Abstract

BUHN, Bernhard; PIMENTEL, Márcio M.; MATTEINI, Massimo  and  DANTAS, Elton L.. High spatial resolution analysis of Pb and U isotopes for geochronology by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). An. Acad. Bras. Ciênc. [online]. 2009, vol.81, n.1, pp. 99-114. ISSN 0001-3765.  http://dx.doi.org/10.1590/S0001-37652009000100011.

Age determinations using the ²³⁵U and ²³⁸U radioactive decay series to the daughter isotopes ²⁰⁷Pb and ²⁰⁶Pb, respectively, using the mineral zircon (ZrSiO4), are widely used to decipher geological processes. A new method developed in the last couple of years, the laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS), overcomes previous laborious sample preparation, and yields isotopic ratios and age data with a high spatial resolution of ten of microns. The present study describes the analytical set-up and data reduction process as presently applied at the Laboratory for Geochronology of the University of Brasília. It explores the precision and accuracy of the method by cross-analysing three international zircon standards. We arrive at a precision of 1.9 to 3.7% (2σ SD) and an accuracy of 0.6 to 3.8% (2σ SD) for and U isotopic ratios of the standards. We also apply the method to two natural zircon samples, which have previously been dated by other analytical methods. A comparison of the results show a good conformity of the age data,being whitin the error limits. The data demonstrate the great analytical potential of the method for rapid, precise and accurate U-Pb isotopic analyses on the micron scale.

Keywords : geochronology; U-Pb isotopes; LA-MC-ICP-MS; zircon; age dating.