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Metrology and traceability of U-Pb isotope dilution geochronology (EARTHTIME Tracer Calibration Part I)

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journal contribution
posted on 20.01.2017, 15:52 by D. J. Condon, B. Schoene, N. M. McLean, S. A. Bowring, R. R. Parrish
Mixed 235U–233U–205Pb(–202Pb) tracers for U–Pb isotope-dilution isotope ratio mass spectrometry have been prepared under the auspices of the EARTHTIME Initiative. The methods and results for the preparation and calibration of the U/Pb ratio and isotopic abundances are given, and the various sources of uncertainty are discussed and quantified. The accuracy of the EARTHTIME U–Pb tracer isotopic composition can be traced back to SI units via a series of assay and isotopic composition reference materials combined with the experiments described herein. The parameters used in calculating U/Pb ratios (and inferentially U–Pb dates) have correlated uncertainties that result in a total uncertainty contribution to 206Pb/238U dates of ± < 0.03% (95% confidence). For suitable terrestrial materials such as zircon, when other sources of uncertainty have been minimised (e.g., open-system behaviour, 238U/235U variation, intermediate daughter product disequilibrium, common Pb, etc.) the U–Pb tracer calibration uncertainty is a limiting factor in the accuracy of U–Pb geochronology – but less so than the uncertainty in the 238U and 235U decay constants (±0.11 and 0.14% 2σ). The calibration approach of the mixed EARTHTIME 235U–233U–205Pb(–202Pb) tracers, in addition to updated values for reference materials (e.g., mixed gravimetric reference solutions), and parameters (e.g., Pb reference material assay), can be applied to other laboratory-specific U–Pb tracers and will facilitate the generation of accurate and directly inter-comparable U–Pb data.

Funding

This research was supported by NERC Fellowship NE/C517909/1, NERC grant NE/I013814/1, NIGFSC award (IP/1028/0508), NSF Award EAR 0451802 (the EARTHTIME project) and recurrent NERC support to NIGL. Open Access funded by Natural Environment Research Council

History

Citation

Geochimica et Cosmochimica Acta 164 (2015) 464–480

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Geology

Version

VoR (Version of Record)

Published in

Geochimica et Cosmochimica Acta 164 (2015) 464–480

Publisher

Elsevier, Meteoritical Society, Geochemical Society

issn

0016-7037

Acceptance date

10/05/2015

Copyright date

2015

Available date

20/01/2017

Publisher version

http://www.sciencedirect.com/science/article/pii/S001670371500321X

Notes

Supplemental files have been deposited with the NERC National Geoscience Data Centre (DOI: 10.5285/a483a041-170a-4072-844e-c2c5d070a3e3).

Language

en