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Anais da Academia Brasileira de Ciências

Print version ISSN 0001-3765

Abstract

CHEMALE JR, Farid et al. U-Pb zircon in situ dating with LA-MC-ICP-MS using a mixed detector configuration. An. Acad. Bras. Ciênc. [online]. 2012, vol.84, n.2, pp. 275-296.  Epub May 15, 2012. ISSN 0001-3765.  http://dx.doi.org/10.1590/S0001-37652012005000032.

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.

Keywords : MC-ICP-MS; SHRIMP; Faraday cups; Multi-ion Counting System; U-Pb in situ zircon dating.

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