Skały czynne magnetycznie na obszarze przedsudeckim

Abstract

MAGNETICALLY ACTIVE ROCKS IN THE FORE-SUDETIC AREASummaryBased on their own magnetic maps. A. Dąbrowski and K. Karaczun for the first time attempted in 1968 to parallel the local magnetic anomalies with the geological structure of the Fore-Sudetic area. The magnetic maps based on the results of recent detailed and semi-detailed surveys carried out by the Geophysical Department of the Geological Institute, allowed the present author to make more detailed analyses, particularly with the aid of both new geological data and results of magnetic subsceptibility measurements. As a result of these studies, the following types of magnetically active rocks have been found to occur within the Fore-Sudetic area:Basalts. Basalts are responsible here for some characteristic local magnetic anomalies showing amplitudes equal to several hundred or several thousand gamma, and for an irregular course of isanomalies without any distinct direction of axis. A considerable set of such anomalies is found to appear between Bolesławiec, Legnica and Świdnica. Other anomalies may be observed along the line Szprotawa - Środa Śląska. Amphibolites and gneisses. With these rocks are connected anomalies that reveal amplitudes from several ten to over hundred gamma, and occur in the form of isanomalies, almost eliptical in shape, with distinctly marked directions of axes. These anomalies appear in an area restricted by the following localities: Szprotawa, Legnica, Wrocław, Środa Śląska and Lubin. The direction of their long axes is parallel to the north-eastern boundary of the Fore-Sudetic block. Serpentinites. The occurrence of the serpentinites may be observed in the magnetic picture, between Świdnica and Oława, in the form of a set of local magnetic anomalies, alternately positive and negative, with the amplitudes reaching to one thousand gamma.Crystalline rocks of unknown nature. Region of Gubin – Zielona Góra - Głogów - Wołów. On the basis of the anomalies observed to appear in this area and to resemble those found in the area between Szprotawa, Legnica, Wrocław, Środa Śląska and Lubin, we may suppose that magnetically active are here also parts of the Eocambrian - Proterozoic substratum, built up, among others, of amphibolites, which occur at greater depths (about 5 km, according to quantitative interpretation of magnetic data).Area situated north-east of Świdnica. Here, amphibolites or basalts may represent magnetically active rocks which may be traced as local magnetic anomalies.Area north of Wałbrzych and Świdnica. A characteristic magnetic anomaly observed to occur in this area in the form of a triangle of isanomalies, may be caused by various factors: basalt outflow, intrusion of deep-seated basic rocks, or uplifted block of metamorphic rocks.Area situated south of Oława. Anomalies, only slightly evidenced by measurements, point here to the presence at either basalts or magnetically active portions of the crystalline basement.