[SIT25-P02] The T-X phase diagram Na2CO3–CaCO3 at 3 GPa
Keywords:carbonate, phase diagram, mantle metasomatism
Considering the present and previous data, a range of the intermediate compounds on the CaCO3-Na2CO3 join changes as pressure increases in the following sequence: Na2Ca(CO3)2, Na2Ca2(CO3)3 (0.1 GPa) → Na2Ca(CO3)2, Na2Ca3(CO3)4 (3 GPa) → Na4Ca(CO3)3, Na2Ca3(CO3)4, Na2Ca4(CO3)5 (6 GPa) (Fig. 1b). Thus, the nyerereite stability field extends to the shallow mantle pressures, whereas the shortite stability field terminates somewhere between 0.1 and 3 GPa. Consequently, findings of nyerereite and shortite among daughter phases in the melt inclusions in olivine from the sheared garnet peridotites are consistent with their mantle origin.
This study was supported by Russian Foundation for Basic Research (No 17-05-00501).
Fig. 1. (a) The system Na2CO3–CaCO3 at 3 GPa. (b) Comparison with previous data at 0.1 GPa (Cooper et al. 1975) and 6 GPa (Shatskiy et al. 2013). (c) Na2CO3 melting. (d) CaCO3 melting. Arg = aragonite; Cal = calcite; Na2 = solid solution of CaCO3 in Na2CO3; Na4Ca = Na4Ca(CO3)3; Na2Ca = Na2Ca(CO3)2; Na2Ca3 = Na2Ca3(CO3)4; Na2Ca4 = Na2Ca4(CO3)5; L = liquid; F = CO2 fluid.