Optimization of the in-situ U-Pb age dating method via LA-Quadrupole-ICP-MS with applications to the timing of U-Zr-Mo mineralization in the Poços de Caldas Alkaline Complex, SE Brazil.
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Date
2015
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Abstract
The high spatial resolution of the LA-ICP-MS systems allows rapid extraction of vital isotopic information from individual growth zones of minerals. This paper describes in detail the optimization of a relatively inexpensive LA-ICP-MS system consisting of a UV 213 Laser Ablation and a Quadrupole ICP-MS. The results of optimization take into account laser energy, beam diameter, frequency and ICP-MS gas conditions. The optimized conditions were tested for precision and accuracy on a number of wellcharacterized zircons, commonly used as primary and secondary quality control standards. The acquisition of the U-Pb data is carried out in automated mode (pre-set points) for up to 12 h/day with only minimal operator presence. Individual U-Pb zircon analysis lasts 80 s. The 2s uncertainties of the standards ranged between 1.4 and 8.2%, and overall their relative deviations ranged from 0.02 to 0.87%. The results are comparable to techniques that use more complex and time-consuming approaches such as LA-MC-ICP-MS and ion-microprobe. We have applied this method to obtain ages of numerous granitoid rocks from the Southern São Francisco Craton and a well-known Archean granitoid of the Kaapvaal Craton, South Africa. We furthermore provide the first results of U-Pb age dating of U-Zr-Mo mineralization in the Poços de Caldas Alkaline Complex, SE Brazil, with a U-Pb age of 85 ± 3 Ma for zircon-bearing hydrothermal veins.
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Poços de Caldas alkaline complex, Zircon
Citation
TAKENAKA, L. B. et al. Optimization of the in-situ U-Pb age dating method via LA-Quadrupole-ICP-MS with applications to the timing of U-Zr-Mo mineralization in the Poços de Caldas Alkaline Complex, SE Brazil. Journal of South American Earth Sciences, v. 62, p. 70-79, 2015. Disponível em: <http://www.sciencedirect.com/science/article/pii/S0895981115000668>. Acesso em: 08 set. 2015.