Hugoniot equation of state of anorthite glass and lunar anorthosite

Abstract

Twenty-one Hugoniot experiments were conducted on an amorphous material of anorthite composition, in the pressure range 8–120 GPa, using both routine and new methods. Two Hugoniot measurements at about 120 GPa were made on lunar gabbroic anorthosite (Apollo 15, 418). Theoretical Hugoniots are constructed for both materials assuming they are disproportionate to their component oxides. These accurately predict the P-ρ behaviour of the lunar anorthosite Hugoniot at 120 GPa and the anorthite glass Hugoniot above 50 GPa, but overestimate the shock temperatures of anorthite glass. The mixed oxide model fails to predict the release paths of either material. We conclude that the mixed oxide model is a good description of the bulk properties of the high-pressure phases of anorthite, but does not represent the actual phases. A significant enrichment of calcic refractory material in the Earth's lower mantle is not precluded by the bulk properties of the anorthite high-pressure phases.