Week 5 - Converging Plates - Ryan Klassy

Mont Blanc (2019).
Retrieved from http://ee.france.fr/en/discover/visit-french-alps

This week I decided to take a trip to the Alps, which are a mountain range in Europe crossing through France, Switzerland, Monaco, Italy, Liechtenstein, Austria, Germany, and Slovenia.

The Alps are a folded mountain belt that was created over many millions of years as the African and Eurasian plates collided with each other. These two plates were both continental plates, so my plate boundary is a continental-continental boundary.

Continental-continental boundaries such as this one were converging upon each other which gives us many clues as to how the mountains were formed. This type of converging creates compressional stress throughout the region. Compressional stress can cause a great deal of deformation in the rocks involved, including folding and faulting.

P. Blair, National Geographic (Photographer). (2018). Wildhauser Schafberg
Retrieved from https://media.nationalgeographic.org

Folds in this region are characteristic of this extreme compressional force. You can see in the first image that these fold lines are extending throughout this entire peak. You can clearly see the syncline in the center of the photo, surrounded by two anticlines, one on either end, although most of the anticline on the left side (near the peak) has been eroded away. Try to use your imagination to visualize what the rest of that looked like. In this example, the very tip-top peak contains some of the younger rocks, however, if you slope down to the right a little bit, you will notice that you get even younger rocks that those of the peak. This is because that syncline that is to the right was folded downward so much that the younger rocks in that area haven't eroded away as badly as the ones on the peak.

Bernhard Edmaier (Photographer). (2016, July 18)
Retrieved from blogs.egu.eu/geolog/tag/dent-de-morcles/

The next photo also demonstrates more folding, but there has been so much movement and changes due to uplift that the folded rocks have been tilted to their side. The darker rock on the left is the younger rock and the lighter colored rock on the right is older. (I only know that specifically because the details listed in the photo).

Alps reverse fault
Retrieved from
http://www.geosci.usyd.edu.au/users/prey/
Teaching/Geol-1002/HTML.Lect3

Folds are not the only type of deformation that were caused in the Alps by compressional stresses. Reverse and thrust faults can also be seen. This first photo shows a great example of a reverse fault in the Alps. You can see a massive wall on the top. That is the hanging wall. In a normal fault, that would have slipped down away from the foot wall, but since this is a reverse fault it was pushed up over the foot wall.

Glarus Thrust, Switzerland. (2017)
Retrieved from
upload.wikimedia.org/wikipedia/commons/thumb

On the left you can see an example of the Glarus Thrust in Switzerland. A thrust fault is a type of reverse fault that was formed at a very low and shallow angle. This low shallow fault is still considered a reverse fault because the hanging wall has been forced over the top of the foot wall and it just kept on going. That is why it has a flat/horizontal appearance like this.

Beltrando M et al. (2010). Retrieved from researchgate.net

This photo shows the boundaries of the different regions of the Alps. It may be a bit much to look at at first, but just notice that all these regions together makeup the complete mountain range, and all the different colors show the different episodes of orogeny.

Due to the many different periods of time and plates involved in the creation of the Alps, there are many different types of rock present. The western Alps have a higher concentration of granite, while the north and south areas contain more limestone. The center region stretching along the divide contains more gneiss than the other areas.