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Folds and Faults

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How do you precisely, quantitatively describe the orientation of faults ... SCARP. Fig. 11.14. Folds. Fig. 11.15. Types of folds. Anticline: Upfolds or arches. ... – PowerPoint PPT presentation

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Title: Folds and Faults


1
Folds and Faults
2
Field Geology
3
Fig 11.1
4
Fig. 11.2
5
Geology is a quantitative science.How do you
precisely, quantitatively describe the
orientation of faults and folds in the field?
6
Strike and Dip
  • Strike Compass direction of a rock layer as it
    intersects with a horizontal surface.
  • Dip The amount of tilt. The angle at which a
    bed is inclined from the horizontal. The
    direction a drop of water travel when dropped on
    a rock layer.

Fig. 11.4
7
Fig. 11.3
8
How do rocks get deformed?
Fig. 11.6
9
How do rocks deform?
  • Brittle material Undergoes little deformation
    until it breaks suddenly. Example Candy cane.
  • Ductile material Undergoes smooth and
    continuous deformation. Does not spring back to
    its original shape once deforming force is
    released. Example Caramel.

10
Ductile rocks fold.
Fig. 11.6
11
Brittle rocks fault.
Fig. 11.6
12
Brittle deformation
Ductile deformation
Fig. 11.7
13
The same rock can undergo brittle and ductile
deformation?
  • Rocks are more ductile
  • The higher the pressure (the deeper they are in
    the Earth).
  • The higher the temperature (the deeper they are
    in the Earth).
  • The faster the deforming force is applied. Quick
    shove break slow push bend.

14
Faults
15
Two types of fractures
  • Joints (Weve seen these before.) A crack
    along which there has been little appreciable
    movement. A nondisplaced fracture.
  • Faults A fracture with relative motion of the
    rocks on either side of it.

16
JOINTS
Fig. 11.9
17
Fig. 11.11
18
San Andreas Fault
  • A strike-slip fault in California
  • Right-lateral

Fig. 11.10
19
Reverse faulting in Nevada
Fig. 11.12
20
Mid-ocean ridges are normal faults.
Fig. 11.13
21
SCARP
Fig. 11.14
22
Folds
23
Fig. 11.15
24
Types of folds
  • Anticline Upfolds or arches.
  • Synclines Downfolds or troughs.

Fig. 11.16
25
Fold terms
  • Axial plane Imaginary surface that divides the
    two halves (limbs) of a fold.
  • Horizontal folds and plunging folds.

Fig. 11.16
26
Fig. 11.16
27
Fig. 11.16
28
Fig. 11.16
29
Fig. 11.16
30
Fig. 11.16
31
  • Plunging synclines or plunging anticlines are
    located where a fold dies out or seems to plunge
    into the ground.

Fig. 11.17
32
Fig. 11.18
33
Fig. 11.19
  • Dome Broad circular or oval structure made of
    rock layers. An anticlinal structure.

34
Fig. 11.19
35
Domes and basins
  • Domes can be formed by
  • Intrusions of buoyant material (e.g., hot igneous
    rock or salt)
  • Successive periods of compressive deformation in
    different directions.
  • Basin Bowl-shaped depression. Synclinal
    structure. Can be formed by
  • Subsidence and cooling of hot crust.
  • Stretching of crust.

36
Putting it together Field observations
Fig. 11.20
37
Fig. 11.21
38
Fig. 11.21
39
Fig. 11.22
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