* Astronomy

Oldest zircon in the solar system

The sensitivity and selectivity afforded by ion probe analysis are well illustrated in the dating of 4.56 Ga zircons from the Vaca Muerta and Simmern meteorites (Ireland and Wlotzka 1992). Meteoritic zircon is quite rare, and it normally occurs as small, sometimes interstitial, grains about 10-µm, and occasionally up to 30-µm, diameter. Making analysis even more difficult, the U content of the zircon can be very low (<1 ppm). Ireland and Wlotzka (1992) analysed three zircon grains <20-µm diameter in thin section, and therefore in a known petrographic context, first for U-Th-Pb to measure their ages, then for rare earth and other trace elements to determine their genesis, still leaving enough sample for subsequent Hf-W isotopic analyses to measure the abundance of extinct 182Hf (Ireland 1991). Even after all this work, most of the zircon still remains for future study.Read more (PDF)