Week 5 - Converging Plates - Taylor Mills

Recently, my best friend and I decided to visit the Andes Mountain Range located in western South America.  Luckily, she also took a geology class so we were both able to recognize that these mountains were formed as a result of converging plates.  More specifically, an oceanic and continental plate collision.  We discussed that in such a collision, and as depicted in Figure 1 below, the thinner, heavier, and denser oceanic plate (the Nazca plate) slips beneath and is overridden by the thicker, less dense, and more buoyant continental plate or continent (the South American plate).  This process is called subduction and a deep ocean trench often forms as a result.  In this case, the Peru-Chile (or Atacama) Trench was formed and reaches an incredible depth below sea level.  Also, a continental volcanic arc was formed, batholiths were emplaced, and its mountainous topography began to take shape along South America's margin.  As a result of continued subduction, friction, heat, and pressure, the Andes Mountains are now home to an andesitic and rhyolitic volcanic chain, as well as seismic activity.  Though, I was able to explain to my friend that the process of Andean orogeny was responsible for the rise of the mountains and the production of its mountain range.

Figure 1. Andes Formation Process (Gamesby, 2015).

A prime example of compressive forces, my friend and I both recognized the domination of thrust faults in the mountain range as illustrated in Figure 2.  And, due to these compressive forces, folding dominates the Andes' structural style as a result of ductile deformation of rocks.  As I informed my friend, as the plates collided, folding occurred due to the said compression and squeezing of the rock strata along the convergent plate boundary.  Then, my friend and I examined the mountain range's rock contents which we both find very interesting and exciting.  We observed quartzite, shale, and marble that were actually once sandstone, siltstone, and limestone until they transformed as a result of sediment erosion and pressure and heat metamorphosis.  Our trip was very exciting and even though she already understood most of the mountain range's geology, it was nice to explore together and teach her a few things :)

Figure 2. Thrust Fault (Allmendinger, n.d.).