Seismic model of the Earth's crust and upper mantle beneath the Fennoscandian Shield

Abstract

Well-founded concepts of the crust and upper mantle structure of the Fennoscandian Shield were developed. Quantitative evidence for horizontal and vertical lithospheric heterogeneities was obtained. Highly detailed integrated geological and geophysical investigations, supported by superdeep drilling, have been conducted in the eastern part of the shield in recent years. Seismogeological crustal models of individual geotectonic provinces were constructed, which indicate that the structure of the crystalline crust displays a pattern of blocks, arranged hierarchically, with no persistent seismic boundaries across the entire shield. Both low- and high-velocity zones, correlatable with geological bodies, occur locally. The structural plans of contours and the velocities of various deep sections were shown to be inconsistent. We conclude that the upper mantle is laterally complex and heterogeneous, and that there is no asthenosphere in the classical sense of the word.