Peridotite–eclogite–carbonatite systems at 7.0–8.5 GPa: concentration barrier of diamond nucleation and syngenesis of its silicate and carbonate inclusions

摘要: Abstract Diamond crystallization in multicomponent melts of variable composition is studied. The melt carbonates are K 2 CO 3 , CaCO ⋅MgCO and K-Na-Ca-Mg-Fe-carbonatites, the silicates model peridotite (60 wt.% olivine, 16 orthopyroxene, 12 clinopyroxene, garnet) eclogite (50 garnet 50 clinopyroxene). In experiments carried out under PT -conditions diamond stability, carbonate-silicate behave like completely miscible liquid phases. concentration barriers nucleation (CBDN) with proportions have been determined at 8.5 GPa. system peridotite–K –CaCO –carbonatite they correspond to 30, 25, 30 silicates, respectively, analogous eclogite–carbonate system, 45, 35 wt.%. silicate-carbonate higher silicate contents seed growth occurs, which accompanied by thermodynamically unstable graphite phase. compositionally corresponding CBDN 7.0 GPa 1200–1700 °C, a full set minerals (olivine, (garnet, clinopyroxene) parageneses was obtained. occur as syngenetic inclusions natural diamonds; moreover, garnets contain an impurity Na, pyroxenes, K. experimental data indicate that peridotite-carbonate eclogite-carbonate highly effective for formation (or graphite) together melts, agrees (carbonatite) mantle formation.