The Hercynian Mountain Belt, stretching from Britain to Eastern Europe, was formed as a result of a continental collision which ended 200 million years ago. This range has been severely eroded over millennia and in many places only exist as "basement" rock, hidden from view by sedimentary deposits. The figures below illustrate the concepts of basement and cover rocks.
Basement and cover rocks of France. Source:http://www.virtual-geology.info/lozere/lozere.html |
Relationship between basement and cover rocks. Source: http://www.virtual-geology.info/lozere/lozere.html |
Formation timeline -- basement and cover rocks Source: http://www.virtual-geology.info/lozere/lozere.html |
Using the Variscan orogeny as an example, Martinez Catalán, et al., see the process as encompassing:
- Shortening and intensely deforming those sediments deposited previously along vast continental margins
- Remobilizing the prior basement on which they laid
- Generating a new crust by partial melting of the former
- Adding fragments of oceanic crust and mantle
- Eroding and re-sedimenting part of the newly formed crust
- Deforming the majority of the new sediments.
Reconstruction of how the Iapetus Ocean and surrounding continents might have been arranged during the late Ediacaran Period. Source: wikipedia.com |
The distribution of mountain ranges at the end of the Caledonian orogeny is illustrated below.
Present day coastlines are indicated in gray for reference. Source: By Woudloper - Own work, CC BY-SA 1.0, https://commons.wikimedia.org/w/index.php?curid=5038110 |
After the Hercynian earth movement, the general area of Italy was covered by the sea for long periods. As such, limestones are typical for the Permian and Mesozoic eras. Towards the end of the Mesozoic, and during the Tertiary, gravels, sands, clay, limestones and marls were deposited.
Source: wikipedia.com |
The most recent activity in the basement formation began with initial compression caused by subduction of the European plate under the African plate in the Jurassic period. Collision between the African and Eurasian plates resulted in increased deformation of Tethyian Sea deposits. The orogeny "produced intense metamorphism of preexisting rocks, crumpling of rock strata, and uplift accompanied by both normal and thrust faulting." Remnants of the Tethys Sea remain as the Mediterranean, Black, Caspian, and Aral Seas. The plate movement resulted in the Italian peninsula being driven northward and compressed into Europe.
Ranges resulting from the Alpine orogeny. Source: wikipedia.com |
A schematic geological map of the Alps is shown below.
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