Partitioning of H2O between olivine and carbonate-silicate melts at 6.3 GPa and 1400 °C: Implications for kimberlite formation

- H2O partitioning between olivine and carbonate-silicate melts was studied.
- It is found that H2O content of olivine depends on melt carbonation degree.
- It drastically decreases as carbonation degree reaches values of kimberlitic melts.
- DH2OOl/liq of olivine and carbonate-silicate melt drops down to ⩽0.001.
- Carbonatite-kimberlite transformation can proceed by H2O extraction from peridotite.

Partitioning of H2O between olivine and carbonate-silicate melts has been studied at 6.3 GPa and 1400 °C using a split-sphere multianvil apparatus. Olivine was synthesized in equilibrium with hydrous silicate and hydrous carbonate-silicate±chloride melts saturated with respect to one of Opx, Grt, Ms or a harzburgitic (Ol+Opx+Grt) residue and had CO2/(CO2+SiO2) molar ratios from 0 to 0.8. The concentration of H2O in olivine was determined using FTIR spectroscopy. We found that depending on the melt carbonation and saturation in equilibrium silicate phases the H2O content in olivine varied from 100 to 1500 ppm. The obtained results and data reported in Sokol et al. (2013) indicate that H2O content in olivine becomes approximately two times lower as CO2/(CO2+SiO2) molar ratios in the equilibrium melt increases from 0 to 0.4-0.8 and the crystallization media transform from hydrous silicate to hydrous carbonate-silicate (kimberlite like) melt. The estimated water partitioning between carbonate-silicate melt and nominally anhydrous mantle minerals indicates that carbonatitic melt can effectively extract water once it invades H2O-poore the peridotite. We suggest that extraction of H2O owing to the freezing point depression may provide the necessary melting degree of metasomatized peridotite source and formation of kimberlitic magma.