Geological map and simplified basement tectonic map. (a) Regional geological map of the study area. Geographical units are indicated. The location of the map within Western Europe is shown in (b). Main cities and boreholes are mentioned in the text. Black bold lines and letters indicate the cross sections A to A’, B to B’, and C to C’. (b) Simplified basement tectonic map of Luxembourg and the surroundings. Rectangle indicates location of geological map shown in (a) with indication of the Rhenish Massif (RM), the Lower and Upper Rhine Grabens (LRG and URG, respectively), the Eifel Depression (ED; hatched zone), and the Trier-Luxembourg Embayment (TLE). Dashed contour indicates the location of the Eifel plume according to Keyser et al. (2002).