Diorite results from the partial melting of a mafic rock above a subduction zone. It is found in volcanic arcs, and in cordilleran mountain building, such as in the Andes Mountains.
Diorite is formed <u><em>deep within the Earth's crust from cooling magma that never made it to the surface</em></u>. It usually occurs as quite small intrusions often associated with larger intrusions like granite. Slow cooling produces the large crystals.
