Abstract

Solid inclusions in quartz samples, collected in Switzerland from the freshwater molasse of Les Éplatures (Vindobonian), from the upper marine molasse of Tavannes (Burdigalian) and from the green marl of Cornaux (Purbeckian), were studied by microthermometry and Raman microprobe techniques. Microthermometry showed that in a temperature range from 130° to 180°C the solid inclusions changed from clear and transparent to dark and opaque. This temperature range corresponds to the gypsum-anhydrite phase transition. Further experiments using a Raman microprobe, showed that the Raman vibrational spectrum at room temperature contains only peaks at the frequency bands of gypsum. Successive heating to 100°, 150° and 200°C indicated partial transformation at ∼150°C, with the intensity of the gypsum bands diminishing as those of anhydrite appeared. The bands of coordinated water shifted towards higher frequency ranges. The transition terminates at 200°C in 24 hr. The Raman spectrum then only contains anhydrite bands, the bands of gypsum having virtually disappeared. These experiments enable, the observation in situ of the transformation of gypsum inclusions to anhydrite, and the determination of the transition temperature.

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