Question

Which one of the following is the typical product of ductile deformation?

• A. Gouge
• B. Breccia
• C. Cataclasite
• D. Mylonite

Hint:

Mylonite is the result of ductile deformation. It forms under high pressure and temperature, leading to fine-grained textures due to recrystallization and dynamic shear.

Answer 1

The Correct Option is D

Ductile deformation occurs when rocks are subjected to high pressure and temperature over long periods of time, causing them to bend and stretch without breaking. This type of deformation typically happens in deeper parts of the Earth’s crust where the conditions of temperature and pressure are conducive to plastic deformation.
Among the options listed:
- Gouge is a type of rock formed in fault zones through the grinding and pulverization of rocks due to friction. It is often associated with brittle deformation, not ductile deformation.
- Breccia is formed by the accumulation of broken fragments of rocks that have been transported and deposited, typically by a more sudden, catastrophic event, like a landslide or an explosive eruption. It is associated with brittle deformation.
- Cataclasite is a type of rock that forms due to the grinding of rocks along fault zones, generally associated with brittle deformation. It is also characterized by the presence of fractures and angular clasts.
- Mylonite, on the other hand, is the typical product of ductile deformation. It forms under high-pressure and high-temperature conditions, typically along deep-seated fault zones. Mylonite is characterized by a fine-grained texture and the presence of foliation due to the dynamic recrystallization of minerals under shear stress.
Step 1: Understanding Ductile Deformation
Ductile deformation occurs when a material (like rock) is subjected to stress that causes it to flow and bend, rather than break. This is a high-temperature, high-pressure process that happens deep within the Earth where rocks experience intense heat and pressure. Unlike brittle deformation, which leads to fractures and faults, ductile deformation results in the smooth, continuous flow of materials.
Step 2: Analyzing the Types of Rocks
- Gouge: It is typically a product of frictional and brittle failure in fault zones, not ductile deformation.
- Breccia: This is a sedimentary rock consisting of angular fragments, often formed by physical weathering or impact events.
- Cataclasite: Similar to gouge, it forms from mechanical processes like faulting, often under conditions that involve brittle deformation.
- Mylonite: This rock forms under conditions of ductile shear deformation, typically along deep-seated fault zones where the rocks have been subjected to intense shearing stress.
Therefore, the correct answer is (D) Mylonite.