Conformity and precision of CO₂ densimetry in CO₂ inclusions: microthermometry <i>versus</i> Raman microspectroscopic densimetry

Abstract

To assess the ability of densimetry for CO 2 fluid in CO 2 inclusions, we compare two methods, microthermometry and Raman microspectroscopic densimetry for CO 2 . The comparative experiment was performed for nine CO 2 inclusions in three mantle xenoliths. The results are as follows: (1) microthermometry precisely determines CO 2 density with the range of 0.65 to 1.18 g/cm 3 compared with Raman microspectroscopic densimetry; (2) CO 2 density obtained by Raman microspectroscopic densimetry is fairly consistent with that by microthermometry; (3) it is hard to determine CO 2 density in CO 2 inclusion with diameter of less than around 3 µm using microthermometry; and (4) microthermometry can be applied only to the CO 2 inclusion whose CO 2 density ranges from around 0.65 to 1.18 g/cm 3 , whereas the Raman microspectroscopic densimetry is applicable to CO 2 density ranging from 0.1 to 1.24 g/cm 3 . The above features carry the potential for estimation of depth origin of mantle‐derived rocks. The depth where the rocks were trapped by host magma can be estimated using both geothermometric data and CO 2 fluid density in CO 2 inclusions in the rocks. Typical precisions of density of CO 2 in CO 2 inclusions obtained by the Raman microspectroscopic densimetry (~0.01 g/cm 3 ) and by the microthermometry (&lt; 0.001 g/cm 3 ) correspond to uncertainties in the depth origin of 2.4 km and &lt; 1.7 km, respectively, at 1000 ± 50 °C. In case of the mantle under 750–1250 °C and 1 GPa, the CO 2 fluid has a density ranging from 1.06 g/cm 3 to 1.21 g/cm 3 , which are well measured by the Raman microspectroscopic densimetry. Combination of both densimetries for CO 2 in mantle minerals elucidates the deep structure of the Earth. Copyright © 2012 John Wiley &amp; Sons, Ltd.