Ion microprobe U–Pb dating of apatite

To illustrate in situ Sensitive High Resolution Ion MicroProbe (SHRIMP) analysis of apatites, Pb isotopes and Pb/U ratios of five apatite samples with different ages have been measured using SHRIMP II ion microprobe at Hiroshima University. The `PRAPʹ apatite from a carbonatite complex at Prairie Lake, Ontario with a 207Pb∗–206Pb∗ age of 1156±45 Ma (2 σ) was used as the standard for 206Pb+/238U+–238U16O+/238U+ calibration. Apatites from the Poohbah Lake alkaline complex give 204Pb/206Pb–238U/206Pb and 204Pb/206Pb–207Pb/206Pb isochron ages of 2726±145 Ma (2 σ) and 2701±86 Ma (2 σ), in agreement with a conventional TIMS 207Pb∗–206Pb∗ age of 2667±10 Ma (2 σ) and a K–Ar isochron age of 2706±46 Ma (2 σ). For the remaining three apatite samples the 204Pb/206Pb–238U/206Pb and 204Pb/206Pb–207Pb/206Pb isochron ages obtained by SHRIMP are consistent with radiometric and geological ages in the literature.