New Constraints on Ages of Glasses Proposed as Reference Materials for Fission-Track Dating |
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Authors: | Marinella A. Laurenzi ,Maria Laura Balestrieri ,Giulio Bigazzi ,Julio C. Hadler Neto ,Pedro J. Iunes ,Pio Norelli ,Massimo Oddone ,Ana Maria Osorio Araya , José G. Viramonte |
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Affiliation: | CNR, Istituto di Geoscienze e Georisorse, via G. Moruzzi 1, 56124 Pisa, Italy;Dep. to Raios Cosmicos e Cronologia, Instituto de Física, Universidade Estadual de Campinas - Unicamp, C.P. 6165, 13083-970 Campinas - SP, Brazil;Dipartimento di Chimica Generale, Universitàdi Pavia, 27100 Pavia, Italy;Departamento de Física, Química e Biologia, Universidade do Estado de São Paulo, UNESP, 19060-900 Presidente Prudente - SP, Brazil;Instituto Geonorte, Universidad Nacional de Salta, Av. Buenos Aires 177, 4400 Salta, Argentina |
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Abstract: | New analyses have been performed in order to enhance the data-set on the independent ages of four glasses that have been proposed as reference materials for fission-track dating. The results are as follows. Moldavite - repeated 40Ar/39Ar age determinations on samples from deposits from Bohemia and Moravia yielded an average of 14.34 ± 0.08 Ma. This datum agrees with other recent determinations and is significantly younger than the 40Ar/39Ar age of 15.21 ± 0.15 Ma determined in the early 1980s. Macusanite (Peru) -four K-Ar ages ranging from 5.44 ± 0.06 to 5.72 ± 0.12 Ma have been published previously. New 40Ar/39Ar ages gave an average of 5.12 ± 0.04 Ma. Plateau fission-track ages determined using the IRMM-540 certified glass and U and Th thin films for neutron fluence measurements agree better with these new 40Ar/39Ar ages than the previously published ages. Roccastrada glass (Italy) - a new 40Ar/39Ar age, 2.45 ± 0.04 Ma, is consistent with previous determinations. The Quiron obsidian (Argentina) is a recently discovered glass that has been proposed as an additional reference material for its high spontaneous track density (around 100 000 cm-2). Defects that might produce "spurious" tracks are virtually absent. An independent 40Ar/39Ar age of 8.77 ± 0.09 Ma was determined and is recommended for this glass. We believe that these materials, which will be distributed upon request to fission-track groups, will be very useful for testing system calibrations and experimental procedures. |
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Keywords: | fission-track dating 40Ar/39Ar dating natural glasses age standards |
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