Recently, calcium orthocarbonate (Ca2CO4-Pnma) has been predicted to be stable under P-T conditions of the Earth's transition zone and the lower mantle. Here, we investigate its stability against the main mantle minerals in the pressure range of 20-100 GPa and temperatures of 1000-2000 K, based on the density functional theory within quasi-harmonic approximation. We found that Ca2CO4 appears in equilibrium with MgO (periclase) in the whole studied P-T range, while its coexistence with MgSiO3 (bridgmanite) is prohibited owing to the following reactions: Ca2CO4 + 2MgSiO3 → 2CaSiO3 + MgCO3 + MgO and Ca2CO4 + MgSiO3 + SiO2 → 2CaSiO3 + MgCO3. Our results revealed that Ca2CO4 can coexist with SiO2 up to 70-90 GPa at 500-2000 K where it reacts to produce carbon dioxide and Ca-perovskite, Ca2CO4 + 2SiO2 → 2CaSiO3 + CO2, typically observed as inclusions in ultradeep diamonds.
Предметные области OECD FOS+WOS
- 1.05 НАУКИ О ЗЕМЛЕ И СМЕЖНЫЕ ЭКОЛОГИЧЕСКИЕ НАУКИ
- 1.04 ХИМИЧЕСКИЕ НАУКИ
- 1.05.GC ГЕОХИМИЯ И ГЕОФИЗИКА