Deep resistivity structure of the Trans-European Suture Zone in central Poland

The deep resistivity structure was estimated along a 400-km profile in central Poland crossing the Malopolska Massif (MM), the Lysogory Unit (LU), the Trans-European Suture Zone (TESZ) and ending at the East European Craton (EEC). Magnetotelluric transfer functions, corresponding to 20 sites, were supplemented by magnetovariational responses obtained at the geomagnetic observatories situated at the same tectonic units. Such a combination made it possible to extend the initial period range, which is from fractions of a second to several hours, up to months in order to reliably cover crustal and upper-mantle depths. The geoelectrical structures, revealed using 2-D inversions, do not contradict the known features of the lithosphere structure determined using seismic and gravity data along the profile. The subsurface conductance, varying from approximately 10 Siemens at the inner part of the EEC to about 600 Siemens in the TESZ, is produced by sediments, the deep part of which contains conductive, highly mineralized water. The existence of two crustal conductive faults at the southwest and northeast of the TESZ were established mainly by the use of induction arrows. It was also revealed that rather high mantle conductivity beneath the MM, LU and TESZ at depths of about 150-200 km contrasts with the resistive upper mantle of the EEC. This can be interpreted as the decrease of asthenosphere conductance and/or as its submersion beneath the EEC. Generally, the results confirm the idea that the TESZ forms not only specific seismic boundaries but also causes peculiar conductivity anomalies in the crust and upper mantle.