.0006
0.0006
0.0006
0.0015
0.0007
0.0012
0.0012
0.0012
0.0011
0.0011
0.0011
0.0011
0.0011
0.0011
0.0011
0.0006
0.0008
0.0008
0.0005
0.0004
0.0005
0.0005
0.0006
0.0006
0.0007
0.0077
0.0068
0.0067
0.0068
0.0135
0.0076
0.282483
0.282481
0.282481
0.282482
0.282483
0.282481
0.282484
0.282487
0.282482
0.282485
0.282481
0.282485
0.282491
0.282489
0.282492
0.282483
0.282485
0.282491
0.282481
0.282487
0.282478
0.282485
0.282479
0.282481
0.282480
0.282478
0.000013
0.000012
0.000012
0.000013
0.000012
0.000013
0.000013
0.000012
0.000012
0.000012
0.000009
0.000008
0.000010
0.000009
0.000008
0.000010
0.000007
0.000010
0.000009
0.000008
0.000012
0.000013
0.000011
0.000011
0.000018
0.000013
1.467219
1.467216
1.467223
1.467222
1.467216
1.467222
1.467220
1.467224
1.467220
1.467218
1.467222
1.467216
1.467182
1.467238
1.467194
1.467238
1.467219
1.467203
1.467222
1.467225
1.467291
1.467300
1.467292
1.467289
1.467290
1.467312
1.886675
1.886655
1.886680
1.886676
1.886684
1.886677
1.886674
1.886671
1.886691
1.886682
1.886673
1.886709
1.886632
1.886634
1.886643
1.886639
1.886686
1.886672
1.886673
1.886656
N/A
N/A
N/A
N/A
N/A
N/A
−2.8
−2.9
−2.9
−2.9
−2.8
−2.9
−2.8
−2.7
−2.8
−2.7
−2.9
−2.8
−2.6
−2.6
−2.5
−2.8
−2.8
−2.6
−2.9
−2.7
−3.0
−2.8
−3.0
−2.9
−2.9
−3.0
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.3
0.3
0.2
0.3
0.3
0.3
0.4
0.5
0.4
0.4
0.6
0.4
Hf/177Hf
Hf/177Hf
Hf/177Hf
Analyses names indicate where the measurements were done: UoB— University of Bergen, JWG— J.W. Goethe University of Frankfurt am Main,
NIGL— NERC Isotope Geosciences Laboratory. εHf337 calculated as an initial value for the age 337 Ma obtained by U–Pb dating of Plešovice
zircon.
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
29
Fig. 13. Hf isotopic composition of the Plešovice zircon sample obtained by solution MC ICP-MS analyses. The mean 176Hf/177Hf composition with
2SD uncertainty for all solution Hf analyses is shown as gray shaded area.
protocol have only little effect on the resulting Hf
isotopic composition due to the insignificant contribution of 176Yb to 176Hf (Wu et al., 2006).
values between −3.4 and − 2.4 also point to formation of
their host potassic granulite from a mature continental
crust source, such as would be expected in the
Moldanubian Zone.
4.5. Implications for granulite facies rocks in southern
Bohemian Massif
4.6. Comparison with other zircon reference materials
The new U–Pb zircon age data, together with the
previous petrological studies of the host potassic
granulite from Plešovice (Vrána, 1989; Janoušek et al.,
2007) can be used to precisely constrain the timing of
mineral growth during granulite facies metamorphism in
the southern Bohemian Massif. Aftalion et al. (1989)
reported identical ages of 338 ± 1 Ma for zircons in the
matrix of the potassic granulite and zircons that occur as
inclusions in garnet. Garnet (pyrope up to 33 mol%;
Vrána, 1989) in this rock is weakly zoned with pyrope
component decreasing from core to rim, which is
compensated for by increase in almandine and spessartine components and it contains exsolution needles of
rutile throughout the garnet grains. The chemical and
textural evidence suggests crystallization of the garnet
from non-eutectic melt at granulite facies conditions at
temperatures exceeding 1000 °C (Vrána, 1989; Janoušek et al., 2007). Other phases that occur both in the
granulite matrix and also as inclusions in the garnet are
K-feldspar, apatite, monazite and zircon. Zircon often
includes K-feldspar and apatite, and rarely also garnet
and quartz. The observed mineral relations point to
simultaneous crystallization of garnet, K-feldspar,
apatite, monazite and zircon, the age of which has
now been constrained to 337.13 ± 0.37 Ma.
