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

Jóźwiak W.

Acta Geophysica

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2013

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Vol. 61, no. 5

1101-1129

EN

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.

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Electrical structure of the upper mantle beneath Central Europe: results of the CEMES project

Semenov V., Jóźwiak W., Pęk J., Adam A., Ladanivskyy B., Logvinov I., Pushkarev P., Vozár J.

Acta Geophysica

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2008

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Vol. 56, no. 4

957-981

EN

In the years 2001–2003, we accomplished the experimental phase of the project CEMES by collecting long-period magnetotelluric data at positions of eleven permanent geomagnetic observatories situated within few hundreds kilometers along the south-west margin of the East European Craton. Five teams were engaged in estimating independently the magnetotelluric responses by using different data processing procedures. The conductance distributions at the depths of the upper mantle have been derived individually beneath each observatory. By averaging the individual cross-sections, we have designed the final model of the geoelectrical structure of the upper mantle beneath the CEMES region. The results indicate systematic trends in the deep electrical structure of the two European tectonic plates and give evidence that the electrical structure of the upper mantle differs between the East European Craton and the Phanerozoic plate of west Europe, with a separating transition zone that generally coincides with the Trans-European Suture Zone.

3

New evidence of the anomalously conductive mantle beneath the Tornquist-Teisseyre zone in Poland

Semenov V., Jankowski J., Jóźwiak W.

Acta Geophysica Polonica

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2002

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Vol. 50, nr 4

517-526

EN

In the summer of 2000, ten deep magnetotelluric soundings were carried out in northeastern Poland. These observations were organized along the 250-km profile crossing the East European Craton (EEC) and the Tornquist-Teisseyre zone (TTZ) up to the Holy Cross Mountains. These data extended by the ultralong period ones obtained at the geomagnetic observatories Minsk (at the EEC) and Belsk (at the TTZ) have allowed estimating the mantle conductivity down to 1000 km depths. The satisfactory analysis of these data has been made by means of the 1D spherical inversions in the context of the reliable conductance distributions. On the background of relatively low conductances of sediments (10-600 S) along the profile it has been revealed that the upper mantle conductivity is increasing from the EEP towards the TTZ. The main conductive property bas been detected at the asthenosphere depths of about 150-300 km beneath the TTZ. A good correlation exists between the present result and the previous one obtained beneath the parallel profile situated 150 km towards the northwest.

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Geoelectrical model along a profile across the Tornquist-Teisseyre zone in southeastern Poland

Ernst T., Jankowski J., Jóźwiak W., Lefeld J., Logvinov I.

Acta Geophysica Polonica

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2002

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Vol. 50, nr 4

505-515

EN

We present results from the Polish part of a long international profile, ranging from the Ukraine to Hungary (PREPAN 95) and traversing the T-T zone in southeastern Poland, extended by data from two new geomagnetic soundings made in 1997. The new data allowed us to create a more detailed and realistic model. The 2-D interpretation was carried out on the basis of the complex induction vectors obtained from six points, supplemented by information derived from deep magnetotelluric soundings in Pawłówka. The results have shown that to the north of the well-known Carpathian anomaly, there are two deep and conductive faults within T-T zone. The joint interpretation of the deep magnetotelluric sounding comprising the results from Pawłówka and magnetovariation data from the Lvov Magnetic Observatory suggests the existence of a conductive zone at depths of about 100-200 km.

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Electromagnetic soundings across the Holy Cross Mountains, Poland

Semenov V. Yu., Jankowski J., Ernst T., Jóźwiak W., Pawliszyn J., Lewandowski M.

Acta Geophysica Polonica

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1998

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Vol. 46, nr 2

171-185

EN

Ten deep electromagnetic soundings were performed along the 150 km profile across the southern part of the Tornquist-Teisseyre zone (TTZ) in SE Poland. Five electromagnetic components have been recorded in the period range from few seconds to several hours. The real induction vectors were estimated at all 10 sets, but data from 6 stations only were good enough for magnetotelluric soundings. The magnetovariation data have shown the presence of a high-conductivity, deeply rooted narrow fractive zone of resistivity of about 5 Ohmm, situated in the northern part of Łysogóry unit of the Holy Cross Mountains (HCM). This zone separates two blocks with different geoelectrical properties, particularly well expressed in their upper part. Juxtaposed together with the earlier magnetotelluric (MT) soundings performed east of that profile, the results ofthis study suggest an existence of the easterly extension of the high resistivity zone of the Łysogóry unit far beyond the HCM. If our interpretation accounts for the Carpathian conductive anomaly, a conductive layer within TTZ at the depth of the crust-mantle boundary can be inferred. The mantle conductivity structure for the 2-D modelling was assumed in accordance with results obtained from the Polish geomagnetic observatories Belsk and Hel together with MT deep sounding from Wola Kanigowska.