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Grotzinger • Jordan

Understanding Earth
Sixth Edition

Chapter 7:
DEFORMATION
Modification of Rocks by
Folding and Fractu...
Chapter 7:

DeformationModification of Rocks
by Folding and
Fracturing
About Deformation
• Deformation mainly occurs near plate
boundaries.
• Field observations of deformation show
us how to re...
Lecture Outline
1. Plate tectonic forces
2. Mapping geologic structure
3. How rocks deform
4. Basic deformation structures...
1. Plate Tectonic Forces

● Deformation
● tensional forces
● compressive forces
● shearing forces
2. Mapping Geologic Structure

● Outcrop – basic source of
geologic information in the
field
2. Mapping Geologic Structure
2. Mapping Geologic Structure
2. Mapping Geologic Structure
2. Mapping Geologic Structure

● Measuring strike and dip
● strike is the compass
direction of a rock layer as it
intersec...
2. Mapping Geologic Structure
N

W
S

ion Strike d
ect
irecti
dir
on

Dip 45°

Dip
angle

E

N

W
S

45°
Dip angle

E
2. Mapping Geologic Structure
N

W
S

ion Strike d
ect
irecti
dir
on

Dip 45°

Dip
angle

E

N

W
S

Water trickles down
s...
Dinosaur Ridge, located
west of Denver, Colorado.
2. Mapping Geologic Structure

● Geologic maps
● geologic maps represent
the rock formations
exposed at Earth’s surface
● ...
2. Mapping Geologic Structure

● Geologic cross sections
● geologic cross sections –
diagrams showing the
features that wo...
3. How Rocks Deform

● Rock behavior in the laboratory
● brittle
● ductile
3. How Rocks Deform

An undeformed sample
Under conditions
representative of the
shallow crust, the
marble is brittle.

An undeformed sample
Under conditions
representative of the
shallow crust, the
marble is brittle.

Under conditions
representative of
the deepe...
3. How Rocks Deform

● Rock behavior in the Earth’s crust
● depths affect brittle v. ductile
● rock type affects way rocks...
4. Basic Deformation Structures

● Types of faults
● dip-slip – normal, reverse,
and thrust
● strike-slip – right- and lef...
4. Basic Deformation Structures
Example
of a strikeslip fault
4. Basic Deformation Structures

● Types of folds
● symmetrical folds anticlines and synclines
● asymmetrical folds
● over...
4. Basic Deformation Structures
4. Basic Deformation Structures
4. Basic Deformation Structures

● Circular structures
● dome
● basin
Example
of a dome
Example
of a basin
4. Basic Deformation Structures

● Other features
● joints
● deformation (cataclastic) textures
● fault breccia
● mylonite
joints
fault
breccia
mylonite
5. Styles of Continental Deformation

● Tensional tectonics
● Compressive tectonics
● Shearing tectonics
5. Styles of Continental Deformation
5. Styles of Continental Deformation
5. Styles of Continental Deformation
Example of
tensional
tectonics
Example of
compressive
tectonics
Example of
shearing
tectonics
Thought questions for this chapter
The submerged margin of a continent has a thick layer of
sediments overlying metamorphi...
6. Unraveling Geologic History

● Geologic history is a
succession of episodes
of deformation and other
geologic processes...
TIME 1
Sediments are deposited
on the seafloor.
TIME 2
Compressive forces cause
folding and faulting.

compressive
forces

faults
TIME 3
Uplift is followed by erosion, which
creates new horizontal surface.
TIME 4
Volcanic eruptions cover
the surface with lava flows.

lava flows
TIME 5
Tensional forces cause
normal faults, creating
down-dropped
blocks and
breaking up
earlier features.

