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. Baddeleyite is a powerful chronometer of mafic magmatic andmeteorite impact processes. Precise and accurate U–Pb ages can be determinedfrom single grains by isotope dilution thermal ionization mass spectrometry(ID-TIMS), but this requires disaggregation of the host rock for grainisolation and dissolution. As a result, the technique is rarely applied toprecious samples with limited availability (such as lunar, Martian, andasteroidal meteorites and returned samples) or samples containing smallbaddeleyite grains that cannot readily be isolated by conventional mineralseparation techniques. Here, we use focused ion beam (FIB) techniques,utilizing both Xe+ plasma andGa+ ion sources, to liberate baddeleyite subdomainsdirectly, allowing their extraction for ID-TIMSdating. We have analysed the U–Pb isotope systematics of domains rangingbetween 200 and 10 µm in length and from 5 to ≤0.1 µg in mass. In total, sixdomains of Phalaborwa baddeleyite extracted using aXe+ plasma FIB (pFIB) yield a weighted mean207Pb∕206Pb age of 2060.1±2.5 Ma (0.12 %; all uncertainties 2σ),within uncertainty of reference values. The smallest extracted domain (ca.10×15×10 µm) yields an internal207Pb∕206Pb age uncertainty of±0.37 %. Comparable control on cutting is achieved usinga Ga+-source FIB instrument, though the slower speedof cutting limits potential application to larger grains. While the U–Pbdata are between 0.5 % and 13.6 % discordant, the extent of discordancedoes not correlate with the ratio of material to ion-milled surface area, andresults generate an accurate upper-intercept age in U–Pb concordia space of2060.20±0.91 Ma (0.044 %). Thus, we confirm the natural U–Pbvariation and discordance within the Phalaborwa baddeleyite populationobserved with other geochronological techniques. Our results demonstrate theFIB-TIMS technique to be a powerful tool for highly accuratein situ 207Pb∕206Pb (and potentiallyU–Pb in concordant materials) age analysis, allowing dating of a widevariety of targets and processes newly accessible to geochronology.

geochronology

Highly accurate dating of micrometre-scale baddeleyite domains through combined focused ion beam extraction and U–Pb thermal ionization mass spectrometry (FIB-TIMS)