Application
Note: 30170
Simultaneous in situ Analysis of U-Pb Age
and Hf Isotopes of Zircon by Laser Ablation
Sector-Field (MC-) ICP-MS
J. B. Schwieters, C. Bouman, M. Deerberg, J. D.Wills, Thermo Fisher Scientific, Bremen, Germany
A. Gerdes, Institut für Geowissenschaften, Johann Wolfgang Goethe Universität, Frankfurt am Main, Germany
Introduction
Key Words
• ELEMENT XR
• NEPTUNE
• Isotope Ratio
• Laser Ablation
• Zircon
The combination of laser ablation with multicollector
inductively coupled plasma mass spectrometers
(LA-MC-ICP-MS) has been shown to produce high
quality zircon age data from U-Th-Pb isotopic studies.
These results however may not correctly indicate the
number of zircon forming events, especially those arising
from multiple growth and alteration processes. This
limitation can be overcome by combining results from
Pb-U and Lu-Hf analyses made on small, well defined
zircon areas.
Static measurements of Pb-U and Lu-Hf can not be
achieved in a single MC-ICP-MS analysis due to the large
mass range that would need to be scanned. This has
previously meant sequential analyses of the Pb-U and the
Lu-Hf systems at the same zircon site1, e.g. an initial Pb-U
analysis by laser ablation coupled to sector-field ICP-MS
(LA-ICP-SFMS) and a subsequent LA-MC-ICP-MS
analysis for Lu-Hf2. The sequential analyses were made
as closely as possible in the same area (growth domain)
of the zircon, for example a 40 µm Lu-Hf spot was drilled
on top of a 30 µm U-Pb spot)2.
In order to overcome the limitations of sequential
sampling of U-Th-Pb and Hf isotopes from different
sites in zircons, a fast scanning single collector and
a multicollector inductive coupled plasma mass spectrometer have been coupled in parallel to a New Wave
UP213 213 nm UV laser ablation system. A low volume
laser ablation sample chamber with fast response (< 1 s)
and rapid washout time was fitted instead of the standard
sample chamber in order to enable sequential sampling
of heterogeneous grains during time-resolved data
acquisition on both instruments. The ablated material
was transported in helium, split after the ablation cell via
a Y-shaped connector and introduced simultaneously into
the two mass spectrometers, the Thermo Scientific
ELEMENT XR for U-Th-Pb analysis and Thermo
Scientific NEPTUNE for high precision Hf isotope
analysis.
For accurate age dating of zircons the control
of common lead contaminations is essential. This can be
done by monitoring mass 204Pb which is not part of the
U-Pb decay scheme. Since the natural abundance of 204Pb
is so small every common lead contribution measured on
204Pb is magnified by about a factor of 15 to 18 on 206Pb
and 207Pb intensities. This means the small 204Pb signal has
to be measured precisely and therefore the highest
sensitivity is required to achieve the smallest statistical
error. In comparison to quadrupole ICP-MS instruments3
the ELEMENT XR sector-field ICP-MS is at least one
order of magnitude more sensitive and as a consequence
the statistical uncertainty on 204Pb is significantly
improved.
Instrumentation
U-Th-Pb analysis
Instrument
Scan mode
Scanned masses
Mass resolution
Dead time
Dwell time/isotope
Settling time/isotope
Number of scans
Integration time
Background
Ablation time
Carrier gas
Laser
Spot size
Laser settings
Laser fluence
Drill speed
Hf isotope analysis
ELEMENT XR
NEPTUNE
E-Scan
Static
202, 204, 206, 207,
171, 173, 175, 176,
208, 235, 232, 238
177, 178, 179, 180
300
300
18 ns
20 ns
4 ms
1s
1 ms
–
1080
50
1 s (= 15 scans)
1s
20 s
50 s
50 s
0.5 L/min He (+1.1 L/min Ar)
UP213 SA (New Wave
Research; Nd:YAG,
213 nm)
55 to 80 µm
5 Hz
~ 3 J/cm2
0.6 µm/s
Table 1: Operating conditions and instrument settings.
The advantages of the low volume laser chamber4
(Figure 2) for discrete laser sampling can be seen in Figure
3. Uptake delays of 1 s were achievable with the low
volume cell, compared to 6 s with the standard sample
cell. In the low volume cell, signal intensities after the end
of the ablation dropped by 2 orders of magnitude in less
than 4 s and 3 orders in about 6 s. In comparison, the
signal from the standard cell needs more than 3 times
longer (13 s and 25 s respectively) to drop to the same
levels. Spiking is still observed in the standard cell up to
50 s after the end of ablation, while the low volume cell
shows no spiking.
Figure 1: Screenshot from the ELEMENT software showing instrument
settings and sensitivity obtained for La and Th in NIST 612 using the laser
sampling parameters as shown.
