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Folds, Faults, and Mountain Building

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Folds, Faults, and Mountain Building Chapter 9 Stress!!! Stress a force exerted on an object Rocks react to stress by Deforming plastically Deforming elastically ... – PowerPoint PPT presentation

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Title: Folds, Faults, and Mountain Building


1
Folds, Faults, and Mountain Building
  • Chapter 9

2
(No Transcript)
3
Stress!!!
  • Stressa force exerted on an object
  • Rocks react to stress by
  • Deforming plastically
  • Deforming elastically
  • Breaking by brittle fracture
  • Question of the hour (1)
  • How will a particular rock react to a particular
    stress?

4
Its all in the Nature
  • Rock composition
  • Ex Hitting a chunk of concrete with a
    sledgehammer VS. hitting a giant rubber tire with
    a sledgehammer

5
I Cant Take the Pressure!!
  • Pressure and Temp. increase with depth
  • Temp vs. pressure
  • Burial promotes plastic deformation

6
If you cant stand the heat
  • Higher temperatures favor plastic deformation
  • Ex. Bending a steel nail
  • Need to be super strong
  • Or just heat the thing up

7
Its About Time
  • Stress applied slowly favors plastic behavior
  • Stress applied suddenly favors brittle behavior

8
May the Tectonic Force be With You.
  • Plate tectonic forces
  • Tensional
  • Stretch and pull formations apart
  • Compressive
  • Squeeze and shorten rock formations
  • Shearing
  • Two sides of a formation are pushed in opposite
    directions (sliding past one another)

9
Geologic Structures
  • Plate tectonicsprimary stressor
  • 3 main types of structures
  • Foldsductile deformation (primarily)
  • Faultsbrittle deformation
  • Jointsbrittle deformation

10
Folds
  • A fold is a bend in the rock
  • Plastic deformation
  • Three characteristics
  • Usually results from compression
  • Folding always shortens the horizontal distances
    in rock
  • A fold usually occurs as part of a group of folds

11
Anticline Vs. Syncline
12
Plunging Folds
13
Overturned and Asymmetric
14
Circular Features
  • Domes
  • Circular anticlinal structure (both pics?)
  • Beds dip away from center
  • Basin
  • Circular synclinal structure
  • Beds dip towards center

15
All My Faults are Stress Related!!!
  • Brittle deformation
  • Faults
  • Cracks in rock along which motion has occurred
  • Movement may be gradual or sudden (earthquake)
  • Usually associated with other faults in a fault
    zone
  • Question of the hour (2) Why do rocks move
    repeatedly along faults and fault zones?

16
Nature is Lazy
  • Rock moves repeatedly along faults and fault
    zones because
  • Tectonic forces often affect one location for a
    long time
  • Its easier
  • Three types of faults
  • Depend on tectonic forces

17
Normal Faulting
18
Reverse Fault (part 1)
19
Reverse Fault (part 2)
20
Strike-slip Fault
21
Ah, How My Joints Ache
  • A joint is a fracture in rock along which no
    motion has occurred
  • Planes of weaknesslike mineral cleavage
  • Good for mining

22
Styles of Continental Deformation
  • Relating Small Structures to Big Picture

23
Question of the Hour (3)
  • Where do mountains come from?
  • In a subducting zone
  • Magmas/lavasstall/erupt
  • High temprocks expand when heated
  • Continent/continent collisionunderthrusting
  • Crust is shoved under other crust
  • Compression squeezes crustthickness increases

24
Tensional Tectonics
  • Plates can split apart
  • Rift valleys long narrow troughs formed by a
    block that has dropped down between two big
    normal faults

25
Rifting and Normal Faulting
26
(No Transcript)
27
Compressive Tectonics
  • Fold and thrust belts
  • When two continental plates collide, crust
    compressed
  • Crust thickened by underthrustingthicken crust
    2x

28
Transverse Margins
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