Interpretacja geologiczna wyników głębokich sondowań sejsmicznych na VII profilu międzynarodowym

Władysław Pożaryski

Abstract


GEOLOGICAL INTERPRETATION OF DSS INTERNATIONAL PROFILE VII

Summary
The international profile VII intersects one of the most important tectonic lines of Europe – the contact between the Old European Platform and Variscan (Hercynian) orogen. In Poland the profile intersects two zones of the orogen - external and internal, corresponding to the Saxo-Thuringian and Rheno-Hercynian zones from the area of Germany. A marked difference in the character of lower part of Earth crust of these zones was noted. The internal zone is characterized by more homogenized physical model of the crust, which is related to intense translocations of magma in infra- and suprastructures. In turn, the external zone is characterized by the development of a transitional zone at the boundary between the Earth crust and upper mantle, as well as by a .zone of reduced velocities (low velocity channel) marked in granitic-gneiss layer of the crust, which is accompanied by an increase of thermal gradient. Such characteristics seems to be typical of external zones of other European orogens. The externides and internides of the Variscan orogen are separated by fault z.one with large amplitude of downthrust. The nature of this zone suggests overthrust of the internides on externides. Block F1 situated between the Variscan orogen and Old European Platform, appears to be depressed. Maximum subsidence took here place in post-Variscan, and possibly pre-Variscan and post-Baikalian times. The physical model of the crust of Old European Platform appears to be analogous to that of Variscan internides. Marginal block F1 is characterized by the crust thinning out towards the periphery of the platform, i.e. towards the area of remarkable subsidence in the Phanerozoic times, presumably related to subcrustal corrosion. The development of the Mid-Polish aulacogen at the margin of the platform during the Mesozoic appears related to these phenomena. The block F, corresponding to the Old Platform markedly differs from the areas of post-Gothian geosynclines in the character of Earth crust structure. Coincidence of boundaries of the blocks with boundaries of units characterized by homogeneous magnetic field seems to support the rift origin of the margin of the Old Platform, related to break down and translocations of pracontinents, previously suggested by the present author.

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