Imaging the East European Craton margin in northern Poland using extended correlation processing of regional seismic reflection profiles
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Abstract. In NE Poland, Eastern European Craton (EEC) crust of Fennoscandian affinity is concealed under a Phanerozoic platform cover and penetrated by sparse, deep research wells. Most of the inferences regarding its structure rely on geophysical data. Until recently, this area was covered only by the wide-angle reflection and refraction (WARR) profiles, which show a relatively simple crustal structure with a typical three-layer cratonic crust. ION Geophysical PolandSPAN™ regional seismic programme data, acquired over the marginal part of the EEC in Poland, offered a unique opportunity to derive a detailed image of the deeper crust. Here, we apply extended correlation processing to a subset (∼950 km) of the PolandSPAN™ dataset located in NE Poland, which enabled us to extend the nominal record length of the acquired data from 12 to 22 s (∼60 km of depth). Our new processing revealed reflectivity patterns, which we primarily associate with the Paleoproterozoic crust formed during the Svekofennian (Svekobaltic) orogeny, that are similar to those observed along the BABEL and FIRE profiles in the Baltic Sea and Finland, respectively. We propose a mid- to lower-crustal, orogeny-normal lateral flow model to explain the occurrence of two sets of structures that can be collectively interpreted as kilometre-scale S–C′ shear zones. The structures define a penetrative deformation fabric invoking ductile extension of hot orogenic crust in a convergent setting. Localized reactivation of these structures provided conduits for subsequent emplacement of gabbroic magma that produced a Mesoproterozoic anorthosite–mangerite–charnockite–granite (AMCG) suite in NE Poland. Delamination of thickened orogenic lithosphere may have accounted for magmatic underplating and fractionation into the AMCG plutons. We also found sub-Moho dipping mantle reflectivity, which we tentatively explain as a signature of the crustal accretion during the Svekofennian orogeny. Later tectonic phases (e.g. Ediacaran rifting, Caledonian orogeny) did not leave a clear signature in the deeper crust; however, some of the subhorizontal reflectors below the basement, observed in the vicinity of the AMCG Mazury complex, can be alternatively linked with lower Carboniferous magmatism.Keywords:
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Since the 1970-ties, large azimuth changes in the equilibrium of quartz horizontal pendulums have been irregularly registered in the Geodynamic Laboratory in Książ. However, azimuth changes of the pendulums did not correlate with meteorological phenomena and the compensation phases of these changes excluded processes of gravitational creep of the rock massif. It was assumed that changes of these azimuths result from tectonic tilt of the rock massif. These were the first observations of contemporary tectonic activity in the Świebodzice Depression (SW Poland). Multiannual observations have allowed for determining temporal and amplitude characteristics of such tectonic activity. Intervals of tectonic activity last from several days to two weeks and are separated by periods of low activity or even no activity. During tectonic events, amplitudes of rock massif deformation reach values of several tens of tidal amplitudes. The distinguished characteristics of tectonic effects and their incidental character have been confirmed by water-tube tiltmeters (WT) activated in the Geodynamic Laboratory in the early 2000s. Unique conditions of the rock massif cause that the WTs, in connection with blocks of the rock massif separated by faults, are natural detectors of tectonic activity, allowing to determine the function of tectonic activity and its derivatives in the surrounding areas.
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The block structure of the Earth crust and tectonic zones are displayed at the dynamic seismic section in the amplitudes of the scattered waves. Tectonic zones are identified with thrusts.<br>The effective density model of the crust was created at the base on the complex interpretation of seismic and gravity data.<br>Revealed tectonic elements of the Earth crust can be use for prognosis of oil perspective areas.<br>
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The signs of the collisional structure are expressed in the upper crust by the advanced Priverhoyansk forland and local hinterland basins is separated by a high-speed array, most likely of magmatic origin. The boundary of the craton at an angle of about 15 ° is submerged under the crust of the folded system, where the characteristic layer of the craton lower crust at velocity of 6,7–6,9 km /s is absent and the velocity in a whole crust is reduced, as well as along the Moho from 8,3 to 7,9-8,0 km / s.
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The first DEKORP profile, DEKORP 2-S, a 250 km long line perpendicular to the Variscan strike direction, has provided evidence of major crustal shortening during the Variscan orogeny. Sporadic dipping events in a generally transparent upper crust are interpreted as thrust faults, while the highly reflective lower crust fits into the general picture of Palaeozoic provinces. Correlations are established between certain reflectivity patterns and rheology. Moho depths and reflecting lamellae are considered to be post-Variscan.
Orogeny
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The latest results of the seismological analysis in the eastern margin of the Bohemian Massif are discussed. The stations of the Institute of Physics of the Earth (IPE) have detected in this region 131 tectonic microearthquakes since 1992. Twenty tectonic events were localised by program HYPO3D. The localisations of epicentres indicate affinity of the seismo-tectonic activity mainly to the NW-SE trending movements along the faults.
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Margin (machine learning)
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