A new calibration for micro-Raman spectroscopy paves the way for easy and accurate quantification of CO2 dissolved in volcanic glasses
CO2 is an important volcanic volatile. It is commonly the second most abundant dissolved gaseous species in a molten rock (after H2O) and it can have a dramatic effect on the phase relations and rheology of degassing magmas. The release of CO2 dissolved in magmas is also a vital part of the global carbon cycle. Thus, there has been considerable experimental effort dedicated to measuring CO2 solubility in silicate melts.
Raman spectroscopy is a non-destructive spectroscopic technique that harnesses the scattering of light to provide information about the molecular structure of sample, e.g., CO2 content. Micro-Raman has advantages over other comparable techniques because it can analyse <10 μm spot sizes and it requires relatively minimal sample preparation; however, the analysis requires a compositionally dependent calibration.
To this end, Morizet and co-authors present a new calibration for the quantification of CO2 in geologically relevant glass compositions by micro-Raman. The study collected micro-Raman CO2 data for an extensive database of synthetic and natural samples, whose CO2 content had previously been quantified by bulk analysis, and found a relationship between the spectral features in the high-frequency region of aluminosilicate glasses and the spectral peak associated with dissolved carbonate. This new calibration is found to be accurate to better than ±0.4 wt% CO2.
Morizet Y, Brooker RA, Iacono-Marziano G, & Kjarsgaard BA (2013) Quantification of dissolved CO2 in silicate glasses using micro-Raman spectroscopy. American Mineralogist, 98(10), http://dx.doi.org/10.2138/am.2013.4516