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U-Pb dating of zircon by LA-ICP-MS


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Chang, Z, Vervoort, JD, McClelland, WC and Knaack, C 2006 , 'U-Pb dating of zircon by LA-ICP-MS' , Geochemistry Geophysics Geosystems, vol. 7, no. 5 , doi: 10.1029/2005GC001100.

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In this study we used LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry) to
determine U-Pb ages of 5 zircon samples of known age (1800 Ma to 50 Ma) in order to determine the
reproducibility, precision, and accuracy of this geochronologic technique. This work was performed using
a ThermoFinnigan Element2 magnetic sector double-focusing ICP-MS coupled with a New Wave
Research UP-213 laser system. The laser ablation pit sizes ranged from 30 to 40 mm in diameter. Laserinduced
time-dependent fractionation is corrected by normalizing measured ratios in both standards and
samples to the beginning of the analysis using the intercept method. Static fractionation, including those
caused during laser ablation and due to instrumental discrimination, is corrected using external zircon
standards. Total uncertainty for each laser analysis of an unknown is combined quadratically from the
uncertainty in the measured isotope ratios of the unknown and the uncertainty in the fractionation factors
calculated from the measurement of standards. For individual analyses we estimate that the accuracy and
precision are better than 4% at the 2 sigma level, with the largest contribution in uncertainty from the
measurement of the standards. Accuracy of age determinations in this study is on the order of 1% on the
basis of comparing the weighted average of the LA-ICP-MS determinations to the TIMS ages. Due to
unresolved contributions to uncertainty from the lack of a common Pb correction and from potential matrix
effects between standards and unknowns, however, this estimate cannot be universally applied to all
unknowns. Nevertheless, the results of this study provide an example of the type of precision and accuracy
that may be possible with this technique under ideal conditions. In summary, the laser ablation technique,
using a magnetic sector ICP-MS, can be used for the U-Pb dating of zircons with a wide range of ages and
is a useful complement to the established TIMS and SHRIMP techniques. This technique is especially well
suited to reconnaissance geochronologic and detrital zircon studies.

Item Type: Article
Authors/Creators:Chang, Z and Vervoort, JD and McClelland, WC and Knaack, C
Keywords: laser ablation; magnetic sector ICP-MS; U-Pb dating; zircon dating.
Journal or Publication Title: Geochemistry Geophysics Geosystems
ISSN: 1525-2027
DOI / ID Number: 10.1029/2005GC001100
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