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Geochronology

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:

  • High mass resolution for peak separation between HfSi molecular ions and Pb isotopes
  • High transmission for analysis of low lead concentration
  • Oxygen flooding for improved sensitivity and highly reproducible analytical conditions
  • Small spot size with high beam density for better lateral resolution
  • 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.


SIMS analytical data for Qinghu zircon

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.


Comparison of weighted average 207Pb-206Pb ages 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.

Although zircon is by far the most commonly utilized mineral for U–Th-Pb dating, monazite, apatite, titanite, rutile and baddeleyite are also commonly dated and provide a wide spectrum of geochronological applications, all perfectly addressed by CAMECA IMS 1280-HR. To learn more, download our application note: Advanced U-Th-Pb Geochronology with CAMECA Ultra High Sensitivity SIMS.


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