Exploring the multicollection approach for the 40Ar/ 39Ar dating technique

Abstract

We present an original analytical system for 40Ar/ 39Ar dating. It makes use of a 180° sector multicollection mass spectrometer equipped with five Faraday cups, which renders peak switching unnecessary during argon isotopic analyses. Compared to the single-collector approach commonly used for argon isotopic analyses, our system presents greater stability during data acquisition. Faraday cup efficiencies, which can be a limiting factor for the multicollection mass spectrometer, were highly reproducible. The analytical validity of the 40Ar/39Ar ages obtained using this new mass spectrometer has been preliminarily tested using geological standard minerals (MMhb-1, FCT-San, and HD-B1) commonly used as neutron fluence monitors. Independent plateau age determinations of Ethiopian samples duplicated over a 1-year interval demonstrated the reproducibility of the analyses. The results of these measurements highlight the good behavior of this new instrument for 40Ar/39Ar step heating dating. The age reproducibility of successive steps leads to analytical errors lower than 0.1% for well-behaved samples. This system, still in its initial stage of development, represents an alternative solution that is worth exploring in order to improve absolute dating by the 40Ar/39Ar technique. Copyright 2004 by the American Geophysical Union.