Rhenohercynian Zone

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Hercynian orogeny in Europe.[1]

The Rhenohercynian Zone or Rheno-Hercynian zone

Laurussia
.

The Rhenohercynian Zone, named for the

greenschist facies). Most geologists consider the South-Portuguese zone
to be a continuation of the zone to the west.

Whether the Rhenohercynian Basin was a continuous feature or rather a string of temporaneously interconnected smaller basins is not well understood, because in many places the Devonian and Carboniferous rock strata are covered with younger deposits. Parts of the basin have their own names, like the

Munster basin in Ireland
or the Rhenisch basin in Belgium and Germany.

Tectonic structure and metamorphism

Hercynian orogeny
.

The Rhenohercynian Zone is a part of the northern

London-Brabant Massif and other Avalonian terranes). From the south it was overthrust by the Mid-German Crystalline High
, part of the Saxothuringian Zone.

The metamorphic grade or degree of metamorphism increases towards the south or southeast. The southern edge of the Rhenish Massif lies in the Northern Phyllite Zone, which has a higher grade than other parts of the zone.

Geodynamic history

The Devonian basin

The Rhenohercynian basin was situated north of the

Mid-German Highs to the south.[3]

In the Middle Devonian (from 390 million years ago) a

Saxothuringian/Armorican basin, developed south of the Rhenohercynian basin. To the west some crustal convergence took place, and the Normannian High was partly thrust
over the sedimentary basin fill of the Rhenohercynian basin.

Carboniferous compression

The Rhenohercynian basin disappeared when the continent Gondwana

Hercynian orogeny). The sedimentary rocks in the basin were thrust in a series of piggyback basins over the northern foreland (the London-Brabant Massif). These rocks now form the folded sequences of Cornwall, the Ardennes, the Eifel
and the Harz.

From the

Visean by a new period of extension.[5]

During the

Laurussia and Gondwana resulted in the destruction of the last oceanic crust of the basin. Its sedimentary fill was, however, not (totally) subducted but instead thrust northward. During the later part of the Carboniferous period (Westphalian and Stephanian) the Rhenohercynian zone formed the foreland of a relatively fast-developing Hercynian mountainbelt to the south. Isostatic subsidence of the foreland resulted in the development of a deep foreland basin. This filled with the products of erosion in the Hercynian mountains and the contemporaneously uplifted London-Brabant Massif to the north. During the Westphalian, the basin was completely filled and rose above sea level.[6]

Stratigraphy

The Rhenohercynian basin was filled with Devonian and Carboniferous sediments. Sedimentation was often disrupted by tectonic phases, but nevertheless the total thickness of the sediments can in some places be more than several kilometers.[7]

When a foreland basin was formed in the Rhenohercynian zone, this was filled with upper Carboniferous (Pennsylvanian) flysch and molasse sediments. The Namurian is characterized by flysch, in the Westphalian this gradually grades into molasse and other continental deposits, among which the thick coal layers of the Belgian coal measures.

References

  1. ^ Map is based on Franke (1992, 2000), Matte (2001), von Raumer et al. (2003) and Walter (2003)
  2. ISBN 978-3-7301-0522-1
    .
  3. ^ As in Ziegler (1990), pp. 31-32 and enclosure 11
  4. ^ Franke (1989); Ziegler (1990), p. 36
  5. ^ Ziegler (1990), pp. 37-38
  6. ^ Ziegler (1990), pp. 41-42
  7. doi:10.1144/GOEWP.10
    .

Literature
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