Electrical Conductivity of Amorphous and Molten CaCO ₃ at High Pressures and Its Implications for Mantle Conductivity Anomalies

Abstract Impedance spectrometry experiments have been conducted on CaCO 3 up to 15 GPa and 2,100 K to identify its state under high pressure. The melting temperature of CaCO 3 was also determined by the falling of a Re sphere observed via X‐ray radiography. The phase transition from aragonite to the amorphous phase does not cause a leap in the Electrical conductivity (EC), while a drastic increase in the EC, by 1.5–2.0 log units, only occurs with the onset of melting. The EC of amorphous CaCO 3 is comparable to other hydrous mantle minerals at similar pressure and temperature conditions. The required fraction of amorphous CaCO 3 implies that it can be excluded from the potential origins responsible for the observed high EC anomalies in the upper mantle. If the conductivity anomalies are induced by the presence of carbonate, a low‐degree melting of carbonate‐bearing peridotite is anticipated.