GEOLOGICAL HISTORY OF THE MORVAN
of the Variscan Belt
The Morvan region is located in the NE part of
the French Massif Central and in the middle of the central zone
of the Hercynian or Variscan Belt. Since the first descriptions [REF], the deep structures of this orogenic belt that extends
across Germany, Belgium and France are best described, deduced
from seismic profiles [REF], as
well as the chronology of the tectonic and magmatic events [REF].
The Variscan Orogenic Belt exhibits a relative
bilateral symmetry along each sides of the central zone.
Following domains extend from N to S:
- The North-European
Continent of Precambrian age.
- The Sub-Variscan
Zone a foredeep including
franco-belgian and Ruhr coal basins.
- The Rhenohercynian
Zone extends through Ardennes
and Harz and is characterized by thick sedimentary series composed of Cambrian to Early Carboniferous deposits. Non-metamorphosed, these
rocks are strongly folded, faulted and northward overthrusted .
- The Saxothuringian Zone
is divided in two belts by the Cadomien Continental Block:
the central Channel belt to the North and the central
Armorican zone to the South. In Germany it is
characterized by the Mid-German Crystalline Rise (ZC) to the
North, possible prolongation of the Cadomian Block and to
the South by Paleozoic sedimentary rocks showing metamorphism
increasing southward. Folds and nappes are overthrusted northward.
- The Cadomian Block comprises volcano-sedimentary
series of Late Proterozoic age (Brioverian) folded, metamorphosed and granitised during the Cadomian Orogeny (600 Ma) and which,
in the northern part, overlies a metamorphic basement 2000 Ma old. The epicontinental and transgressive
Paleozoic rocks are weakly deformed by the Variscan
- The Central Armorican
Brioverian deposits are overlain by epicontinental
Paleozoic rocks slightly folded during the Variscan
- The South Armorican Zone comprises Brioverian and tectonic nappes
composed of Cambrian to Early Devonian series intruded by granites of Carboniferous
- The Central
or Moldanubian Zone
in Germany, Arverno-vosgian
zone in France, represents the
inner zone of the Variscan Orogen. It is characterized by
a gneissic basement
structured and consolidated between Late Ordovician and Early
Devonian and in the NE Massif central and Vosges by
an overlying cover of non-metamorphosed volcano-sedimentary
rocks of Late Devonian to Early Carboniferous age (Devono-Dinantian). The complex structure of the gneissic
basement comprises tectonic nappes overthrusted
southward, except in the northern part of the South
Vosges where the structures are similar to the
Saxothuringian zone structures northward overthrusted .
- The Montagne
Noire Zone (M.N.)
where Precambrian rocks are overlain by Paleozoic units
(Cambrian to Lower Carboniferous) both being
engaged in a system of faulted folds and nappes
southward overthrusted .
- The Aquitanian
Block belonging to the
Precambrian Gondwana continent is overlain by Paleozoic
Variscan orogeny part 2