Crustal structure of the Trans‐European suture zone region along POLONAISE'97 seismic profile P4

Abstract

[1] The large-scale POLONAISE'97 seismic experiment investigated the velocity structure of the crust and upper mantle in the Trans-European suture zone (TESZ) region between the Precambrian east European craton (EEC) and Paleozoic platform that comprises terranes added during the Caledonian and Variscan orogenies respectively). This experiment included 64 shots recorded by 613 seismic stations during two deployments. Very good quality data were recorded along five profiles, and the longest and most important one (P4) is the focus of this paper. Clear first arrivals and later phases of waves reflected/refracted in the crust and Moho were interpreted using two-dimensional (2-D) tomographic inversion and ray-tracing techniques. The crustal thickness along the profile varies from 30-35 km in the Paleozoic platform area to $40 km below and due northeast of the TESZ, to $43 km in the Polish part of the EEC, and to $50 km in Lithuania. The Paleozoic platform and EEC are divided by the Polish basin, so the upper crustal structure varies considerably. In the area of the Polish basin, the P wave velocity is very low (V P < 6.1 km/s) down to depths of 15-20 km, indicating that a very thick sedimentary sequence is present. We suggest two possible tectonic interpretations of the velocity models: (1) Baltica indented Avalonia, obducting its upper crust and underthrusting its lower crust in a tectonic flake structure and (2) a rifted margin of Baltica underlies the Polish basin. This model is similar to other interpretations of seismic profiles recorded in the Baltic Sea. The second model implies that the Paleozoic platform solely consists of Avalonian lithosphere and the EEC of Baltica lithosphere. It offers a simple explanation of the difference in crustal thickness of the two platforms. It also implies that the Caledonian and Variscan orogenies in this area were relatively ''soft'' collisions that left this continental margin largely intact.

Seismic basement in Poland

“…The edge of the EEC in the basement level is relatively clear and defines the southwestern range of the craton. However, another criterion in the continental scale could be one more-crustal criterion, e.g., range of the high velocity lower crust beneath EEC (Grad et al , 2003a(Grad et al , b, 2008.…”

“…Basement in the TESZ area is not reached by boreholes (see dashed pink lines at depth of 5 km), so its depth and velocity is available only from seismic profiles. FSB Fore-Sudetic Block, K-P Synclinorium Kościerzyna-Puławy Synclinorium, MPA Mid-Polish Anticlinorium, NSS North-Sudetic Synclinorium, Sz-M Synclinorium Szczecin-Miechów Synclinorium, WEP West European Platform, WS Western Sudetes, Compilation from Karnkowski (2008Karnkowski ( ), Ż elaźniewicz et al (2011, and Grad et al (1991Grad et al ( , 2003a ▸ 1 3 (WEP), as shown in Fig. 2.…”

“…2d) show similar sequences of layers, including complicated Permian (Zechstein) salt diapirs and salt pillows in the TESZ (Krzywiec 2006a, b;Mazur et al 2005). However, the major structural features of the seismic profiles are the basement depth and its velocity differentiation: c. 6.1 km/s for the EEP and c. 5.8 km/s for the WEP (Grad et al 1991(Grad et al , 2003a. Differentiation of the basement is also observed in the complicated pattern of the Bouguer anomalies, the irregular pattern of the magnetic anomalies, electromagnetic properties, and the heat flow.…”

The Uncertainty of 2D Models Along Wide Angle Seismic Profiles

“…The next profile we discuss is P4 from the POLONAISE'97 experiment. As presented by GRAD et al (2003a), a complicated transition structure across the Trans European Suture Zone (TESZ) from the East European Craton in the North (EEC) to Palaeozoic Platform was derived. The result was a complicated multi layers model [Fig.…”

Morphotectonic implication of the Paleoproterozoic Mid-Lithuanian Suture Zone

“…The MLSZ is traced into north east ern Po land as in di cated by a thick en ing of the crust de fined in the DSS pro files POLONAISSE P4 and P5 (Czuba et al, 2002;Grad et al, 2003). The beltiform lithological fab ric is less dis tinct in this part of the MLSZ be cause on the zone there are su per im posed large cratonic in tru sions such as those of Suwa³ki, Go³dap and Kêtrzyn, form ing a chain in an E-W di rec tion pos si bly con trolled by the large-scale fault struc ture (Wiszniewska et al, 2007).…”