Fluid inclusions are defined as small cavities of minerals that have trapped tiny quantities of fluids. They are generally composed of mixtures of water, salts and gas depending of the fluid origin, the geological context, the physico-chemical processes occurring on the host rock, ...

Some examples of natural fluid inclusions

In the image above you have some examples of natural fluid inclusions :

  • A. Two-phase fluid inclusion with a relatively high vapour volume and a hexagonal shape (negative crystal in quartz).

  • B. Two-phase fluid inclusion with a low vapour volume and an irregular shape.

  • C. Saturated fluid inclusion.

  • D. Three-phase CO2-bearing fluid inclusion (Source: Dubois, 2003[1]).

L = liquid ; V = vapour ; CS = salt cube (halite) ; M = mica

Amongst the large variety of techniques used to characterize fluid inclusions, microthermometry is the most widespread in laboratories. Indeed this is the more complete technique as it allows the quantification of the fluid density and the chemical composition in terms of major components. In addition this is probably the cheapest technique in terms of apparatus and consumable cost – whereas the working time can be very, very,long ! ! !

Microthermometry is defined as the measurement of temperature of phase transitions during cooling and heating a fluid inclusion-bearing sample (Huraï et al, 2015[2]). The apparatus used is a microthermometric stage that allows the observation of phase changes under a microscope in the temperature range of -200°C to 500°C, perhaps 700°C or 1500°C depending of the device type.

The main experience of an “inclusionist” is to interpret phase changes. This experience is therefore based on numerous hours of observation of experiments and a minimal knowledge of phase diagrams of the more represented chemical systems in natural fluids.

The aim of the site is to present the most classical phase change sequences observed in fluid inclusions using videos captured on the microthermometric equipment of the fluid inclusion laboratory of the University of Lille (Laboratory of Civil Engineering and geo-Environment).

For the 7different sequences, a comment of the video is provided and an interpretation in terms of composition and/or density.

Additional references and suggested reading are added in the "Tools section"