A Review of Fluid Inclusions in Diagenetic Systems

The study of fluid inclusions can help constrain the conditions at which diagenetic minerals precipitated, leading to a better understanding of the geologic controls and relative timing of changes in porosity and/or mineralising events. Many of the diagenetic minerals are easily deformed and it is important to check for any post-entrapment changes to the inclusions. Possible post-entrapment changes include reaction with the host crystal, necking down, nucleation metastability and thermal re-equilibration. The recommended method of detecting these problems is to examine individual fluid inclusion assemblages (FIAs) and report data for each individual FIA. These studies have been enhanced by the development of new micro-analytical techniques such as micro-fluorescence spectroscopy, micro-infrared spectroscopy, nuclear magnetic resonance, various mass spectrometry techniques and the analysis of individual fluid inclusions using laser ablation/decrepitation methods. Special techniques have been developed for hydrocarbon-bearing inclusions such as the Grains containing Oil Inclusions (GOI), Fluid Inclusion Stratigraphy (FIS), and the Molecular Composition of Inclusions (MCI) techniques. The fluid inclusions that form in some minerals during diagenesis provide the only direct means of examining the fluids present in these systems. They provide useful temperature, pressure, and fluid composition data that cannot be obtained by other means.