View article

Latest advances in laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS) allow for accurate in-situ U-Pb dating of carbonate material, with final age uncertainties usually > 3 % 2σ. Cross-laboratory reference materials (RMs) used for sample-bracketing are currently limited to WC1 calcite with an age of 254.4 ± 6.5 (2σ). The minimum uncertainty on any age determination with the LA-ICPMS method is therefore ≥ 2.5 %, and validation by secondary RMs are usually performed on in-house standards. This contribution present a new reference material, ASH-15, a flowstone that is dated here by high-precision Isotope Dilution (ID) TIMS analysis using 36 sub-samples, 1–7 mg each. Age results presented here are slightly younger compared to previous ID dating of ASH-15, but in agreement with in-situ analyses (using WC1 as a RM). We provide new correction parameters to be used as primary or secondary standardization. The suggested ²³⁸U/²⁰⁶Pb apparent age, not corrected for disequilibrium and without common-lead anchoring, is 2.965 ± 0.011 Ma (2σ). The new results could improve the propagated uncertainties on the final age with a minimal value of 0.4%, which is approaching the uncertainty of typical ID analysis on, for example, zircon (< 1 % 2 s). We show that although LA-ICPMS spot analyses of ASH-15 exhibits significant scatter in their isotopic ratios, the down-hole fractionation of ASH-15 is similar to that of other reference materials. For LA work, we recommend the use of the new ID-TIMS ages that are 1.3&ndasdh;1.5 % younger than previously suggested, because of the lower uncertainties (0.4 %), the …