U–Pb zircon geochronology by LAICPMS combined with thermal annealing: Achievements in precision and accuracy on dating standard and unknown samples

• We tested the capability of thermal annealing on zircon U–Pb ages and REE distribution, by LAICPMS
• More accurate U–Pb ages and improved MSWD are obtained with thermal annealing
• REE and trace elements in annealed zircons present lower dispersion
• Age and chemical composition is preserved in natural zircons with overgrowths
• The Hf-isotope composition of thermally annealed zircons is comparable, in terms of accuracy and precision to that of not annealed ones

U–Pb zircon dating by LAICPMS is one of the most popular geochronological techniques, however it still suffers from some accuracy and precision problems. These are mostly due to the slight differences in behavior between zircons, and differential coupling with the laser radiation, probably the result from crystal damage induced by the radioactive decay of U and Th. These result in difficult-to-predict and even irreproducible matrix effects, impinging on the precision and accuracy of the technique.Here, we explore the effect that thermal annealing has on the analysis of zircons by LAICPMS, to improve U–Pb age results obtained We document the advantages of thermal annealing by means of two experiments on standard and several igneous zircons, spanning different degrees of crystallization history complexity. In general, pretreatment of zircons by thermal annealing yields more accurate ages (e.g., 336.87 ± 0.49 Ma for the annealed Plešovice standard zircon, vs 340.24 ± 0.49 Ma when not annealed) with significantly less dispersion (e.g., MSWD decreasing as much as 80%). We also demonstrate that thermal annealing significantly reduces the scatter of the trace element data in zircon, yet they preserve the primary characteristics (such as REE anomalies, Hf isotopes, igneous fluctuations and differences in overgrowth composition). This method allows the production of more accurate U–Pb ages, but also has implication for petrogenesis and geothermometry studies.