1. Magma Intrusion:
* Magma, molten rock beneath the Earth's surface, rises towards the surface.
* It may intrude into existing rock layers, forming bodies called plutons or dikes.
2. Heat Transfer:
* The magma is extremely hot (up to 1200°C).
* This heat is transferred to the surrounding rocks, causing them to recrystallize and change their mineral composition.
* The zone of rock affected by the heat is called the aureole.
3. Chemical Alteration:
* Magma also releases chemically active fluids (like water vapor and dissolved minerals).
* These fluids interact with the surrounding rocks, causing chemical reactions that change their mineral composition.
4. Recrystallization:
* As the surrounding rocks are heated, their minerals become unstable and rearrange themselves into new, more stable minerals.
* This process is called recrystallization.
5. Formation of Contact Metamorphic Rocks:
* The combination of heat and chemically active fluids results in the formation of new metamorphic rocks.
* These rocks have a different mineral composition and texture compared to the original rocks.
Characteristics of Contact Metamorphic Rocks:
* Fine-grained: The recrystallization process often creates fine-grained textures.
* Layered or banded: The interaction of fluids can create layers or bands of different minerals.
* High-grade minerals: The intense heat can create minerals that are only stable at high temperatures.
Examples of Contact Metamorphic Rocks:
* Hornfels: A hard, fine-grained rock formed from the contact metamorphism of shale or mudstone.
* Marble: Formed from the contact metamorphism of limestone.
* Skarn: A complex rock formed by the alteration of limestone or dolomite by magmatic fluids.
In summary, contact metamorphism is a process of rock transformation driven by the heat and fluids from a nearby magma intrusion. This results in the formation of new metamorphic rocks with distinct mineral compositions and textures.