The primary advantages of ICP-SFMS offers over
other ICP-MS instrumentation for U-Th-Pb analyses are
shown in Figure 1 and can be summarized as:
• The characteristic flat-top peaks of sector-field mass
spectrometers in low mass resolution allow the reliable
use of single point per peak analyses.
• The high sensitivity of ICP-SFMS allows for increased
accuracy on the common lead correction that is made
when measuring 202Hg as well as 204Pb+Hg. With less
sensitive instrumentation small common lead
contaminations detected at mass 204 would be
otherwise magnified on masses 206Pb and 207Pb, leading
to worsened Pb-U dating accuracy.
Figure 3: Improvement in sample uptake and washout when using the low
volume laser sample chamber.
Figure 2: Low volume laser sample chamber used in all analyses.
Results
data-point error ellipses are 2σ
91500
Concordia age = 1066.2 ± 3.3Ma
MSWDC+E = 0.56
0.170
1.72 1.76 1.80 1.84 1.88 1.92 1.96 2.00
207
Pb/235U
data-point error ellipses are 2σ
GJ-1
GJ-1
206
Concordia age = 607.6 ± 2.4Ma
MSWDC+E = 0.56
206
206
Concordia age = 414.5 ± 2.0Ma
MSWDC+E = 0.89
Pb/238U age (Ma)
1090
1070
average = 0.282689 ± 0.000049
Hf/177Hf
Hf/177Hf
0.28275
Hf/177Hf
412
0.28270
408
0.28265
404
0.28260
Mean = 414.9 ± 2.0 [0.48%] 95% conf.
MSWD = 0.83, probability = 0.62
spot size 65 and 55 µm, respectively
0.28255
206
0.178
Concordia age = 1094.9 ±3.3Ma
MSWDC+E = 1.06
0.170
1.76 1.80 1.84 1.88 1.92 1.96 2.00 2.04 2.08
207
Pb/235U
data-point error ellipses are 2σ
0.128
error bars are 2σ
As3 (~Fc1)
0.28230
1110
0.28226
1090
1070
0.28214
1030
0.28206
error bars are 2σ
MudTank
Pb/238U age (Ma)
740
0.120
0.28260 MudTank
average =0.282522 ± 0.000019
750
0.28256
730
0.28252
206
720
spot size 65 and 55 µm, respectively
error bars are 2σ
770
760
0.124
average = 0.282185 ± 0.000043
0.28222
0.28210
Mean = 1095.6 ± 4.1 [0.37%] 95% conf.
MSWD =1.2, probability = 0.20
As3 (~Fc1)
0.28218
1050
176
206
Pb/238U
1110
206
0.28280
error bars are 2σ
Temora
error bars are 2σ
0.190
710
700
0.112
0.92 0.96
0.28248
Concordia age = 729.0 ± 2.6Ma
MSWDC+E = 1.07
1.00
1.04
207
Pb/235U
1.08
1.12
1.16
spot size 80, 65 and 55 µm, respectively
690
Mean = 728.8. ± 2.4 [0.33%] 95% conf.
MSWD = 0.91, probability = 0.69
Figure 4: Simultaneous U-Pb and Hf isotope analyses in zircon.
91500:
GJ-1:
Plešovice:
Temora 2:
AS3 (~FC1):
MudTank:
0.28285
Temora
416
1130
MudTank
spot size 65 and 55 µm, respectively
0.28238
420
400
As3 (~Fc1)
0.174
0.28246
0.28242
Mean = 338.6 ± 1.6 [0.48%] 95% conf.
MSWD = 1.06, probability = 0.39
424
0.495 0.505 0.515 0.525
207
Pb/235U
data-point error ellipses are 2σ
0.186
0.28250
176
Pb/238U age (Ma)
Pb/238U
206
410
0.0635
0.475 0.485
176
330
error bars are 2σ
0.0665
error bars are 2σ
0.28258
0.28254 average =0.282486 ± 0.000028
334
428
420
0
Plešovice
338
322
0.385 0.395 0.405 0.415
207
Pb/235U
data-point error ellipses are 2σ
430
Temora
400
0.28190
342
0.050
0.365 0.375
0.0645
spot size 65 and 55 µm, respectively
Mean = 607.0 ±2.4 [0.39%] 95% conf.
MSWD =0.63, probability = 0.89
326
Concordia age = 337.7 ± 2.0Ma
MSWDC+E = 1.34
0.0655
0.28198
590
Hf/177Hf
206
330
0.0675
0.28202
error bars are 2σ
Pb/238U age (Ma)
340
320
600
350 Plešovice
346
350
0.054
610
0.28194
0.82 0.84 0.86 0.88
207
Pb/235U
data-point error ellipses are 2σ
0.052
Pb/238U
average = 0.282015 ± 0.000029
0.28206
580
0.80
Plešovice
0.116
GJ-1
0.28210
176
0.093
0.76 0.78
0.182
error bars are 2σ
error bars are 2σ
176
Pb/238U age (Ma)
Pb/238U
206
590
0.194
spot size 65 and 80 µm, respectively
0.28220
GJ-1
610
0.095
0.0685
0.28224
Mean = 1065.6 ±4.3 [0.40%] 95% conf.
