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

摘要: Abstract. Baddeleyite is a powerful chronometer of mafic magmatic and meteorite impact processes. High precision accuracy U-Pb ages can be measured from single grains by isotope dilution thermal ionisation mass spectrometry (ID-TIMS), but this requires destruction the host rock for highly challenging grain isolation dissolution. As result, technique rarely applied to precious samples with very limited availability (such as lunar, Martian asteroidal meteorites returned samples) or containing small baddeleyite that cannot readily isolated conventional mineral separation techniques. Here, we use focused ion beam (FIB) techniques, utilising both Xe+ plasma Ga+ sources, liberate subdomains in-situ, allowing their extraction ID-TIMS dating. We have analysed systematics domains ranging between 200 um 10 um in length 5 ug 0.1 ug mass. In total, seven Phalaborwa extracted using Xe+-pFIB yield weighted mean 207 Pb/206 Pb age 2060.1 ± 2.4 Ma (0.12 %; all uncertainties 2 sigma), within uncertainty reference values. The smallest domain (ca. 10 × 15 times; 10 um) yields an internal ±0.15 %. Comparable levels are achieved Ga+-source FIB instrument (±0.20 %), though slower cutting speed limits potential application larger grains. While data 0.5 13.6 % discordant, results generate precise upper intercept concordia space 2061.1 × 7.4 Ma; (0.72 %). Importantly, extent discordance does not correlate ratio material ion-milled surface area, showing induce disturbance even domains. Instead, confirm natural variation population observed other geochronological Our demonstrate FIB-TIMS tool high-accuracy in-situ dating, which makes wide range targets processes newly accessible geochronology.