The Himalayas were formed by the shifting of continental plates beneath the Earth's surface. As two plates hit each other -- called continent-continent collision -- the pressure forced the plates upwards. The Himalayas continue to increase in height slowly every year.
The majority of rocks found in the Himalayas are sedimentary rocks including sandstones, shale and mudstone. This composition proves to geologists that the Himalaya mountains were originally underwater. The rocks show horizontal layers caused by the hardening of soil deposits on top of previous layers of rocks. They also have diagonal folds caused by the vertical push of the plates that created the mountains.
I-type granites are rocks formed by melting of igneous (lava) rocks. They contain biotite and hornblende minerals and don't have peraluminous or peraalkine minerals, which are typical of other types of granite. I-type granites in the Himalayas were created by continent-continent collisions.
S-type granites are caused by the melting of sedimentary or metasedimentary rocks (rather than the lava rocks of I-type granites). These have peraluminous minerals such as muscovite or corundum. They are generally considered to be orogenic granites because they were formed through continent-continent collisions.
