Electrical conductivity of molten basalt and andesite to 25 kilobars pressure: geophysical significance and implications for charge transport and melt structure.

Electrical conductivities of molten Hawaiian tholeiite and Crater Lake andesite were measured between 1200oC and 1400oC at atmospheric pressure and at pressures up to 17 and 25 kbar, respectively. Isobaric plots of log sigma versus 1/T (sigma is electrical conductivity) are linear, with the exception of the zero pressure tholeiite melt data. Conductivities decrease with increasing pressure in both melts, with the andesitic melt exhibiting a greater pressure dependence. Between 5 and 10 kbar abrupt decreases in the slopes of isothermal log sigma versus P plots (ie. decreases in activation volume) are observed for both rock melts. This discontinuity probably reflects changes in melt structure.-from Authors