NEOTECTONICS AND STRUCTURE OW WESTERN SIBERIA AT DEPTH

Abstract

To define regional patterns of change in the amplitudes of neotectonic movements, we constructed a chart of their average values (the averaging conditions were optimized by autocorrelation analysis). We analyzed the geophysical data primarily to determine the patterns of change in the density of the crust and upper mantle and in the thickness of the crust. The density of crustal rock complexes mapped by seismic exploration was calculated from a regression equation relating the density to the velocity of seismic waves in a given crustal layer. The authors used a generalized parameter, the relative elevation of the 'free surface of the mantle' [1], define the density nonuniformity of the crust and the upper mantle, and to evaluate the isostatic state of the lithosphere. It is found that the positive correlation between the depths of the free surface of the mantle and the thickness of the crust in west-central Siberia suggests that a decompacted mantle has persisted for a long time in this zone at depths greater than those of isostatic compensation. The neotectonic movements typical of west-central Siberia are produced directly by the latest stage of active crustal downwarping.