1. Heat:
* Contact Metamorphism: This occurs when rocks come into contact with a heat source, like an intrusion of magma or lava. The heat causes minerals to recrystallize and change their texture.
* Regional Metamorphism: This happens over large areas due to the pressure and heat associated with tectonic plate collisions. The heat comes from the Earth's interior.
2. Pressure:
* Confining Pressure: This is the pressure exerted by the weight of overlying rocks.
* Differential Pressure: This occurs when pressure is unevenly applied, like during mountain building, causing rocks to deform and recrystallize.
3. Chemically Active Fluids:
* Hot Water: Water heated by the Earth's interior can react with minerals, dissolving some and depositing others, resulting in changes to the rock's composition.
* Other Fluids: Gases like carbon dioxide and sulfur dioxide can also interact with minerals during metamorphism.
Key Processes Involved:
* Recrystallization: Existing minerals change size, shape, and orientation.
* Neocrystallization: New minerals form from the existing ones.
* Texture Changes: Rocks can become more foliated (layered) or develop other textures.
* Chemical Changes: The overall chemical composition of the rock may change due to reactions with fluids.
Examples of Metamorphic Rocks:
* Marble: Formed from limestone by recrystallization of calcite.
* Slate: Formed from shale by the alignment of clay minerals under pressure.
* Gneiss: Formed from granite or other rocks by intense heat and pressure.
* Schist: Characterized by a distinct foliation created by aligned platy minerals.
In summary, metamorphic rocks form when existing rocks undergo transformation under conditions of heat, pressure, and/or chemically active fluids. These processes alter the mineral composition, texture, and sometimes even the chemical composition of the original rock.
