What are the main forces governing the formation of Metamorphic rock?

Metamorphic rock arises from the transformation of existing rock into new types of rock in a process called metamorphosis. It makes up a large part of the Earth's crust and 12% of the Earth’s land surface.
The main forces governing the formation of metamorphic rocks are both Heat and pressure. These rocks are subjected to high heat, high pressure and mineral-rich fluids.