Central Europe I

GO 568 Structural Geology
James S. Aber

Tectonic overview of the Alps

The Alps of west-central Europe have been regarded by many as the climax of European geology. The mountain range extends in a great arc from the French Riviera to Vienna, Austria. The Alps display tremendous structural and stratigraphic complexity; these mountains gave rise to the sport of mountaineering and the earliest scientific studies of alpine environments in the late 1700s. Early investigations revealed confusing sequences in which older rocks are on top of younger rocks, but major facies changes made long-distance correlation impossible. Continued studies gradually led to a modern understanding that the Alps are "rootless mountains" composed of great nappes and thrust blocks that have been transported long distances. The Alps include three main structural belts.

  1. Austrides -- Southern Alps are best developed in northern Italy. They consist of high-grade metamorphic rocks plus granite of Variscan age (Carboniferous), all deeply altered by Alpine metmorphism (Tertiary). Massive carbonate breccias of Mesozoic age are also included. This zone is separated from the next by the Insubric Line, which is a deep fault that may represent an old transform plate boundary.

  2. Pennides -- Middle Alps are well known across Switzerland and Austria. They include an exceedingly complex assemblage of different terranes that originated in oceanic settings of the Tethys Sea. Ophiolite sequences are present along with gneisses and granites of Variscan origin. All were subjected to Alpine metamorphism.

  3. Helvetides -- Northern Alps are best developed in France, Switzerland and Austria. The basement rocks forms a series of massifs that support the highest peaks of the Alps--Mont Blanc, Jungfrau, etc. The basement is made of metamorphic rocks ranging in age from Proterozoic to Carboniferous, but with little or no Alpine metamorphism. These massifs are comparable to the Blue Ridge province of the southern Appalachians.

    Helvetide sedimentary cover strata include exceptionally thick Mesozoic (J & K) limestones, which are more prominent toward the east and are strongly deformed but not metamorphosed. Volcanic rocks are generally lacking. This portion is similar to the Appalachian valley-and-ridge province.

    During the Eocene and Oligocene, initial uplift of the Alps led to rapid erosion, and sediments were deposited in adjacent marine flysch basins of the Helvetide zone. The flysch strata were subsequently deformed by continuing mountain uplift. Later, during the Miocene, thick terrestrial sediment accumulated in continental troughs north of the mountains--the so-called molasse basin. Once again a comparison can be made with the "deltas" (clastic fans) of the Appalachians.

In general terms, the Alps were created as a consequence of subduction and closing of the Tethys Sea, which culminated with continental collisions during the Tertiary (Eocene-Miocene). The scarcity of andesitic volcanic rocks suggests the subduction zone dipped southward beneath the converging Tethyan plate. It is clear that Africa has not yet collided with this section of Europe--the Mediterranean basin still separates Italy from Africa. Nonetheless, a full spectrum of classic mountain development is represented in the Alps. The Alpine Orogeny may be interpreted as a result of collisions involving terranes or microplates. The western Alps were deformed by convergence and collision of Apulia (Italy) with the southern margin of Europe. Whether Apulia was an independent microplate or simply a promontory of Africa is uncertain, however.

Alps of Switzerland

Prealps seen from Interlaken Ost. The Pre-Alps are a huge klippe, transported across the molasse basin and thought to be derived from the Pennides. Photo date 4/79, © J.S. Aber.
Landslide debris on mountain slope, west of Schwendi. Chalets are situated among large blocks on an old landslide fan below the mountain side. Photo date 4/79, © J.S. Aber.
View down the alpine valley between Schwendi and Lütschental. Typical ice-carved valley with steep side walls and a gently rounded floor. The bedrock is entirely sedimentary, namely Mesozoic carbonates--see closeup view in next picture. Photo date 4/79, © J.S. Aber.
Cliff exposure of Mesozoic shale and limestone strata; gently dipping portion of a larger fold structure, west of Schwendi. Photo date 4/79, © J.S. Aber.
Alpine stream boulders display numerous veins in marble and schist, near Lütschental. Such vein-filled rocks are quite common in mountains. Coin is approximately 1 inch (2½ cm) in diameter. Photo date 4/79, © J.S. Aber.
Jungfrau Peak, 13,642 feet altitude, a typical ice-carved horn. Jungfrau Peak is part of the Aar massif, consisting of crystalline basement rocks in the Helvetides. Photo date 4/79, © J.S. Aber.
Mönch Peak, 13,449 feet altitude, a classic ice-carved horn. This peak is also part of the Aar massif, consisting of pre-alpine crystalline basement rocks. Photo date 4/79, © J.S. Aber.
Bedrock exposure on the side of Mönch Peak displaying dark-colored phyllite and schist. Photo date 4/79, © J.S. Aber.
Overview of the city of Bern, its cathedral, and the Aare River. Bern is located in the Tertiary molasse basin of central Switwerland, as are most other large Swiss cities. Photo date 4/79, © J.S. Aber.
City of Bern seen from the cathedral tower. The large tile-roofed building in scene center is the Rathaus (city hall). Note the light-brown color of most building walls, which are constructed of soft Tertiary sandstone. Photo date 4/79, © J.S. Aber.
Cleaning exterior building walls in Bern. The workers use metal brushes to remove the stained surface of soft sandstone blocks. This sandstone is typical of poorly consolidated molasse deposits of the vicinity. Photo date 4/79, © J.S. Aber.

Central Europe II.

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Notice: Structural Geology is presented for the use and benefit of students enrolled at Emporia State University. Others are welcome to view the course webpages. Any other use of text, imagery or curriculum materials is prohibited without permission of the instructor. GO 568 © J.S. Aber (2002).