MSWD = 1.5, probability = 0.087
630
0.097
0.0695
0.28228
620
0.099
Pb/238U
1050
1030
630
0.101
0.056
0.28232
Hf/177Hf
0.103
1070
1010
average =0.282299 ± 0.000026
0.28236
Hf/177Hf
Pb/238U age (Ma)
206
1050
206
Pb/238U
1070
0.174
91500
1090
1090
0.178
error bars are 2σ
0.28240
91500
0.186
0.182
error bars are 2σ
1110
1100
176
0.190
U-Pb age
176
1065 Ma5
607 Ma2
337.1 Ma6
417 Ma7
1099 Ma9
732 Ma10
0.282306 ± 0.0000088
0.282103 ± 0.0000081 (unpublished)
0.282484 ± 0.0000086
0.282686 ± 0.0000068
0.282184 ± 0.0000167
0.282507 ± 0.0000068
Hf/177Hf
Table 2: Reference U-Pb age and Hf isotope data for the zircons analyzed in
Figure 4.
0.28244
Conclusions
In addition to these
Coupling the Thermo Scientific ELEMENT XR and the
NEPTUNE to the laser ablation system was easy to
achieve and demonstrated to be a powerful instrumental
solution for the simultaneous analysis of U-Th-Pb and Hf
isotope ratios in small zircons. The low volume laser cell
used in this study demonstrated fast sample uptake and
fast washout, resulting in low backgrounds without
spiking signals. U-Pb ages and Hf isotope ratios of all
zircons obtained in this study are in very good agreement
with the published data.
offices, Thermo Fisher
References
1 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 Sciences Letters
249, 47–61.
2 Gerdes, A., Zeh, A., 2008. Zircon formation versus zircon alteration –
New insights from combined U–Pb and Lu–Hf in-situ LA-ICP-MS
analyses, and consequences for the interpretation of Archean..., Chemical
Geology, doi:10.1016/j.chemgeo.2008.03.005
3 Hong-Lin Yuan, Shan Gao, Meng-Ning Dai, Chun-Lei Zong,
Detlef Günther, Gisela Helene Fontaine, Xia-Ming Liu, ChunRong Diwu;
Simultaneous determindations of U-Pb age, Hf isotopes and trace element
compositions of zircon by excimer laser-ablation quadrupole and
multiple-collector ICP-MS; Chem Geol. 247, 110-118.
4 The laser ablation cell is of similar design to that described in: Davide
Bleiner, Detlef Günther; Theoretical description and experimental
observation of aerosol transport processes in laser ablation ICPMS,
J. Anal. At. Spectrom., 2001, 16, 449-456.
5 Wiedenbeck, M. et al, 1995. Three natural zircon standards for U–Th–Pb,
Lu–Hf, trace element and REE analyses. Geostandards Newsletter 19,
1-23.
6 Slama, J. et al, 2008. Plešovice zircon – A new natural reference material
for U–Pb and Hf isotopic microanalysis. Chemical Geology 249, 1-35
7 Black, L.P. et al, 2004. Improved Pb-206/U-238 microprobe
geochronology by the monitoring of a traceelement related matrix effect;
SHRIMP, ID-TIMS, ELA-ICP-MS and oxygen isotope documentation for
a series of zircon standards. Chemical Geology 205, 115–140.
8 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.
9 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
10 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.
Scientific maintains
a network of representative organizations
throughout the world.
Africa-Other
+27 11 570 1840
Australia
+61 2 8844 9500
Austria
+43 1 333 50 34 0
Belgium
+32 2 482 30 30
Canada
+1 800 530 8447
China
+86 10 8419 3588
Denmark
+45 70 23 62 60
Europe-Other
+43 1 333 50 34 0
Finland / Norway /
Sweden
+46 8 556 468 00
France
+33 1 60 92 48 00
Germany
+49 6103 408 1014
India
+91 22 6742 9434
Italy
+39 02 950 591
Japan
+81 45 453 9100
Latin America
+1 608 276 5659
Middle East
+43 1 333 50 34 0
Netherlands
+31 76 579 55 55
South Africa
+27 11 570 1840
Spain
+34 914 845 965
Switzerland
+41 61 716 77 00
UK
+44 1442 233555
USA
+1 800 532 4752
www.thermo.com
©2009 Thermo Fisher Scientific Inc. All rights reserved. All trademarks are the property of Thermo Fisher Scientific Inc. and its subsidiaries.
Specifications, terms and pricing are subject to change. Not all products are available in all countries. Please consult your local sales representative for details.
Thermo Fisher Scientific
(Bremen) GmbH is certified
DIN EN ISO 9001:2000
AN30170_E 02/09C
Part of Thermo Fisher Scientific