Shock compression of preheated silicate liquids: Apparent universality of increasing Grüneisen parameter upon compression

Shock compression experiments achieving ≥ 100 GPa pressures are available for seven silicate liquid compositions in the system CaO-MgO-FeO-Al_2O_3-SiO_2. Especially when liquid states have been sampled along multiple Hugoniots, these data are sufficient to evaluate the dependence of Grüneisen γ on volume in silicate liquids. The increase in γ upon compression in these liquids is a surprising feature, but this behavior is seen consistently in all studied compositions, by multiple experimental techniques and also in ab initio molecular dynamics (MD) simulations. The remarkable observation when comparing all the studied liquids is that the rate of increase of γ upon compression is approximately universal. It can be described by q = (dln γ/dlnV) = -1.5±0.25 in all seven compositions. This places very strong constraints on microscopic models for silicate liquid compression behavior and suggests a general rule for computing isentropes and densities of silicate liquids of arbitrary composition under any conditions likely to occur in a terrestrial mantle or magma ocean.