The plunge of the fold is
- Aa line drawn parallel to the hinge line of a fold
- Bthe angle of inclination of the fold axis with the horizontal as measured in a vertical planeCorrect
- Ca line representing the intersection of the axial plane of a fold with any bed of the fold
- Da line drawn vertical to the hinge line of a fold
Solution
Concept
Plunge of a fold
Step-by-step solution
1. Plunge is the inclination of the fold axis (hinge line) from the horizontal, measured in a vertical plane.
Explanation
A fold whose axis is inclined is called a plunging fold; the angle of the axis with the horizontal is its plunge.
Why the other options are wrong
(a) describes the fold axis, (c) describes the hinge line, and (d) has no standard meaning.
Shortcut
Plunge = dip of the fold axis.
Common mistake
Choosing the hinge line.
Correct answer: B) the angle of inclination of the fold axis with the horizontal as measured in a vertical plane