Question

In which of the following shear zones, the physical break cannot be noticed?

• A. brittle shear zone
• B. ductile shear zone
• C. semi brittle shear zone
• D. ductile-brittle shear zone

Hint:

Ductile deformation = flow without fracture = no visible physical break.

Answer 1

The Correct Option is B

To determine in which shear zone the physical break cannot be noticed, we analyze the characteristics of different shear zone types.

1. Understanding Shear Zone Types:
Shear zones are zones of concentrated deformation that occur at various crustal levels with different rheological behaviors.

2. Evaluating Each Option:
- Brittle shear zone: Shows clear physical breaks (faults, fractures)
- Ductile shear zone: Correct answer - deformation occurs without visible breaks
- Semi-brittle shear zone: Shows some discontinuous fractures
- Ductile-brittle shear zone: Transitional with partial breaks

3. Characteristics of Ductile Shear Zones:
- Deformation occurs at higher temperatures/pressures
- Rock flows plastically without loss of cohesion
- Shows gradual strain gradients
- Features include mylonites, stretching lineations
- No discrete fracture surfaces visible

4. Why Other Zones Show Breaks:
- Brittle zones form at shallow depths with fracturing
- Semi-brittle shows both plastic flow and fractures
- Ductile-brittle transitional shows some fractures

5. Field Identification:
Ductile shear zones are recognized by:
- Progressive grain size reduction
- Development of foliation and lineation
- Lack of discrete slip surfaces
- Strain localization without visible breaks

Conclusion:
The ductile shear zone is the type where physical breaks cannot be noticed.

Final Answer:
The correct option is: ductile shear zone.