The Process of Metamorphism
1. Heat: The most important factor in metamorphism is heat. Deep within the Earth, temperatures increase with depth. As sedimentary rocks are buried deeper, they are subjected to higher temperatures. This heat provides the energy to cause changes within the rock's mineral structure.
2. Pressure: The weight of overlying rocks creates intense pressure on buried sedimentary layers. This pressure can cause the minerals in the rock to recrystallize and align themselves in a more organized manner.
3. Fluids: Hot, chemically active fluids often circulate through rocks during metamorphism. These fluids can react with the minerals in the rock, altering their composition and causing new minerals to form.
The Transformation
* Recrystallization: The existing minerals in the sedimentary rock are rearranged and recrystallized. This often results in larger crystals and a more tightly packed, denser texture.
* New Mineral Formation: The intense heat and pressure, along with the influence of fluids, can cause new minerals to form. These new minerals may be different from the original minerals in the sedimentary rock.
* Texture Changes: The original texture of the sedimentary rock, such as layering or fossils, can be changed or destroyed during metamorphism. Metamorphic rocks often have a characteristic foliation, a layered appearance, or other textures.
Types of Metamorphism
* Contact Metamorphism: Occurs when hot magma or lava intrudes into existing rocks. The heat from the magma causes the surrounding rocks to undergo metamorphism. This is a localized process.
* Regional Metamorphism: Occurs over large areas, often associated with mountain building. The intense pressure and heat associated with the collision of tectonic plates cause widespread metamorphism.
Examples of Metamorphic Rocks:
* Slate: A fine-grained metamorphic rock formed from shale.
* Marble: A metamorphic rock formed from limestone.
* Gneiss: A coarse-grained metamorphic rock with a banded appearance.
* Schist: A metamorphic rock with a foliated texture.
Key Points:
* Metamorphism doesn't melt the rock; it changes the existing minerals and their arrangement.
* The type of metamorphic rock that forms depends on the original sedimentary rock, the intensity of heat and pressure, and the presence of fluids.
* Metamorphic rocks provide valuable clues about the geological history of an area.
