Velocities and compressibilities of komatiitic melts

Ultrasonic measurements of compressional wave velocities for six komatiitic melts containing 13–30 wt% MgO are reported in the frequency range 3–20 MHz and in the temperature range 1280–1661°C. Melts with less than about 20 wt% MgO have velocities that are 6% lower and relaxed compressibilities, βr, that are 15% higher than melts with more than about 20 wt% MgO. The general trend of increasing velocity with increasing MgO content correlates well with increasing depolymerization (decreasing molar volume) of the melts as reflected in the NBO/T, (CaO + MgO)/Al2O3, and Al/(Al+Si) ratios. The value of dβr/dw (w=wt% MgO) for the high MgO melts is more than four times greater than dβr/dw for the low MgO melts.