Question

Which one of the following statements is correct for Class 1B (Parallel) folds?

• A. Orthogonal thickness at hinge>that at limb
• B. Axial planar thickness at hinge = that at limb
• C. Dip isogons are parallel
• D. Dip isogons are convergent

Hint:

In structural geology, Class 1B (parallel) folds are characterized by convergent dip isogons, which reflect the symmetrical nature of these folds.

Answer 1

The Correct Option is D

Step 1: Understanding the question.
Class 1B folds, or parallel folds, are characterized by parallelism in their structure. The question specifically asks about the characteristics of their isogons.
Step 2: Analyzing the options.
(A) Orthogonal thickness at hinge>that at limb: This is incorrect as it does not apply to Class 1B folds.
(B) Axial planar thickness at hinge = that at limb: This statement does not correctly describe Class 1B folds.
(C) Dip isogons are parallel: This is incorrect. In parallel folds, the dip isogons are typically convergent, not parallel.
(D) Dip isogons are convergent: Correct — In Class 1B (parallel) folds, the dip isogons are convergent, meaning they converge towards the fold axis.
Step 3: Conclusion.
The correct answer is (D) Dip isogons are convergent, as this is the defining characteristic of Class 1B folds.