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

Abstract

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 207Pb/235U and 206Pb/238U 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 Serçeören wollastonite skarn (Turkey) can be used as a secondary reference material provided detailed imaging of the crystals is undertaken. ID‐TIMS data yielded 207Pb/235U and 206Pb/238U 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.