NATURE OF INTRACRUSTAL SUBHORIZONTAL SEISMIC BOUNDARIES (AN INTERPRETATION OF RESULTS OBTAINED FROM THE KOLA SUPERDEEP DRILLHOLE)

Abstract

In the vicinity of the Kola superdeep drillhole (SG-3), within the Pechenga volcanotectonic basin and its surroundings a subhorizontal boundary was identified by seismic exploration (deep seismic sounding, DSS) at a depth of 7 to 8 km. Profile DSS in the vicinity of the SG-3 drillhole established a correlation between the boundary velocity Vb and the composition of the rocks exposed along the profile. Deep seismic boundaries are located at relatively great depths (they 'downwarp') in those parts of the section where low-density migmatites and granitoids occur at great depths, while at shallower depths (where they are 'uplifted') they occur where denser structures (metamafics) predominate near the surface. Similar patterns are found in other regions. Measurements confirm that the subhorizontal seismic boundary through which the SG-3 drillhole passes is associated with the present-day stress of the rocks. The generation of reflectors and waveguides in the crust in response to stress can be explained by several theoretical models. Additional aspects of the subject are discussed.