Similar to the previous evidence based on Sr and Nd
isotopes for crustal origin of the parent magma of the
granulites in southern Bohemian Massif (Janoušek et al.,
2007), the new zircon Hf isotopic data with epsilon
In addition to many in-house zircon reference
materials used for microanalytical techniques, several
natural zircons have been proposed as reference
materials for in-situ U–Pb and/or Hf isotopic analyses
(Tables 6 and 7). From these, the 91500 zircon has been
well characterized for U–Pb, Hf and O isotopic
composition, trace elements and crystal structural
properties (Wiedenbeck et al., 1995; 2004).
Isotopic analyses by LA ICP-MS require that zircon
reference material should be isotopically homogeneous
and available in sufficient quantity (at least tens,
preferably hundreds of grams), should contain radiogenic Pb at ppm or higher concentrations and should also
have at least mm-scale grain size suitable for repeat
analyses by laser beam that can be up to several tens of
micrometers in diameter. The 91500 zircon (Wiedenbeck
et al., 1995) possesses most of the properties required for
a reference sample but its supply will soon be exhausted
(Woodhead and Hergt, 2005). The alternatives include
the Temora 2 zircon (Black et al., 2004) which occurs as
small grains that are difficult to sample for LA ICP-MS
analysis (Woodhead and Hergt, 2005), the Mud Tank
zircon that has rather low U and radiogenic Pb contents
(Table 6) and the GJ-1 zircon (Jackson et al., 2004) that
has variable 207Pb/235U ratios within as well as between
individual zircon grains. From the available zircon
reference samples, the Plešovice zircon has the highest
content of U (Table 6) but this study provides no
evidence for Pb loss from the actinide-rich domains in
30
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
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. The
176
Hf/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 calculated
mean 176Hf/177Hf values with 2SD uncertainty.
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
31
Table 6
Summary of natural zircon reference materials used/proposed for in-situ isotopic analysis and compilation of their U–Pb data
Reference material
a
Age (Ma) Reference U (ppm)
Pbrad (ppm)
QGNG
AS3
91500
Mud tank
GJ-1 a, b
SL 13 a
Z6266 (Br266)
R33
Temora 1
Temora 2
Plešovice
1850
1099
1065
732
609
572
559
419
417
417
337.1
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(8)
This work
35–1151
113–626
71–86
6.1–36.5
212–422
240 ± 20
871–958
61–398
64–846
82–320
465– 3084
21–158
61.308A b, 61.308B b
2.5
(3)
132–242
0.064–0.131
(3)
21.3–26
G42728A b, G42728B b 1
22–135
13–16
0.73–4.39
19.3–37.4
76.5–84.2
14.3 (aver.)
Grain size
Comments
0.05–0.3 mm
Up to 0.5 mm
Variable size; 238 g
mm–cm
ca. 1 cm
N/A
2–5 mm
N/A
Up to 0.6 mm
0.05–0.3 mm
1–6 mm
Available from rock outcrop; probable Pb loss
Available from rock outcrop; probable Pb loss
Almost exhausted supply
Available from rock outcrop
Several crystal from a gem dealer
One single crystal; probable Pb loss
2.5 g prepared for distribution
Available from rock outcrop; probable Pb loss
Available from rock outcrop
Available from rock outcrop
Available from rock outcrop; 500 g prepared
for distribution
Limited supply; very small sample
0.49 and 0.71 g
crystals
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) Kinny
et 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 Plešovice
zircon makes it a potentially suitable reference material
for U–Pb dating of high-U zircons.
