HR: 1340h
AN: DI33A-1117    [Abstracts]
TI: Calibration of the infrared molar absorption coefficients by elastic recoil detection analysis (ERDA) for H measurements in olivine and clinopyroxene crystals and rhyolitic glasses
AU: * Aubaud, C
EM: aubaud@ipgp.jussieu.fr
AF: IPG-Paris, 2 place Jussieu, Paris, 75005, France
AU: Bureau, H
EM: helene.bureau@cea.fr
AF: LPS, CEA Saclay, Gif Yvette, 91191, France
AU: Raepsaet, C
EM: caroline.raepsaet@cea.fr
AF: LPS, CEA Saclay, Gif Yvette, 91191, France
AU: Khodja, H
EM: hicham.khodja@cea.fr
AF: LPS, CEA Saclay, Gif Yvette, 91191, France
AU: Hirschmann, M M
EM: hirsc022@umn.edu
AF: Dept Geol & Geophys, University of Minnesota, Minneapolis, MN 55455, United States
AU: Withers, A C
EM: withe012@umn.edu
AF: Dept Geol & Geophys, University of Minnesota, Minneapolis, MN 55455, United States
AU: Bell, D R
EM: david.r.bell@asu.edu
AF: SESE, Arizona State University, Tempe, AZ 85287, United States
AB: Fourier transform infrared (FTIR) spectroscopy is the most widely applied technique for measuring hydrogen in nominally anhydrous minerals (NAMs) and silicate glasses. FTIR is rapid, sensitive, widely available and gives information on the bonding environment of H-bearing species. H determination relies on the Beer-Lambert law and therefore requires constraints on the applicable molar absorption coefficient, ε. Values of ε may be derived only from independent absolute methods. These ε are now reasonably well known for glasses, but to date determinations of ε applicable to NAMs are extremely limited and subject to uncertainties. Most notably, the Paterson (1982) calibration gives H contents in olivine that are a factor of 2.5- 3.5 lower than those suggested by the Bell et al. JGR 2003 calibration. We performed elastic recoil detection analysis (ERDA) on a range of samples that had been previously analyzed by FTIR, including natural rhyolitic glasses (1430-1772 ppm H₂O), natural and synthetic olivine (0-910 ppm), natural orthopyroxene (38-147 ppm), and natural clinopyroxene crystals (0-490 ppm). ERDA is a nuclear microprobe technique that yields matrix-independent absolute determinations of H concentration. A 3 MeV beam of ⁴He is employed at high spatial resolution (50 × 200 microns). The detection limit, determined from analysis of dry minerals is 150±20 ppm H₂O, too great for analysis of many NAMs from the upper mantle, but applicable to H-rich natural and synthetic NAMs. For glasses, synthetic olivines, and clinopyroxenes, we found good proportionality between the measured ERDA hydrogen concentration and the linear (rhyolite) or integrated (minerals) absorbance measured by FTIR. The ε found for rhyolite (103±9 l/mol per cm) is close to that of 88±2 l/mol per cm given by Dobson et al. (GCA, 1989). For clinopyroxene, we obtain ε 47010±6070 l/mol per cm², slightly larger than 38300±1700 l/mol per cm² found by Bell et al. (Am. Min. 1995). Finally, for olivine we obtain ε 34330±4000 l/mol per cm² (to be compared to the 28450±1830 l/mol per cm² of Bell et al. JGR 2003). Thus, our results confirm the previous conclusion of Bell et al. (2003) that the Paterson (1982) calibration yields strong underestimates of H in olivine.
DE: 1025 Composition of the mantle
DE: 1037 Magma genesis and partial melting (3619)
DE: 3621 Mantle processes (1038)
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8145 Physics of magma and magma bodies
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting