Dominerende forkastningszoner på Bornholm baseret på anomalierne af den vertikale magnetiske intensitet

Abstract

In earlier works (1945, 1957) the author has, among other things, demonstrated horizontal displacements of 4-500 m. from the existence of rift valleys in the Bornholm bedrock. By magnetic measurements across the bedrock-sediment boundary both horizontal displacements of 100-200 m. and vertical movements have been demonstrated. The present work discusses further studies of the same problem; the author has used the vertical magnetic intensity (Z) to localize large, dominating fault zones in the Bornholm bedrock, (600-2500 m.).

It has been found that the granite varieties and gneiss in southern Bornholm are so different, magnetically speaking, that their limits become visible on the map. The construction of an Z-anomaly chart showing the variations in the vertical magnetic intensity gives the necessary basis for the main section of this work (section B). The chart (supplement plate I) is based on measurements over the whole of Bornholm on a standard quadrat grid with station intervals of 500 m. (more than 3,000 stations). As well as the magnetic measurements which form the basis for the Z-anomaly chart, a great number of magnetic detail profiles have been measured in the boundary zone between the bedrock area and the sediment-covered areas. These detail profiles have been utilized to determine where the boundary is formed by a fault, and where it represents an erosion boundary (section C).