In addition to the U–Pb systematics, the 91500 and
Plešovice zircons have also been characterized for Hf
isotopes (Table 7). The 91500 zircon was reported to
have a heterogeneous Hf isotopic composition (Griffin
et al., 2006, 2007), although this was recently disputed by
Corfu (2007). Woodhead and Hergt (2005) proposed the
Temora 2 and Mud Tank zircons as potential reference
materials for in-situ Hf isotopic measurements by LA
ICP-MS. While Temora 2 occurs as grains that are too
small for repeat laser ablation sampling, the Mud Tank
zircon is both homogeneous in Hf isotopic composition
and has a suitable size for laser ablation ICP-MS analysis
(Table 7). The Plešovice zircon is also homogeneous in
Hf isotopes and it has a large range of Lu/Hf and Yb/Hf
ratios. Compared to Temora 2, the Plešovice zircon has a
lower Yb/Hf ratio which requires to make the isobaric
interference corrections using Hf (see Section 4.4).
5. Conclusions
The new ID-TIMS and laser ablation ICP-MS dating
of the Plešovice zircon material gave consistent concordant U–Pb ages that are in average only 1 Ma younger
Table 7
Summary of natural zircon reference materials used/proposed for in-situ isotopic analysis and compilation of their Lu–Hf data
Reference material
Reference
Hf (ppm)
176
Hf/177Hf (±2SD)
Lu/Hf
QGNG
As3
91500
Mud tank
GJ-1
SL 13
Z6266 (Br266)
R33
Temora 1
Temora 2
Plešovice
61.308A, 61.308B
G42728A, G42728B
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(8)
This work
(3)
(3)
10600 ± 340
0.281612 ± 0.000004
0.0053
5610– 29748
0.282303 ± 0.000021
0.282507 ± 0.000006
0.0004–0.0217
0.0003
Yb/Hf
0.0106–0.0168
0.0156
8310 ± 90
8980–14431
5350–6060
0.282686 ± 0.000008
0.282482 ± 0.000013
0.282977 ± 0.000014 (1SD)
0.0078
0.0004–0.0015
0.0126–0.0178
0.0262–0.0554
0.0038–0.0245 (aver. 0.0100)
0.0302–0.0636
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) Kinny
et al., 1991 (7) Stern 2001 (8) Black et al., 2004 (9) Black et al., 2003a. Other references used to compile this table: Amelin et al., 2000; Woodhead
and Hergt 2005; Izuka and Hirata 2005; Nebel-Jacobsen et al., 2005; Wu et al., 2006; Griffin et al., 2006, 2007; Corfu 2007; Woodhead et al., 2004.
32
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
than the previously reported U–Pb age of zircon from the
potassic granulite by Aftalion et al. (1989). The new mean
ID-TIMS U–Pb age of 337.13 ± 0.37 Ma (2SD) is
considered to represent the best age estimate for the
Plešovice zircon.
Solution and laser ablation MC ICP-MS analyses of a
multigrain sample of the Plešovice zircon suggest it has
a homogenous Hf isotopic composition. The low Lu/Hf
(up to 0.001) and Yb/Hf (up to 0.025) ratios in the zircon
result in only a small influence of the choice of isobaric
interference correction procedure on the value and
uncertainty of the corrected 176Hf/177 Hf ratios. The
mean 176Hf/177 Hf value of 0.282482 ± 0.000013 (2SD)
is considered as the best estimate of the Hf isotopic
composition of the Plešovice zircon.
Raman spectroscopy, optical and BSE imaging and
trace element analysis revealed the presence of strongly
radiation-damaged domains in ca. one third of studied
Plešovice zircon grains. These domains are rich in
actinides (U and Th) and appear as bright patches on
BSE images that can be easily avoided during the laser
ablation ICP-MS analysis. Although there has been no
significant Pb loss found in these zones, they should be
avoided during routine laser ablation ICP-MS analysis
because of likely space charge effects and different
ablation properties. On the other hand these areas could be
used in U–Pb analyses of unknown zircons with similar
level of actinides concentration. Occasional inclusions of
K-feldspar and apatite can be easily identified under an
optical microscope and avoided during the analysis.
