A Raman Geothermometer for Carbonaceous Chondrites

Samples of the Murchison meteorite (carbonaceous chondrite, type CM2) were kept isothermally in a specially designed device at temperatures of 200, 500, and 800°C. After the samples cooled down in an inert helium atmosphere, Raman scattering spectra were taken. An increase in the intensity of the G- and D‑lines of graphite was detected depending on the degree of heating. It is shown that using such a characteristic parameter of these lines as the area ratio, S_D/S_G, it is possible to define a geothermometer to determine the maximum temperature of thermal metamorphism of the parent bodies of carbonaceous chondrites. A comparison with the known data for carbonaceous chondrite Allende (CV3), which has experienced a significant thermal metamorphism, is carried out.