THE PECULIARITIES OF HIGH-PRESSURE COESITE TRANSFORMATION INTO QUARTZIN THE PRESENCE OF WATER OR CARBON-DIOXIDE AND SOME GEOLOGICAL CONSEQUENCES

The new experimental data on the rates of synthetic coesite transforma tion into quartz at high pressure in the presence of volatiles (water, carbon dioxide) are presented. It has been established that the inita l temperatures of the conversion are lowering relatively to,,dry'' sys tem approximately on 200 degrees C in the presence of carbon dioxide a nd on 400-500 degrees C in the presence of water fluid. On the basis o f the data obtained, some features of the conditions providing metasta ble quenching of coesite from xenolyths during kimberlite formation ar e reconstructed.