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Strefa Teisseyre’a-Tornquista : dawne koncepcje a nowe dane

Narkiewicz Marek, Petecki Zdzisław

Przegląd Geologiczny

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2019

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Vol. 67, nr 10

837--848

EN

Concepts prevailing among the Polish geoscientists during the last decades assumed that the Teisseyre-Tornquist Zone is a major tectonic discontinuity separating the pre-Ediacaran East European Craton (EEC) crust from the Paleozoic Platform composed of terranes accreted during the Caledonian and Variscan orogenic processes. The recent interpretations of the TTZ by Mazur and collaborators, basedon gravity modelling and new PolandSPAN seismic reflection data, revive earlier ideas of the EEC crust extending to the western Poland and NE Germany. These authors propose that the TTZ is in fact a Sveconorwegian (ca. 1 Ga old) collisional suture marked by a crustal keel expressed as the Pomeranian and Kuiavian gravity lows in northern and central Poland. However, the present review of seismic data available, as well as a closer evaluation of the modelling results, do not confirm the keel/suture concept. On the other hand, the idea of the TTZ as an Early Paleozoic tectonic discontinuity is supported by several lines of evidence, including a strong regional magnetic gradient and a contrast in the crustal structure. The latter is revealed by seismic velocity distribution from the refraction data, in the results of magnetotelluric profiling and in recent seismicity patterns. The interpretation of the PolandSPAN data attempting to prove the continuity of the cratonic crust and its Ediacaran-Lower Paleozoic cover across the TTZ appears questionable. At the same time the POLCRUST-01 deep seismic profile in SE Poland documents that the zone is associated with the subvertical Tomaszów Fault. The basement top displacement by ca. 0,5 km and associated change in its slope are related to the fault whose deep crustal roots are further documented by reflectivity patterns in the lower crust. The recent modelling exercise by Krzywiec and collaborators aimed at questioning the thick-skinned nature of this fault does not present compelling results, being based on a poorly constrained geological model. The general conclusion from the present review is that the recently published data either support or at least do not contradict the concept of the TTZ as a tectonic zone separating the continuous EEC crust from several allochtonous blocks - mostly proximal Early Paleozoic terranes to the south-west. Thelithospheric memory of the TTZ echoed in successive stages of its reactivation in different intra-plate tectonic regimes - transpressive Variscan, mostly extensional or transtensional Permian through Early Cretaceous, compressional Late Cretaceous and finally Neogene, related to the Carpathian orogenic compression.

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Analyses of total magnetic anomalies over the northeastern marginal areas of Central India

Singh V., Singh O., Agrawal B., Shanker D.

Acta Geophysica Polonica

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2003

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Vol. 51, nr 2

165-177

EN

Detailed ground magnetic survey has been carried out with the station spacing of 2 to 5 km around Jabalpur-Mandala region. Stron magnetic anomalies are observed in the adjoining areas of Habalpur-Mandala and adjoining areas of Central India. The anomalies are generally closed and aligned in the E-W to NE-SW direction. Magnetic interpretation predicts an average thickness of 0.6 km for the Deccan traps, besides bringing out shallow and deeper intrusive boodies at 1.5 and 4.5 km, respectively. The average thickness of the trap is in good agreement with DSS (Deep Seismic Sounding) and magnetotelluric results. 2-D modeling along six profiles also suggests a number of sheet and dyke-like structures to be present in the region up to a depth of 4.7 km. It is inferred that many zones of weakness along the E_W to NE-SW direction might have existed prior to the Deccan traps volcanism, along which several intrusives.

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Models of the Earth's crust structure in the East Carpathian Region determined from inversion of farfied P-waveforms

Starodub G., Gnyp A.

Acta Geophysica Polonica

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1999

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Vol. 47, nr 4

375-400

EN

P-waveform inversion study of local crustal structure beneath the three broadband seismic stations of the East Carpathian Regional Seismic Network has been carried out. Our inversion technique involves inverting a set of radial components of observed seismograms in the frequency domain to estimate layer thicknesses, Vp, Vs, Qp, Qs. Initial four- and five-layer models of the Earth's crust under the station Uzhgorod (SU, east-northern fringe of the Pannonian deep) and Mizhgirya (SM, Folded Carpathians) were derived from deep seismic sounding data (International Geotraverse II). Final models show comparably moderate changes in the positions of the main seismic boundaries except for the disappeared boundary between two upper layers of the SM model where Vp contrast dropped from 0.9 km/s (in the initial model) to 0.15 km/s (in the final one). The total crustal thickness at SU site changed from 27.0 to 28.7 km and at SM site - from 55.0 to 57.1 km. Low Vs layer at midcrustal depths (7.2-21.0 km) is obtained for the SU model. A significant increase of Vp is observed in the crust-mantle transition layer (38.2-57.1 km) of the SM model. The most unusual result is obtained for the station Kosiv (SK, Frontcarpathian foredeep). SK site is characterized by a complex geological structure. The tectonic boundaries are running very closely there. The initial four layer model was built using common depth point data. Its thickness was 43.0 km and increased to 51.3 km in the final model due to the thickening of three upper layers. The fairly abrupt crust-mantle boundary is found with Vs contrast of 1.2 km/s (against 0.6 km/s initially).