Aqueous solutes in fluid inclusions

The properties of fluids are of major importance in understanding processes that alter rocks and materials, e.g. weathering and metamorphism. Rocks often contain traces of these processes that have happened in the geological past, however, the pore fluid itself is in general not present anymore. Minerals within the rock have the capacity to entrapped small amounts of this fluid. Presently, these fluid inclusions (ø 5-20 m) can be studied by microscope and they give direct evidence of the palaeo-geological environment and processes, mainly by determining its composition and density. Salts can be dissolved within this fluid, and they have a huge influence on its properties. Identification of these salts is, therefore, of major importance. Two generally applied analytical techniques can be used to estimate the fluid properties in inclusions, i.e. microthermometry and Raman spectroscopy. Fluid phase changes can be observed with microthermometry, and Raman spectroscopy identifies directly those compounds that have covalent bonding (like CO 2 or N2 ). However, salts or dissolved salts are Raman-inactive and can not be directly identified in both methods. At lower temperatures, H 2 O and dissolved salts will form specific salt- hydrates, which can be identified by Raman spectroscopy. A combination of both methods, therefore, allows the identification of the type of dissolved salt and an exact method to determine the temperature of phase changes, which define the salinity of the entrapped fluid. Standard Raman spectra of salt-hydrates are not available in literature, and phase changes at low temperatures (between -196C and +20C) in fluid inclusions are not yet well understood. The aim of this project is the construct a data bank of Raman spectra with all relevant types of salt- hydrates by using experimentally trapped fluids of known compositions. These fluid inclusions are monitored with Raman spectroscopy during temperature cycles in microthermometry to understand the phase behaviour at low temperatures. The results are compared with natural material, i.e. saline fluid inclusions in dolomites, to analyse natural fluids that were responsible for the dolomitisation of the carbonate rock. This project will be a major methodological contribution to the analysis of the chemical composition and density of salt-bearing inclusions, which occur in most type of rocks within the earth-crust, by relatively simple and non-destructive means.

The properties of fluids are of major importance in understanding processes that alter rocks and materials, e.g. weathering and metamorphism. Rocks often contain traces of these processes that have happened in the geological past, however, the pore fluid itself is in general not present anymore. Minerals within the rock have the capacity to entrapped small amounts of this fluid. Presently, these fluid inclusions (ø 5-20 m) can be studied by microscope and they give direct evidence of the palaeo-geological environment and processes, mainly by determining its composition and density. Salts can be dissolved within this fluid, and they have a huge influence on its properties. Identification of these salts is, therefore, of major importance. Two generally applied analytical techniques can be used to estimate the fluid properties in inclusions, i.e. microthermometry and Raman spectroscopy. Fluid phase changes can be observed with microthermometry, and Raman spectroscopy identifies directly those compounds that have covalent bonding (like CO 2 or N2 ). However, salts or dissolved salts are Raman-inactive and can not be directly identified in both methods. At lower temperatures, H 2 O and dissolved salts will form specific salt- hydrates, which can be identified by Raman spectroscopy. A combination of both methods, therefore, allows the identification of the type of dissolved salt and an exact method to determine the temperature of phase changes, which define the salinity of the entrapped fluid. Standard Raman spectra of salt-hydrates are not available in literature, and phase changes at low temperatures (between -196C and +20C) in fluid inclusions are not yet well understood. The aim of this project is the construct a data bank of Raman spectra with all relevant types of salt- hydrates by using experimentally trapped fluids of known compositions. These fluid inclusions are monitored with Raman spectroscopy during temperature cycles in microthermometry to understand the phase behaviour at low temperatures. The results are compared with natural material, i.e. saline fluid inclusions in dolomites, to analyse natural fluids that were responsible for the dolomitisation of the carbonate rock. This project will be a major methodological contribution to the analysis of the chemical composition and density of salt-bearing inclusions, which occur in most type of rocks within the earth-crust, by relatively simple and non-destructive means.