,+ 2,,* FT-IR Micro Reflectance Measurements of Water Content in Melt Inclusions. Atsushi Y ASUDA

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1 /0 (,*++), FT-IR,*+* 2,,* FT-IR Micro Reflectance Measurements of Water Content in Melt Inclusions Atsushi Y ASUDA A technique based on micro reflectance spectroscopy using a vacuum Furier Transform infrared (FT-IR) spectrometer has developed for the quantitative measurement of dissolved water in melt inclusions in phenocrysts. The technique is superior in sample preparation to the conventional transmission method, which requires doubly polished samples with known thickness. Four synthesized glass samples with H, O contents ranging ++1. to.*/. wt were examined in this study. A linear correlation between the logarithm of reflectance intensities around -0/* cm by H-bearing species and the water content of the glasses is obtained. At the lateral resolution of -*, the precision of the measurement caused by random error is *,-. wt ( + s), and the value is low enough to apply the technique to the measurement of dissolved water in melt inclusions. A method which corrects possible contamination of inclusion spectra by the olivine host is also proposed. Key words : FTIR, reflectance measurement, melt inclusion, olivine contamination + HO, Bureau et al., +332 ; Luhr,,**+ ; Saito et al.,,**+ ; Wallace,,**/ FT-IR +/. Roggensack et al., +331 ; Metrich et al.,,**+ / Fourier transform infrared (FT-IR) + Grzechnik et al., +330 ; Stolper, +32, ; Dixon et al., +33/ * (Grzechnik et al., +330 ; Moore et al.,,*** ; Hervig et al.,,**-) ++- **-, + Corresponding author: Atsushi Yasuda yasuda@eri.u-tokyo.ac.jp Earthquake Research Institute, Univ. Tokyo, Yayoi + + +, Bunkyo-ku, Tokyo ++- **-,, Japan

2 42 Larson,,**2 FT-IR Fig. +. Reflectance spectra of gold obtained at pressures of l atm ( +* Pa) and +* Pa. /, Infrared absorption by water vapor (-0/* cm by, FT-IR the fundamental stretching vibration and +0-* FT-IR FTIR- cm by the fundamental bending vibration) and carbon dioxide (,.** cm by molecular CO,) in 00* plus IRT--* VC the sample chamber quite reduced by evacuation. GeKBr, MCT -, FT-IR./ MCT + CCD,* PC PC XYZ 3** 1*** cm. cm,*,* +** ** cos SN (S/N) +,2,*.2,*.2,/, + ( +* Pa) (Fig. + ) -0/* cm ; +301 p ** cm,.** cm, +* Pa -0/* cm, -* / - FT-IR

FT-IR 43 Table +. Data for of transmission measurements at -0/* cm. Fig.,. Comparison of FT-IR reflectance spectrum with transmittance spectrum of hydrous basaltic glass (A-,,. 0* wt H, O).

3 FT-IR 43 Table +. Data for of transmission measurements at -0/* cm. Fig.,. Comparison of FT-IR reflectance spectrum with transmittance spectrum of hydrous basaltic glass (A-,,. 0* wt H, O). Aperture sizes are /* /* for transmission measurement and +** ** for reflectance measurement. SiO.3. 1 TiO. + Al O 1.* FeO (total),,, - +*/. MgO 10. CaO +,. Na O,,. (wt ); XRF -cm, +,/,/* FT-IR (Table + ),** +,** - +/ () +.+ (), () - Fig., (). n I ( n) ** * s R ( n) I ( n)/ I ( n) s * T() n I()/I() n n Lambert-Beer log (II ) ( + ) e ()cd, n e () n n (). d c : absorbance A ( n) log T ( n) +/ -*, : +/.* C C 2.*, A ()/d n r e () n +33. r * w s * +* s +* *

4 44 e () n n Lambert-Beer A( n) log () n,*** 1*** cm --**.*** cm -0/* cm Fig.,, Fig. -. E# ect of evacuation on FT-IR reflectance OH spectra of hydrous glasses, A+ and A.. Each (Stolper, +32, ) +0** cm spectrum consisted of +,2 scans from the sample molecular H O using a /* /* aperture.,*** cm Si, Al-O (Fine and k A Stolper, +320) ka/( 3.,+, pnd) Moore et al.,,*** (/), ( 0) K-K OH -0/* cm K-K + ** K-K SN K-K, +* Pa. +1 wt..*/ wt Fig. - (Table + ) Table, Fig.. -0/* cm SN ++1. wt.*/. wt,/, +* Pa wt -+/* cm..** cm..*/ wt -0/* cm.,, w ( Abs ), (Fig..(a)) (Fig.. (b)) Hervig et al. (,**-) -0/* cm al.,,***) Kramers- R R (Hervig et al.,,**- ; Moore et +* R.*** cm -0/*.*** Kronig (K-K) k +33. p 0-0. ; Moore et al.,,*** K-K -0/*

FT-IR 45 Table,. Analytical conditions and results of FT-IR reflective measurements for plotting regression lines. cm Hervig (Fig.. (a)) log Hervig et al. (,**-).*** et al. (,**-) -0/* cm R R (Fig.

5 FT-IR 45 Table,. Analytical conditions and results of FT-IR reflective measurements for plotting regression lines. cm Hervig (Fig.. (a)) log Hervig et al. (,**-).*** et al. (,**-) -0/* cm R R (Fig.. (c)) -0/* (Fig.. (d)) Fig.. (b) base Fig... Detail of a reflectance spectrum showing the definition of (a) Abs -0/*, and (c) R-0/* and R base. (b) Plot of Abs-0/* versus dissolved water content, and (d) plot of R -0/*/Rbase versus dissolved water content determined by the FT-IR transmission measurement. Solid diamond: /* /* aperture, open square : +** ** aperture. The horizontal error bars show the uncertainty (, s) in the water content determined by transmission method (Table + ); where error bars are not shown, the error was smaller than the symbols. The vertical error bars are from Table -. Regression lines are also shown for plots (b) and (d). Bold solid lines in plots (a) and (c) represent baselines.

