Geology: general rock composition
Categories: Nature and Environment › Geology and raw materials › Geology and tectonics
On the geological map, a basic differentiation may be seen between the crystalline basement (metamorphic gneiss and schists, granite), sediments and loose rock (alluvial deposits, glacial sediments). In the crystalline rock and sediments, the rocks are summarised into groups according to similar rock type and age.
Jura Mountains
The Jura mountains have a clearly curved shape: their eastern end forms the Lägern and the south-western end of the chain is Mt. Gresse near Chambéry. The mountains were thrust toward the north-west, compressed and folded. The highest range of the Jura mountain chain is located on the side toward the Central Plateau. In many cases, individual chains, from a geological point of view, can be identified as anticlinals and arches (e.g. Moutier gorges), while the valleys often form synclinals and hollows. In these synclinals the youngest sediments are preserved; they may be seen on the geological map as narrow strips.
North of the Swiss Jura mountains, tertiary sediments are found at the depth of the Rhine pit north of Basle, flanked by outcropping crystalline Vogesen and Black Forest rock. The emptying and filling of the Rhine pit and the heaving of the Vogesen and Black Forest took place approximately 30 million years ago.
Molassic basin
The molassic basin includes the Swiss Central Plateau and becomes progressively narrower from Lake Constance to Lake Geneva. The sediments (Nagelfluh and conglomerate, sandstone and marl) are alluvial deposits (erosion detritus) resulting from the development of the Alps. On the Central Plateau, the molasse strata are flat while, near the Alps, they are partially sub-vertical due to involvement in Alpine folding (so-called subalpine molasse).
Alps
The Alps are easily recognised as a WSW-ENE running chain. In the south, they are limited by the Po Plain, in the north by the molassic basin of the Central Plateau. On the northern side of the Alps runs a wide band of sedimentary rocks. In the Ticino Alps and the zone immediately to the north, crystalline rocks dominate the basement. The largest uplift occurred through the erosion resistant granites of the Mont Blanc massif, the southern part of the canton Wallis (Dent Blanche zone), the border zones between the cantons of Wallis and Bern (Aletschhorn to Finsteraarhorn) and in the southern part of the canton Graubünden (Mt. Disgrazia, Bernina). The large alpine longitudinal valleys follow narrow sediment lineaments in the crystalline rock or in the limiting region between crystalline and sedimentary rocks. This is due to the easy erodibility of the sedimentary rocks.
Within the Alps, the geological map shows a complex juxtaposition of pre-Mesozoic crystalline basement (metamorphic gneiss and magmatic, principally granite rocks) and Mesozoic-Tertiary sedimentary rocks.
Text Sources
- Pfiffner (2004): Schweizer Weltatlas Kommentar
Data Sources
- swisstopo, Landesgeologie (2010): GeoKarten500, GeoCover
Data Owners: Swiss Federal Office of Topography (swisstopo)
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