CONDUCTIVE ZONES IN THE LITHOSPHERE OF THE FOLD BELT OF EURASIA AND THEIR RELATIONSHIP TO MODERN GEODYNAMIC PROCESSES

Here is a general review of long-term magnetotelluric (MT) studies of the lithosphere of the Fold Belt of Eurasia (North Caucasus, Altai-Sayan, Koryak-Kamchatka, and Tien Shan regions). The results have contributed to the development of the geological and geophysical database for seismic zoning, identification of active tectonic structures, and exploration of mineral resources. In the course of integrated interpretation of the MT data, regional geoelectric models have been constructed, conductive anomalies have been related to low-velocity and high-absorption zones, deep-seated conductive faults and rheologically weak zones have been identified, and their relationship to the location of earthquake hypocenters and miscellaneous volcanic features has been studied. The research involved 1D, 2D, and 3D MT data inversions. The inversions were preceded by the analysis of the invariants of the impedance tensor. The initial models for solving 3D inverse problems by trial-and-error method or method of formalized inversion of all components (or invariant parameters) of impedance were based on the results of previous 1D and 2D inversions. As a result, a correlation has been found between lithospheric low-resistivity blocks and low-velocity or high-absorption domains in most of the regions. This provides a basis for more reliable identification of weak zones and estimation of water fraction content in a fluid or melt. However, not all crustal conductive blocks and layers are fluid-related. It has been shown that high conductivity of the Lower Paleozoic – Proterozoic gold-bearing formations in the Southern Tien Shan is attributed to the presence of related graphite and sulfide inclusions.