Despite the significant variations in trace element
contents that preclude the use of the Plešovice zircon as
a reference material for in-situ trace elements analyses,
the zircon is well suited as calibration and reference
material for laser ablation ICP-MS U–Pb and Hf
isotopic measurements. At this stage of characterization,
the Plešovice zircon is not suitable as a reference
material for the SIMS U–Pb isotopic dating.
Acknowledgements
We thank A.K. Kennedy for experimental assistance
on SHRIMP, F. Veselovský for assistance with mineral
separation and A. Wagner for sample preparation for
Raman spectroscopy. Assistance with BSE imaging was
provided by N. Groschopf and J. Götze acquired the CL
images. J. Sláma has been financially supported by the
Grant Agency of the Academy of Sciences of the Czech
Republic (KJB300130701), Czech Science Foundation
(205/05/0381) and the Charles University (264/2005/BGEO). Two anonymous reviewers provided careful and
constructive reviews of the manuscript.
References
Aftalion, M., Bowes, D.R., Vrána, S., 1989. Early Carboniferous
U–Pb zircon age of garnetiferous, perpotassic granulites, Blanský les
massif, Czechoslovakia. Neues Jahrbuch für Mineralogie, Monatsheftem, 4, 145–152.
Amelin, Y., Lee, D.C., Halliday, A.N., 2000. Early-middle Archaean
crustal evolution deduced from Lu–Hf and U–Pb isotopic studies 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 Australian
Geology 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 zircon
standard for phanerozoic U–Pb geochronology. Chemical Geology
200, 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-218
microprobe geochronology by the monitoring of a trace-elementrelated matrix effect; SHRIMP, ID-TIMS, ELA-ICP-MS and
oxygen 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 to
phanerozoic geochronology: a critical appraisal of four zircon
standards. Chemical Geology 200, 171–188.
Blichert-Toft, J., Albarede, F., 1997. The Lu–Hf isotope geochemistry
of chondrites and the evolution of the mantle–crust system. Earth
Planetary Science Letters 148, 243–258.
Carswell, D.A., O'Brien, P.J., 1993. Thermobarometry and geotectonic significance of high-pressure granulites: examples from the
Moldanubian 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 from
the 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. Hf
isotope ratio analysis using multi-collector inductively coupled
plasma mass spectrometry: an evaluation of isobaric interference
corrections. Journal of Analytical Atomic Spectrometry 17,
1567–1574.
Cooke, R.A., 2000. High-pressure/temperature metamorphism in the
St. Leonhard Granulite Massif, Austria: evidence from intermediate pyroxene-bearing granulites. International Journal of Earth
Sciences 89, 631–651.
Corfu, F., 2007. Comment to short-communication ‘Comment: Hfisotope 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 of
zircon in the Bishop Tuff at the millennial scale. Geology 35 (12),
1123–1126.
Dallmeyer, R.D., Franke, W., Weber, K. (Eds.), 1995. Pre-Permian
Geology of Central and Eastern Europe. Springer-Verlag, Berlin.
Debievre, P., Taylor, P.D.P., 1993. Table of the isotopic compositions
of the elements. International Journal of Mass Spectrometry and
Ion 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
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
sample of thallium. Journal of Research of the National Bureau of
Standards 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 granulites
and related rocks: petrology, geochemistry, and radioactivity.
Rozpravy Československé akademie věd, řada matematických a
přírodních věd 97, 1–102.
Firestone, R.B., Shirley, V.S., 1996. Table of Isotopes. Wiley, New York.
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 tectonic
evolution. In: Franke, W., Haak, V., Oncken, O., Tanner, D. (Eds.),
Orogenic Processes: Quantification and Modelling in the Variscan
Belt. 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 on
multiple zoned zircons from a South-Bohemian granulite. Journal
of the Czech Geological Society, 48, 51–52.
