8  Practical Resources

Test your knowledge by describing the tectonic setting and key features of these important locations:

8.1 Plate Boundaries

Mid-Ocean Ridges:

  • Juan de Fuca Ridge (offshore Pacific Northwest)
  • East Pacific Rise
  • Mid-Atlantic Ridge

Subduction Zones:

  • Tonga-Kermadec
  • Cascadia
  • Japan (Tohoku 2011 M9.0 earthquake)
  • Chile
  • Alaska (2021 M8.2 earthquake)

Transform Faults:

  • San Andreas Fault (California)
  • Romanche and Chain transforms (Mid-Atlantic)

Triple Junctions:

  • Afar Depression (Ethiopia)
  • Mendocino (offshore California)

8.2 Continental Collision

  • Himalayas and Tibet: Ongoing India-Asia collision
  • Alps: Classic nappe structures
  • Caledonides: Ancient orogen, post-orogenic extension

8.3 Extensional Provinces

  • East African Rift: Active continental rifting
  • Basin and Range Province: Metamorphic core complexes
  • North Sea: Rift basins, petroleum province
  • Gullfaks Field: Domino fault system

8.4 Strike-Slip Systems

  • San Andreas Fault: 1200 km, >300 km offset
  • Dead Sea Transform: Pull-apart basin
  • North Anatolian Fault: Major Turkish earthquakes
  • Alpine Fault: New Zealand

8.5 Special Examples

  • Chief Mountain, Montana: Classic thrust, Precambrian over Cretaceous
  • Carrizo Plain: San Andreas, visible offset streams
  • Sheep Mountain Anticline, Wyoming: Spectacular fold

9 Key Terminology Checklist

Can you define and explain the significance of each of these terms?

9.1 Plate Tectonics Terms

  • Lithosphere / Asthenosphere / LAB
  • Euler pole / Angular velocity
  • Magnetic anomaly / Magnetic reversal
  • Seafloor spreading / Age-depth relationship
  • Megathrust / Outer rise / Slab rollback
  • Focal mechanism / P, T, N axes
  • Triple junction / Stability
  • Escape tectonics / Lateral extrusion

9.2 Structural Geology Terms

  • Strike / Dip / Dip direction
  • Plunge / Trend
  • Hanging wall / Footwall
  • Allochthon / Autochthon
  • Décollement / Detachment
  • Nappe / Klippe / Window
  • Horse / Duplex
  • Graben / Horst / Half-graben
  • Flower structure (positive/negative)
  • Pull-apart basin / Pop-up structure
  • Transpression / Transtension
  • Ramp / Flat (frontal, lateral, oblique)

9.3 Stress and Strain Terms

  • Stress tensor / Traction vector
  • Principal stress (\(\sigma_1\), \(\sigma_2\), \(\sigma_3\))
  • Normal stress / Shear stress
  • Deviatoric stress / Mean stress
  • Mohr circle / Failure envelope
  • Mohr-Coulomb criterion
  • Effective stress / Pore pressure
  • Strain tensor / Strain ellipsoid
  • Volumetric strain / Deviatoric strain
  • Strain rate / Second invariant
  • Elongation / Beta factor

9.4 Rheology Terms

  • Young’s modulus / Poisson’s ratio
  • Shear modulus / Bulk modulus
  • Viscosity / Power-law creep
  • Yield stress / Plastic deformation
  • Diffusion creep / Dislocation creep
  • Dynamic recrystallization
  • Brittle-ductile transition

9.5 Fracture and Fault Terms

  • Mode I, II, III fracture
  • Joint / Vein / Dike
  • Plumose structure / Hackle marks
  • Systematic / Non-systematic joints
  • Slickenlines / Slickensides
  • Fault gouge / Fault breccia / Mylonite
  • Throw / Heave / Rake
  • Stick-slip / Earthquake cycle
  • Magnitude / Moment / \(M_w\)
  • Byerlee’s Law

9.6 Fold Terms

  • Hinge / Hinge zone / Limb
  • Axial surface / Axial trace
  • Inflection line
  • Antiform / Synform
  • Anticline / Syncline / Monocline
  • Interlimb angle
  • Upright / Inclined / Recumbent / Overturned
  • Cylindrical / Non-cylindrical / Periclinal
  • Chevron / Box / Kink fold
  • Dome / Basin
  • Anticlinorium / Synclinorium
  • Parallel / Similar folds (Class 1B / Class 2)
  • Buckling / Bending / Passive folding
  • Flexural slip / Flexural flow

9.7 Cleavage and Fabric Terms

  • Axial planar cleavage
  • Crenulation cleavage
  • S-C fabric / Shear bands
  • Foliation / Lineation
  • Porphyroclast (σ-type, δ-type)
  • Mica fish
  • Mylonite / Protomylonite / Ultramylonite

10 Quantitative Skills

Can you apply these concepts quantitatively?

10.1 Calculations You Should Be Able to Do

  1. Calculate extension from elongation:
    • Given stretched fossil: original 3 cm, now 5 cm
    • \(e = (l - l_0)/l_0 = (5-3)/3 = 0.67\) (67% extension)
  2. Calculate beta factor:
    • \(\beta = l/l_0 = 5/3 = 1.67\)
  3. Use Mohr circle to find stress on a plane:
    • Given \(\sigma_1 = 100\) MPa, \(\sigma_3 = 20\) MPa
    • Find normal and shear stress on plane at 30° to \(\sigma_1\)
  4. Predict fault angle from Anderson’s theory:
    • Given friction coefficient \(\mu = 0.6\)
    • \(\tan 2\theta = \mp 1/\mu = \mp 1.67\)
    • \(\theta \approx 30°\) to \(\sigma_1\)
  5. Calculate effective stress:
    • Given total stress \(\sigma_n = 100\) MPa, pore pressure \(P_f = 40\) MPa
    • \(\sigma'_n = \sigma_n - P_f = 60\) MPa
  6. Apply Mohr-Coulomb to predict failure:
    • \(\tau = C + \sigma_n \cdot \tan \phi\)
    • Given \(C = 10\) MPa, \(\phi = 30°\), \(\sigma_n = 50\) MPa
    • \(\tau = 10 + 50 \cdot \tan(30°) \approx 39\) MPa
  7. Use Byerlee’s Law:
    • At shallow depth (<2 km): \(\tau = 0.85\sigma_n\)
    • At greater depth: \(\tau = 50 + 0.6\sigma_n\)

10.2 Graphical Skills

  1. Interpret and construct Mohr circles
  2. Use stereographic projections:
    • Plot planes and lines
    • Find fold axis from limb data
    • Analyze fault slip data
    • Determine true dip from apparent dips
  3. Construct cross-sections from maps:
    • Maintain bed thickness (parallel folds)
    • Or maintain bed area (similar folds)
    • Project faults to depth
    • Show fold geometry
  4. Use down-plunge projection
  5. Interpret seismic reflection data