Experimental modeling of syngenesis of diamond and minerals of peridotite and eclogite parageneses

Study of physicochemical conditions of syngenesis of diamond and mineral phases of peridotite and eclogite paragenese sin changeable carbonatite parental media is started at 8 GPa and 1200– 1800С. Experimental determinations testify that the compositions of parent media for diamond and inclusins belog to the phase field “boundary carbonatite–peridotite30carbonatite70 eclogite35carbonatite65”. It is found that the processes of olivine carbonatization as well as garnetization while it reacts with jadeite component are developed at regions of complete and partial melting of the compositions rich in peridotite constituents. As the result of the processes, the stability region for the minerals of peridotite paragenesis is contracted, but that is extended in the case of eclogite paragenesis. Introduction. Analytical mineralogy of primary (“syngenetic”) inclusions is the only plausible source of information on chemical composition of the parental media for natural diamonds and phases trapped by these while growing. Along with this, physicochemical experiment permits to obtain the objective information on genetic links of diamond and phases included therein. It becomes possible if the diamondforming systems which boundary compositions are chosen to take into account the evidence of the inclusions mineralogy. The mantle-carbonatite theory of diamond genesis [Litvin, 2007, 2009] is developed as a result of generalization of mineralogical and experimental data that sort of. According to the theory, the natural parental medium is basically multi-component completely miscible carbonate-silicate melt with dissolved elemental carbon (in the frames of the peridotite-eclogite-boundary carbonatite-diamond system. The composition limits for diamond-forming melts are experimentally determined using the concentration barriers of diamond nucleation (CBDN) and correspond to the values (wt.%): peridotite30carbonatite70 and eclogite35carbonatite65 [Bobrov & Litvin, 2009]. Generalized diagram of the parental medium composition is constructed [Litvin, 2010; Litvin, et al., 2011]. The diagram determines the boundaries for the phase region of parental media for diamond and inclusions. It has been ascertained in this case that compositions of the natural diamond-forming media belong to the carbonatite classification interval. In this work, study of physicochemical conditions of syngenesis of diamond and mineral phases of peridotite and eclogite parageneses in carbonatite parental media is started at 8 GPa and 1200–1800С. Experimental study of formation of diamond and paragenetic phases. This is evident from the phase region for parental media (fig. 1) that their compositions are extremely changeable in respect tas content of silicate components ofp eridotite-pyroxenite and eclogite-grospydite parageneses so the indicators of the silicate/carbonate ratio. The value of mid-weighted composition for the parental medium is calculated for its concentration triangle «peridotite30carbonatite70 eclogite35carbonatite65–boundary carbonatite» (composition 10 in the fig. 1 and in the table. 1). Experimental investigation of diamond and inclusions syngenesis is started within the section (wt. %) boundary carbonatite– (peridotite30carbonatite70)50(eclogite35carbonatite65)50 which is formally the composition triangle for the parental media onto two parts – peridotitic and eclogitic. The starting experimental compositions NoNo 9, 10 and 4 are given in the table 1 together with the boundary compositions used at their calculations. POKROVSKAYA AND LITVIN: SYNGENESIS OF DIAMOND