V32B-05
Metrologically-Calibrated 40Ar Concentrations and Ages of Mineral Standards Used in 40Ar/39Ar Geochronology
Wednesday, 16 December 2015: 11:12
308 (Moscone South)
Leah E Morgan, USGS, Central Mineral and Environmental Resources Science Center, Denver, CO, United States, Brett Davidheiser-Kroll, University of Glasgow, Glasgow, G12, United Kingdom, Klaudia Kuiper, VU University Amsterdam, Faculty of Earth and Life Sciences, Amsterdam, Netherlands, Jan R Wijbrans, Free University of Amsterdam, Amsterdam, Netherlands and Darren F Mark, Scottish Universities Environmental Research Center at the University of Glasgow, East Kilbride, United Kingdom
Abstract:
In geochronology, isotopic ages are determined from the ratio of parent and daughter nuclide concentrations in minerals. For dating of geological material using the K‐Ar system, the simultaneous determination of 40Ar and 40K concentrations on the same aliquot is not possible. Therefore, a widely used variant, the 40Ar/39Ar technique, involves the production of 39Ar from 39K by neutron bombardment and the reliance on indirect natural calibrators of the neutron flux, referred to as “mineral standards.” Many mineral standards still in use rely on decades‐old determinations of 40Ar concentrations; resulting uncertainties, both systematic and analytical, impede the determination of higher accuracy ages using the K‐Ar decay system. We present results for the 40Ar concentrations and ages of mineral standards determined based on a modern gas delivery system (Morgan et al. 2011), which delivers metrologically-traceable amounts of 40Ar and thus allows for the sensitivity calibration of noble gas mass spectrometers.
