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Electromagnetic study of lithospheric structure in the marginal zone of East European Craton in NW Poland

100%

Jóźwiak W.

tom Vol. 61, no. 5

1101-1129

The marginal zone of the East European Platform, an area of key importance for our understanding of the geotectonic history of Europe, has been a challenge for geophysicists for many years. The basic research method is seismic survey, but many important data on physical properties and structure of the lithosphere may also be provided by the electromagnetic methods. In this paper, results of deep basement study by electromagnetic methods performed in Poland since the mid-1960s are presented. Over this time, several hundred long-period soundings have been executed providing an assessment of the electric conductivity distribution in the crust and upper mantle. Numerous 1D, 2D, and pseudo-3D electric conductivity models were constructed, and a new interpretation method based on Horizontal Magnetic Tensor analysis has been applied recently. The results show that the contact zone is of lithospheric discontinuity character and there are distinct differences in geoelectric structures between the Precambrian Platform, transitional zone (TESZ), and the Paleozoic Platform. The wide-spread conducting complexes in the crust with integral conductivity values reaching 10 000 S at 20–30 km depths are most spectacular. They are most likely consequences of geological processes related to Caledonian and Variscan orogenesis. The upper mantle conductivity is also variable, the thickness of high-resistive lithospheric plates ranging from 120–140 km under the Paleozoic Platform to 220–240 km under the East European Platform.

2-D seismic models of the lithosphere in the area of the Bransfield Strait, West Antarctica

75%

Grad M. , Guterch A. , Janik T. , Środa P. , Grad M. , Guterch A. , Janik T. , Środa P.

nr 2

Seismic structure of the lithosphere between the East European Craton and the Carpathians from the net of CELEBRATION 2000 profiles in SE Poland

75%

Janik T. , Grad M. , Guterch A.

tom Vol. 53, No 1

141-158

During the CELEBRATION 2000 experiment, the area of SE Poland was investigated by relatively dense system of deep seismic sounding profiles. Apart from five main profiles CEL01–CEL05, eight additional profiles were executed between the edge of the East European Craton and the Carphatians: CEL06, CEL11, CEL12, CEL13, CEL14, CEL21, CEL22 and CEL23. In this paper, we present results of modelling of refracted and reflected waves with use of a 2D ray tracing technique. All 13 profiles were jointly inter reted with verification of models at crossing points, and a quasi 3D model of the crust and upper mantle was developed. The obtained P-wave velocity models of the crust and uppermost mantle are very complex and show a differentiation of the seismic structure for tectonic units in SE Poland. The depth of the Moho discontinuity in the investigated area changes from about 30 to about 52 km. As a summary of all seismic models, the Moho depth map for SE Poland is presented, as well as a map of the extent of the most characteristic crustal elements in the area: a high velocity body in the upper crust, division into two- and three-layer consolidated crust, ranges of very deep layers with low velocities in the upper and middle crust, aproximate ranges of detected velocity anisotropy in the upper/middle crust, ranges of the high-velocity lower crust and high-velocity uppermost mantle. Both maps are com pared with the main struc tural el e ments from tec tonic map. This could form the base for a new geotectonic in ter pre ta tion of this com plex area.

Polish Geodynamic Expeditions - seismic structure of West Antarctica

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Guterch A. , Grad M. , Janik T. , Środa P. , Guterch A. , Grad M. , Janik T. , Środa P.