Fuchs, G., Matura, M., 1976. Zur Geologie des Kristallins der
süddlichen Böhmishe Masse. Jahre plante die Geologische
Bundesanstalt 119, 1–43.
Gerdes, A., Zeh, A., 2006. Combined U–Pb and Hf isotope LA-(MC-)
ICP-MS analyses of detrital zircons: comparison with SHRIMP
and new constraints for the provenance and age of an Armorican
metasediment in Central Germany. Earth and Planetary Science
Letters 249, 47–62.
Gerstenberger, H., Haase, G., 1997. A highly effective emitter
substance for mass spectrometric Pb isotope ratio determinations.
Chemical Geology 136, 309–312.
Götze, J., 2000. Cathodoluminescence microscopy and spectroscopy
in 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. Chemical
Geology 233, 358–363.
Griffin, W.L., Pearson, N.J., Belousova, E.A., Saeed, A., 2007. Reply to
“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)”
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. Eleventh
Annual V.M. Goldschmidt Conference, Abstract # 3712, LPI
Contrib No. 1088, Lunar Planet Inst, Houston (CD-ROM).
Horn, I., Rudnick, R.L., McDonough, W.F., 2000. Precise elemental
and isotope ratio determination by simultaneous solution nebulization and laser ablation-ICP-MS: application to U–Pb geochronology. 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 accessory
mineral geochronology by LA-MC-ICP-MS. Journal of Analytical
Atomic Spectrometry 18, 837–846.
Hoskin, P.W.O., Schaltegger, U., 2003. The composition of zircon and
igneous and metamorphic petrogenesis. In: Hanchar, J.M., J.M.,
Hoskin, P.W.O. (Eds.), Zircon. Reviews in Mineralogy and
Geochemistry, vol. 53. Mineralogical Society of America,
Washington, DC., pp. 27–62.
33
Iizuka, T., Hirata, T., 2005. Improvements of precision and accuracy in
in situ Hf isotope microanalysis of zircon using the laser ablationMC-ICPMS technique. Chemical Geology, 220 (1–2), 121–137.
Irmer, G., 1985. Zum Einfluß der Apparatefunktion auf die Bestimmung
von Streuquerschnitten und Lebensdauern aus optischen Phononenspektren. 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-mass
spectrometry to in situ U–Pb zircon geochronology. Chemical
Geology, 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 of
235U 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 largely
undepleted felsic granulites from the Moldanubian Zone of the
Bohemian Massif. 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 and
chemical approach to zircon geochronology: refining the Archaean
history of the Napier Complex, east Antarctica. Contributions to
Mineralogy 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 Lower
Aillik Group, Makkovik Province, Canada: evolution of a passive
margin-foredeep sequence based on petrochemistry and U–Pb
(TIMS and LAM-ICP-MS) geochronology. Precambrian Research
105, 331–356.
Kinny, P.D., Compston, W., Williams, I.S., 1991. A reconnaissance
ion-probe study of hafnium isotopes in zircons. Geochimica et
Cosmochimica Acta 55, 849–859.
Kodym, O., et al. (Ed.), 1981. Základní Geologická Mapa ČSSR
1:25 000. 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 provenance
studies — a comparison of laser ablation ICP-MS and SIMS
techniques. Chemical Geology 182, 605–618.
Košler, J., Sylvester, P.J., 2003. Present trends and the future of zircon
in geochronology: laser ablation ICP-MS. In: Hanchar, J.M., J.M.,
Hoskin, P.W.O. (Eds.), Zircon. Reviews in Mineralogy and
Geochemistry, 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 Lower
Carboniferous conglomerates — evidence for rapid exhumation
at the eastern margin of the Variscan Bohemian Massif.
Geophysical Research Abstracts 5, 434.
Kotková, J., Harley, S.L., 1997. Mineral controls on the trace
element and REE geochemistry of high-pressure leucogranulites
from the Bohemian Massif. Journal of the Czech Geological
Society 42, 40.
Krogh, T.E., 1973. Low-contamination method for hydrothermal
decomposition of zircon and extraction of U and Pb for isotopic
age determinations. Geochimica et Cosmochimica Acta 37,
485–494.
