Calibration of GA1550 biotite standard for K/Ar and 40Ar/ 39Ar dating

• Published in: Chemical geology Vol. 280; no. 1; pp. 19 - 25
• Main Authors: McDougall, Ian, Wellman, Peter
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2011
• Subjects: Age; age determination; Argon; argon (noble gases); Atmospherics; Biotite; Biotite standard; Calibration; Calibrations; K/Ar geochronology; Mount Dromedary, Australia; Radioactive age determination; tracer techniques; Tracers; Biotite standard; K/Ar geochronology; Mount Dromedary, Australia; Calibrations
• ISSN: 0009-2541; 1872-6836
• DOI: 10.1016/j.chemgeo.2010.10.001

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. ► GA1550 biotite as a standard for K/Ar and 40Ar/ 39Ar dating. ► Primary calibration of 38Ar tracers versus known amounts of air argon. ► GA1550 biotite versus tracers from same batch to determine radiogenic argon content. ► K measured by flame photometry, yielding age of GA1550 biotite of 98.5 ± 0.5 Ma.