U-Pb ID-TIMS reference ages and initial Pb isotope compositions for Durango and Wilberforce apatites

We present new Isotope Dilution Thermal Ionisation Mass Spectrometry (ID-TIMS) U-Pb reference ages for apatites from type locations Durango, Cerro de Mercado, Mexico and Wilberforce, Ontario, Canada. A weighted mean 206Pb/238U obtained from 14 Durango apatite fragments yields an age of 32.716 ± 0.061/0.063/0.072 Ma (2σ analytical uncertainty; analytical and tracer uncertainty combined; analytical, tracer, and decay constant uncertainties combined; MSWD = 0.81). Correction of excess 206Pb from Th-disequilibrium in Durango apatite, using a Th/Umelt of 3.5 ± 1, yields a weighted mean 206Pb/238U age of 32.29 ± 0.12/0.12/0.12 Ma. A concordia-constrained linear 3-D isochron yields an age of 32.683 ± 0.050 Ma for Durango apatites (ratio + error (%) + correlation coefficients; MSWD = 7.6; no propagation of decay constant and Pbc composition uncertainty, isoplot v. 4.15). A weighted mean 206Pb/238U obtained from 9 Wilberforce apatite fragments yield an age of 930.9 ± 8.0/8.0/8.1 Ma (MSWD = 0.65). Excess 206Pb correction for Wilberforce is negligible (