Which geological process is responsible for the formation of metamorphic rocks?

Metamorphic rocks are formed through a geological process known as metamorphism, which involves the alteration of existing rock types due to changes in temperature, pressure, and the presence of chemically active fluids. This process typically occurs deep within the Earth's crust, where high temperatures and pressures can transform igneous, sedimentary, or other metamorphic rocks into new metamorphic rock types.

During metamorphism, the mineral composition and texture of the rock can change significantly without the rock actually melting. For example, the heat can promote the recrystallization of minerals, while pressure can lead to foliation, where minerals are aligned in parallel layers. This process can result in the formation of various metamorphic rocks such as schist, gneiss, and marble, depending on the original rock and the conditions it is subjected to.

While other geological processes like weathering, lithification, and subduction play important roles in the rock cycle, they do not create metamorphic rocks directly. Weathering breaks down rocks at the Earth's surface, lithification refers to the process where sediments transform into sedimentary rocks, and subduction involves the movement of tectonic plates, which can contribute to the conditions under which metamorphism occurs but is not the process that forms the rocks