Thrust faults (Ch.6, 319-339)

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Thrust faults (Ch.6, 319-339)
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Profile through the Canadian Rockies
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1. Strain- significant shortening can compute
2. Faults form at low angle (consistent with S1
   horizontal)
3. Fault system propagates left to right
4. Old rocks are thrusted on top of young
5. Some rock units preferentially used in faulting
   (why?)
6. Geometry of faulting is characterized by a
   bending pattern
7. The hanginwall deforms footwall stays rather
   intact
8. Folding of the hangingwall
9. Newer structurally deeper faults lead to
   rotation of older faults

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Strain analysis
L0178 km
Lf83 km
S-(lf-l0)/l0 (178-83)/178 0.53 53
shortening
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1. Strain- significant shortening can compute
2. Faults form at low angle (consistent with S1
   horizontal)
3. Fault system propagates left to right
4. Old rocks are thrusted on top of young
5. Some rock units preferentially used in faulting
   (why?)
6. Geometry of faulting is characterized by a
   bending pattern
7. The hanginwall deforms footwall stays rather
   intact
8. Folding of the hangingwall
9. Newer structurally deeper faults lead to
   rotation of older faults

Sigma 1 -horizontal Sigma 3- vertical
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Propagation of thrusts (in sequence)
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Propagation of thusting
Foreland
Note the presence of a basal detachment- no
deformation structurally below the detachment
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• Faults form at low angle (consistent with S1
  horizontal)
• Fault system propagates left to right
• Old rocks are thrusted on top of young
• Some rock units preferentially used in faulting
  (why?)

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• Faults form at low angle (consistent with S1
  horizontal)
• Fault system propagates left to right
• Old rocks are thrusted on top of young
• Some rock units preferentially used in faulting
  (why?)

10

• Old rocks are thrusted on top of young
• Some rock units preferentially used in faulting
  (why?)
• Geometry of faulting is characterized by a
  bending pattern
• The hanginwall deforms footwall stays rather
  intact
• Folding of the hangingwall

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Ramps cutting up-stratigraphy and flats
parallel to strata
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Ramping Gliding
Repetition
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Mt Yamnaska
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Thrust fault never cut down section Could be
Hwall or Fwall flat or ramp
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Example from the Argentinian Cordillera
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Lateral ramps
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Klippe- island of h-wall surrounded by
f-wall Window (or fenster)- oppositte
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How do thrust faults move?
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Fault-propagation folding
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Typical map view in thrust terranes
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Horse
Imbricate fan
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Duplex
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Classic duplex in the Canadian Rockies
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Fault termination Gradual decrease in slip
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More examples from the Canadian Cordillera
Exshaw thrust
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Exshaw thrust-hangingwall flat, footwall ramp
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Mt Kidd
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Mt Rundle _at_ Banff
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A different example- the Himalayas
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Major issues

• mechanical paradox of thrusting - why such thin
  sheets (e.g. 100 km long/2-3 km thick) can remain
  intact during faulting?
• What happened to the missing basement?
• Why are almost all faults dipping one way when
  rock mechanics predict equal chance for both
  thetas around sigma 1?