tensional for...
Key terms and concepts
Anticline
Basin
Brittle
Compressive force
Deformation
Dip
Dip-slip fault
Dome
Ductile
Fault
Fold
Fo...
Key terms and concepts
Joint
Normal fault
Shearing force
Strike
Strike-slip fault
Tensional force
Thrust fault
 deformation
 deformation
 deformation
 deformation
 deformation
 deformation
 deformation
 deformation
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  1. 1. Grotzinger • Jordan Understanding Earth Sixth Edition Chapter 7: DEFORMATION Modification of Rocks by Folding and Fracturing © 2011 by W. H. Freeman and Company
  2. 2. Chapter 7: DeformationModification of Rocks by Folding and Fracturing
  3. 3. About Deformation • Deformation mainly occurs near plate boundaries. • Field observations of deformation show us how to reconstruct geologic history. • Deformation includes faulting of rigid rocks and folding of rocks that can be bent.
  4. 4. Lecture Outline 1. Plate tectonic forces 2. Mapping geologic structure 3. How rocks deform 4. Basic deformation structures 5. Unraveling geologic history
  5. 5. 1. Plate Tectonic Forces ● Deformation ● tensional forces ● compressive forces ● shearing forces
  6. 6. 2. Mapping Geologic Structure ● Outcrop – basic source of geologic information in the field
  7. 7. 2. Mapping Geologic Structure
  8. 8. 2. Mapping Geologic Structure
  9. 9. 2. Mapping Geologic Structure
  10. 10. 2. Mapping Geologic Structure ● Measuring strike and dip ● strike is the compass direction of a rock layer as it intersects a horizontal surface ● dip is the amount of tilting of the layer and is measured at right angles to strike
  11. 11. 2. Mapping Geologic Structure N W S ion Strike d ect irecti dir on Dip 45° Dip angle E N W S 45° Dip angle E
  12. 12. 2. Mapping Geologic Structure N W S ion Strike d ect irecti dir on Dip 45° Dip angle E N W S Water trickles down slope parallel to dip. 45° Dip angle E
  13. 13. Dinosaur Ridge, located west of Denver, Colorado.
  14. 14. 2. Mapping Geologic Structure ● Geologic maps ● geologic maps represent the rock formations exposed at Earth’s surface ● a common scale for geologic maps is 1:24,000
  15. 15. 2. Mapping Geologic Structure ● Geologic cross sections ● geologic cross sections – diagrams showing the features that would be visible if vertical slices were made through part of the crust
  16. 16. 3. How Rocks Deform ● Rock behavior in the laboratory ● brittle ● ductile
  17. 17. 3. How Rocks Deform An undeformed sample
  18. 18. Under conditions representative of the shallow crust, the marble is brittle. An undeformed sample
  19. 19. Under conditions representative of the shallow crust, the marble is brittle. Under conditions representative of the deeper crust, marble is ductile. An undeformed sample
  20. 20. 3. How Rocks Deform ● Rock behavior in the Earth’s crust ● depths affect brittle v. ductile ● rock type affects way rocks deform ● rate of deformation is a factor
  21. 21. 4. Basic Deformation Structures ● Types of faults ● dip-slip – normal, reverse, and thrust ● strike-slip – right- and leftlateral ● oblique-slip
  22. 22. 4. Basic Deformation Structures
  23. 23. Example of a strikeslip fault
  24. 24. 4. Basic Deformation Structures ● Types of folds ● symmetrical folds anticlines and synclines ● asymmetrical folds ● overturned folds ● plunging folds
  25. 25. 4. Basic Deformation Structures
  26. 26. 4. Basic Deformation Structures
  27. 27. 4. Basic Deformation Structures ● Circular structures ● dome ● basin
  28. 28. Example of a dome
  29. 29. Example of a basin
  30. 30. 4. Basic Deformation Structures ● Other features ● joints ● deformation (cataclastic) textures ● fault breccia ● mylonite
  31. 31. joints
  32. 32. fault breccia
  33. 33. mylonite
  34. 34. 5. Styles of Continental Deformation ● Tensional tectonics ● Compressive tectonics ● Shearing tectonics
  35. 35. 5. Styles of Continental Deformation
  36. 36. 5. Styles of Continental Deformation
  37. 37. 5. Styles of Continental Deformation
  38. 38. Example of tensional tectonics
  39. 39. Example of compressive tectonics
  40. 40. Example of shearing tectonics
  41. 41. Thought questions for this chapter The submerged margin of a continent has a thick layer of sediments overlying metamorphic basement rocks. That continental margin collides with another continental mass, and the compressive forces deform it into a fold and thrust belt. During the deformation, which of the following geologic formations would be likely to behave as brittle materials and which as ductile materials? (a) sedimentary formations in the upper few km (b) metamorphic basement rocks at depths of 5-15 km (c) lower crustal rocks below 20 km In which of these layers would you expect earthquakes?
  42. 42. 6. Unraveling Geologic History ● Geologic history is a succession of episodes of deformation and other geologic processes. ● Can be described in time steps 1, 2, 3, …
  43. 43. TIME 1 Sediments are deposited on the seafloor.
  44. 44. TIME 2 Compressive forces cause folding and faulting. compressive forces faults
  45. 45. TIME 3 Uplift is followed by erosion, which creates new horizontal surface.
  46. 46. TIME 4 Volcanic eruptions cover the surface with lava flows. lava flows
  47. 47. TIME 5 Tensional forces cause normal faults, creating down-dropped blocks and breaking up earlier features. tensional forces normal faults
  48. 48. Key terms and concepts Anticline Basin Brittle Compressive force Deformation Dip Dip-slip fault Dome Ductile Fault Fold Foot wall Formation Geologic cross section Geologic map
  49. 49. Key terms and concepts Joint Normal fault Shearing force Strike Strike-slip fault Tensional force Thrust fault
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