CaCl2-hydrate nucleation in synthetic fluid inclusions

CaCl2 is occasionally the major or only important chloride species in natural aqueous fluid inclusions. The presence of CaCl2 can be proven by a combination of Raman spectroscopy and microthermometry. Inclusions containing H2O–CaCl2 have been synthesised in quartz in order to study phase relationships and phase transitions at low temperatures. The synthetic inclusions reveal variable freezing behaviours depending on the salinity, reflecting highly metastable phase assemblages. Nevertheless, Raman spectra of antarcticite (3240 ± 2, 3387 ± 2, 3402 ± 2 and 3430 ± 1 cm− 1), α-tetrahydrate (3197 ± 2, 3369 ± 6, 3425 ± 3, and 3446 ±2 cm− 1), γ-tetrahydrate (3435 cm− 1) and sinjarite (3377 ± 1, 3405 ± 3, 3424 ± 2, 3464 ± 2, 3559 ± 2 cm− 1) were measured at − 190 °C. Final melting of ice, antarcticite and α-tetrahydrate correspond to stable phase transitions and can be used to calculate the salinity. Eutectic temperatures were not detected in this experimental study due to the absence of stable phase assemblages at low temperatures. The nucleation and melting behaviour of fluid inclusions during microthermometrical investigations can only be fully understood by Raman spectroscopic identification of the phase assemblages, either stable or metastable ones.