VOLATILE COMPONENTS IN THE UPPER-MANTLE ( FROM DATA ON FLUID INCLUSIONS)

Cryometry, thermometry, Raman and IR spectrometry, and gas chromatogra phic analysis were used to determine the composition of fluid inclusio ns in natural and synthetic diamonds as well as in garnets from mantle -derived xenoliths in kimberlite pipes of Yakutia. Fluid inclusions lo calized in healed cracks, which are not exposed on the surface, have b een found in natural diamonds from the placers of Yakutia, using light microscopy and a freezing stage. Preservation of these inclusions see ms to have occurred after crystallization of diamond but still under t he conditions of its thermodynamic stability. All the inclusions are o ne phase and contain a high-density liquid. Based on the results of cr yometric and Raman spectroscopic analyses, three types of fluid inclus ions were established: carbon dioxide-nitrogen-hydrocarbon, carbon dio xide-nitrogen, and essentially hydrocarbon. By means of Raman spectros copy the composition of primary fluid inclusions in synthetic diamonds , produced in their stability field, was found to be represented mainl y by hydrocarbons. The primary inclusions in garnets, typical of webst erite xenoliths from the Mir kimberlite pipe (Yakutia), according to t he results of cryometric and infrared spectroscopy, also consist of hy drocarbons. On the basis of chromatographic analyses of volatiles from garnets of cataclastic lherzolites from the Udachnaya kimberlite, and thermodynamic modelling of the chemical composition, oxygen fugacity was calculated at PT-parameters and H/(O+H) values specific to these r ocks. The value of oxygen fugacity of cataclastic lherzolites lies bet ween the CCO and IW buffers at 50 kbar.