Determination of Mineralogy and Peak Metamorphic Temperature of Selected Carbonaceous Chondrite Meteorites using MicroRaman Spectroscopy

We utilized confocal microRaman spectroscopy to examine the organics and mineral phases in seven carbonaceous chondrite meteorites: Allende (CV3), Ivuna (CI1), Jbilet Winselwan (CM2), Murchison (CM2), NWA 10675 (CO3), NWA 12328 (CM1), and Tagish Lake (C2-ung). Two of these meteorites (NWA 10675 and NWA 12328) have previously not been examined using this technique. Using the full width half maxima (FWHM) of the organic matter D band, we estimated their peak metamorphic temperature (PMT). The PMTs show that Allende and NWA 10675 have experienced the highest temperatures (500-700 °C) while Ivuna and Tagish Lake experienced the lowest temperatures (<230 °C), consistent with their petrologic classifications. Additionally, we successfully examined the following mineral phases in detail: olivine, pyroxene, and phosphates. For the olivine, we calculated the Fo# (a measure of the Mg content) using the doublet peak located in the 800-860 cm-1 region. For the phosphates, we identified the type of phosphate (apatite, merrillite, or whitlockite) present based on previously published spectra in the literature. Finally, we show that the D3 band is well correlated with the PMT, opening the possibility for a new Raman thermometer.