11.1

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11.1 Rock Deformation
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Do Now

• Describe the different types of stress.

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Do Now

• Describe the different types of stress.
• Tensional
• Compressional
• Shear

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Key Words

• Influence
• Formation

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Vocab Words

• Anticline
• Deformation
• Monocline
• Normal Fault
• Reverse Fault
• Strain
• Stress
• Strike-slip Fault
• Syncline
• Thrust Fault

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Rock Deformation

• Mountains provide some of the most spectacular
  scenery on our planet.
• It is theorized that all continents were once
  mountainous masses and grow by the addition of
  mountains to their edges
• As geologists unravel the secrets of mountain
  formation, they also gain a deeper understanding
  of the evolution of Earths continents.

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Factors Affecting Deformation

• Factors that influence the strength of a rock and
  how it will deform include temperature, confining
  pressure, rock type, and time.
• Deformation is a general term that refers to all
  changes in the original shape and/or size of a
  rock body.
• Most crustal deformation occurs along plate
  margins.
• Stress is the force per unit area acting on a
  solid.
• Strain is the change in shape or volume of a body
  of rock as a result of stress.

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Temperature and Pressure

• Rocks deform permanently in two ways brittle
  deformation and ductile deformation.
• Brittle deformation is the fracturing of an
  object once its strength is exceeded.
• Rocks near the surface, where the temperatures
  and confining pressures are low
• Ductile deformation is a type of solid state flow
  that produces a change in the size and shape of
  an object without fracturing the object.
• Rocks, where temperatures and confining pressures
  are high

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Rock Type

• Mineral composition and texture of a rock also
  greatly affect how it will deform.
• Rocks like granite and basalt that are composed
  of minerals with strong internal molecular bonds
  usually fail by brittle deformation.
• Rocks that are weakly cemented, like sedimentary
  rocks or metamorphic rocks, contain zones of
  weakness and fail by ductile deformation.

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Time

• Forces that are unable to deform rock when first
  applied may cause rock to flow if the force is
  maintained over a long period of time.
• In nature small stresses applied over a long
  period of time plays an important role in the
  deformation of rock.

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Types of Stress

• Rocks are exposed to many different forces due to
  plate motions.
• The three types of stress are tensional,
  compressional and shear.
• Tensional when rocks are pulled in opposite
  directions
• Compressional when rocks are pushed together or
  squeezed.
• Shear when rocks are distorted from different
  pulling.

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Types of Stress
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Folds

• The three main types of folds are
• Anticline are most commonly formed by the
  upfolding, or arching, of rock layers.
• Syncline are linear downfolds in sedimentary
  strata.
• Found along with anticlines
• Monocline are large step-like folds in
  otherwise horizontal sedimentary strata.

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Folds
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Folds
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Faults

• The major types of faults are
• Normal occur when the hanging wall block moves
  down relative to the footwall block
• Reverse are faults in which the hanging wall
  block moves up relative to the footwall block
• Thrust are reverse faults with dips less than
  45 degrees
• Strike-slip - are faults in which the movement is
  horizontal and parallel to the trend, or strike,
  of the fault surface

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Faults
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Joints

• Joints are fractures along which no appreciable
  movement has occurred.

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Group Activity

• Copy and label the following pictures
• p. 309 Figure 2
• p. 310 Figure 3
• p. 312 Figure 6