Dissolution of Peridotite in a Volatile-Rich Carbonate Melt as a Mechanism of the Formation of Kimberlite-like Melts (Experimental Constraints)

In the experiments at 3.0-6.3 GPa and 1200-1350 degrees C, it is found that under P-T parameters close to the conditions in ascending kimberlite magma, the carbonate melt enriched in potassium and volatiles is able to dissolve effectively the entire amount of xenogenic peridotite material that can potentially transport. As a result of this process, the melt is enriched in SiO2 (up to 30 wt %) and is transformed from carbonate to a kimberlite-like one. In the range of parameters studied, due to the high solubility of CO2 in the melt and the appearance of magnesite, an equilibrium fluid phase is not formed in the system. The interaction realized in the experiments may be the most important factor at the initial stage of magma evolution. The calculations performed in this work show that even after the dissolution of 30-50 wt % of lherzolite, the volatile-rich carbonate-silicate melt has a high degree of depolymerization (the ratio of the number of nonbridging oxygen atoms to the number of tetrahedrally coordinated ions (100NBO/T from 250 to 390) remains low-viscous (0.3-32.6 Pa s) and able to ascend to the surface rapidly. The obtained data indicate that immiscibility occurs between the potassium-rich carbonate-silicate and highly silicate melts only at 5.5 GPa and 1350 degrees C and is likely to have a minor impact on the evolution of magma.