Comparison of the crustal structures of the Barents Sea and the Baltic Shield from seismic data

A compilation of the available seismic refraction and wide-angle reflection data from the Barents Sea and the Baltic Shield and a comparison of the crustal structures of both areas are presented, Seismic cross-sections and velocity-depth models of the crust have been analyzed. Six areas differing in crustal structure are revealed and outlined in the Barents Sea region as a result of the velocity-depth models analysis. Three main layers are distinguished in the central area: the upper layer with an average velocity of 3.5 km/s overlies two layers with velocities of 5.5 and 6.8 km/s, The average thickness of the crust is 33 km. The crustal structure in the area is anomalous, as compared to the marginal areas of the sea, and is distinguished by the absence of the 6.2 km/s velocity layer. Combined seismic cross-sections for the coastal and marine seismic profiles show that the main seismic boundaries with velocities of 6.2-6.5, 6.8-7.2 and 8.0-8.2 km/s can be confidently interpolated from the northern part of the Baltic Shield to the southern part of the Barents Sea. The junction of their crusts is marked by a deepening of the crystalline basement with a seismic velocity of 6.2 km/s, The sedimentary cover thickness increases to 15-20 km, and the total thickness of the crust is reduced northward from 40-60 to 28-30 km, A comparison of the models shows that the Barents Sea Basin and the Baltic Shield appreciably differ in the total thickness of the earth's crust: under the basin, it is just about 10 km less than on the shield. Both regions have an important similarity: seismic velocities in the lower crystalline crust (7.0 km/s) are similar. Their fundamental difference is that the upper parr of the crystalline crust with a seismic velocity of 6.0-6.5 km/s, characteristic of the Baltic Shield, is absent in the central Barents Sea Basin, and a thick sedimentary layer with velocities to 5.8 km/s exists instead of it. The anomalous crustal structure in the central part of the Barents Sea is assumed to be of a riftogenic nature, (C) 2000 Elsevier Science B.V. All rights reserved.