GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 79-13
Presentation Time: 11:40 AM


SCHOENE, Blair, Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544 and SZYMANOWSKI, Dawid, Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544

Fifteen years ago the EARTHTIME consortium established a goal of achieving 0.1% precision and accuracy for multiple geochronometers. Within 5 years, the U-Pb ID-TIMS community was able to achieve and exceed that goal among many labs globally. Since then, it is not uncommon for dates of 0.02% or better precision to be reported in the literature on weighted mean dates. However, reproducibility between labs at that level of precision has not been demonstrated.

Here we review the most important sources of potential bias between reported dates, and point to recent advances aimed at overcoming those biases. Potential biases range from analytical, meaning those involving sample preparation and mass spectrometry, and geologic, which includes open-system behavior and prolonged mineral growth. Recent intercalibration studies show that analytical biases exist at the 0.02% level that have yet to be nailed down. Perhaps more importantly for geologic applications of ID-TIMS U-Pb geochronology are differences in data interpretation, for example whether and when to use weighted mean dates given observed prolonged mineral growth.

“Geologic” uncertainty and data interpretation has been tackled by integrating multiple analytical and numerical techniques with ID-TIMS geochronology to improve context and ability to relate to geologic process. In terms of analytical advances, we present data from a new Isotopx Phoenix TIMS with ATONA faraday amplifiers that permit faraday measurements on smaller aliquots of U and Pb, permitting evaluation of analytical biases associated with ion counters and promising the ability to achieve higher precision and accuracy on smaller samples. In the end, the goal of 0.01% precision and accuracy on reported dates is on the horizon and but is a formidable target.