Question

Consider these statements about Contact Metamorphism:Which are correct?

1. It occurs when rocks come into contact with hot magma or lava.
2. New materials are never added to the rock during this process.
3. Recrystallization occurs specifically under high temperatures.

• A. 3 only
• B. All
• C. 1 only
• D. 1, 3

Answer 1

Answer:

D. 1, 3

Contact Metamorphism Explained

• Contact metamorphism, also known as thermal metamorphism, occurs when pre-existing rocks (country rocks) are heated by the intrusion of magma or lava. This proximity to a heat source causes the minerals within the existing rocks to change.
• The primary driver of change in contact metamorphism is heat. The intense heat from the magma or lava bakes the surrounding rocks, leading to the formation of new minerals and textures.
• Recrystallization is a key process in contact metamorphism. Existing mineral grains grow larger, and new minerals may form, all while the rock remains essentially in a solid state. This recrystallization happens specifically under the influence of high temperatures.
• Chemical changes, while less significant than in regional metamorphism, can occur. Fluids released from the magma can sometimes interact with the country rock, introducing or removing certain chemical elements. However, the statement that new materials are *never* added is generally considered incorrect in a strict sense, though the addition of material is typically minimal compared to other metamorphic processes.
• The area affected by contact metamorphism is usually relatively small, forming a zone called a metamorphic aureole around the igneous intrusion.
• Examples of rocks formed by contact metamorphism include hornfels, often found around granite intrusions.