9  Exam Preparation

These questions require synthesizing knowledge across multiple modules:

9.1 Scenario 1: Himalayan Orogen

You are studying the Himalayan mountain belt. Using your knowledge of plate tectonics, stress, strain, and structures:

Questions:

1. Can you explain why the Himalayas formed (plate tectonic setting)?
2. What is the orientation of principal stresses in this region?
3. What types of structures would you expect to find? (Consider contractional structures, escape tectonics)
4. Why do we see normal faults in Tibet despite ongoing convergence?
5. How does the India-Asia collision illustrate the difference between oceanic and continental convergence?
6. What role do conjugate strike-slip faults play in accommodating deformation?

9.2 Scenario 2: East African Rift

You are mapping in the East African Rift System:

Questions:

1. What type of plate boundary is this (or is it even a plate boundary yet)?
2. What is the stress regime and orientation of principal stresses?
3. What structures would you expect to map? (Normal faults, graben, etc.)
4. Is this active or passive rifting? How would you tell?
5. What might happen if rifting continues?
6. How does volcanism relate to the rifting process?
7. Why are there sedimentary basins forming in the rift?

9.3 Scenario 3: San Andreas Fault System

You are investigating the San Andreas Fault:

Questions:

1. What type of plate boundary is this?
2. What is the relative motion of the Pacific and North American plates?
3. Why is the fault slightly transpressional rather than pure strike-slip?
4. What structures would you expect to find along the fault? (Pull-apart basins, pop-ups, etc.)
5. How can you determine the total offset on the fault?
6. What controls earthquake distribution along the fault?
7. Why do some segments creep while others are locked?
8. How does the stick-slip behavior relate to the earthquake cycle?

9.4 Scenario 4: North Sea Basin

You are exploring for hydrocarbons in the North Sea:

Questions:

1. What tectonic setting formed this basin (extensional)?
2. What structures control the geometry of the basin? (Normal faults, half-graben, etc.)
3. Where would you drill for oil (structural traps)?
4. How does the Gullfaks Field domino system work?
5. What is the relationship between extension, subsidence, and sedimentation?
6. How do growth faults form and what do they tell you about syn-rift sedimentation?

9.5 Scenario 5: Fold and Thrust Belt

You are mapping in a fold-and-thrust belt:

Questions:

1. What is the tectonic setting (convergent, continent-continent or arc-continent)?
2. What is the orientation of principal stresses?
3. Can you identify the transport direction from fold vergence and thrust sense?
4. How do you distinguish thick-skinned from thin-skinned tectonics?
5. What is the geometry of ramps and flats and why do they form?
6. How do duplexes develop?
7. What role does a weak décollement layer play?
8. How are folds related to thrusts (fault-bend, fault-propagation, detachment folds)?
9. What does axial planar cleavage tell you?
10. How would you predict structure at depth?

9.6 Scenario 6: Subduction Zone

You are studying a subduction zone:

Questions:

1. Why is the subducting plate bending and what stresses result?
2. Why do we see normal faulting at the outer rise?
3. What is the megathrust and what type of earthquakes occur there?
4. How do you distinguish megathrust earthquakes from outer rise earthquakes from upper plate earthquakes?
5. What is slab rollback and how does it differ from plate convergence rate?
6. How does the upper plate respond to coupling with the downgoing plate?
7. What happens when a megathrust earthquake occurs (coseismic deformation)?
8. What structures form in the accretionary wedge?
9. Why is the geometry of the wedge like it is (critical taper)?

9.7 Scenario 7: Shear Zone

You find a mylonitic shear zone in the field:

Questions:

1. What deformation mechanisms produced the mylonite?
2. How can you determine the sense of shear? (S-C fabrics, porphyroclasts, etc.)
3. What does the degree of recrystallization tell you about temperature?
4. Is this simple shear or general shear? How would you determine the vorticity?
5. What is the relationship between the shear zone and the regional stress field?
6. How does strain vary across the shear zone (strain profile)?
7. What metamorphic conditions existed during deformation?

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10 Common Mistakes and Misconceptions

Be aware of these common pitfalls:

10.1 Plate Tectonics

Common Mistakes

✘ Mistake: Thinking plates are just the crust

✔ Correct: Plates are lithosphere (crust + upper mantle)

✘ Mistake: Confusing plate motion with trench motion

✔ Correct: Slab rollback means these can be different

✘ Mistake: Thinking all convergent boundaries produce the same structures

✔ Correct: Ocean-ocean, ocean-continent, continent-continent are very different

10.2 Stress and Strain

Common Mistakes

✘ Mistake: Confusing stress and strain

✔ Correct: Stress is force/area (cause), strain is deformation (effect)

✘ Mistake: Thinking high stress always means high strain

✔ Correct: Rheology controls the relationship; strong rocks can support high stress with little strain

✘ Mistake: Confusing principal stress directions with fault slip directions

✔ Correct: Faults form at ~30° to \(\sigma_1\), not parallel to it

10.3 Faults

Common Mistakes

✘ Mistake: Thinking all faults in convergent settings are thrusts

✔ Correct: Can have normal faults (outer rise, extensional collapse)

✘ Mistake: Confusing stratigraphic separation with true slip

✔ Correct: Need 3D analysis to determine actual displacement

✘ Mistake: Thinking friction coefficient varies greatly between rock types

✔ Correct: Byerlee’s Law shows it’s remarkably constant (\(\mu \approx 0.6\text{-}0.85\))

