Skały magnetycznie czynne strefy obniżeń Żytawa-Siekierczyn i zachodniej części niecki północnosudeckiej

Abstract

MAGNETICALLY ACTIVE ROCKS IN THE ŻYTAWA-SIEKTERCZYN DEPRESSION ZONE AND IN THE WESTERN PART OF THE NORTH SUDETIC TROUGHSummaryAlmost the entire area of the West Sudetes was covered by semidetailed magnetic mapping. The authors of this mapping only perfunctorily interpreted the results analysing the maps or Z component of the Earth's magnetic field intensity calculated from a provisional formula of the normal field of this component. The present paper reviews the results interpreted on the basis of the Z component anomalies maps recently compiled by A. Dąbrowski, the values having been calculated from a more precise formula for the normal field. These maps cover the Żytawa-Siekierczyn depressions zone and the western part of the north Sudetic trough.To establish the interpretation procedure the results at measurements of magnetically susceptible rocks of the area were analysed and the magnetic maps constructed were compared with the geological maps of the area. Comparative studies indicate that in the area in question basalts are the only rocks of high magnetic susceptibility causing anomalies at amplitudes higher than 300 γ. Besides the basalts some other types of rocks may be regarded as sources local anomalies the amplitudes of which do not exceed 300 γ. These are diabases, crystalline schists within the Izera gneisses, and some parts of the Rumburk granites and Zawidów granodiorites. The map presented on fig. 1 has been based on the above findings. On the basis of the Z component maps individual types of magnetically active rocks have been outlined. Only anomalies of amplitudes higher than 300 γ have been univocally ascribed to basalts, whereas only alternative sources of anomalies or amplitudes lower than 300 γ have been defined.