CONDITIONS OF DIAMOND CRYSTALLIZATION IN KIMBERLITE MELT: EXPERIMENTAL DATA
Experiments on diamond crystallization in kimberlite melt were performed for 40 h at 6.3 GPa in the temperature range of 1300-1570 ºC and at 7.5 GPa in the temperature range of 1450-1570 ºC, using a multianvil high-pressure in the temperature range of apparatus of split-sphere type. Group I kimberlite from the Udachnaya-East pipe and a synthetic multicomponent mixture modeling the average composition of group II kimberlites were used as starting materials. The experiments have shown that diamond growth on seed crystals in the kimberlite melt in equilibrium with olivine, pyroxene, and garnet starts from 1400 ºC at 7.5 GPa and from 1520 ºC at 6.3 GPa. Diamond nucleation requires higher temperature and pressure, 1570 ºC and 7.5 GPa. The alkali-enriched and silicate-depleted derivates of kimberlite melts ensure the growth and nucleation of diamond at lower P and T values: 1400 ºC at 7.5 GPa and 1520 ºC at 6.3 GPa. The results obtained evidence that temperature, pressure, and the composition of crystallization medium are the main factors controlling diamond formation processes in the kimberlite melts and their derivates.