Analysis of salt-bearing aqueous solutions in synthetic fluid inclusions by microthermometry and cryogenic Raman spectroscopy

Miriam Baumgartner

Research output: ThesisDoctoral Thesis

2013 Downloads (Pure)

Abstract

Fluid inclusions, containing salt-H2O mixtures of NaCl-H2O, CaCl2-H2O, MgCl2-H2O, FeCl2-H2O, FeCl3-H2O, LiCl-H2O, ZnCl2-H2O, NaCl-CaCl2-H2O, NaCl-MgCl2-H2O and CaCl2-MgCl2-H2O, were synthesised in natural quartz to study phase equilibria and salt hydrate nucleation at low temperatures. Variable freezing and melting behaviours occur depending on the composition and the salinity of the inclusions. Most systems show unpredictable phase equilibria and highly metastable phase assemblages during cooling experiments.This study reveals that microthermometry is still the main tool for analysing the salinity and composition of fluid inclusions. Additionally, Raman spectroscopy must be used to verify microthermometric results or to specify in more detail the analysed phase changes. The results obtained from synthetic fluid inclusions present fundamental knowledge of phase equilibria at low temperatures, which can be used for the interpretation of natural fluid inclusions. In addition, Raman spectra of salt-hydrates were gained, which can be used as reference spectra to compare them with spectra obtained from natural inclusions. Raman spectra of antarcticite (CaCl2.6H2O), CaCl2.4H2O (- and -modification) and sinjarite (CaCl2.2H2O) were gained, which can be used as references for natural fluid inclusion studies. In addition, Raman spectra of different salt hydrates, such as NaCl.2H2O, MgCl2.12H2O and FeCl2.6H2O, are presented in the study. The spectra illustrate, that the different salt hydrates can be distinguished due to the occurrence of characteristic vibrational modes in the stretching region of water (2900 to 3900 cm-1). A new Raman spectroscopic method to estimate the salinity of fluid inclusions is introduced in the present study. The morphology of Raman spectra of aqueous solutions (H2O-NaCl mixtures) in the stretching region of water can be analysed by deconvolution using Gaussian-Lorentzian functions. The presence of salt in aqueous solutions induces a peak shift, which can be correlated to the amount of dissolved ions in a solution. For an aqueous solution in a fluid inclusion, the morphology of a Raman spectrum produced by a polarised laser beam is also influenced by the optical properties of the host crystal (birefringence), by the orientation of the mineral-fluid interface and by the depth of the inclusion within the sample. Those parameters cause polarisation effects, which are reflected in the morphology of the Raman spectrum. The impact of the individual effects on the spectra have been evaluated in detail in the present study.
Translated title of the contributionMikrothermometrische und Raman-spektroskopische Untersuchungen von salzhaltigen wässrigen Lösungen in synthetischen Flüssigkeitseinschlüssen
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Prochaska, Walter, Assessor B (internal)
  • Bakker, Ronald Jack, Assessor A (internal)
Publication statusPublished - 2009

Bibliographical note

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Keywords

  • Fluid inclusions
  • Raman spectroscopy
  • Salt hydrates

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