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

摘要: Electrical conductivities of molten Hawaiian tholeiite and Crater Lake andesite were measured between 1200°C 1400°C at atmospheric pressure pressures up to 17and 25 kbar, respectively. Isobaric plots log σ versus 1/T (σ is electrical conductivity) are linear, with the exception zero melt data. Conductivities decrease increasing in both melts, andesitic exhibiting a greater dependence. Between 5 10 abrupt decreases slopes isothermal P (i.e., activation volume) observed for rock melts. This discontinuity probably reflects changes structure, as opposed conduction mechanism. In each range, data can be described reasonably well by an equation form = σ′0 exp[−(Ea + PΔV′σ)/kT], where preexponential constant, Ea energy, ΔV′σ volume. A qualitative model involving depolymerization increased leading efficiency packing explain volume dependences other physical properties such viscosity density. Conductivity fraction curves partially peridotite reevaluated using high tholeiitic crystalline conductivity values recently determined workers. Minimum estimates 5–10% required upper mantle regions anomalously terms partial melting hypothesis.