ИСТИНА

One of the repositories for K in mantle rocks are the clinopyroxenes. Potassium-bearing clinopyroxene has been described in various high pressure gneiss’s, as inclusion in diamonds, in eclogitic and peridotitic xenoliths from kimberlites, in garnet-clinopyroxenes-bearing carbonate rocks from metamorphic complexes, in eruptive lamproites, and in alkalic igneous rocks. The K content in natural clinopyroxene can reach up to 1.5 wt. %. The origin of these rocks in the upper mantle is linked to the existence of the melts and fluids enriched in K. Their presence is confirmed by the presence of carbonate-silicate melts and alkali-containing fluids associated with minerals from peridotites and eclogite originating in the upper mantle. Formation K-bearing clinopyroxene in these ultra high-grade rocks immediately suggests that it must have originated under high P-T conditions in the presence alkalic-carbonaceous fluids. Subsequently, K-bearing clinopyroxene has been experimentally studied in the presence of H2O or H2O+CO2 fluids. Experiments were carried out and quenched in a multi-anvil apparatus at 4 GPa and 1200- 1400ºC. The starting material consisted of a powdered natural olivine basalt along with Na2CO3 +/- K2CO3. Dehydration of ethanedioic acids were the source for H2O or H2O+CO2 fluids. The volatile content in the system was kept at 5 wt%. Samples were placed and sealed in Fe-bearing platinum capsule. Temperature were measured using a Pt30Rh/Pt6/Rh thermocouple. Pressures at high temperature were calibrated utilizing the quartz – coesite equilibrium. Error in temperature and pressure is estimated at ± 5ºC and ± 0.1 GPa, respectively. The duration of an experiment was from 6-8 hours. Experimental products were studied by scanning electron microscope CamScan V2300 with YAG detector for secondary and reflected electrons and an energy-dispersive x-ray microanalyzer with a semi-conductor Si (Li) detector Link INCA Energy for semi-quantitative EDX analysis.