Abstract
AbstractThe 40Ar/39Ar dating method is among the most versatile of geochronometers, having the potential to date a broad variety of K-bearing materials spanning from the time of Earth’s formation into the historical realm. Measurements using modern noble-gas mass spectrometers are now producing 40Ar/39Ar dates with analytical uncertainties of ∼0.1%, thereby providing precise time constraints for a wide range of geologic and extraterrestrial processes. Analyses of increasingly smaller subsamples have revealed age dispersion in many materials, including some minerals used as neutron fluence monitors. Accordingly, interpretive strategies are evolving to address observed dispersion in dates from a single sample. Moreover, inferring a geologically meaningful “age” from a measured “date” or set of dates is dependent on the geological problem being addressed and the salient assumptions associated with each set of data. We highlight requirements for collateral information that will better constrain the interpretation of 40Ar/39Ar data sets, including those associated with single-crystal fusion analyses, incremental heating experiments, and in situ analyses of microsampled domains. To ensure the utility and viability of published results, we emphasize previous recommendations for reporting 40Ar/39Ar data and the related essential metadata, with the amendment that data conform to evolving standards of being findable, accessible, interoperable, and reusable (FAIR) by both humans and computers. Our examples provide guidance for the presentation and interpretation of 40Ar/39Ar dates to maximize their interdisciplinary usage, reproducibility, and longevity.
Highlights
Since 2003, the international EARTHTIME Initiative has focused on enhancing the precision and accuracy of commonly used geochronologic methods, which has resulted in community-wide improvements in metrologic traceability, interlaboratory reproducibility, precision, accuracy, and intercalibration between the 40Ar/39Ar method and other dating methods (e.g., U-Pb zircon ages, astronomical time scale)
The level of analytical uncertainty (∼0.1%) for dates obtained from a new generation of mass spectrometers—as well as the high spatial resolution afforded by excimer laser microsampling techniques—has led to increasingly dispersed data sets for individual minerals or hand samples, including fluence monitors (Phillips and Matchan, 2013; Mercer et al, 2015; Rivera et al, 2016; Andersen et al, 2017; Yancey et al, 2018)
The 40K decay constants and 40Ar*/40K ratio reported by Renne et al (2010, 2011) for the Fish Canyon sanidine (FCs) monitor mineral were determined using data sets that depended
Summary
Since 2003, the international EARTHTIME Initiative (www.earth-time.org) has focused on enhancing the precision and accuracy of commonly used geochronologic methods, which has resulted in community-wide improvements in metrologic traceability, interlaboratory reproducibility, precision, accuracy, and intercalibration between the 40Ar/39Ar method and other dating methods (e.g., U-Pb zircon ages, astronomical time scale). The level of analytical uncertainty (∼0.1%) for dates obtained from a new generation of mass spectrometers—as well as the high spatial resolution afforded by excimer laser microsampling techniques—has led to increasingly dispersed data sets for individual minerals or hand samples, including fluence monitors (Phillips and Matchan, 2013; Mercer et al, 2015; Rivera et al, 2016; Andersen et al, 2017; Yancey et al, 2018). The 40K decay constants and 40Ar*/40K ratio reported by Renne et al (2010, 2011) for the Fish Canyon sanidine (FCs) monitor mineral were determined using data sets that depended
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