Some Observations Concerning U-Pb Data Quality Based on the G-Chron Proficiency Testing Scheme

Some Observations Concerning U-Pb Data Quality Based on

the G-Chron Proficiency Testing Scheme

Michael Wiedenbeck¹

¹GFZ Helmholtz Centre for Geosciences, Potsdam, Germany

Starting in 2019, the International Association of Geoanalysts has run a Proficiency Testing programme designed to aid geochronology laboratories test their U-Pb zircon data for unsuspected bias. Test samples are dispatched world-wide to roughly 70 laboratories at roughly 2-year intervals. To date, three such rounds have been completed; this talk will provide some insights based the results that have been reported. The three zircon materials that have been distributed range in age from Late Archean to Mesozoic, with each material having its U-Pb homogeneity tested using the Potsdam SIMS instrument. Subsequently the target ²⁰⁶Pb/²³⁸U and ²⁰⁷Pb/²⁰⁶Pb values were defined by the results pooled from between three and seven ID-TIMS laboratories. From the rank distribution plots from the 70-odd laboratories it can be seen that roughly 20 % of those reporting have significant biases in their reported ²⁰⁶Pb/²³⁸U values. Likewise, for the two older samples it is also apparent that around 20 % of the reported ²⁰⁷Pb/²⁰⁶Pb results differ substantially from the ID-TIMS-defined target values. Another important observation is that the bias from the target values correlates poorly with the reported analytical uncertainties. A further surprise from the submitted data is that quadrupole ICPMS instruments generally report more precise results as compared to sector instruments.