Azbej, Tristan, Severs, Matthew J., Rusk, Brian G., and Bodnar, Robert J. (2007) In situ quantitative analysis of individual H2O–CO2 fluid inclusions by laser Raman spectroscopy. Chemical Geology, 237 (3). pp. 255-263.

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Abstract

Raman spectral parameters for the Raman ν1 (1285 cm−1) and 2ν2 (1388 cm−1) bands for CO2 and for the O–H stretching vibration band of H2O (3600 cm−1) were determined in H2O–CO2 fluid inclusions. Synthetic fluid inclusions containing 2.5 to 50 mol% CO2 were analyzed at temperatures equal to or greater than the homogenization temperature. The results were used to develop an empirical relationship between composition and Raman spectral parameters. The linear peak intensity ratio ( IR=ICO2 / ( ICO2+IH2O)) is related to the CO2 concentration in the inclusion according to the relation: Mole% CO2 ¼ e−3:959 IR2 þ8:0734 IR where ICO2 is the intensity of the 1388 cm−1 peak and IH2O is the intensity of the 3600 cm−1 peak. The relationship between linear peak intensity and composition was established at 350 °C for compositions ranging from 2.5 to 50 mol% CO2. The CO2–H2O linear peak intensity ratio ( IR) varies with temperature and the relationship between composition and IR is strictly valid only if the inclusions are analyzed at 350 °C. The peak area ratio is defined as AR=ACO2/(ACO2+AH2O), where ACO2 is the integrated area under the 1388 cm−1 peak and AH2O is the integrated area under the 3600 cm−1 peak. The relationship between peak area ratio (AR) and the CO2 concentration in the inclusions is given as: Mole% CO2 ¼ 312:5 AR The equation relating peak area ratio and composition is valid up to 25 mol% CO2 and from 300 to 450 °C. The relationship between linear peak intensity ratio and composition should be used for inclusions containing ≤50 mol% CO2 and which can be analyzed at 350 °C. The relationship between composition and peak area ratios should be used when analyzing inclusions at temperatures less than or greater than 350 °C (300–450) but can only be used for compositions ≤25 mol% CO2. Note that this latter relationship has a somewhat larger standard deviation compared to the intensity ratio relationship. Calibration relationships employing peak areas for both members of the Fermi diad (ν1 at 1285 cm−1 and 2ν2 at 1388 cm−1) were slightly poorer than those using only the 2ν2 (1388 cm−1) member owing to interference from quartz peak at approximately 1160 cm−1.

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