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Issue 3, 2017
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ID-TIMS U–Pb geochronology at the 0.1‰ level using 1013 Ω resistors and simultaneous U and 18O/16O isotope ratio determination for accurate UO2 interference correction

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Abstract

We document recent advances in analytical protocols that employ 1013 Ω resistors in the Faraday cup amplifier feedback loop for high-precision U–Pb geochronology by isotope dilution thermal ionisation mass spectrometry (ID-TIMS). We present a direct comparison of high-precision U–Pb data obtained using different detector systems, including dynamic peak hopping on a secondary electron multiplier and static multicollection routines that use 1013 Ω resistors in the amplifier feedback loop. The high-ohmic resistors also allow the precise and accurate measurement of the minor 272(UO2) isotopologues (mostly 238U18O16O) in a static multicollection routine, which permits precise and accurate determination of the 18O/16O ratio of UO2 molecules during the U-isotope ratio measurement without compromising signal intensity on the more abundant UO2 isotopologues. This enables the precise determination of U abundances in zircons by isotope dilution with within-run correction of isobaric interferences from the minor UO2 isotopologues, thereby eliminating one of the major sources of uncertainty in ultra-high-precision U–Pb data sets. This approach permits the determination of single U–Pb dates with uncertainties <0.2‰ and corresponding weighted mean dates with uncertainties <0.1‰ (n ∼ 6 to 10). Furthermore, the ability to use different combinations of detector setups for the same analysis within the same mass spectrometer allows for direct comparison of independently calibrated detector systems.

Graphical abstract: ID-TIMS U–Pb geochronology at the 0.1‰ level using 1013 Ω resistors and simultaneous U and 18O/16O isotope ratio determination for accurate UO2 interference correction

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Publication details

The article was received on 29 Jul 2016, accepted on 23 Jan 2017 and first published on 24 Jan 2017


Article type: Paper
DOI: 10.1039/C6JA00278A
Citation: J. Anal. At. Spectrom., 2017,32, 579-586
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    ID-TIMS U–Pb geochronology at the 0.1‰ level using 1013 Ω resistors and simultaneous U and 18O/16O isotope ratio determination for accurate UO2 interference correction

    J. Wotzlaw, Y. Buret, S. J. E. Large, D. Szymanowski and A. von Quadt, J. Anal. At. Spectrom., 2017, 32, 579
    DOI: 10.1039/C6JA00278A

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