How were the Himalayan and Andes mountains formed?

The Himalayan range is one of the youngest mountain ranges on the planet and consists mostly of uplifted sedimentary and metamorphic rock. According to the modern theory of plate tectonics, its formation is a result of a continental collision or orogeny along the convergent boundary between the Indo-Australian Plate and the Eurasian Plate.
The Andes are the result of plate tectonics processes, caused by the subduction of oceanic crust beneath the South American plate. The main cause of the rise of the Andes is the compression of the western rim of the South American Plate due to the subduction of the Nazca Plate and the Antarctic Plate.