EGU21-9325
https://doi.org/10.5194/egusphere-egu21-9325
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Lherzolite - carbonatite melt interaction in the presence of additive CO2 and H2O: Experimental data at 5.5 GPa and 1200-1450°C

Aleksei Kruk and Alexander Sokol
Aleksei Kruk and Alexander Sokol
  • V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Russian Federation, ave. Koptyuga 3, Novosibirsk, 630090 Russia.

We study the reaction of garnet lherzolite with carbonatitic melt rich in molecular CO2 and/or H2O in experiments at 5.5 GPa and 1200-1450°C. The experimental results show that carbonation of olivine with formation of orthopyroxene and magnesite can buffer the CO2 contents in the melt, which impedes immediate separation of CO2 fluid from melt equilibrated with the peridotite source. The solubility of molecular CO2 in melt decreases from 20-25 wt.% at 4.5-6.8 wt.% SiO2 typical of carbonatite to 7-12 wt.% in more silicic kimberlite-like melts with 26-32 wt.% SiO2. Interaction of garnet lherzolite with carbonatitic melt (2:1) in the presence of 2-3 wt.% H2O and 9-13 wt.% molecular CO2 at 1200-1450°С yields low SiO2 (<10 wt.%) alkali‐carbonatite melts, which shows multiphase saturation with magnesite-bearing garnet harzburgite. Thus, carbonatitic melts rich in volatiles can originate in a harzburgite source at moderate temperatures common to continental lithospheric mantle (CLM).

Having separated from the source, carbonatitic magma enriched in molecular CO2 and H2O can rapidly acquire a kimberlitic composition with >25 wt.% SiO2 by dissolution and carbonation of entrapped peridotite. Furthermore, interaction of garnet lherzolite with carbonatitic melt rich in K, CO2, and H2O at 1350°С produces immiscible kimberlite-like carbonate-silicate and K-rich silicate melts. Quenched silicate melt develops lamelli of foam-like vesicular glass. Differentiation of immiscible melts early during ascent may equalize the compositions of kimberlite magmas generated in different CLM sources. The fluid phase can release explosively from ascending magma at lower pressures as a result of SiO2 increase which reduces the solubility of CO2 due to decarbonation reaction of magnesite and orthopyroxene.

The research was performed by a grant of the Russian Science Foundation (19-77-10023).

How to cite: Kruk, A. and Sokol, A.: Lherzolite - carbonatite melt interaction in the presence of additive CO2 and H2O: Experimental data at 5.5 GPa and 1200-1450°C, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9325, https://doi.org/10.5194/egusphere-egu21-9325, 2021.

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