Metodyka i wyniki kompleksowych badań geofizycznych i geologicznych podłoża krystalicznego wschodniej części bloku przedsudeckiego

Andrzej Grocholski, Robert Kucharski

Abstract


METHODS AND RESULTS OF COMPLEX GEOPHYSICAL AND GEOLOGICAL INVESTIGATIONS ON CRYSTALLINE BASEMENT SITUATED IN THE EASTERN PART OF THE FORE-SUDETIC BLOCK

Summary

The area lying immediately to the North-East of the Sudetic Mountains is called the Fore-Sudetic Block. It is made up of the rocks older than the Permian formations (with mere exception to the granitoid intrusion), bordering along with numerous faults and covered with the Cainozoic deposits varying in thicknese from at least several meters to 280 meters. The north-eastern boundary of the above-mentioned structural unit is shown elearly by the system of dislocations generally determined as the "Odra Fault"(H. Teisseyre, 1957) or sometimes as "the lineament of the Odra" (T. Dvořak, 1968). The crystlline rocks of the Fore-Sudetic Block border on the Permian and Triassic deposits of the Fore-Sudetic monocline along that dislocation line. The complex geophysical investigations have been recently carried out, including the gravimetric and magnetic maping, within the eastern part of the Fore-Sudetic Block completely covered, situated on the southern and south-eastern side of Wrocław City. While tracing the depth of crystalline substratum one could complete in traversing of the electrical sounding by Schlumberger system. In order to check and complete the information yielded through detailed geophysical studies eleven sample bore-holes have been boved in which set of electric logging have been made. The selected samples of crystalline basement rocks have been subjected to a petrographic examination. The results based upon detailed geoelectric tests can be illustrated through figures 1 to 2. The Fig. 5 and 6 show the comparison of the electric resistivities to the geologic profiles taken from the selected drillings. The results of the geophysical and geological investigations are shown on cross-sections (Fig. 3 and 4). The map showing the shape of the pre-Tertiary surface (Fig. 7) and the geological sketch (Fig. 8) constitutes the ultimate results of complex researches. The results of a primary importance can be qualified as followed:

1. The geoe1ectric investigations seemed to be entirely useful for determining the depth of the pre-Cainozoic substratum and tracing the fossil decomposed rocks. They also allow for isolating of the certain rocks forming the basement eg. gneisses.

2. The geological and especially petrographic investigations indicated that one should admit mica and quartz schists sampled from the l/VIII bore-hole as the strongly metamorphosed rocks. They may represent, perhaps the Older Proterozoic.

3. The mica schists and paragneisses occurring southward and south-eastward of Wrocław feature the widest spread. They are somewhat metamorphosed in amphibolic facies contacting closely with the greenstone fades. Their age can be determined through analogy to the Northern Provinces of Bohemia as the Younger Proterozoic.

4. Weakly metamorphosed metagrauwackes and metasiltstones indicated in the eastern part of the prospected terrain in the 1/IX bore-hole, may represent, perhaps, the uppermost Proterozoic or the Lower Cambrian.

5. The gravimetric and magnetic investigations indicated the existance of wide-spread cupola rock made up of basic intrusive rocks. It is largely covered under the shield of mica schists featuring the mediocre degree of metamorphism.


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