In-situ SIMS U–Pb dating of phanerozoic apatite with low U and high common Pb

Apatite is a common accessory mineral in various igneous, metamorphic and sedimentary rocks. It has strong potential to provide important information for geochronology and petrogenesis. However, precise U–Th–Pb dating of apatite, especially young samples, is difficult due to low abundances of U and less radiogenic Pb, posing significant challenges for accurate common Pb correction. An additional issue is the lack of suitable apatite to serve as a standard for in-situ analyses. Here we present both analytical and data reduction protocols for SIMS in-situ U–Pb analyses on apatite with low U and high common lead. With NW-1 apatite as the U–Pb age standard, which was separated from ~ 1160 Ma carbonatite in the Prairie Lake complex in Canada, apatites from the Kovdor carbonatite in the Kola peninsula which contains low U (mostly ~ 2.5 ppm) and high common Pb (20–80%) yielded weighted average 207Pb-corrected U–Pb ages of 375 ± 13 Ma (KV-8 and KV-18) and 377 ± 11 Ma (KV-A), respectively. Apatites from the Quruqtagh ultramafic intrusion in NW China containing low U (~ 2.3 ppm) and high common Pb (> 70%) yield 207Pb-corrected U–Pb age of 805 ± 21 Ma. The Cenozoic Durango apatite was dated at 31 ± 2 Ma. All these new apatite U–Pb ages are indistinguishable from independently known age constraints to within 2–4%. Our results demonstrate that a U–Pb age can be accurately and precisely measured for apatite with low U (< 3 ppm) and high common Pb (> 50%) by SIMS with a suitable standard and a careful choice of common Pb composition.