Paleogeography of the Alps

Alpenseminar by Taufeeq Dhansay

The formation of the Alpine Mountains can be broadly defined by the convergent movement of several continental plates and the associated opening and closing of oceanic basins. The science of Paleogeography aims to travel back in deep time and figure out how these different plates would have moved, and ultimately collided to form these magnificent mountains. 

The protagonists

Firstly, we should identify the main players (i.e. plates) in this story. This includes the larger African/Nubian and European plates, and the smaller Adriatic/Apulian and Iberian Plates. Below is a figure of the present-day alps and how its underlying tectonic units fit together:

Broad overview of the major plates associated with the Alpine Orogeny, after Handy et al., 2010

Importantly, zones between these plates (i.e. demarcated by darker colours on the above map) represent regions that, in particular, experienced varying levels of tectonism and/metamorphism. These zones comprise of sedimentary and/or oceanic basement rocks, which act as geographical markers. These markers have allowed for much of our current paleo-reconstruction knowledge.

How did the plates move?

As an overview, the formation of the Alps can be attributed to the relative motions between Europe, Africa and North America, this is shown in the video below. Note: the extension that results from North America and the opening of the Atlantic Ocean plays a very important role in defining tectonic stress in the Alpine region.

Paleogeographic reconstuction for the last 140 million years, after Gurnis et al., 2012

We may further summarise Alpine evolution with several important phases of movement between Europe and Africa at specific time intervals:

Relative motions between Europe and Africa, after Dewey et al., 1973

In general, the time-steps shown in the figure above highlight the following:

A – Africa and North America drifts toward the SE, this creates an extensional regime relative to Europe.

B – Africa rotates counterclockwise with respect to Europe. Toward the W, this emanates as dextral strike-slip tectonics, but in the E this results in compressional tectonics.

C – Africa moves W with respect to Europe, This is aided by Europe moving away from North America relatively faster than it does from Africa.

D – The relative motion (C) exasperates E-W oriented strike-slip tectonics.

E – N-S oriented compression between Africa and Europe is re-initiated, largely due to counterclockwise rotation that is aided by slow spreading between Europe and North America.

F – Finally, to the present-day, N-S compressional tectonics dominates.

Orogenesis related to this motion

We now may further consider these relative plate motions with regard to the effect on plate tectonic (i.e. divergent/convergent) boundaries. This can be summarised as follows:

Tectonic overview leading to the birth of the Alps, modified after Frisch, 1979

The importance of the Atlantic

The opening of the Atlantic Ocean, in response to the relative drifting motion of North America from Africa and Europe played a very important role in Alpine evolution. Extensive forces related to the opening of the Atlantic resulted in far-reaching strike-slip movement that ultimately enabled much of the tectonism in the Alpine region. The Atlantic effect can be shown as follows:

Effect of the opening of the Atlantic Ocean, after Dewey et al., 1973

A closer look at the birth

Most of the action leading the Alps as we know it occurred from 35 to 20 million years ago. At this time, the Adriatic plate was launched into the European plate. This was largely enabled by the north-south oriented compression between Africa and Europe. This can be summarised by:

Note how Adria crashes in Europe, after Handy et al., 2015

The effect of this collision

Finally, we are left with the aftermath of this collision. A complex melange of oceanic and continental units squeezed together and tectonically bounded (what the geologists see):

Cross section of the present-day Alps, after Bradner, 2013

And, of course, what we all see, and hope to see on our trip:

Julian Alps, after Dan Briski