MAP-2 apatite: A new young age reference material for U–Pb dating with LA-ICPMS analysis

Apatite is an essential mineral for geochronology and geochemistry. Precise and accurate U–Pb Laser ablation (LA)-inductively coupled plasma mass spectrometry (ICPMS) dating of apatite requires suitable matrix-matched reference materials (RMs), but young RMs (<30Ma) are lacking from existing apatite RMs. We provided a gem-quality apatite MAP-2 collected from Myanmar and subjected it to detailed chemical composition and U–Pb dating analyses to assess its homogeneity and suitability as a reference material for LA-ICPMS age determination. The results of comprehensive analyses of multiple methods show that the MAP-2 apatite is largely free of inclusions and is relatively homogenous in chemical and isotopic content. Notably, MAP-2 apatite could be the youngest apatite U–Pb dating reference material (about 22 Ma) with relatively high U contents range from 161 μg g−1 to 231 μg g−1 and an average of 210 μg g−1. The isotope dilution-thermal ionization mass spectrometry (ID-TIMS) U–Pb measurements yielded weighted mean isotopic ratio values of 0.00345 ± 0.00003 for 206Pb/238U, 0.0243 ± 0.0039 for 207Pb/235U, 0.0512 ± 0.0082 for 207Pb/206Pb and the weighted mean 206Pb/238U ages of 22.18 ± 0.22 Ma (2SD, MSWD = 0.01, n = 6) as the recommended reference value. LA-ICPMS analyses yielded 207Pb-corrected weighted mean 206Pb/238U age of 22.0 ± 0.1/0.2 Ma (2SD, MSWD = 4.2, n = 232) and the results are consistent with ID-TIMS data within the limits of the ID-TIMS analytical uncertainly, which indicates that MAP-2 apatite has the potential as a reference material for microbeam determination of U–Pb ages.