The study area - the western part of the Eger (Ohře) Rift (Fig. 1) - belongs to the European Cenozoic rift system (ECRIS) (Ziegler 1992, Prodehl et al. 1995, Dezes et al. 2004). This system of graben structures and intraplate volcanic fields spreads over a distance of some 1100 km from the Mediterranean to the North Sea coast, including the French Massif Central, the Upper Rhine Graben, the Eifel, the North Hessian Depression, the Vogelsberg, and the Eger Rift (Fig. 1, inset map). There are different models to explain the widespread rifting and associated volcanism in the foreland of the Alpine orogen. Most of them are related to the effects of Alpine collision (e.g. Ziegler 1992). However, there also exist ideas of a mantle plume or several small mantle plumes (mantle fingers) as the source of the magmatic activity (e.g., Granet et al. 1995, Goes et al. 1999). © 2007 Springer-Verlag Berlin Heidelberg.