A technique has been developed for measurement of the shock wave, pressure-density equation of state of molten silicates initially at temperatures of up to ~2000 K. A 40-mm propellant gun apparatus accelerates metal flyer plates plates to speeds of up to 2.5 km s-1; these flyer are capable of driving shock waves with amplitudes of 35--40 GPa (350--400 kbar) into molten silicate samples. Modifications to the standard equation of state experiments that are described here include design of a molybdenum sample container for the molten silicate; use of a 10-kW radio frequency induction heater to melt the sample prior to impact; implementation of shuttering systems to protect the optical system and prevent preexposure of the film in the rotating-mirror continuously writing, streak camera; and reduction of Hugoniot data taking into account the effect of the sample capsule. Data for a model basaltic liquid (36 mol % anorthite, 64 mol % diopside) at an initial temperature of 1673 K and initial density of 2.61 Mg m-3, yield a shock velocity-particle velocity (US-UP) relation given by US=3.06+1.36 UP km s-1 up to values of UP=1.7 km s-1. The zero-pressure, bulk sound speed is in good agreement with ultrasonic measurements.

The best fit Birch-Murnaghan equation of state for this model basaltic liquid is K0S=24.2 GPa and K'=4.85 based on Hugoniot point at low pressures (25 GPa) the Hugoniot data suggest that the liquid stiffens considerably. This may indicate that the gradual structural changes characteristic of the lower-pressure regime, such as changes of Al3+ and Si4+ coordination by oxygen from fourfold to sixfold, are essentially complete by ~25 GPa. These high-pressure Hugoniot data are fit by US=0.85+2.63 UP km s-1. The high-pressure regime is similar to that obtained in initially solid silicates upon shock compression. Shock temperature calculations yield values of 2400--2600 K at 25 GPa, and the states achieved are believed to lie metastably in the liquid field. ¿ American Geophysical Union 1988