Most metamorphic rocks form deep within the Earth’s crust. This process occurs when existing rocks are subjected to high temperatures and pressures, causing them to change in structure and mineral composition without melting. The conditions necessary for metamorphism are typically found at depths of several kilometers below the Earth’s surface, where tectonic forces such as continental collisions and subduction zones create the required pressure and heat.
There are two main types of metamorphic environments: regional and contact. Regional metamorphism happens over large areas and is often associated with mountain-building processes. Contact metamorphism, on the other hand, occurs when rocks are heated by nearby magma or lava, usually in smaller, localized areas.
In summary, metamorphic rocks primarily form in the Earth’s crust under conditions of high pressure and temperature, often due to tectonic activity.