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Chapter 9 Folds, Faults,and Mountains

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Chapter 9 Folds, Faults,and Mountains Stress: Force per unit area Strain: Change in length/area/volume to original length/area/volume Rocks are subjected to great ... – PowerPoint PPT presentation

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Title: Chapter 9 Folds, Faults,and Mountains


1
Chapter 9 Folds, Faults,and Mountains
  • Stress Force per unit area
  • Strain Change in length/area/volume to original
    length/area/volume
  • Rocks are subjected to great forces- particularly
    at plate margins
  • Compression- converging plate boundary
  • Tension- diverging plate boundary
  • Shearing- transform plate boundary
  • Strain- rocks response to stress

2
Three types of stresses
3
Types of Deformation
  • ELASTIC DEFORMATION
  • BRITTLE FAILURE
  • PLASTIC DEFORMATION
  • Elastic deformation
  • deformation not permanent (minor amount of
    stress)
  • Brittle
  • stress amount exceeds the yield point or elastic
    limit
  • Plastic (Ductile) deformation
  • stress applied gradually to deep warm rocks

4
Elastic Deformation
5
Plastic Deformation
6
Brittle Failure
7
Folding at Converging Plate Boundaries
8
Factors affecting rock deformation
  • Intensity of Applied Stree
  • Lithostatic Pressure
  • Heat
  • leads to stretching of rocks at near Earths
    surface without breaking
  • at depth- plastic deformation
  • Time
  • Composition
  • different minerals have different strength

9
Deformed rocks in the field
  • Most apparent in Sedimentary Rocks
  • Importance of deformation
  • Indicate Past Plate Motions
  • Indicates other Past Geological Events
  • Locates Specific Natural Resources
  • Rock Orientation Strike and Dip

10
Interpretation of Rock Deformation-Folds
  • In describing folds, need to know the orientation
    of the rock in space- STRIKE and the angle at
    which rock is inclined to the horizontal- DIP
  • Folds- rocks deform plastically (most occur at
    convergent plates)
  • Syncline- trough-like
  • Anticline- arch-like
  • Types of folds- symmetrical, broad, open,
    overturn, recumbent
  • Basin
  • Rock deformation that is bowl shaped.
  • Domes
  • Rock deformation that is ova-shaped bulges

11
Geometry of anticlines and synclines
12
Artificial valleys and synclinal ridges
13
Artificial valleys and synclinal ridges-contd.
14
Various folds Symmetrical (open)
15
Various Folds - Assymetrical
16
Various Folds - Overturned
17
Various Folds - Recumbent
18
Various Folds - Plunging
19
Structural Domes and Basins
20
Faults
  • A fracture is a break in a rock (joint or a
    fault)
  • Joints Fractures with no relative movement
  • Fault is when there is relative movement along
    the break
  • Fault Types
  • Strike-Slip fault
  • horizontal movement (transform plate boundary)
  • Dip-Slip fault
  • Normal (tensional stress)
  • Reserve (compressional stress)
  • Thrust (low angle reserve fault)
  • Oblique (combination of strike-slip dip-slip)

21
Evidence of Faults
  • Visible displacement of rocks
  • Pulverized rock
  • Slickensides
  • Discontinuity of Rock Sequences
  • Types of Faults
  • Strike-Slip Fault
  • Dip-Slip Fault

22
Fault Planes
23
Fault Disruption
24
Map of San Andreas Fault
25
Horizontal movement along strike-slip fault
26
Dip-slip Fault
27
Mid-Atlantic Ridge
28
Plate Tectonics and Faulting
  • Normal Faults Mid-Ocean Ridge Continental
    Rifts
  • Reverse and Thrust Faults Convergent Plate
    Boundaries
  • Strike-Slip Faults Transform Boundaries

29
Geology at a Glance
30
Oblique Slip
31
Correlation of different fault types
32
Accumulation of Oil Natural Gas
33
Accumulation of oil along fault planes
34
A terrace-producing scenario
35
The mountain ranges of North America
36
A terrace-producing scenario
37
Provinces of the Applachian mountain system
38
Mountainbelt collapsing
39
Mountainbelt collapsing-contd.
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