Metamorfik wschodniej części bloku przedsudeckiego w okolicy Niedźwiedzia koło Ziębic

Abstract

Przedstawiono charakterystykę petrograficzną i strukturalną masywu amfibolitowego Niedźwiedzia położonego między Ziębicami a Paczkowem (Dolny Śląsk). Występujące tu skały metamorficzne (amfibolity i gnejsy) należą do jednego piętra strukturalnego. W czteroetapowej historii deformacji skał metamorficznych najważniejsze znaczenie regionalne mają fazy deformacji D₁ i D_2. Faza deformacji D₁ i synkinematyczny metamorfizm M₁ w warunkach facji amfibolitowej spowodowały powstanie amfibolitów i gnejsów, natomiast faza D₂ w warunkach metamorfizmu retrogresywnego M₂ przyczyniŁa się do powstania makrowrzecionowatej formy masywu amfibolitowego Niedźwiedzia - najważniejszej regionalnej makrostruktury tektonicznej omawianego obszaru.

METAMORPHIC ROCKS OF EASTERN PART OF THE PRESUDETlC BLOCK IN THE REGION OF NIEDŹWlEDŹ NEAR ZIĘBICE

On the basis of the new data from boreholes (Niedźwiedź IG 1, Niedźwiedź IG 2) and scarce outcrops of the metamorphic basements the geological position of eastern part of the Presudetic block in the Niedźwiedź region south of Ziębice was presented. This metamorphic complex is composed of: gneisses and schists, amphibolites and similar rocks and blastomylonites originated from quartz-feldspar rocks and crystalline limestones. The most common are here amphibolitic rocks which form great about 3800 m thick, one of the greatest in Lower Silesia. Amphibolites of this massif from the west are intercalated with gneisses and micaceous schists (borehole Niedźwiedź IG 1) but, in the east are underlaided by series of blastomylonites and mylonites (borehole Niedźwiedź IG 2). Composition of this massif for which the name “Niedźwiedź amphibolic massif” is proposed is differentiated on the basis of the structural and petrographical varieties.

The writers admit, that interbedding of gneisses and schists with amphibolites of the upper part, and occurrence of intercalations of crystalline limestones and quartz-feldspar rocks in lower part of amphibolite complex indicates the primary continuity of the whole massif and its connection with rocks, from which originated blastomylonites. In this sense metamorphic rocks of discussed area the most probably represent one and the same structural complex but not two different complexes (series) jointly folded as it was thus for presented.

Results of tectonical studies indicate existence at least four stage deformation history (D₁-D₄) of metamorphic rocks. The first stage of D₁, deformation occurred in conditions of regional metamorphism of amphibolitic facies. Second deformation phase (D₂) was responsible for development of shear zones and thrust sheets. Then mainly in peripherial parts of amphibolitic complex arose mylonitic and blastomylonitic zones. In the course of D₂ deformation phase arose also main macrostructure of discussed area, that is macrolens (macroboudin) of the Niedźwiedź amphibolitic massif.

The geometric form of macrolens is confirmed by:

-          cumulative diagram of S₁ penetrative foliation (Fig. 4);

-          lenticular outline of amphibolite massif on the geological map (Fig. 1);

-          ringlike shape of gravimetric anomalia (Fig. 2);

-          occurrence around elongated macrolens of ductile shear zones with mylonites and blastomylonites (borehole Niedźwiedź IG 2) and mylonites and phyllites (borehole Niedźwiedź IG 1);

-          inclination of linear structures to the Wand WSW (Fig. 6).

-          If D₁ deformation phase and M₁ synkinematic metamorphism belong to Early-Variscan foldings then younger phases (D₂-D₄) are bound with younger Variscan deformations. It was pointed out the possibility of regional correlation between the amphibolitic massif of Niedźwiedź and petrologically, structurally and in respect of age similar amphibolitic massif of Jesenik and Sobotin in Czechoslovakia.