Which process leads to the formation of metamorphic rocks?

The process that leads to the formation of metamorphic rocks is metamorphism. This geological process involves the alteration of existing rocks—whether they are igneous, sedimentary, or even other metamorphic rocks—due to changes in temperature, pressure, and the presence of chemically active fluids. During metamorphism, the minerals within the rock can recrystallize, change chemically, or be realigned, resulting in a new rock that has distinct characteristics differing from the original rock.

Metamorphic rocks are typically formed deep within the Earth’s crust, where heat and pressure conditions are optimal for these transformations. This process distinguishes metamorphic rocks from other rock types that are formed through different mechanisms, such as the cooling of magma leading to igneous rocks or the compaction and cementation of sediments forming sedimentary rocks.

While weathering involves the breakdown of rocks at the Earth's surface, lithification refers to the processes that convert sediments into solid rock, and melting relates to the transformation of solid rock into magma. Therefore, these processes do not contribute directly to the formation of metamorphic rocks in the way that metamorphism does.