ID3506, a New/Old Lipari Obsidian Standard for Characterization of Natural Glasses and for Tephrochronology
Abstract
Samples of Holocene obsidians from Lipari Island, Italy, have been used as primary (calibration, e.g. for Na-Al-Si-K) and secondary (verification) standards for electron probe microanalysis (EPMA) at several laboratories since the late 1960s, primarily in tephra correlation studies. Supplies of two such obsidians, UA5831 (=CCNM-211) and a sample distributed by J. Hunt and P. Hill at the University of Edinburgh, are now largely exhausted. To serve as a replacement, we have characterized a third Lipari sample, ID3506, from the Harvard Mineralogical Museum. Harvard supplied a 250 g sample (about half of the original) which we chipped and separated into three size fractions. Linear traverses and randomized, nested analysis of multiple fragments by EPMA demonstrate a high degree of homogeneity with measured variations very close to the theoretical limits expected from counting statistics. Raw X-ray count rates measured with fixed spectrometer positions and major-element oxide abundances are also indistinguishable from the two obsidians that ID3506 is intended to replace. The microlite and microcryst abundance of ID3506 is similarly very low, about 0.05 +/- 0.04% by area/volume based on 30 BSE images from three fragments. To develop major-element reference values and trace-element information values, ID3506 obsidian has been analyzed by EPMA (multiple labs), XRF (2 labs, majors and traces), ICP-MS (1 lab), LA-ICP-MS (1 lab), INAA (1 lab), and FTIR (1 lab, for total H2O). Similar published analyses by EPMA, wet chemistry, and XRF are available for the other two Lipari samples. To provide improved traceability, we have also analyzed ID3506 together with several other glass microanalysis standards, including ATHO-G, BHVO-2G, VG-2 (USNM 111240/52), VG A-99 (USNM 113498/1), and VG-568 (USNM 72854). Supplies of ID3506 will be available from Harvard Mineralogical Museum.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.V31E2010K
- Keywords:
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- 1194 GEOCHRONOLOGY / Instruments and techniques;
- 3694 MINERALOGY AND PETROLOGY / Instruments and techniques;
- 8455 VOLCANOLOGY / Tephrochronology;
- 8494 VOLCANOLOGY / Instruments and techniques