Borehole logs from the Precambrian basement on Bornholm, eastern Denmark: geology and groundwater flow

Bornholm is situated in the Sorgenfrei–Tornquist Zone that separates the North-West European Craton from the Baltic Shield and the East European Platform (Fig.1). The Precambrian basement of northern and eastern Bornholm consists of different granitic and gneissic Mesoproterozoic rocks that are dated to c. 1455 Ma (Waight et al. 2012). It appears from the age data that granitic magmatism, deformation and metamorphism occurred over a relatively short time period. The rocks contain abundant pegmatite and aplite bodies. More than 250 mafic dykes occur. The dykes were intruded during three Precambrian events at c. 1326 Ma, 1220 Ma, 950 Ma and during a Permian event at c. 300 Ma (Holm et al. 2010).