Final answer:
A deep trench along the west coast of South America is forming due to the subduction of the Nazca Plate beneath the South American Plate, which also results in the uplift of the Andes Mountains and volcanic activity.
Step-by-step explanation:
The correct answer is option D. Along the west coast of South America, a deep trench is forming due to the subduction of the Nazca Plate beneath the South American Plate. This tectonic activity is characterized by the Nazca Plate being forced down into the mantle where it encounters high pressure and temperature, leading to melting and the recycling of its material into the mantle.
The process of subduction not only forms the deep trench but also the Andes Mountains due to the uplift of overlying crustal material. Additionally, the subduction-related volcanic activity along the margin gives rise to significant mountainous relief and igneous activity, contributing to the dynamic geological landscape of the region.
The correct answer is option a. Phase 1 - A rapid drop of the seafloor caused by the massive weight of the mountains. The load causes the lithosphere to bend, creating a concave basin in front of the uplifting mountains. It is characterized by a sudden change to deep-water sediments such as shales.