6 46 Table -. Noise level ( + s) in Abs determination at FT-IR di# erent measurement conditions. FT-IR,** Table -.,, /* /* +** **, +** ** +,2 (Fig.. (b)) *.,3 wt +*,..- *+*. wt -* -*,*.2 *.,- wt.. A wt,3**.,** cm /* cm ( + s)

7 FT-IR 47 Fig. /. Variation of reflectance spectra ( +*,. scans, -* -* ) changing olivine content within the analytical area. With increasing olivine content absorption around +***,** cm increases. Fig. 0. A plot of Abs-0/* versus peak height at +*,* cm shown in Fig. /. The peak heights are normalized to unity by dividing the peak height Nichols and Wysoczanski, corresponding to +** olivine. Error bars are,**1 from Table - ( +*,. scans and -* -* except for the upper left one which measured using a,*,* aperture). *,/. Mg 1/ /*.0-2. wt +** (baseline) (Fig. /) baseline -* -* baseline +*,. +***,** cm -0/* cm Mg Fe, Si-O (Duke and Stephens, +30. ),*,* Fig. / baseline ++** cm +*,* cm baseline ++** cm +*,* +*** +*,* cm +** +,** cm (Fig. 1) + -0/* cm ( Abs ) cm -0/* (Fig. 0) / +** FT-IR

8 48 Fig. 1. Representative FT-IR reflectance spectrum of plagioclase. Reflectance spectra of olivine and Bureau, H., Metrich, N., Pineau, F. and Semet, M.P. ( +332) basaltic hydrous glass are shown for comparison. Magma-conduit interaction at Piton de la Fournaise volcano (Reunion Island): a melt and fluid inclusion study. J. Volcanol. Geotherm. Res., 2., -30*. Dixon, J.E., Stolper, E.M., Holloway, J.R. ( +33/ ) An experimental study of water and carbon dioxide solubilities in Mid-Ocean Ridge Basaltic liquids. Part I: -* -* Calibration and solubility models. J. Petrol., -0, +0*1 *,-. wt ( + s) Duke, D.A. and Stephens, J.D. ( +30. ) Infrared investigations of the olivine group minerals, Amer. Mineral.,.3, +-22.*0. Fine, G. and Stolper E. ( +320) Dissolved carbon dioxide in basaltic glasses : concentrations ans speciation, Earth Planet. Sci. Lett., 10,,0-,12. ( +301 ).-, p. Grzechnik, A., Ziermann, H.D., Hervig, R.L., King, P. L. and McMillan, P.F. ( +330) FTIR micro-reflectance, measurements of the CO- ion content in basaltic and leucitie glasses. Contrib. Mineral. Petrol., +,/, Silver et al., +33* Hervig, R.L., Mazdab, F.K., Moore, G. and McMillan, P. F. (,**-) Analyzing hydrogen (H, O) in silicate glass by Hervig et secondary ion mass spectrometry and reflectance Fourier al. (,**-) transform infrared spectroscopy. in Melt inclusions in volcanic systems : methods, applications and problems (De Vino, B. and Bodnar R.J. eds), 2- *-, Elsevier, Amsterdam. Larsen, J.F. (,**2) Heterogeneous bubble nucleation and disequilibrium H,* exsolution in Vesuvius K-phonolite melts, J. Volcanol. Geotherm. Res., +1/,,12,22. Luhr, J.F. (,**+) Glass inclusions and melt volatile contents at Paricutin Volcano. Mexico. Contrib. Mineral. Petrol., +.,,,0+,2-. Metrich, N., Bertagnini, A., Landy, P. and Rosi, M. (,**+) Crystallization Driven By Decompression and Water Loss at Stromboli Volcano (Aeolin Islands, Italy). J. SN Petrol.,.,, *. Moore, G., Chizmeshya, A. and McMillan, P.F. (,***) Calibration of a reflectance FTIR method for determina- FT-IR tion of dissolved CO, concentration in rhyolitic glasses. Goechim. Coscmoshim. Acta., 0., -/1+ -/13. Nichols, A.R.L. and Wysoczanski, R. J. (,**1) Using

9 FT-IR 49 micro-ftir spectroscopy to measure volatile contents in Silver, L.A., Ihinger, P.D. and Stolper, E.M. ( +33* ) The small and unexposed inclusions hosted in olivine crystals. influence of bulk composition on the speciation of water Chem. Geol.,,.,, in silicate glasses, Contrib. Mineral. Petrol., +*., +., 0,. Roggensack, K., Hervig, R.L., Mcknight, S.B., Williams, S. Stolper, E.M. ( +32, ) Water in silicate glasses : an infrared N. ( +331 ) Explosive basaltic volcanism from Cerro spectroscopic study. Contrib. Mineral. Petrol., 2+, ++1. Negro volcano: influence of volatiles on eruptive style. ( +33. ) FT-IR, Science,,11, ,.,-* p. Saito, G., Kazahaya, K., Shinohara, H., Stimac, J. and Kawanabe, Y. (,**+) Variation of volatile concentration Wallace, P. J. (,**/) Volatiles in subduction zone magmas : concentrations and fluxes based on melt inclusion and in a magma system of Satsuma-Iwojima volcano deduced volcanic gas data. J. Volcanol. Geotherm. Res., +.*,,+1 from melt inclusion analyses. J. Volcanol. Geotherm.,.*. Res., +*2,

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