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.
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.
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.