Download U4-T3.1-Forces and Factors that affect Crustal Deformation

Earth Systems 3209
Unit: 4
The Forces Within Earth
Reference:
Chapters 4, 15, 16, 19; Appendix A & B
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Unit 4:
Topic 3.1
Forces and Factors that affect Deformation
Focus on . . .
 defining crustal deformation, force, and stress.
 outlining and describing three types of deformation.
 identifying and describing the forces that cause deformation.
 identifying and describing the factors that affect deformation.
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Terminology associated with Crustal Deformation:
Crustal Deformation is associated with Internal Forces within Earth!
Crustal Deformation
 General term that refers to all changes that occur to the original form
and/or size of a rock body.
 It may also produce changes in the location and orientation of rocks.
 Most crustal deformation occurs along plate tectonic margins.
 Plate motions and the interactions along plate boundaries generate
tectonic forces that cause rock units to deform.
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Terminology associated with Crustal Deformation:
Force
 anything that tends to put stationary objects in motion or change the
motion of moving bodies.
Stress
 is defined as the amount of force applied to a given area.
 Two types of stress;
1) Uniform – equal stress in all directions.
2) Differential – varying stress in different directions.
Strain
 causes an irreversible change in the shape and size of a rock body.
Original configuration is not retained during deformation.
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Types of Crustal Deformation:
Differential Stresses:
Compressional
 stresses that shorten a rock body
are compressional in nature
Tensional
 stresses that elongate a rock body
Shear
 stresses that cause sections of a
rock body or two separate rock
bodies to slide past one another
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Types of Crustal Deformation:
 When rocks are subjected to stresses greater than their own
strength, they begin to deform, usually by folding, flowing, or
fracturing.
3 types of deformation:
1) Elastic Deformation - recoverable
2) Brittle Deformation - permanent
3) Ductile Deformation - permanent
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Types of Crustal Deformation:
3 types of deformation:
1) Elastic Deformation
 stress is applied gradually and when the stress is removed the rock
will return to nearly its original size and shape.
 elastic deformation is recoverable after stressing.
 earthquakes result from stored elastic energy.
 once the elastic limit is reached it either flows (ductile) or fractures
(brittle).
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Types of Crustal Deformation:
3 types of deformation:
2) Brittle Deformation
 stress is applied gradually and when the rocks strength is exceeded
the rock will behave like a brittle solid where it will fracture and the
rock will not return to its original size and shape.
 occurs near the surface where temperature and confining pressures
are lower.
 brittle deformation is permanent.
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Types of Crustal Deformation:
3 types of deformation:
3) Ductile Deformation
 stress is applied gradually and when the rocks strength is exceeded
the rock will flow in solid state and produce a change in the original
size and shape without fracturing.
 occurs at great depths beneath Earth’s surface where temperature
and confining pressures are higher.
 ductile deformation is permanent.
 An example would be similar to a penny placed on a railway track
and flattened by a passing train. Metal is permanently changed.
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Factors that Affect Crustal Deformation:
 The factors that influence the strength of a rock and
thus how it will deform include;
1) Temperature
2) Confining Pressure
3) Rock Type
4) Time
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Factors that Affect Crustal Deformation:
 The factors that influence the strength of a rock
and thus how it will deform include;
1) Temperature
 the colder the Earth materials, the more brittle
the deformation will be.
 the warmer the Earth materials, the more
elastic or ductile the deformation will be.
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Factors that Affect Crustal Deformation:
 The factors that influence the strength of a rock
and thus how it will deform include;
2) Confining Pressure
 confining pressure will only result in elastic or
ductile deformation at varied depths beneath
Earth’s surface.
 brittle deformation typically occurs on the
surface when there is no confining pressure
from above.
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Factors that Affect Crustal Deformation:
 The factors that influence the strength of a rock
and thus how it will deform include;
3) Rock Type
 all rock types can be deformed.
 however, sedimentary rocks could be more
easily deformed since they are softer.
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Factors that Affect Crustal Deformation:
 The factors that influence the strength of a rock
and thus how it will deform include;
4) Time
 rapid deformation tends to result in brittle
deformation.
 slower deformation over longer periods of time
tends to result in elastic or ductile deformation.
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Example 1:
Which factors would cause a rock to deform by brittle
deformation ?
Time
Temperature
(A)
Shorter
Colder
(B)
Shorter
Warmer
(C)
Longer
Colder
(D)
Longer
Warmer
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Example 2:
Which type of stress and faulting occurs at divergent
plate boundaries?
Stress
Faulting
(A)
shear
normal
(B)
shear
reverse
(C)
tension
normal
(D)
tension
reverse
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Your Turn . . .
Take the time and complete the following questions . . .
(Solutions to follow)
Question:
Which rock type is most easily deformed by
stresses in Earth’s crust?
(A) igneous plutonic
(B) igneous volcanic
(C) metamorphic
(D) sedimentary
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Solutions . . .
Question:
Which rock type is most easily deformed by
stresses in Earth’s crust?
(A) igneous plutonic
(B) igneous volcanic
(C) metamorphic
(D) sedimentary
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Summary . . .
Overview of Points covered:
 Crustal deformation is a direct result of stresses put on rocks.
 3 types of stress include;
1) Tensional, 2) Compressional, 3) Shear
 3 types of crustal deformation include;
1) Elastic, 2) Brittle, 3) Ductile
 Factors affecting crustal deformation include;
1) Temperature, 2) Confining Pressure, 3) Rock Type, 4) Time
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