Kröner, A., O'Brien, P.J., Nemchin, A.A., Pidgeon, R.T., 2000. Zircon
ages for high pressure granulites from South Bohemia, Czech
34
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
Republic, and their connection to Carboniferous high temperature
processes. 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 model
ages of high-grade Moldanubian metasediments, Bohemian
Massif, Czechoslovakia. Contributions to Mineralogy and Petrology 99, 257–266.
Lapen, T.J., Mahlen, N.J., Johnson, C.M., Beard, B.L., 2004. High
precision Lu and Hf isotope analyses of both spiked and unspiked
samples: a new approach. Geochemistry, Geophysics and
Geosystems 5. doi:10.1029/2003GC000582, Q01010.
Lee, J.K.W., Tromp, J., 1995. Self-induced fracture generation in
zircon. Journal of Geophysical Research 100, 17753–17770.
Ludwig, K.R., 1980. Calculation of uncertainties of U–Pb isotope
data. Earth and Planetary Science Letters 46 (2), 212–220.
Ludwig, K.R., 2003. Isoplot/Ex Version 3.00: a Geochronological
Toolkit for Microsoft Excel. Berkeley Geochronology Center,
Berkeley, CA.
Matte, P., Maluski, H., Rajlich, P., Franke, W., 1990. Terrane
boundaries in the Bohemian Massif: result of large-scale Variscan
shearing. Tectonophysics 177, 151–170.
Mattinson, J.M., 2003. CA (chemical abrasion)-TIMS: high-resolution
U–Pb zircon geochronology combining high-temperature annealing
of radiation damage and multi-step partial dissolution analysis. Fall
Meeting 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 dissolution
analysis 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. American
Mineralogist 76, 1510–1532.
Nasdala, L., Irmer, G., Wolf, D., 1995. The degree of metamictization
in zircon: a Raman spectroscopic study. European Journal of
Mineralogy 7, 471–478.
Nasdala, L., Kronz, A., Hanchar, J.M., Tichomirowa, M., Davis, D.D.,
Hofmeister, W., 2006. Effects of natural radiation damage on backscattered electron images of single-crystals of minerals. American
Mineralogist 91, 1738–1746.
Nasdala, L., Wenzel, M., Vavra, G., Irmer, G., Wenzel, T., Kober, B.,
2001. Metamictisation of natural zircon: accumulation versus
thermal annealing of radioactivity-induced damage. Contributions
to 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 in
Mineralogy and Geochemistry, vol. 53. Mineralogical Society of
America, 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 combined
U–Pb dating and Hf isotope measurements by TIMS and MCICPMS. 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. Journal
of Metamorphic Geology 21, 3–20.
Owen, J.V., Dostal, J., 1996. Contrasting corona structures in mafic
granulite from the Blanský Les complex, Bohemian Massif, Czech
Republic. Canadian Mineralogist 34, 959–966.
Paces, J.B., Miller, J.D., 1993. Precise U–Pb ages of Duluth Complex
and related mafic intrusions, northeastern Minnesota: geochronological insights into physical, petrogenetic, paleomagnetic and
tectonomagmatic processes associated with the 1.1 Ga midcontinent
rift system. Journal of Geophysical Research 98, 13997–14013.
Patchett, P.J., 1983. Importance of the Lu–Hf isotopic system in
studies of planetary chronology and chemical evolution. Geochimica et Cosmochimica Acta 47, 81–91.
Patchett, P.J., Tatsumoto, M., 1980. A routine high-precision method
for Lu–Hf isotope geochemistry and chronology. Contributions to
Mineralogy and Petrology 75, 263–267.
Pupin, J.P., 1980. Zircon and granite petrology. Contributions to
Mineralogy and Petrology 73, 207–220.
Roberts, M.P., Finger, F., 1997. Do U–Pb zircon ages from granulites
reflect peak metamorphic conditions? Geology 25, 319–322.
