Which one of the following statements is correct for Class 1B (Paralle...
Overview of Class 1B (Parallel) Folds
Class 1B folds, also known as parallel folds, are a type of fold structure commonly observed in rock formations. These folds are characterized by their parallel limbs and hinge lines. In this type of fold, the axial planes are parallel to each other, and the dip isogons (lines connecting points of equal dip on the folded surface) are either parallel or convergent.
Statement Explanation
The correct statement for Class 1B (Parallel) folds is option 'D', which states that the dip isogons are convergent. Let's understand why this statement is correct.
Dip Isogons in Class 1B Folds
Dip isogons are lines that connect points of equal dip (the angle at which a rock layer is inclined from the horizontal plane) on a folded surface. In Class 1B (Parallel) folds, the dip isogons can either be parallel or convergent.
Parallel Dip Isogons
Parallel dip isogons occur when the dip of the rock layers remains constant along the folded surface. This means that the inclination of the rock layers does not change as they are folded. However, this is not a characteristic of Class 1B folds.
Convergent Dip Isogons
Convergent dip isogons occur when the dip of the rock layers changes as they are folded. In Class 1B (Parallel) folds, the dip isogons are convergent, meaning that the inclination of the rock layers changes towards the hinge line of the fold. This convergence of the dip isogons is a key characteristic of Class 1B folds.
Conclusion
In conclusion, the correct statement for Class 1B (Parallel) folds is that the dip isogons are convergent. This means that the inclination of the rock layers changes towards the hinge line of the fold. Understanding the characteristics of different fold classes is important in geology and structural geology, as it helps in interpreting the deformation history of rock formations.