1. Baking and Thermal Metamorphism:
* The heat from the molten dike will bake the surrounding rock, causing changes in its mineralogy and texture. This process is called contact metamorphism.
* The intensity of metamorphism depends on the temperature of the dike, the duration of contact, and the composition of the original rock.
* Common metamorphic changes:
* Recrystallization: Existing minerals may recrystallize into new, more stable minerals.
* Formation of new minerals: New minerals may form from the original minerals due to the heat and pressure.
* Changes in texture: The rock may become more compact and may develop a foliated texture (layers) if the pressure is high enough.
2. Changes in Chemical Composition:
* The molten material from the dike can react with the surrounding rock, altering its chemical composition.
* This can result in the formation of new minerals or the enrichment of existing minerals.
* The chemical changes can be significant, particularly near the contact zone.
3. Formation of Xenoliths:
* If the surrounding rock is resistant to melting, it may be incorporated into the molten dike as fragments called xenoliths.
* These xenoliths are like little pieces of the original rock that are trapped within the dike. They can provide valuable information about the composition and history of the surrounding rock.
4. Formation of Contact Aureoles:
* The zone of altered rock surrounding the dike is called a contact aureole.
* The aureole can be quite large, depending on the size and temperature of the dike.
* The metamorphic changes in the aureole decrease with distance from the dike.
5. Changes in Strength and Durability:
* The baked and metamorphosed rock near the dike may become stronger and more durable than the original rock.
* This is because the metamorphic processes can create new minerals that are more resistant to weathering and erosion.
Examples:
* In areas with volcanic activity, you can often find contact aureoles around dikes that have intruded into sedimentary or metamorphic rocks.
* The baking and changes in the surrounding rock can result in the formation of unique mineral assemblages and textures, which can be studied by geologists to understand the history of the intrusion.
Overall, the interaction between a dike and the surrounding rock is a fascinating process that can result in significant changes in the physical and chemical properties of the rock.
