Polarization effects at grain-boundaries

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The electrical conductivity of partially molten rocks mainly depends on the interconnectivity of the melt phase. Different electrical conductivity mechanisms dominate in melts and minerals. If an electrical field is applied to a partially molten rock, polarizations should occur at meltmineral-interfaces due to different charge carriers in melts (ions) and crystals (electrons). This polarization will significantly influence the scaling behavior of electrical conductivity experiments. Within this project we want to test the following hypothesis: "The complex electrical conductivity of partially molten rock is significantly influenced by polarization effects at melt-mineral interfaces" and discuss the consequences of polarizations at the melt-mineral interface a) for the interpretation of laboratory experiments and b) for the inversion and interpretation of field observations. The qualitative and quantitative understanding of polarization effects on the electrical conductivity of partially molten systems should give us a deeper insight into the scaling behaviour of systems where polarization effects at meltmineral-interfaces occur. At low frequencies (direct current - DC experiments) the polarization will significantly contribute to the observed overall resistivity. At higher frequencies-such as in laboratory experiments - this polarization is usually overprinted by electrode polarizations. One consequence might be that the deduced melt portions to explain observed conductivity anomalies are underestimated while neglecting polarization effects. Therefore, a consequence, the existing magnetotelluric data for the Andes, in Tibet, or in the Pyrenees need to be re-evaluated while taking polarization effects at melt-mineral-interfaces into account.