Seismological characteristics of the earth's crust of southeastern part of the Phennoscandian shield (Russia)
© Sharov N.V., Kulikov V.S., Kulikova V.V., Isanina E.V., Krupnova N.A.
The deep structure of the Arkhangelsk region Karelia border area was studied by generalizing of earlier data, obtained by RWM, DSS and ECWM, and the results of new geological studies carried out by the Institute of Geology, Karelian Research Centre, RAS. The associated results of seismic (RWM, DSS, ECWM) research and other geophysical and geological data are discussed. This integrated approach makes it possible to reveal all principal differences in the seismic parameters of the upper crust in the section interval from the surface to the depth of 5-7 km and their variation patterns that are due to geological-structural characteristics at the modern erosion section level. An increase in wave velocity near the surface is assumed to be connected with the presence of highly metamorphosed complexes or mafic-ultramafic magmatic rocks. Seismic parameters in the depth range 7-12 to 25-30 km are stable over the entire territory studied, and depth-dependent variations in velocity (maximum velocity in the upper and middle portions of the crust is not more than 6.2-6.5 km/s) show an inversion pattern. The rock composition of the Earth's crust to a depth of 25-30 km is assumed to differ negligibly from that of the upper part of the section. A hypothesis of the nature of the crust-mantle transition layer in the region as a relict of the crystallized head portion of a Palaeoproterozoic Windy Belt plume is put forward. The evolution of the region's crust and the directions of large-scale tectonic movements in it are shown in general terms.