Question

The lineations which are formed due to shearing of rocks during asymmetric deformation of a rock mass are known as:

• A. intersection lineations
• B. crenulation lineations
• C. mineral lineations
• D. stretching lineations

Hint:

Stretching lineations = elongation direction due to shear.

Answer 1

The Correct Option is D

To identify the correct type of lineation formed during asymmetric shearing, we analyze structural geology concepts of deformation fabrics.

1. Understanding Lineations in Deformed Rocks:
Lineations are linear structural features that record the direction of tectonic forces during rock deformation.

2. Evaluating Each Option:
- Intersection lineations: Form by intersection of two planar surfaces (not shear-related)
- Crenulation lineations: Develop from folding of existing foliation (different mechanism)
- Mineral lineations: Result from mineral grain alignment (may occur without shearing)
- Stretching lineations: Correct answer - form parallel to shear direction during asymmetric deformation

3. Characteristics of Stretching Lineations:
- Develop in shear zones under non-coaxial strain
- Align parallel to the maximum stretching direction (X-axis of strain ellipsoid)
- Typically marked by elongated minerals or aggregates
- Fundamental kinematic indicators in ductile deformation

4. Formation Process:
1. Application of shear stress causes asymmetric deformation
2. Minerals/rock components stretch along flow direction
3. Progressive deformation enhances linear fabric
4. Preserves record of shear sense and magnitude

5. Field Significance:
- Critical for determining shear zone kinematics
- Used to reconstruct regional deformation patterns
- Helps quantify strain in tectonites
- Important in metamorphic core complex studies

Conclusion:
The lineations formed during asymmetric shearing are properly termed stretching lineations.

Final Answer:
The correct option is: stretching lineations.