Wielkoskalowe ruchy przesuwcze wzdłuż SW brzegu platformy wschodnioeuropejskiej we wczesnym paleozoiku

Wojciech Brochwicz-Lewiński, Władystaw Pożaryski, Henryk Tomczyk



There is growing evidence for a very sharp contrast of Upper Precambrian and Lower Paleozoic formations at the contact of the East- and Central-European Platforms, coinciding with widely discussed Teisseyre-Tornquist Line (Zone) from Polish coast of the Baltic to the Black Sea. The differences are reflected by rapid changes in thickness, facies and other features including tectonic involvement and metamorphism. Crystalline epi-Gothian sockle of the East-European Platform contacts Dalslandian basement in Dobrogea and Romanian Carpathians and the Cadomian in western Ukraine and SE Poland. Weakly diagenesed sedimentary cover of the sockle contacts folded and more or less strongly metamorphic Upper Precambrian- Middle Cambrian sequences in the former areas and also folded but less metamorphic in the latter. In the case of the Ordovician, the contrast is related to contact of thin (usually below 100 m thick) platform carbonates and black clays and very thick (up to 2 km or more) series of ,miogeosynclinal" claystones, siltstones and coarser rocks from the forefield of the East-European Platform. The differences remain marked in the Silurian and lowermost Devonian to cease completely in the Emsian. So sharp differences and the lack of transitions in the contact zone suggest tectonic, or more precisely, strike-slip fault nature of the contact. The differentation of Emsian “cover" indicates that the movements ceased in the Siegenian.
The presence of the Dalslandides and Cadomides in the forefield of the East European Platform in SE Poland, western Ukraine and Romania suggests movement of relevant crustal blocks to SE along the Platform margin. Such direction of movement explains truncation of boundary of the Dalslandides and Gothides (schistosity zone in Scania) in SW Baltic. If this is the case, we would be dealing here with strike-slip fault with displacement at distance of at least 1500 km.
Paleogeographic reconstruction made by pushing back the Dalslandides to their inferred original position (beyond the extension of schistosity zone in SW Baltic) shows that folded arid metamorphic Upper Precambrian-Middle Cambrian series of Romania and adjoining areas become placed surprisingly close to orthotectonic metamorphic Caledonides of the British Isles. From new works on the latter (32 and others) it follows that the development of orthotectonic Caledonian zone ended in the British Isles in the Grampian polyphase (before Middle Arenigian). It should be noted that folding and metamorphism of Upper Precambrian-Middle Cambrian series from the forefield of the East-European Platform are dated at Świętokrzyska phase (latest Middle-Late Cambrian) or Sandomierz phase (before Arenigian) (26, 27, 35) or Late Cambrian-Early Ordovician (18). This implicates that we are dealing here with a part of the same Grampian fold belt, cut off of the main mass and moved apart by strike-slip fault after its folding and metamorphism. In the British Isles, the displacement was taking place along Solvey Line, i.e. boundary of metamorphic and non-metamorphic Caledonides, along which such movements were assumed but in the opposite direction (21).
Further eastwards, the strike-slip boundary may be traced along S margin of Ringkobing Fyn High and, from Koszalin at the Baltic coast to the Black Sea, along deep crustal fractures treated as SW margin of the East-European Platform. The movements resulted in displacement of a part of Scottish-Irish Caledonides and their Dalslandian basement as far as the Black Sea and the scale is estimated at over 2000 km. At the place of displaced elements, there came non-metamorphic Caledonides from areas west of Ireland, from SE margin of the Iapetus Ocean, distant from the zone of Grampian collision. These Caledonides, developed on Cadomian basement, display sequences typical of the Appalachians and they may be treated as Taconides which, thanks to the displacement, have escaped intense folding and metamorphism of the Taconian polyphase. They are nowadays distributed south of the Solvey Line (or Southern Uplands Fault) and Ringkobing Fyn High and further eastwards as far as NW Poland. The lack of any more intense Taconic deformations implicates that the movement began before the polyphase, i.e. before the Llandeilan.
The movement presumably began when a mid-oceanic ridge, responsible for sea-floor spreading in the Variscan Proto-Tethys Ocean (between North America and Africa - 47) reached the margin of Grampian fold belt at southern slope of Laurasian continent. The ridge was reaching the margin in similar way as the East Pacific Rise is nowadays approaching North American continent. Sea-floor spreading was being compensated by subduction in the west (which explains Andean nature of the Appalachians - 47, 16) and the above discussed strike-slip fault in the east. The course of strike-slip zone presumably became somewhat modified in Variscan and Laramic tectonic epochs. There is growing evidence for its reactivation in these epochs but the movements were undoubtedly on much smaller scale and in opposite direction (1, 47, 23). The Teisseyre-Tornquist Zone as interpreted nowadays (from the Black Sea to Scania), most probably originated during the Variscan epoch, due to reactivation of the Caledonian strike-slip zone and its propagation to NW so it should be treated as heterogenous.

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