The study of the geology of the Alps has played a significant role in the history of geology, dating back to the time of Saussure and Deluc. A brief overview of the structure of the chain might be useful. There are many summaries of Alpine geology – one recent one that I like is: O. Adrian Pfiffner, 2014, Geology of the Alps, second edition, 376 p, Wiley-Blackwell. It is a bit detailed but the illustrations (maps and cross-sections) are great.

The Alps form a broad arc that extends north from the Mediterranean along the French-Swiss border (western Alps), curve northeast and then east through Switzerland (central Alps), and then extend across Austria to Vienna (eastern Alps). The chain formed due to the subduction of the European plate under the Adriatic/Apulian/African plate (essentially Italy). In this continental collision, a variety of tectonic realms were compressed and stacked up. Each realm has an unique lithology due to their contrasting setting.

The main realms (listed north to south – see diagrams) are:

1. European authochthonous crust: in-place part of underthrusted plate
2. European para-authochthonous crust (Jura Mtns): thrust and fold belt (but not transported far) part of underthrusted plate
3. Helvetic realm: European continental margin of underthrusted plate
4. Penninic realm: ocean and continental margin of overriding Adriatic-Apulian plate (a slice off the African plate)
5. Austroalpine realm: continent of overriding plate
6. Southern Alps: slightly deformed continent of overriding plate

These realms have been “telescoped” so that they are stacked up

• In the Alps, the sense of movement is that nappes move to the north, overriding the immediately adjacent nappe to the north. This results in a regular “stacking” of nappes originating in each of these realms.
• Units 2-5 were thrust onto the European continent to create a stack of nappes with those that originated farthest to the south forming the uppermost thrust sheets.

 

 

 

The regional map emphasizes the major packages. The key is:

• Authochthonous European crust  (light green)
• Helvetic and Jura Mtns = deformed European margin (dark green)
• Pennine = oceanic rocks (purples)
• Austroalpine = deformed African margin (blues)
• Southern Alps = slightly deformed African crust (dark brown)
• Foreland basin deposits = yellow

Even in a generalized cross-section, you can see that this rather complex.

If you look at the map carefully, you will see that in the western Alps, the Austroalpine nappes are preserved but in the central and eastern Alps, the equivalent nappes have been eroded away. This resulted in a puzzling structural and stratigrapic contrast between these areas that was only resolved when the nature of the “Hohe Tauern” window was recognized (Termier 1903).