GEOTHERMAL EFFECTS IN FORMATION OF ELECTRICALLY CONDUCTING ZONES AND TEMPERATURE DISTRIBUTION IN EARTH

Pollack and Chapman have shown that the surface heat flow in continental regions is dependent not only on the earth's crust below the observation site, but also on the upper mantle there. Therefore heat flow can be used to investigate the role of the thermal conditions in the creation of the electrically conductive zones in both the crust and mantle. Empirical exponential formulas describe the depth to the conductivity increase in the crust corresponding to granitization, the depth to the conductive zone at the top of the asthenosphere (SLVZ), as a function of heat flow. Comparing the latter with temperature estimations in the asthenosphere it is concluded that partial melting of the upper mantle occurs only where q {similar or greater-than} 42m W m-2 ≅ 1HFU. The depth to the conductivity increase corresponding to the mineralogic phase transition in the upper mantle is increased with high temperatures. Such a conductive zone shows that the maximum temperature difference between stable platform areas and active zones is about 1000°C. © 1978.