The magnetotelluric (MT) investigation of the Diósjenő dislocation belt

Abstract

Firstly the authors give an overview on the geological, geophysical and tectonical features of the Diósjenő dislocation belt (or zone, according to some authors) around the river Ipoly near the Hungarian-Slovak border among great structural units: Vepor, Gemericum and formations of the Mid Hungarian Mts. The longest magnetic anomaly of the Pannonian Basin lies in this belt. It is assumed that it is due to ultrabasic magmatite of greenschist facies. The near-surface geoelectric soundings did not find any conductivity increase near Diósjenő (western part of the zone), but there are graphitic micaschists in the boreholes around Szécsény. There is some earthquake activitiy in the region with hypothetical depth of 7-8 km. Two deep magnetotelluric (MT) profiles cross the dislocation zone. The resistivity distribution from the surface to the conductive asthenosphere along these profiles was obtained by using instruments, operating in two different period ranges. After processing the measured data by 1D/2D inversion, it became obvious that the dislocation zone includes electrically conducting roots at a depth of 7-11 km. This result hints at the presence of fluid in the broken rocks having increased porosity in the dislocation zone. Another component that can increase the conductivity could be the graphite (carbon) originating from the Paleozoic crystalline rocks of the Gemericum (or Vepor). The ductile phase (fluid/graphite) observed by high conductivity in the centre of the dislocation zone can play an important role in the generation of the earthquakes according to the most recent statements of the international literature.