10.4 Folds

Common Mistakes

✘ Mistake: Using anticline/syncline for folds with unknown age relationships

✔ Correct: Use antiform/synform unless you know which rocks are older

✘ Mistake: Thinking axial plane cleavage is always vertical

✔ Correct: It’s parallel to the axial surface, which can have any orientation

✘ Mistake: Confusing fold axis with axial surface

✔ Correct: Axis is a line, surface is a plane

10.5 Rheology

Common Mistakes

✘ Mistake: Thinking temperature and pressure have the same effect

✔ Correct: Temperature promotes ductile behavior, confining pressure promotes brittle

✘ Mistake: Thinking brittle-ductile transition is at a fixed depth

✔ Correct: Depends on rock type, strain rate, and thermal gradient

✘ Mistake: Confusing elastic with brittle

✔ Correct: Elastic is reversible deformation; brittle is fracturing (irreversible)

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11 Exam Preparation Strategies

11.1 Topic Integration

When studying, don’t think of modules in isolation:

1. Connect stress to structures:
   • Normal faulting regime → \(\sigma_1\) vertical → normal faults, graben, rifts
2. Link plate boundaries to stress regimes:
   • Divergent → extensional → normal faults
   • Convergent → compressional → thrusts and folds
   • Transform → wrench → strike-slip
3. Connect deformation style to conditions:
   • Shallow, cold, fast → brittle → fractures, faults
   • Deep, hot, slow → ductile → folds, shear zones

11.2 Practice Problems

Work through problems that require:

• Calculations (stress, strain, fault angles)
• Graphical analysis (Mohr circles, stereonets)
• Map interpretation
• Cross-section construction
• Structure identification from photos

11.3 Real-World Examples

For each major structure type, know at least one real example:

• Can you locate it?
• Describe its characteristics?
• Explain its tectonic setting?
• Relate it to theory?

11.4 Terminology Precision

• Be precise with terms (anticline vs. antiform, stress vs. strain)
• Use proper notation (\(\sigma_1\), \(\varepsilon\), \(\tau\), \(\mu\))
• Know units (Pa for stress, \(s^{-1}\) for strain rate)

11.5 Conceptual Understanding

Don’t just memorize - understand:

• WHY faults form at 30° to \(\sigma_1\) (minimize work)
• WHY oceanic crust is uniform thickness (spreading center structure)
• WHY Tibet extends despite convergence (gravitational collapse)

11.6 Visual Learning

• Study photographs and diagrams
• Draw sketches of structures
• Visualize in 3D
• Practice stereographic projections

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12 Final Checklist

Before your exam, ensure you can:

12.1 Global Tectonics

• Describe Earth’s layered structure with correct thicknesses
• Explain plate motions and measurement methods
• Identify and describe all three plate boundary types
• Explain triple junctions and stability
• Contrast oceanic and continental deformation
• Describe the Himalayan collision as a detailed example
• Explain subduction zone complexity (rollback, bending, outer rise)

12.2 Structural Geology Regimes

• Predict structures for each tectonic regime
• Describe contractional structures (thrusts, folds, nappes, duplexes)
• Describe extensional structures (normal faults, graben, rifts)
• Describe strike-slip structures (transforms, flower structures, pull-aparts)
• Explain orogenic wedge geometry and models
• Distinguish pure shear vs. simple shear rift models

12.3 Stress, Strain, and Rheology

• Define and distinguish stress and strain
• Describe the stress and strain tensors
• Explain principal stresses and principal strains
• Identify tectonic regimes from stress orientations
• Use Mohr circle for stress analysis
• Apply Mohr-Coulomb failure criterion
• Calculate extension, elongation, beta factor
• Explain elastic, viscous, and plastic rheology
• Describe deformation mechanisms (brittle and ductile)
• Explain the brittle-ductile transition

12.4 Brittle Deformation

• Describe fracture modes (I, II, III)
• Explain Griffith crack theory
• Apply failure criteria (Mohr-Coulomb, Byerlee’s Law)
• Explain effective stress and pore pressure effects
• Describe joint characteristics and origins
• Interpret plumose structures
• Classify faults by slip and dip
• Describe fault zone anatomy
• Identify kinematic indicators
• Explain the earthquake cycle

12.5 Ductile Deformation

• Label fold elements
• Classify folds by all schemes (tightness, orientation, shape, thickness)
• Distinguish antiform/synform from anticline/syncline
• Explain folding mechanisms (buckling, bending, passive)
• Describe fold classes (parallel vs. similar)
• Identify second-order folds and interpret them
• Explain axial planar cleavage formation
• Describe fold-fault relationships
• Identify shear sense indicators in shear zones
• Classify mylonites

12.6 Integration and Application

• Connect stress regimes to plate boundaries to structures
• Explain scale relationships (Pumpelly’s Rule)
• Describe lithospheric strength profile
• Apply structural geology to resource exploration
• Apply structural geology to earthquake hazards
• Interpret structures in maps and cross-sections
• Use stereographic projections
• Analyze multi-phase deformation
• Think in 3D

12.7 Real-World Examples

• Himalayas (collision, escape tectonics)
• East African Rift (active rifting)
• San Andreas Fault (transform, transpression)
• Juan de Fuca (divergent boundary, subduction)
• North Sea (rift basins)
• Alps (nappe structures)

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13 Remember

Keys to Success

Success in structural geology exams requires:

1. Understanding fundamental concepts rather than just memorizing
2. Integrating knowledge across different topics
3. Thinking in 3D and visualizing structures
4. Applying theory to real-world examples
5. Using precise terminology correctly
6. Practicing quantitative skills (calculations, graphical methods)
7. Learning from diagrams and photos as much as from text

The most successful students can:

• Explain WHY processes occur, not just WHAT happens
• Predict structures from tectonic settings
• Work backwards from structures to infer conditions
• See connections between topics
• Apply knowledge to unfamiliar scenarios

Good luck with your revision!