How are metamorphic rocks formed?
Metamorphic rocks are formed when existing rocks, called parent rocks, are subjected to intense heat and pressure. This can occur deep within the Earth's crust due to tectonic forces or near the Earth's surface due to contact with magma or hot fluids. The high temperatures cause the minerals in the parent rock to recrystallize and rearrange their structure, resulting in the formation of new minerals and a new rock with a different texture and composition. The pressure, on the other hand, causes the minerals to align and compact, often forming distinct layers or banding in the rock. This process of transformation, known as metamorphism, can occur over millions of years.
How are metamorphic rocks related to plate tectonics?
Metamorphic rocks and plate tectonics are closely related because the majority of metamorphic processes occur due to the movement and collision of tectonic plates. Plate tectonics is the theory that describes the movement and interaction of large pieces of Earth's lithosphere.
When tectonic plates collide or undergo subduction (one plate being pushed beneath another), immense pressure and heat are generated. This process causes the rocks in the crust to undergo metamorphism. The high temperatures and pressures associated with plate tectonics can lead to the recrystallization of minerals and the formation of new minerals in the parent rocks, resulting in the creation of metamorphic rocks.
For example, during a collision between two continental plates, immense pressure and heat can be generated, causing the rocks on both plates to be subjected to metamorphism. This process can produce regional metamorphic rocks, such as gneiss or schist, which are characterized by distinct layering or banding.
Similarly, subduction zones, where one tectonic plate is forced beneath another, can create conditions for high-pressure and low-temperature metamorphism. This can result in the formation of metamorphic rocks like blueschist or eclogite.
In summary, plate tectonics provide the driving forces of heat, pressure, and deformation that are essential for the formation of metamorphic rocks.