U-Pb zircon in situ dating with LA-MC-ICP-MS using a mixed detector configuration

the la-mc-icp-ms method applied to u-pb in situ dating is still rapidly evolving due to improvements in both lasers and icp-ms. to test the validity and reproducibility of the method, 5 different zircon samples, including the standard temora-2, ranging in age between 2.2 ga and 246 ma, were dated using both la-mc-icp-ms and shrimp. the selected zircons were dated by shrimp and, after gentle polishing, the laser spot was driven to the same site or on the same zircon phase with a 213 nm laser microprobe coupled to a multi-collector mixed system. the data were collected with a routine spot size of 25 μm and, in some cases, of 15 and 40 μm. a careful cross-calibration using a diluted u-th-pb solution to calculate the faraday reading to counting rate conversion factors and the highly suitable gj-1 standard zircon for external calibrations were of paramount importance for obtaining reliable results. all age results were concordant within the experimental errors. the assigned age errors using the la-mc-icp-ms technique were, in most cases, higher than those obtained by shrimp, but if we are not faced with a high resolution stratigraphy, the laser technique has certain advantages.