fluidinclusion

Fluid inclusions are microscopic pockets of fluid trapped within minerals during their formation or through later hydrothermal processes. They form when a crystal grows from a melt or solution and seals a small amount of surrounding liquid, vapor, or supercritical fluid. Inclusions can be primary, forming with the host crystal, or secondary, resulting from later fracturing and sealing of fluids. They may contain aqueous brines, pure water, gas-rich phases, or supercritical fluids, and can also host dissolved salts or solids.

The fluids preserved inside inclusions record the chemical composition and the physical conditions at the time of entrapment. This makes them valuable for reconstructing pressure-temperature histories, fluid evolution, and mineralizing events in metamorphic, igneous, and hydrothermal systems. They are widely used to investigate ore-forming processes, hydrocarbon reservoirs, and, in some cases, ancient climatic or hydrological conditions preserved in rocks.

Analytical methods for fluid inclusions include microthermometry, which measures phase transitions and homogenization temperatures to infer entrapment conditions and salinity. Spectroscopic techniques such as Raman and infrared spectroscopy identify dissolved gases and molecular species. In some cases, the vapor or liquid phases are extracted and analyzed by gas chromatography, mass spectrometry, or other techniques to determine detailed compositions.

Limitations include post-entrapment re-equilibration and secondary alteration, which can modify original compositions. Proper interpretation relies on contextual geological data and careful sample selection.