Skały czynne magnetycznie na obszarze monokliny śląsko-krakowskiej

Abstract

MAGNETICALLY ACTIVE ROCKS IN THE AREA OF THE SILESIAN-CRACOW MONOCLINE

Summary

Magnetic nature of the Silesian-Cracow monocline was known, in general outlines, already a dozen years ago, mainly on the basis of magnetic maps prepared on various scales. At that time, these maps were used by the present authors in an analysis, the results of which were an attempt at relating various types of local magnetic anomalies with the occurrences of various geological, magnetically active formations and at drawing conclusions with regard to the regional geological elements on the basis of the regional magnetic picture. In 1967, a new magnetic map was worked out in the Geophysical Department of the Geological Institute, using both level and formula for the normal field of component Z calculated the basis of fundamental measurements. This assures the proper picture of the regional anomalous elements. The analysis of these elements demonstrates that in the area of the Silesian-Cracow monocline, magnetically active basement occurs, built up of low-susceptible rocks found at a depth of some kilometers. The basement dips in the north-western, northern end north-eastern directions, plunging under the magnetically non-susceptible formations. The zone or this plunging runs through the area of Brzeg, south-east of Oleśnica, north of Byczyna and Wieluń, between Działoszyn and Szczerców, and north of Częstochowa. Against the regional background, a series of local anomalies appear, related to the occurrences of magmatic rocks of various character.
Basalts. They produce anomalies in the region of Nysa-Opole-Niemodlin (anomalies of Nowy Dwór, Pakosławice, Goszczowice, and Szydłów).
Rhyolites and porphyrites. These are proved by the anomaly at Rybno-Zalas.
Melaphyres and melaphyre tufs. These are related to the anomalies observed in the areas of Alwernia-Kwaczała-Rudno and Miękinia.
Diabases. They make the anomaly of Niedźwiedzia Góra.
Magmatic rooks of unknown, nature. Between Cracow and Częstochowa a series of local magnetic anomalies occur (Dębnik, Bębno, Zimnodół, Imbramowice, Krzywopłoty, Smoleń, Ryszów, Kiełkowice, Siamoszyce, Zawiercie, Mrzygłód, Myszków, Woźniki, Przybyszów, Częstochowa). Magmatic rocks (porphyries) pierced in this area are magnetically very low-susceptible.
We may suppose that all the anomalies mentioned above are related to the deep-seated magmatic sources; however, it is not known whether they are the effect of the large masses of the low-susceptible rocks pierced, or of the deeper-seated, more basic magnetic rocks characterized by high magnetic susceptibility. Similarly, the character of the magnetic rocks responsible for an anomally at Oldrzyszowice, north of Niemodlin, is unexplained as well. In the region Działoszyn-Koniecpol, three elongated local anomalies may be observed, probably related to the fracture zones of the crystalline basement.