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Geology Exam 2 (2)

Terms in this set (34)

Structural geology
the study of the deformation of rocks and its effects
four major factors if a rock folds (bends) or faults (breaks)
1) Type of force applied (stress)
2) Pressure
3) Temperature
4) Rock (mineral) composition
Deformation
all changes in the size, shape, orientation or position of a rock
Stress
the amount of force applied to a given area
differential stress
applied in unequal
directions, causes rock to deform
three types of stress
1. Compression
2. Tension
3. Shear
Compression
Action of oppositely directed
forces acting towards each other at the
same time
Tension
Action of oppositely directed
forces acting away from each other
Shear
Action of oppositely directed forces
acting parallel to each other across a surface
Strength
ability to resist deformation
Strain
when stress causes an irreversible change in the shape and size of a rock body
3 types of deformation
1. Elastic
2. Ductile (plastic)
3. Brittle (rupture or fracture)
Elastic
temporary change in the shape or size that is recovered when the deforming force is removed
Ductile
applied stress causes a permanent change in shape or size, does NOT recover original shape
Brittle
it suddenly breaks
Describe the differences between stress and strain. Provide examples of each.
Stress is the amount of force applied to a given area and strain is the effects of that force on that given area. An example of stress is differential stress that pulls the rock in various directions and causes deformation. An example of strain is plastic or ductile strain in which the rocks remain out of shape after the acting force stops
rock fractures
Fractures & Joints
Faults
Joints
Cracks in rocks with no appreciable movement or displacement
Faults
there has been relative movement of the rock
Fault Movements
1. Dip-slip faults (Up/Down)
2. Strike-slip fault (Left/Right)
3. Oblique-slip fault
Hanging Wall
above
Footwall
below
Types of Dip-Slip faults
Normal (DOWN dip, tension stress)
Reverse (UP dip, compression stress)
Horst
uplifted
Graben
downdropped
Types of Stike-slip faults
Left-lateral and Right-lateral
If a rock deforms under stress by forming fractures and shattering, the deformation behavior is described as:

A. Explosive
B. Elastic
C. Brittle
D. Bending
E. None of the above.
C. Brittle
Axial plane
the plane of mirror symmetry dividing the fold into two limbs
Axis
the line formed by the intersection of the axial plane and a bedding plane
Horizontal fold
fold where the axis is horizontal
Plunging fold
fold where the axis is not horizontal
Anticline
up-folding, Oldest rocks are along the axial plane
Syncline
down-folding, Youngest rocks are along the axial plane
Evidence of ductile deformation of rocks can be seen from...
Overturned limbs in the Swiss Alps
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