Advances in U-Pb geochronology using a frequency quintupled Nd : YAG based laser ablation system (lambda=213 nm) and quadrupole based ICP-MS

The analytical potential of a 213 nm laser system coupled to a quadrupole based ICP-MS for U-Pb dating of zircon is investigated. The study was performed on zircons from a Neoproterozoic granitoid of the Cadomian belt of Brittany. Seven zircon fractions of the same sample including two single grains were dated by ID-TIMS to obtain a reference age and error to evaluate the accuracy and precision of LA-ICP-MS U-Pb results. The best estimate for the age of crystallisation obtained by ID-TIMS is 603 +/- 2 Ma. LA-ICP-MS analyses were conducted in two essions, one using only Ar as carrier gas and one using Ar + He. In both cases the age results are within analytical uncertainty of the ID-TIMS age (601 +/- 9 Ma for the Ar analyses and 600 +/- 2 Ma for the He analyses). It is demonstrated that the use of He carrier gas significantly improves reproducibility and precision of the elemental U-Pb ratios and allows the collection of data with a 2s relative precision < ca. 1.5% for Pb-206/U-238 ratios and < ca. 2.5% for Pb-207/Pb-206 ratios at ca. 25 x 35 mum sample resolution. It is also demonstrated that the various sources of uncertainty associated with LA-ICP-MS U-Pb dating do not preclude the possibility of obtaining precise and accurate age results if an appropriate methodology is applied.