ASBOG Structural Geology and Tectonics 2 — Questions and Answers
Question 1: Which type of fold has its oldest rocks in the core?
- Syncline
- Anticline (Correct answer)
- Monocline
- Homocline
Correct answer: Anticline
Anticlines arch upward with the oldest rocks exposed at their core due to erosion.
Question 2: A thrust fault is characterized by which dip angle range?
- Greater than 45°
- Exactly 90°
- Less than 45° (Correct answer)
- Between 45° and 60°
Correct answer: Less than 45°
Thrust faults dip at less than 45° and involve the hanging wall moving up relative to the footwall under compressional stress.
Question 3: The Wilson Cycle describes the repeated opening and closing of which geological feature?
- Rift valleys
- Ocean basins (Correct answer)
- Mountain belts
- Volcanic arcs
Correct answer: Ocean basins
The Wilson Cycle describes the cyclical opening and closing of ocean basins driven by plate tectonics.
Question 4: What is the term for the angle between a fault plane and the horizontal?
- Strike
- Dip (Correct answer)
- Rake
- Pitch
Correct answer: Dip
Dip is the angle measured downward from horizontal to the fault or bedding plane.
Question 5: Boudinage structures form when a competent layer is subjected to what type of stress?
- Compression perpendicular to layering
- Extension parallel to layering (Correct answer)
- Simple shear
- Isotropic compression
Correct answer: Extension parallel to layering
Boudinage forms when a rigid layer is stretched and necked into sausage-shaped segments under extensional stress parallel to layering.
Question 6: Which plate boundary type is associated with transform faults?
- Convergent boundary
- Divergent boundary
- Conservative boundary (Correct answer)
- Subduction zone
Correct answer: Conservative boundary
Transform (conservative) boundaries involve plates sliding horizontally past each other along transform faults with no creation or destruction of crust.
Question 7: A conjugate fault set consists of two fault orientations that indicate what about the principal stress axes?
- The maximum stress bisects the acute angle between faults (Correct answer)
- The minimum stress bisects the acute angle between faults
- Stresses are equal in all directions
- The intermediate stress is vertical
Correct answer: The maximum stress bisects the acute angle between faults
In a conjugate fault set, the maximum compressive stress (σ1) bisects the acute angle between the two fault planes.
ASBOG Structural Geology and Tectonics 2
Which type of fold has its oldest rocks in the core?