TITLE:
The Variscan Deformation Front (VDF) in Northwest Germany and Its Relation to a Network of Geological Features Including the Ore-Rich Harz Mountains and the European Alpine Belt
AUTHORS:
Heinz-Jürgen Brink
KEYWORDS:
Variscan Deformation Front, Eastern Avalonia, Harz Mountains, Lower Saxony Basin, Bramsche Massif, Lower Carboniferous, Alpine Deformation Belt, Moho Seismic Reflections/Refractions, Magnetotellurics
JOURNAL NAME:
International Journal of Geosciences,
Vol.12 No.5,
May
20,
2021
ABSTRACT: The crustal basement of Northwest Germany can be interpreted as an
“Avalonian Terrane Assemblage” subdivided by a roughly NW-SE (Hercynian) and
SW-NE (Rhenish) running horst and graben system. In Late Devonian and Early
Carboniferous times, this assemblage was flooded by the sea and mainly marine
carbonates were deposited on the horsts and Stillwater shales in the grabens,
as interpretable through magnetotelluric measurements. During the Late Carboniferous Variscan Orogeny, this
terrain became the coal-rich foreland
of the colliding Rhenohercynian belt. The shale-filled grabens reacted through folding and thrusting with different
anticlinal patterns, the main carbonate covered horst in a still unknown
way. This horst was the location of the Late Carboniferous basin center and of
the inverted oil-rich Mesozoic Lower Saxony Basin (southwestern sector),
respectively, with the so-called Bramsche Massif therein. It probably acted as
an indenter for the evolution of the Variscan ore-rich Harz Mountains and
forced the approaching Rhenohercynian orogen to stack the appropriate tectonic
nappes by horizontal shortening to very high altitudes and the root into large
depths. Based on seismic evidence this root is still an uncompleted
crust/mantle transition zone with a deep reflection seismic and petrological
Moho and a shallower hardly reflecting refraction seismic velocity Moho. The
alternative, partly unsolved location of the Variscan Deformation Front in
Northwest Germany may represent the new findings. The results may be supported
by a comparison with features of the northern Alpine deformation belt.