Calibration of GA1550 biotite standard for K/Ar and 40Ar/39Ar dating |
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Authors: | Ian McDougall Peter Wellman |
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Institution: | 1. Department of Geology, Trinity College Dublin, Dublin 2, Ireland;2. Department of Earth Sciences, Laurentian University, Sudbury, Canada;1. UMR CNRS 6118, Géosciences Rennes, OSUR, Université, Rennes 1, 35042 Rennes Cedex, France;2. Planetary and Space Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK;3. GeoRessources UMR 7359, CREGU, Campus Sciences-Aiguillettes, BP 70239, 54506 Vandoeuvre-lès-Nancy, France |
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Abstract: | The mineral separate GA1550 biotite has become an international standard for K/Ar and 40Ar/39Ar dating studies, although it was prepared as an intralaboratory standard at ANU to monitor tracer depletion from a gas pipette. It is one of a small number of samples that has been calibrated against 38Ar tracers, some of which had been mixed with known amounts of atmospheric argon, so that a so-called primary calibration has been performed. By measuring GA1550 biotite against additional tracers from the same batch we have determined the radiogenic argon content of this sample as 1.342 (± 0.007) × 10? 9 mol/g, and together with the measured K content of 7.645 (± 0.050) weight percent, we derive a best estimate for the K/Ar age as 98.5 ± 0.5 Ma, where the error is derived from averaging the ages determined relative to the 38Ar tracer. |
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