The phase diagram of CaCO3 in relation to shock compression and decomposition

The phase diagram for calcite (CaCO3) is re-evaluated in relation to dynamic compression and following release from shock. Available shock compression data on Hugoniot dynamic measurements, analysis of recovered samples, and observation at terrestrial impact sites are compared with theoretically derived equations of state (EOS) for CaCO3 and its decomposition products CaO and CO2. The study results in a refined phase diagram for CaCO3 in which the major change is the extension of the liquid field of CaCO3. A general outcome of this analysis is that release of CO2 from naturally shocked carbonates to the atmosphere is (grossly) overestimated if based on the calcite phase diagram constructed from thermodynamic equilibrium conditions.