Three-dimensional model of electrical conductivity distribution in the southwestern part of the Baikal rift zone and adjacent territories

The results of interpreting a unique collection of three-dimensional observations of the Earth's magnetotelluric field, covering more than 250,000 square kilometers of the southwestern flank of the Baikal Rift Zone, are discussed. A notable feature of the resulting model are large zones of anomalously elevated electrical conductivity identified at the junction of the Sayan fold belt and the Siberian Craton, as well as the Siberian Craton and the Amur Block (with the anomaly extending 300 km into the Amur Block). These zones are associated with fluid saturation in the upper portion of the probed space (down to depths of 40 km), while in the lower portion, they are associated with solid-state conductivity caused by hydration of upper mantle rocks associated with the thermal influence of two plumes previously identified using a combination of geophysical methods in northern Mongolia. An interesting observation made during the analysis of the resulting regional electrical conductivity model is the association of deep subvertical anomalies of low electrical conductivity in the volcanic fields identified in the Tunka Valley region. It is hypothesized that this electrical conductivity anomaly is caused by metasomatic changes that occurred during the ascent of hot magmatic fluids from the upper mantle to the surface.