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Regional Geology

by Theresa König last modified 2008-02-19 14:51

Regional Geology

At the spot of the plate where you are standing now, the underground consists of varying nappes of different origin. If you drilled near Vandans, you would first hit the Austroalpine nappes of the Northern Calcareous Alps, afterwards the Penninic nappes that originated from two ocean floors and a small continent that disappeared in the innermost crust of the earth and then follow the Helvetic nappes (Säntis nappe), which form part of the European continent. Below the Helvetic nappes you will finally find the Molasse zone at a depth of 6,000 m, whose sediments originate from the developing Alps and which are the result of erosion and fluvial transport by the early Rhine, Danube, Inn or Aare rivers. If you continued drilling, you would finally reach the bright carbonates of the Swabian Alb at a depth of about 8,000 m below the Montafon valley. You can find the same sediments at the surface in southern Germany about 100 km from the Montafon valley.

The nappe stack is visibly exposed at the border of the Eastern to the Central Alps through the forces of erosion. Normally, the situation is simple but here it is highly complicated through the internal folding and shearing of the different nappes as they consist of layers or schists with different mechanical properties – some are weak like gypsum, and some are stiff and brittle like the Hauptdolomite. This type of layering is clearly exposed at the opposite side of the valley, forming the peak of the Zimba.

To get an idea of the structure of a nappe, you have to picture a sandwich: It consists of two slices of bread and in between there are different layers of cold cuts, cheese, and vegetables.  If you fold and stack several sandwiches, you get the model of a nappe stack with various types of rocks.
The trough of the Rellstal-or Rells Valley follows the border of two different types of rocks. To the right you will find the sediments of the Northern Calcareous Alps and to the left the crystalline rocks of the Silvretta Crystalline. This distinctive contact zone is disturbed, its sediments, however, rest on the crystalline basement.

The nappe stack of the Alps is a result of the stacking of parts of the Earth’s crust from different regions reaching internal distances of several hundred kilometres. The stacking of different types of rocks – also of older layers on younger ones – is the result of plate tectonics over the last 150 million years. This plate is located at the transition zone of the Silvretta gneisses to the sediments of the Northern Calcareous Alps. You will walk over these sediments, starting with the oldest ones at the bottom and working your way uphill to the youngest ones.


P02-2 Regional Geology.mp3

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