Relations between electrical conductivity and petrological parameters of the crust and upper mantle

Abstract

Laboratory data of the electrical conductivity of rocks and minerals pertinent to the deeper crust and upper mantle and summarized. They are discussed in the context of a theory to calculate effective conductivities of materials in the state of partial melt. Most published data have been obtained by too rapid measurements, i.e. without reaching an equilibrium state of the sample. Conductivity measurements on a material similar to the composition of pyrolite are not het known, their importance is outlined. A global conductivity distribution obtained by electromagnetic induction studies is represented by a few results covering oceanic and continental areas. Till today it seems to be a doubtful venture to deduce the temperature of the upper mantle or even the existence of a partial molten asthenosphere from a global conductivity distribution. On a more local scale the correlation of electrical conductivity with temperature and state of the material seems to be more realistic. This is tentatively shown by two petrological models of the Afar depression in Ethiopia and of the midoceanic rift.