Spatially resolved CO₂ carbon stable isotope analyses at the microscale using Raman spectroscopy

Area of Science:

• Geochemistry
• Geology
• Spectroscopy

Background:

• Measuring the carbon stable isotope ratio (δ13Cco2) in geogenic CO2 fluids is vital for understanding Earth's degassing.
• Traditional bulk mass spectrometry is used, but Raman spectroscopy has faced challenges in determining CO2 isotopic signatures.

Purpose of the Study:

• To report on in-situ, non-destructive analyses of carbon stable isotopic composition of CO2 in fluid inclusions using a novel Raman spectroscopy configuration.
• To demonstrate the accuracy and applicability of Raman spectroscopy for microscale carbon isotope analysis.

Main Methods:

• Applied a novel high-resolution Raman spectroscopy configuration to analyze 42 high-density CO2 fluid inclusions.
• Collected multiple spectra per inclusion with varying acquisition times at high spectral resolution.
• Calculated integrated 13CO2/12CO2 band area ratios for isotopic analysis.

Main Results:

• Achieved reproducibility better than 4‰ for 58 out of 84 spectra sets.
• Demonstrated determination of δ13Cco2 with an error better than 2.5 ‰ in individual fluid inclusions.
• Results satisfactorily matched bulk mass spectrometry analyses from the same rock samples.

Conclusions:

• Raman spectroscopy is a viable method for accurate, non-destructive, site-specific, and spatially resolved carbon isotope analysis at the microscale.
• This technique offers a fundamental new methodology for geochemical studies of Earth's degassing and fluid evolution.
• The findings support the use of Raman spectroscopy for detailed investigation of carbon isotopes in geological samples.