The application of Raman spectroscopy in the study of fluid and melt inclusions

Abstract

In this contribution we show, using several examples, that Raman spectroscopy is a very important qualitative and quantitative analytical tool in geochemical research, particularly in the field of melt and fluid inclusions. Due to the high lateral and depth resolution of 1 μm and 2 μm, respectively, volumes with dimensions in the order of 1 μm3 and masses of 1 pg can be studied rapidly, with high resolution, with minimal, and in some case with no sample preparation. Examples of the detection of small known or unknown mineral phases (graphite, diamond, ramanite-[Cs] and others) are given. Because water does not cause interference, aqueous solutions can be advantageously studied with Raman spectroscopy. Moreover, one can use the OH-bands of the inclusion water as an internal standard for the quantitative determination of numerous dissolved species such as H3BO3, CO32-, HCO3-, and SO42- in a single measuring run. The development of Raman spectroscopy for the determination of water concentrations in natural melt systems (melt inclusion, glasses) opened a new chapter in the petrology. We can now determine water concentrations in glasses, from basaltic to granitic composition, in small samples down to diameters of about 5 μm from the ppm level to over 40 % (g/g) non-destructively, and critically, in unexposed inclusions in a mineral matrix. For the granite-pegmatite system results of water determinations are shown by examples.