1 - Overview of the Alps

The Alps belong to a great series of mountain chains of young origin that stretch from Spain and North Africa to Indochina. The Alps and other Cenozoic mountains of the Mediterranean region formed as the African plate moved northward against the Eurasian. In most of this zone of orogenic activity, the African continent has not actually been sutured to the Eurasian continent. However, many small plates of lithosphere have been caught between the African and Eurasian cratons, and these microplates have been pushed against one another and against the Eurasian craton.

The Alps are a relatively young mountain system that formed largely during the Eocene and Oligocene epochs. At the start of the Mesozoic Era, Africa and Eurasia were both part of the supercontinent Pangaea. Then, during the Triassic Period, large-scale rifting began in what is now the Mediterranean Sea. A sea named Tethys had inundated this region before rifting began. The Eurasian plate remained to the north of this narrow ocean, to the south were the African plate and a few microplates. Two of these microplates moved northward against Eurasia during Late Cretaceous time. Today, one represents the Iberian Peninsula (Spain and Portugal), while the other, the Adriatic plate, includes the Peninsula of Italy. The Adriatic plate made contact with Eurasia in the vicinity of Switzerland about 45 million years ago. The crust was thickened by this doubling and by the accumulation of igneous rocks above the subducted plate.

Click on the two sections in Fig. 2 to see detailed profiles.

The Alps can be divided into zones that roughly parallel the regional strike. For example, the igneous core of the system lies in the zone known as the Southern Alps, where plutonic rocks have been exposed by erosion. North of the igneous core, in the Pennine zone, rocks were metamorphosed and flowed in a plastic manner while being deformed under intense heat and pressure. These rocks constitute the metamorphic belt of the mountain system.

Still further north, in the zones known as the Helvetic Alps, the Molasse Basin, and the Jura, rocks behaved in a less brittle fashion during Alpine orogenic activity. These zones constitute a fold-and-thrust belt resembling that of the idealized mountain range. The sedimentary rocks within this belt have moved northwestward along large thrust faults. At the northwest extremity, in the Jura Mountains, folding, rather than faulting, prevails because most of the thrust faults of the Alps terminate at the surface rather to the southeast.