Experimental study of diamond crystallization in carbonate-carbon systems in connection with the problem of diamond genesis in magmatic and metamorphic rocks

Diamond crystallization in carbonate-carbon systems was studied on a "split sphere" device BARS at P = 7 GPa and T = 1700-1750 degrees C (experiment t ime 18.5 h). It has been established that the heterogeneous nucleation of d iamond in the studied systems is realized both at the melt-graphite interfa ce and in the bulk of a carbon-saturated carbonate melt. Regular sequences of the catalytic activities of alkali and alkali-earth carbonates have been determined - Li2CO3 > Na2CO3 > K2CO3 > Cs2CO3 and CaMg(CO3)(2) > CaCO3 > M gCO3 > SrCO3, respectively. It is experimentally shown that diamond nucleat ion strongly depends on kinetic factors. A possible decrease in the minimum PT-parameters of diamond synthesis in carbonate-carbon systems is justifie d. Analysis of the results on diamond synthesis together with petrological dat a suggests that carbonate and carbonate-silicate melt-fluids are the most p robable medium of natural diamond formation in deep magmatic and metamorphi c processes.