FOLDS, FAULTS AND
GEOLOGIC MAPS
Objectives
• Define three types of stress.
• Describe the differences between elastic, brittle, and
ductile deformation.
• Define cratons and orogens.
• Define strike and dip.
• Define and describe synclines, anticlines, and other
types of folds.
• Distinguish between a topographic map and a
geologic map.
Rock Deformation
• Stress
– The force acting on a
surface, per unit area
– May be greater in
certain directions than
in others
• Pressure
– A kind of stress in
which the forces acting
on a body are the same
in all directions
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Rock Deformation
• Tension
– A stress that acts in a
direction perpendicular
to and away from a
surface
• Compression
– Stress that acts in a
direction perpendicular
to and toward surface
Rock Deformation
• Shear
– A stress that acts in a direction parallel to a surface
• Strain
– A change in shape or volume of a rock in response to
stress
• Uniform stress causes change in volume only
• Differential stress may causes change in shape
Rock deformation
• Elastic deformation
– Temporary change in shape or volume from which a
material rebounds after the stress is removed
Paper clip permanently
deformed: stress was
greater than elastic limit
Paper clip returns to
original shape
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• Ductile deformation
– Permanent but gradual change in shape or volume of a
material, caused by flowing or bending
•Brittle deformation
Permanent change in shape or volume, in which a
material breaks or cracks
Brittle at room temperature
Ductile at high temperature
Rock deformation
Ductile
Brittle
Rock Deformation
• Main factors that
affect rock
deformation
– Temperature
– Confining pressure:
uniform pressure due
to depth
– Rate of deformation
– Composition
High confining
pressure
Low confining
pressure
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Rate of deformation
Rock Deformation
• Where rock deformation occurs
– Craton
• A region of continental crust that has remained tectonically stable
for a very long time
– Orogen
• An elongated region of crust that has been deformed and
metamorphosed through a continental collision
• Isostasy
– Similar to an ice berg floating in water; it floats at a level determined
by the density contrast
– The flotational balance of the lithosphere on the asthenosphere
Rock Deformation
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Rock Deformation
Structural Geology
• Structural geology the study of:
– Stress and strain
• Processes causing
stress and strain
• Deformation and rock
structures that result
from stress and strain
Structural Geology
• Strike
– The compass orientation of the line of intersection between a
horizontal plane and a planar feature (e.g. rock layer or fault)
• Dip
– The angle between the tilted surface and a horizontal plane
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Structural Geology
Structural Geology
• Faults and fractures
– Fault; fracture with movement
along the fracture surface
– Normal fault
• The block of rock above the
fault surface moves
downward relative to the
block below
Structural Geology
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Structural Geology
• Faults and fractures
– Reverse fault
• The block on top of the fault surface moves up and over the block on the
bottom
– Thrust fault
• A reverse fault with a shallow angle of dip
Structural Geology
• Strike-slip fault
– A fault in which the direction of the movement is mostly
horizontal and parallel to the strike of the fault
• San Andreas Fault
Strike-slip fault
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Structural Geology
Offset drainages
San Andreas
San Jacinto fault
The fault on the left is a right-lateral fault because the offset
stream is to your right as you face the fault.
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Structural Geology
• Folds
– A bend or warp in a layered
rock
• Monocline
– A local steepening in
otherwise uniformly
dipping strata
• Anticline
– A fold in the form of an
arch, with the rock strata
convex upward and the
older rocks in the core
Monocline
Parts of a fold
• Syncline
• A fold in the form of a
trough, with the rock
strata concave upward
and the younger rocks in
the core
• The geometry and the
orientation of a fold is
described by the:
–
–
–
–
–
Limb
Axial plane
Axial trace
Limbs
Axis
Plunge
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Domes and basins
Dome
Michigan Basin
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Geologic Maps
• Geologic map…
– Shows the locations, kinds, and orientation of rock units
– Shows structural features such as faults and folds
• Topographic maps…
• Show the shape of a ground surface, as well as the location and
elevation of surface features, usually by means of contour lines
Topographic Map
Geologic Maps
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Structural Geology
Structural Geology
Geologic Maps
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Geologic Maps
The Canadian Rockies
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