V51A-3028
Toward Improvements in Inter-laboratory Calibration of Argon Isotope Measurements
Friday, 18 December 2015
Poster Hall (Moscone South)
Sidney R Hemming1, Alan L Deino2, Matthew Thomas Heizler3, Kip V Hodges4, William C. McIntosh5, Paul R. Renne2, Carl C Swisher III6, Brent D Turrin6 and Matthijs C Van Soest7, (1)Columbia University of New York, Palisades, NY, United States, (2)Berkeley Geochronology Center, Berkeley, CA, United States, (3)New Mexico Institute of Mining and Technology, Bureau of Geology and Mineral Resources, Socorro, NM, United States, (4)Arizona State University, Tempe, AZ, United States, (5)New Mexico Institute Mining & Tech, Socorro, NM, United States, (6)Rutgers University, Piscataway, NJ, United States, (7)Arizona State University, School for Earth and Space Exploration, Tempe, AZ, United States
Abstract:
It is important to continue to develop strategies to improve our ability to compare results between laboratories chronometers. The U-Pb community has significantly reduced inter-laboratory biases with the application of a community tracer solution and the distribution of synthetic zircon solutions. Inevitably sample selection and processing and even biases in interpretations will still lead to some disagreements in the assignment of ages. Accordingly natural samples that are shared will be important for achievement of the highest levels of agreement. Analogous improvements in quality and inter-laboratory agreement of analytical aspects of Ar-Ar can be achieved through development of synthetic age standards in gas canisters with multiple pipettes to deliver various controlled amounts of argon to the mass spectrometer. A preliminary proof-of concept comes from the inter-laboratory calibration experiment for the 40Ar/39Ar community. This portable Argon Pipette Intercalibration System (APIS) consists of three 2.7 L canisters each equipped with three pipettes of 0.1, 0.2 and 0.4 cc volumes. The currently traveling APIS has the three canisters filled with air and 40Ar*/39Ar of 1.73 and canister 2 has a 40Ar*/39Ar of 40.98 (~ Alder Creek and Fish Canyon in the same irradiation). With these pipettes it is possible to combine them to provide 0.1, 0.2, 0.3 (0.1+0.2), 0.4, 0.5 (0.1+0.4), 0.6 (0.2+0.4), and 0.7 (0.1+0.2+0.4) cc. The configuration allows a simple test for inter-laboratory biases and for volume/pressure dependent mass fractionation on the measured ratios for a gas with a single argon isotope composition. Although not yet tested, it is also possible to mix gas from any one of the three canisters in proportions of these increments, allowing even more tightly controlled calibration of measurements. We suggest that ultimately each EARTHTIME lab should be equipped with such a system permanently, with a community plan for a traveling system to periodically repeat the inter-calibration tests. The composition(s) of such systems may not be the same for each lab, depending on the requirements of equipment and main age ranges targeted. But with a relatively small number of end member compositions it should be possible to greatly improve the calibration capability of the community.
