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Zircon Dating with the CAMECA IMS 1280-HR
Zircon has long been recognized as the most important geochronometer, and several key instrumental features of the CAMECA IMS 1280-HR make it the best suited instrument for zircon dating, among which:
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High mass resolution for peak separation between HfSi molecular ions and Pb isotopes
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High transmission for analysis of low lead concentration
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Oxygen flooding for improved sensitivity and highly reproducible analytical conditions
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Small spot size with high beam density for better lateral resolution
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Outstanding ion image capability for Pb and U mapping in zircon grains (inhomogeneity, zonation)
Precise age determination of very young zircon
The 207Pb/206Pb isotope ratio provides a direct age measurement that does not require U-Pb age standards, which are still rare... Measurement of Pb/Pb age by SIMS is a common practice for zircons and other U-rich minerals older than 1.0 Ga, but not for the relatively young samples (<1.0 Ga and particularly Phanerozoic) because of limitations in the analytical precision.
The large radius magnetic sector multicollector of the CAMECA IMS 1280-HR, in combination with a NMR magnet controller and oxygen flooding technique allowed to achieve 207Pb/206Pb analytical precision of <0.2% or better for Phanerozoic zircons. These results indicate that the multicollector SIMS is able to determine zircon Pb/Pb ages as young as the Mesozoic age with age uncertainties of geological significance.
(a) Conventional U-Pb Concordia plot showing SIMS analytical data for Qinghu zircon.
(b) Comparison of weighted average 207Pb/206Pb ages for Qinghu zircon using monocollector and multicollector modes.
Courtesy Xian-Hua Li et al., IGGCAS, Beijing, China.