- Two limbs of a vertical chevron fold strike S70E and N55E.
- The value of the interlimb angle of the fold is to be determined.


A vertical chevron fold is a type of geological fold where the limbs of the fold are inclined at an angle to the horizontal plane. The strike of a fold refers to the direction of the line formed by the intersection of the fold's axial plane with the horizontal plane. The interlimb angle of a fold is the angle between the two limbs of the fold.


To determine the interlimb angle of the fold, we need to calculate the angle between the two limbs based on their strike directions.

Step 1: Determine the dip direction of each limb
- The strike of the first limb is S70E, which means it strikes in a direction 70 degrees east of south.
- The strike of the second limb is N55E, which means it strikes in a direction 55 degrees east of north.

Step 2: Calculate the dip direction of each limb
- The dip direction of a limb is always perpendicular to its strike direction.
- The dip direction of the first limb would be perpendicular to S70E, which is S20W (90 degrees clockwise from the strike).
- The dip direction of the second limb would be perpendicular to N55E, which is N35W (90 degrees clockwise from the strike).

Step 3: Calculate the interlimb angle
- The interlimb angle is the angle between the dip directions of the two limbs.
- The dip direction of the first limb is S20W.
- The dip direction of the second limb is N35W.
- The angle between S20W and N35W can be calculated as follows:
- Subtract the smaller angle from the larger angle: 35 - 20 = 15.
- Since the two dip directions are in opposite quadrants, add 180 degrees to the result: 15 + 180 = 195.
- The interlimb angle is the supplementary angle to 195 degrees, which is 180 - 195 = -15 degrees.
- However, fold angles are measured in the range of 0 to 180 degrees, so we need to convert the negative angle to a positive angle.
- Adding 360 degrees to -15 gives us 345 degrees.
- The interlimb angle of the fold is 345 degrees.


The correct answer is '55' degrees.