Calibration of the infrared molar absorption coefficients for H in olivine, clinopyroxene and rhyolitic glass by elastic recoil detection analysis
Résumé
We use a nuclear microbeam technique (Elastic Recoil Detection Analysis or ERDA) to measure the H content in 2 rhyolitic glasses, 4 olivines, 4 orthopyroxenes, and 7 clinopyroxenes. These samples have been characterized previously for their OH absorption spectra by infrared (FTIR) spectroscopy. We use ERDA and FTIR data to calibrate the infrared molar absorption coefficients. The blank level of the ERDA method is 102 ± 81 ppm H2O, too great for the analysis of many natural nominally anhydrous minerals (NAMs) from the upper mantle, but applicable to H-rich glasses, natural and synthetic NAMs. Calibration of the molar absorption coefficient ε with the ERDA results gives 95 ± 8 l mol− 1 cm− 1 for rhyolitic glasses (peak height), 34,515 ± 7050 l mol− 1 cm− 2 for olivine and 46,103 ± 5300 l mol− 1 cm− 2 for clinopyroxene (integrated area). The olivine calibration of the present study is intermediate between that of Bell et al. [Bell, D.R., Rossman, G.R., Maldener, J., Endisch, D. and Rauch, F., 2003. Hydroxide in olivine: a quantitative determination of the absolute amount and calibration of the IR spectrum. Journal of Geophysical Research, 108(B2). doi:10.1029/2001JB000679] and that of Libowitzky and Rossman [Libowitzky, E. and Rossman, G.R., 1997. An IR absorption calibration for water in minerals. American Mineralogist, 82: 1111-1115]. For clinopyroxene, the best agreement with the ERDA data is obtained for the Libowitzky and Rossman [Libowitzky, E. and Rossman, G.R., 1997. An IR absorption calibration for water in minerals. American Mineralogist, 82: 1111-1115] calibration (5% lower than the ERDA data). The present calibration also confirms that the Paterson [Paterson, M.S., 1982. The determination of hydroxyl by infrared absorption in quartz, silicate glasses and similar materials. Bulletin de Mineralogie, 105: 20-29] calibration systematically underestimates the OH content in olivine.