The tectonics of the Elbtalschiefergebirge-Osterzgebirge-Zone and the role of the Mid-Saxon-Fault

The Elbe zone constitutes a complex fault zone on the northern edge of the Bohemian Massif. As part of this zone, the Elbtalschiefergebirge is juxtaposed with the Lausitz to the northeast and the Osterzgebirge to the southwest. The tectonic boundary with the Osterzgebirge is traditionally defined by the Mid-Saxon-Fault. In the course of a tunnel project for the railroad line Dresden-Prague structural geological investigations were carried out. Here first results are presented. The entire area was overprinted by the Variscan orogeny and can be divided into three principal units. (i) The northeastern section consists of very low-grade metamorphic lithologies representing the remnants of an early Carboniferous synorogenic basin. The adjoining unit (ii) is predominantly made up by phyllites that differs from unit (i) by its stronger tectonic and metamorphic overprint and partly inverted stratigraphy. Mylonites on both sides of the Mid-Saxon-Fault reveal the existence of a ductile shear zone (iii) affecting high- to medium-grade metamorphic units of the Osterzgebirge as well as low-grade units of the Elbtalschiefergebirge. This Elbe-zone parallel, i.e., NW-SE striking shear zone suite is characterized by dextral strike slip tectonics and the transition from ductile to brittle-ductile material behavior. The existence of ESE-WNW to E-W stretching lineations on both sides of the Mid-Saxon-Fault , however, indicates a more complex tectonic evolution. Furthermore, the mylonites adjacent to the “Tourmaline-granite” of the Elbtalschiefergebirge resemble the shear zone rocks of the Erzgebirge. Thus, the traditional view of the Mid-Saxon-Fault as a strict tectonic boundary between both units must be questioned.