Scherer, E.E., Münker, C., Mezger, K., 2001. Calibration of the Lu–Hf
Clock. Science 293, 683–687.
Schmitz, M.D., Bowring, S.A., Ireland, T.R., 2003. Evaluation of
Duluth Complex anorthositic series (AS3) zircon as a U–Pb
geochronological standard, new high-precision isotope dilution
thermal ionization mass spectrometry results. Geochimica et
Cosmochimica Acta, 67 (19), 3665–3672.
Schmitz, M.D., Schoene, B., 2007. Derivation of isotope ratios, errors
and error correlations for U–Pb geochronology using 205Pb–
235U–(233U)-spiked isotope dilution thermal ionization mass
spectrometric data. Geochemistry, Geophysics and Geosystems 8.
doi:10.1029/2006GC001492 (G3), Q08006.
Sláma, J., Košler, J., Pedersen, R.B., 2007. Behaviour of zircon in
high-grade metamorphic rocks — evidence from Hf isotopes, trace
elements and textural studies. Contributions to Mineralogy and
Petrology 154, 335–356.
Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial lead.
isotope evolution by a two-stage model. Earth and Planetary
Science Letters 26, 207–221.
Stern, R.A., 2001. A new isotopic and trace element standard for
the ion microprobe: preliminary TIMS U–Pb and electron microprobe data, current research. Radiogenic Age and Isotopic
Studies: Report 14. Geological Survey of Canada, Ottawa,
Canada.
Stern, R.A., Amelin, Y., 2003. Assessment of errors in SIMS zircon
U–Pb geochronology using a natural zircon standard and NIST
SRM 610 glass. Chemical Geology, 197 (1–4), 111–142.
Svojtka, M., Košler, J., Venera, Z., 2002. Dating granulite-facies
structures and the exhumation of lower crust in the Moldanubian
Zone of the Bohemian Massif. International Journal of Earth Sciences
91, 373–385.
Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: its
Composition 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 the
Bohemian Massif, Czechoslovakia, and their significance in the
evolution of Central Europe. Transactions of the Royal Society of
Edinburgh, Earth Sciences 73, 89–108.
Vrána, S., 1989. Perpotassic granulites from southern Bohemia — a
new rock-type derived from partial melting of crustal rocks under
upper mantle conditions. Contributions to Mineralogy and
Petrology 103, 510–522.
Vrána, S., Blümel, P., Petrakakis, K., 1995. Metamorphic evolution. In:
Dallmeyer, R.D., Franke, W., Weber, K. (Eds.), Pre-Permian Geology
of Central and Eastern Europe. Springer, Berlin Heidelberg New
York, pp. 453–466.
Wendt, J.I., Kröner, A., Fiala, J., Todt, W., 1994. U–Pb zircon and
Sm–Nd dating of Moldanubian HP/HT granulites from south
Bohemia, Czech Republic. Journal of the Geological Society of
London 151, 83–90.
J. Sláma et al. / Chemical Geology 249 (2008) 1–35
Whitehouse, M.J., Claesson, S., Sunde, T., Vestin, J., 1997. Ionmicroprobe U–Pb zircon geochronology and correlation of Archaean
gneisses from the Lewisian Complex of Gruinard Bay, north-west
Scotland. Geochimica et Cosmochimica Acta 61, 4429–4438.
Whitehouse, M.J., Kamber, B., Moorbath, S., 1999. Age significance
of U–Th–Pb zircon data from early Archaean rocks of west
Greenland—a reassessment based on combined ion-microprobe
and 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 natural
zircon standards for U–Th–Pb, Lu–Hf, trace element and REE
analyses. 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.
35
Further characterisation of the 91500 zircon crystal. Geostandards
and Geoanalytical Research 28 (1), 9–39.
Woodhead, J.D., Hergt, J.M., 2005. A preliminary appraisal of seven
natural zircon reference materials for in situ Hf isotope determination. 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. Hf
isotopic compositions of the standard zircons and baddeleyites
used in U–Pb geochronology. Chemical Geology 234 (1–2),
105–126.