METHODS TO STUDY ELECTRICAL CONDUCTIVITY OF CONTINENTAL LITHOSPHERE

Abstract

With the development of geosciences, more and more attention is focused on the study of electrical conductivity of continental lithosphere. And the super wide band MT sounding, which combines the broad bound MT system(MT 24NS or V5 2000) and long period intelligent MT system (LIMS), is by far the most effective and advanced method to detect the conductivity of continental lithosphere. Using the method, the data of the natural electromagnetic field, frequency ranging from n ×10 -4 to n ×10 2 Hz, can be acquired, processed and inversed. Thus, the electrical structure model of lower crust and upper mantle are inferred. Not only can it provide the information about the geologic structure of the lithosphere, the model also suggests the thermal and mass distribution character in lower curst. For many years, the study of electrical conductivity in the Tibetan plateau, using the super wide band MT sounding, has shown that high electrical conductivity ranging from the middle to lower crust. Such pervasive high conductance suggests that partial melt or aqueous fluids is widespread within the Tibetan crust. The study of profiling from Yingxian to Shanghe, using the super wide band MT sounding, represents that the Taihang Mountain fault is a deep fault descending eastward. The fault divides North China lithosphere into eastern and western parts. The former is low conductivity region, which agrees with the electrical character of active tectonic region of lithosphere. In contrast, the latter is high conductivity, showing the electrical character of stable continental regions.