GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 238-7
Presentation Time: 9:00 AM-6:30 PM


MERCER, C.M. and HODGES, K.V., School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287,

The K/Ar and 40Ar/39Ar dating methods have been widely employed to constrain the ages and thermal histories of potassic minerals and rocks from diverse settings on the Earth, the Moon, and asteroids. Since these techniques were developed, however, the accepted values for a variety of assumed physical parameters that are needed to convert isotopic data into dates have often been questioned and, in some cases, fundamentally changed. These parameters include: (1) the relative abundances of potassium isotopes (e.g., [1–3]); (2) 40K decay constants (e.g., [2, 4–6]); and (3) the ages of minerals commonly used to monitor 40Ar/39Ar irradiation parameters (e.g., Fish Canyon sanidine, FCs [6–8]). Thus, K/Ar and 40Ar/39Ar dates published by different labs or at different times may not reflect the same values for these parameters. This makes it difficult to robustly compare legacy K/Ar and 40Ar/39Ar datasets to one another and to other geochronological datasets (such as U/Pb zircon results [5]). Dalrymple [9] first addressed this issue for K/Ar dates published using a limited set of parameter values. We have generalized Dalrymple’s approach and created the Argon Age Recalculator (ArAR) software to enable the rapid conversion of both K/Ar and 40Ar/39Ar dates from any set of parameters to another [10]. ArAR has user-editable libraries to enable quick selection of the appropriate parameter sets before recalculating K/Ar and 40Ar/39Ar dates, and all values involved in calculations are tracked and exportable into a change log for future reference. ArAR is written in JavaTM, and is freely available as a platform-independent executable application at:

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