マントル捕獲岩に適用できる地質圧力計 : 流体包有物の顕微ラマン分光分析

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Fluid inclusions in mantle-derived minerals can serve as a messenger from the deep Earth. If CO2 is a dominant phase of the fluid, the relationship between intensity ratio and frequency separation of the Fermi diad bands in the Raman spectra of CO2 can be used for determination of density of the inclusions. The intensity ratio and the frequency separation between the peaks thereby increase with density of CO2. Kawakami et al . (2003) have established the relationship between density of CO2 and the frequency separation of the Fermi diad bands using the Raman data on CO2 fluid with densities from 0.1 to 1.21 g/cm3, including super critical fluids at 58-59°C. Thus, micro-Raman spectroscopic analysis allows us to reveal multiple densities of the small fluid inclusions by one-by-one density analysis. Generally, inclusions show CO2 densities (pressure) specific to the individual host minerals in the order of spinel > orthopyroxene ∼ clinopyroxene » olivine. The density of CO2 reflects how strong host minerals are to withstand the pressure differential between the inclusion’s internal pressure and the external environmental pressure during transport of xenoliths to near the Earths surface. Olivine underwent considerable plastic deformation resulting in the density reduction of CO2 fluid inclusions. On the other hand, the slightly higher density of CO2 in spinel can be explained by elastic deformation of the minerals during ascent and cooling of the xenoliths. Conversely, the density of CO2 inclusions in pyroxene will work as a useful geobarometer requisite for discussions on the origin of mantle-derived minerals.
日本鉱物科学会の論文
2005-07-30

マントル捕獲岩に適用できる地質圧力計 : 流体包有物の顕微ラマン分光分析

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