Shock-induced superheating and melting curves of geophysically important minerals

Shock-state temperature and sound-speed measurements on crystalline materials, demonstrate superheating-melting behavior distinct from equilibrium melting. Shocked solid can be superheated to the maximum temperature, Tc′ . At slightly higher pressure, Pc, shock melting occurs, and induces a lower shock temperature, Tc. The Hugoniot state, (Pc, Tc), is inferred to lie along the equilibrium melting curve. The amount of superheating achieved on Hugoniot is, Θ+ H = Tc′/Tc − 1. Shock-induced superheating for a number of silicates, alkali halides and metals agrees closely with the predictions of a systematic framework describing superheating at various heating rates [Appl. Phys. Lett. 82 (12) (2003) 1836]. High-pressure melting curves are constructed by integration from (Pc, Tc) based on the Lindemann law. We calculate the volume and entropy changes upon melting at (Pc, Tc) assuming the R ln 2 rule (R is the gas constant) for the disordering entropy of melting [J. Chem. Phys. 19 (1951) 93; Sov. Phys. Usp. 117 (1975) 625; Poirier, J.P., 199