A New Natural Secondary Reference Material for Garnet U-Pb Dating by TIMS and LA-ICP-MS

Gem quality andradite-rich garnet (IUC-1), obtained from the Miocene trachyte dome near Ankara city (Turkey), has been identified as a potential natural secondary reference material for U-Pb dating. In this study, U-Pb dating was performed in five different laboratories using isotope dilution TIMS and laser ablation ICP-MS to determine the homogeneity of euhedral garnet crystals. The U-Pb ID-TIMS data for IUC-1 yielded Pb-207/U-235 and Pb-206/U-238 ages of 20.9 +/- 0.4 and 20.6 +/- 0.8 Ma respectively, and these values are consistent with U-Pb LA-ICP-MS analyses, in which different garnet crystals yielded ages of 20.8 +/- 0.1, 20.7 +/- 0.1, 20.7 +/- 0.2 and 20.2 +/- 0.1 Ma. An andradite (IUC-2) from the Serceoren wollastonite skarn (Turkey) can be used as a secondary reference material provided detailed imaging of the crystals is undertaken. ID-TIMS data yielded Pb-207/U-235 and Pb-206/U-238 ages of 20.4 +/- 0.4 and 20.9 +/- 1.0 Ma respectively, and yielded U-Pb ages on different grains of 20.5 +/- 0.1, 20.7 +/- 1.0, 20.8 +/- 1.7 and 20.9 +/- 1.6 Ma. The assigned weighted mean age of IUC-1 (20.4 +/- 0.5 Ma, 2s) is proposed as a 2023 reference value. IUC-1 garnet is expected to contribute significantly to rapidly developing garnet geochronology in the near future.