Przekrój geologiczny przez brzeżną część platformy prekambryjskiej na obszarze lubelsko-podlaskim (bez kenozoiku)

Abstract

Na obszarze lubelsko-podlaskim w podłożu asymetrycznej niecki brzeżnej zbudowanej z utworów kredy i jury wydzielone są od NE następujące jednostki - obszar obrzeżenia masywu ukraińskiego stanowiący podniesioną część platformy prekambryjskiej, rów mazowiecko-lubelski wypełniony osadami dewonu i karbonu, rozwinięty na obniżonej części platformy prekambryjskiej oraz podniesienie radomsko-kraśnickie utworzone z osadów dewonu spoczywających na sfałdowanym młodokaledońskim fliszu. Jednorodność skorupy ziemskiej w obu tych strefach skłania do wysunięcia hipotezy o nasunięciu kaledonidów na platformę prekambryjską. Sięga ona po linię Starachowice - Nisko i krawędź jej odpowiada tzw. dolnej skarpie w podłożu. Młodopaleozoiczne zapadlisko - rów mazowiecko-lubelski – uformowane zostało w wyniku ruchu przesuwczego w brzeżnych partiach platformy i znajduje swe odzwierciedlenie w obecności rozłamów w skorupie o typie granicznych rozłamów ryftów.GEOLOGICAL CROSS-SECOON THROUGH IN MARGINAL PART OF THE PRECAMBRIAN PLATFORM IN THE LUBLIN-PODLASIE AREA (CENOZOIC EXCLUDED)Since the last century, one of main tectonic lines has been drawn through south-eastern Poland. The line, known in the literature as the Teisseyre-Tornquist line, was drawn on the basis of general premises by A. Jentsch, W. Teisseyre and A. Tornquist Its course was subsequently modified by S. Pawłowski, A. Dąbrowski and K. Karaczun with reference to magnetic and gravimetric data. In the last years, the course and tectonic significance of that line were discussed by J. Znosko who followed H. Stille in interpreting the line as the boundary between the Precambrian (recently précised as Prevendian) and PaIeozoic platforms. Similar point of view concerning the course of the Precambrian platform boundary is held by the author. The tectonics of this area is interpreted in somewhat different way by W. Pożaryski and H. Tomczyk, according to whom the Precambrian (Epigothian) platform contacts here the Małopolska Assynthian ( = Baikalian) massif. Recent deep seismic soundings, the results of which were discussed by A. Guterch and his team, made it possible to define the nature of the Earth crust in this area. In recent papers there is a trend to replace the term "line" by "zone".The Lublin-Podlasie area is situated at two different crustaI block (Fig. 1). Its north-eastern part, with Earth crust 48 km thick (block A), corresponds to the slope of the Ukrainian Massif which forms uplifted segment of the Precambrian platform. On the south-west, that block is delineated by the Lubartów fracture, correlated with Kock anticline developed in younger PaIeozoic cover above the fracture (Fig. 3). The anticline represents north-eastern boundary of the Mazowsze – Lublin trough. A zone of increased thickness of the Earth crust (up to 48 - 54 km, block B), is about 110 km wide in the Lublin area. Within its boundaries is developed fracture zone with strongly downwarped Moho surface, interpreted as intracontinental rift (A. Guterch, 1977). Two younger PaIeozoic tectonic units, Mazowsze - Lublin trough and Radom - Kraśnik elevation, are developed above the block B. The basement of the trough is formed of relatively thin platform Devonian, Silurian, Ordovician and Cambrian rocks. The trough is infilled with Carboniferous rocks up to 1800 m thick. The Radom - Kraśnik elevation (Fig. 2) is formed of the Devonian more or less eroded (in places completely missing) and underlain by folded older Paleozoic (including Lowermost Devonian). Flyschoid SiIurian, Cambrian and Ordovician rocks display strong tectonic deformations. Geophysical data suggest that they may be underlain by older Paleozoic platform deposits.Structural and facies analysis of the younger Paleozoic made it possible to put forward hypothesis on the contribution of transcurrent faults in generation of the Mazowsze - Lublin trough. The trough began to form in the Late Devonian and its main framework is of the latest Carboniferous age. The distribution of the Permian and Mesozoic cover suggests that the movements were continuing at least till Early Triassic. The crustal block is delineated by a fracture found at the 210 km in the profile LT-3 (Fig. 3), coinciding with the Łysogóry overthrust Identical fracture was found somewhat further to the south, in the vicinities of Nisko. This line is interpreted as a margin of the Precambrian platform, on which the zone of Caledonian externides is overthrusted from the south-west. Younger tectonic deformations are overprinted on the Paleozoic tectonics. Faults oblique to the front of the PaIeozoic platform are related to folding of the Carpathians and origin of the Carpathian foredeep. The faults are usually of the transcurrent nature.