A statistical approach to evaluating uncertainties in the calibration of multi-element isotopic tracers has been developed and applied to determining the isotopic composition of mixed U{\textendash}Pb (202Pb{\textendash}205Pb{\textendash}233U{\textendash}235U) tracers used for accurate isotope dilution U{\textendash}Pb geochronology. Our experiment, part of the EARTHTIME initiative, directly links the tracer calibration to first-principles measurements of mass and purity that are all traceable to SI units, thereby quantifying the accuracy and precision of U{\textendash}Pb dates in absolute time. The calibration incorporates new more accurate and precise purity measurements for a number of commonly used Pb and U reference materials, and requires inter-relating their isotopic compositions and uncertainties. Similar methods can be used for other isotope systems that utilize multiple isotopic standards for calibration purposes. We also detail the inter-calibration of three publicly available U{\textendash}Pb gravimetric solutions, which can be used to bring the same first-principles traceability to in-house U{\textendash}Pb tracers from other laboratories. Accounting for uncertainty correlations in the tracer isotope ratios yields a tracer calibration contribution to the relative uncertainty of a 206Pb/238U date that is only half of the relative uncertainty in the 235U/205Pb ratio of the tracer, which was historically used to approximate the tracer related uncertainty contribution to 206Pb/238U dates. The tracer uncertainty contribution to 206Pb/238U dates has in this way been reduced to \<300ppm when using the EARTHTIME and similarly calibrated tracers.
}, year = {2015}, journal = {Geochimica et Cosmochimica Acta}, volume = {164}, pages = {481 - 501}, month = {09/2015}, isbn = {0016-7037}, url = {https://doi.org/10.1016/j.gca.2015.02.040}, doi = {10.1016/j.gca.2015.02.040}, language = {eng}, }