Metamorficzne skały kaledońskiego podłoża w okolicy Zawiercia

Abstract

METAMORPHIC ROCKS OF THE CALEDONIAN BASEMENT IN THE VICINITY OF ZAWIERCIE

Summary

Metamorphic rocks have been encountered near Zawiercie in the north-eastern margin of the Upper Silesian Coal Basin. They occur in an almost W-E trending zone of outcrops of sub-Permian basement from Mrzygłód in the west, through Zawiercie, as far as Chrząstowice in the east. Similar metamorphic rocks have been encountered when drilling within oil considerably larger area, i.e. at Lubliniec, north of Zawiercie in the basement of the Nida trough and in the vicinity of Olkusz.
In the vicinity of Zawiercie the metamorphic rocks are represented by sericite, sericite-chlorite, sericite-chlorite-epidote, chlorite-alblte-muscovite phyllites, chlorite-albite-muscovite-stilpnomelane, albite-stilpnomelane and albite-actinolite schists, as well as by albitofelses and epidosites. A clay-arenaceous complex, with numerous intercalations of tufts, tuffites, and bentonites was the source material of these rocks here. The sedimentary rocks were laid down under conditions of quick weathering of crystalline rocks, short, intense transportation, and permanent deposition in the sedimentary basin. Stratigraphically, they represent members from Precambrian up to Silurian inclusive.
Metamorphic alteration took place under conditions of greenstone facies, in the chlorite zone, and within the shallower area of the biotite zone, the upper boundary of which was limited by the temperature somewhat lower than 400°C, and by the pressure higher than 4000 bars. These alterations were accompanied by a feeble sodium metasomatosis manifesting itself by the porphyroblastesis of albito-felses. During the terminal phase of the alterations differentiation movements displaced some series of the metamorphic rooks in various zones of greenschist facies, pumpellyite-prehnite facies and not metamorphosed mantle. The regional metamorphosis process was characterized by one stage only. No differences have been ascertained in the degree of the metamorphosis of the Precambrian and Caledonian rocks here.

Two schistosity directions in the Precambrian rocks, unrecurring in the younger formations, can be connected only with the Precambrian tectonic movements, without any metamorphic processes. The presence of the Precambrian rock blocks within the younger Caledonian formations can be explained by the tectonic abbreviation of profile rocks of the older basement, and the Caledonian folds. Both petrographic and tectonic analyses demonstrate that the metamorphic processes are related here to the Cracow phase.