What process leads to the formation of metamorphic rocks?

The formation of metamorphic rocks occurs primarily due to the application of extreme pressures and heat on existing rocks. This process alters the mineral composition, texture, and structure of the original rock without melting it, which differentiates it from igneous rocks that form from the cooling of magma.

Specifically, when existing rocks, whether they are sedimentary, igneous, or other metamorphic rocks, are subjected to high temperatures and pressures, the minerals within them can recrystallize or chemically react, leading to new minerals forming. This process results in features such as foliation or banding, depending on the intensity and directionality of the pressure applied.

Other processes listed, such as the cooling of magma, involve igneous processes where molten rock solidifies to form new rock. Layering of sediments is related to sedimentary rock formation, where particles accumulate and compact over time. Weathering and erosion of limestone, while contributing to sediment formation and landscape alteration, do not directly lead to metamorphic rock formation. Thus, the conditions of pressure and temperature are uniquely significant in the metamorphosis of existing rocks into metamorphic ones.