Metamorphic rocks arise from the transformation of existing rock to new types of rock, in response to changes in temperature, pressure, and chemical environment. The original rock (known as the "parent rock" or "protolith") can be of igneous, sedimentary, or even other metamorphic origin. Being in these conditions over millions of years will physically or chemically modify the rocks (or both). In this article, we will learn about Metamorphic Rocks which is part of Geomorphology, an integral part of the Geography Syllabus.

What are Metamorphic Rocks?

• The term "metamorphic" refers to a change in form.
• When rocks are subjected to high heat, high pressure, hot mineral-rich fluids, or, more typically, some combination of these variables, metamorphic rocks develop.
• Such conditions can be encountered deep within the Earth or where tectonic plates collide.
• The minerals and texture of these rocks help to identify them.
• New minerals grow during metamorphism, having different sizes, shapes, and orientations than the initial minerals.
• The chemical composition of the original rock may also alter as fluids moving through the rocks carry away some elements and add others.
• Metamorphosis happens when tectonic processes move rocks to lower levels or when molten magma rising through the crust comes into touch with crustal rocks.
• Metamorphism does not melt rocks but rather converts them into denser, more compact rocks.
• New minerals are formed either by mineral component rearrangement or through interactions with fluids that enter the rocks.
• Even previously metamorphosed rocks can undergo changes due to pressure or temperature.
• Squished, smeared out, and folded metamorphic rocks are common.
• Some rocks' grains or minerals are arranged in layers or lines during metamorphism. Foliation or lineation is the term for this type of layout.
• Minerals or materials from several groups are sometimes placed in alternating thin and thick layers. Banding is a term for construction like this.
• Metamorphic rocks include gneissic, slate, schist, marble, quartzite, and others.

Categories of Metamorphism

Dynamic Metamorphism

• Dynamic metamorphic rocks are limited to small areas along faults or thrusts.
• High shear stress, high pressure, high strain, high fluid partial pressure, and changeable temperature are all factors in dynamic metamorphism. Water plays an important part in many situations.
• Breaking and crushing cause mechanical disruption and reorganization of the original minerals within rocks, but no substantial chemical changes occur.
• As the depth from the surface increases, so does the surrounding pressure and temperature, resulting in a variety of rock types formed by dynamic metamorphism.

Thermal Metamorphism

• Thermal Metamorphism is the process of changing from one state to another.
• Thermal metamorphism is the change in form or re-crystallization of minerals in sedimentary and igneous rocks caused by high temperatures.
• The peak of Mount Everest, which is made up of metamorphosed limestone, was formed by a magmatic intrusion that caused thermal metamorphism.
• Sandstone becomes quartzite and limestone becomes marble as a result of thermal metamorphism.

i) Contact Metamorphism

• Rocks come into contact with hot magma and lava and the rock components recrystallize at high temperatures.
• New materials frequently formed from magma or lava is added to the rocks.
• Contact Metamorphism does not involve the squashing of rock layers, so these rocks do not have foliated textures like regionally metamorphosed rocks.

ii) Regional Metamorphism

• Most metamorphic rocks occur in fold mountain belts or cratonic areas.
• Such rocks cover large areas of the Earth's crust and are therefore termed regional metamorphic rocks.
• Recrystallization of rocks occurs as a result of deformations generated by tectonic breaking combined with high pressure and temperature.
• As a result of tectonic shearing, rocks undergo reorganization due to high heat/pressure.

Metamorphic Rocks

Types of metamorphism

Classification of Metamorphic Rocks on the Basis of Metamorphism

Foliated Rocks

• Foliated rocks are formed under high equal pressure and have parallel bands of grains.
• Foliation occurs when the flat or elongate minerals within a rock are pressed together and aligned.
• These rocks form platy or sheet-like structure that reflects the direction of the applied pressure.
• Example – Granite gneiss, biotite schist, etc.

Non-foliated Rocks

• Non-foliated rocks do not have any arrangement or bands of grain and are formed under high temperatures.
• They lack foliated texture because they often lack platy minerals such as micas.
• They commonly result from contact or regional metamorphism.
• Example – Marble, quartzite, greenstone, hornfels, and anthracite.

Foliated and nonfoliated metamorphic rocks

Significance of Metamorphic Rocks

• The most prevalent metamorphic rocks are quartzite and marble.
• Quartzite is frequently utilized as dimension stone in the form of slabs for flooring, walls, and stair treads.
• Quartzite makes up around 6% of crushed stone, which is largely utilized for road aggregate.
• They are commonly used in construction and artwork.
• Statues and decorative items such as vases are made of marble.
• Marble is also used for building construction and as a medium for sculpture.
• Marble powder is also found in toothpaste, plastics, and paper.

Conclusion

Metamorphic rocks are formed when sedimentary or igneous rocks move deep inside the earth and come into contact with the high temperature and pressure of overlying material. Metamorphic rocks are formed as a result of tectonic events such as continental collisions, which can result in pressure and temperature changes. Magma intrusion on the surface of the earth is another key factor in metamorphic transition.