Question

Evaluate the following statements about Thermal Metamorphism:

1. It involves chemical changes and recrystallization.
2. Regional metamorphism is a subtype of thermal metamorphism.
3. Contact metamorphism is a subtype of thermal metamorphism.

• A. All of these
• B. 1 only
• C. 2 only
• D. 1, 3

Answer 1

Answer:

A. All of these

Thermal Metamorphism

Understanding the Process:

• Thermal metamorphism, also known as contact metamorphism, is a type of metamorphic rock formation.

• It occurs when rocks are exposed to high temperatures, primarily due to proximity to magma or lava intrusions.

• The heat causes changes in the rock's mineralogy and texture through processes like recrystallization and the formation of new minerals.

• While heat is the dominant factor, chemically active fluids released from the magma can also contribute to chemical changes.

Key Aspects and Subtypes:

• Statement 1 is correct: Thermal metamorphism inherently involves chemical changes (due to fluid interaction) and recrystallization (rearrangement of mineral grains to form larger, interlocking crystals).

• Statement 2 is incorrect: Regional metamorphism is a distinct type of metamorphism characterized by large-scale pressure and temperature changes over broad areas, often associated with tectonic plate collisions. It is not a subtype of thermal metamorphism.

• Statement 3 is correct: Contact metamorphism is essentially synonymous with thermal metamorphism. The term 'contact' emphasizes the process occurring at the boundary (contact) between the intruding magma and the surrounding country rock.