Sistema de blogs Diarium
Universidad de Salamanca
Gabriel Gutiérrez-Alonso
Departamento de Geología-Área de Geodinámica Interna


Advances in U-Pb geochronology using a frequency quintupled Nd:YAG based laser ablation system (l = 213 nm) and quadrupole based ICP-MS. T.E. Jeffries, J. Fernández-Suárez, F. Corfú, G. Gutiérrez-Alonso. 2003, Journal of Analitycla Atomic Spectroscopy, 18, 847-855. DESCARGAR-DOWNLOAD.

Back scattered electron images of zircons from ZD-7 sample. Most zircons show simple growth patterns and no discernible cores. Length of white bars is ca. 50 microns.

(a) Selected examples of time-integrated ratio signals. The upper panel illustrates a case where the laser beam penetrated a domain with inherited (older) lead. The lower panel illustrates a case where at ca. 95 s the laser enters a domain featuring lead-loss, common lead contamination and inconsistent behaviour of the U-Pb and Th-Pb systems. In both cases the dotted box indicates the signal interval used for age calculation. Note that the vertical scale is arbitrary for ease of comparison of the different ratios. (b) Concordia plot of U-Pb analyses obtained in the argon runs. Ellipses represent 2σ uncertainties. The inset shows the weighted average of the 207Pb/206Pb ages of the 16 analyses.RESUMEN-ABSTRACT

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 sessions, 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 2σ relative precision < ca. 1.5% for 206Pb/238U ratios and < ca. 2.5% for 207Pb/206Pb ratios at ca. 25 × 35 µm 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.


Simplified geological maps of the area where sample ZD-7 was collected. Modified after Chantraine et al.29<br />
(A) and Barrière et al.30<br />



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