title: Micro-Raman densimeter for CO2 inclusions in mantle-derived minerals.
abstract: We investigated the applicability of Raman microprobe spectroscopy for determining the density of CO2 in fluid inclusions in minerals of mantle-derived xenolith samples. A separation (delta) between two Raman bands of CO2 due to Fermi resonance can be a reliable densimeter for CO2 fluid. The relationship between the density of CO2 (g/cm3) and delta (cm-1) can be expressed as: d = -0.03238697 delta 3 + 10.08428 delta 2 - 1046.189 delta + 36163.67. This equation was obtained from the Raman data on CO2 fluid with densities from 0.1 to 1.21 g/cm3, including super critical fluids at 58-59 degrees C. The delta value was constant with increasing temperature from room temperature to 200 degrees C. This indicates that the Raman densimeter is not affected by a possible rise in temperature, an artifact induced by the high flux of the incident laser. The minimum size of measurable inclusions is 1 micron, and the precision in the determination of delta is 0.1 cm-1, corresponding to 0.02 g/cm3 for inclusions of 1 micron in size. The precision can be better for larger inclusions. The micro-Raman densimeter can determine the density of CO2 fluid inclusions over a wide range. In particular, densities of gas and mixtures of gas and liquid phases, which cannot be measured by microthermometry, can be determined.
authors.affiliation: Laboratory for Earthquake Chemistry, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Kawakami
authors.forename: Junji
authors.initials: J
authors.lastname: Yamamoto
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kagi
mesh_terms: D002138:Calibration; D002245:Carbon Dioxide / Q000032:analysis* / Q000737:chemistry*; D003720:Densitometry / Q000295:instrumentation / Q000379:methods*; D019015:Geologic Sediments / Q000032:analysis* / Q000737:chemistry*; D008365:Manometry / Q000295:instrumentation / Q000379:methods; D008903:Minerals / Q000032:analysis* / Q000737:chemistry*; D008904:Miniaturization; D044367:Phase Transition; D011312:Pressure; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013059:Spectrum Analysis, Raman / Q000295:instrumentation / Q000379:methods*
chemical_list: D008903:Minerals; D002245:Carbon Dioxide