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Electric Resistivity Distribution in the Earth’s Crust and Upper Mantle for the Southern East European Platform and Crimea from Area-wide 2D Models

Logvinov I. M., Tarasov V. N.

Acta Geophysica

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2018

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Vol. 66, no. 2

131--139

EN

Previously obtained magnetotelluric 2D models for 30 profiles made it possible to create an overview model of electric resistivity for the territory between 28°E and 36°E and between 44.5°N and 52.5°N. It allows us to distinguish a number of low resistivity objects (LRO) with resistivities lower than 100 Ω m the Earth’s crust and mantle. Two regional conductivity anomalies are traced. The Kirovograd conductivity anomaly extends south to the Crimea mountains. A new regional conductivity anomaly (Konkskaya) can be distinguished along the southern slope of the Ukrainian Shield from 29° to 34°E. In addition, many local LROs have been identified. According to the modeling results, the local low resistivity objects on the East European Platform appear along fault zones activated during last 5–7 M years and the model suggests their relation to known zones of graphitization and polymetallic ore deposits. Local LROs in the Dnieper–Donets Basin correlate with the main oil and natural gas fields in this area. The depth of the anomalous objects amounts to 5–22 km. This is consistent with the hypotheses that hydrocarbon deposits are related to generation and transport zones of carbon-bearing fluids.

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Upper lithospheric structure in the central Fennoscandian shield: Constraints from P- and S-wave velocity models and Vp/Vs ratio distribution of the BALTIC wide-angle seismic profile

Janik T.

Acta Geophysica

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2010

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Vol. 58, no. 4

543-586

EN

The paper presents an analysis of the crust and upper mantle structure in the central Fennoscandian shield based on new P- and S-wave 2D velocity models of the BALTIC wide-angle reflection and refraction profiles. Using reprocessing of the old data, new P- and S-wave velocity models and V p /V s ratio distribution were developed. Moving from SW to NE, the thickness of the crust varies strongly, from ∼36 km to extremely thick, 58-64 km, crossing Wiborg rapakivi massif, Saimaa and Outokumpu areas, and Eastern Finland complex. Based on the lateral variations of V p , V p /V s and thickness of the crust, three main blocks of the crust and upper mantle were distinguished from SW to NE: southwestern, associated with Wiborg rapakivi massif; the central, having the highest thickness of the crust; and the northeastern, not well documented, with Archaean basement.

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Upper mantle seismic model of Central Europe (including the Alpine orogen) based on seismic events from the Lubin Copper Basin

Nita B., Thybo H.

Acta Geophysica Polonica

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2005

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Vol. 53, nr 2

127-141

EN

The Lubin Copper Basin in Poland is situated in the vicinity of the Trans- -European Suture Zone, in the region of the Variscan orogen. It is characterized by high seismicity, mainly induced by mining. The epicentral location is particu-larly suitable for the determination of lithospheric velocity structure for the two tectonic units in Central Europe: Alpine orogen and Variscides. We analyze traveltime curves constructed on the basis of the P-wave arrival times reported by European stations and listed in the International Seismic Bulletins for the pe-riod 1985-2000. The dense azimuthal coverage of the stations situated around the Alps and in the Variscides enables the determination of 1-D velocity struc-ture down to 180 km depth. Corrections for origin times, focal depths and station elevation were applied. The main feature visible in the obtained traveltime and velocity-depth distributions is the considerable difference in the upper mantle seismic structure between the two tectonic regions. The delay of P-wave arrivals is by about 3 s larger at the Alpine stations than at the stations located in the Variscides. We at-tribute this delay to differences between "fast" and "slow" structures in the "cold" and "hot" upper mantle, respectively. The 8° discontinuity can be clearly distinguished in the proposed models by a distinct delay at the offsets around 800-900 km from the source.

4

Electrical conductivity anomalies in the crust and upper mantle of the Ukraine

Kulik S., Burakhovich T., Khazan Y.

Acta Geophysica Polonica

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2002

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Vol. 50, nr 4

547-565

EN

A wide range of tectonic structures exists on the territory of the Ukraine. Observations of geomagnetic induction vectors revealed anomalously high conductivity of many of them. A quasi-3D geoelectrical model of the Earth's crust and upper mantle of the Ukraine is based upon a thin-sheet approximation inside a regional cross-section of the electric conductivity. As the initial data we used induction vectors measured over the whole Ukrainian territory (about 2500 measurement points) for periods of geomagnetic variations ranging from 150 up to 2000 seconds. After removing the influence of the known distribution of the subsurface conductance (sediments), the residual vectors have been analyzed as being caused by the Earth's crust and upper mantle sources. The model demonstrates that values of the local conductance reduced to thin-sheets range from 0.5 to 20 kS in the Earth's crust and from 2 to 6 kS in the upper mantle. Both, the nature and the origin, of these high conductivity zones are different for different regions. Some possibilities including a contribution of the percolation process in two-phase media are discussed.