Tectonics and Structural Geology

brittle

Features from the Field: Shear Zones and Mylonites

Samuele Papeschi, Sandra McLaren and Hannah Davies January 25, 2021

Dextral, ductile shear zones crosscut foliated schist at Cap de Creus (Catalona, Spain). Photo © Jordi Carreras

The San Andreas Fault in California, the Alpine Fault in New Zealand, or the Main Frontal Thrust in the Himalayas are some of the most famous and largest fault zones that accommodate the relative displacement between two adjacent crustal blocks. Such faults, however, represent only the shallower expression of something much bigger: a crustal shear zone. In the first 10 kilometers or so of the crus ...[Read More]

Features from the field: Boudinage

Samuele Papeschi May 19, 2019

Boudins of amphibolite layers (metamorphosed basalts) that were stretched within quartz schists (Norway). Photo credits © Haakon Fossen.

The Features from the Field series is back! In our previous posts, we have shown how rocks can deform during ductile deformation, producing folds. Folds very commonly develop in rocks when rock layers are shortened by tectonic forces in a specific direction. On the other hand, when layers are extended, we develop boudins. Boudins – the term comes from the French word for ‘sausage’ – are frag ...[Read More]