Download Faults

X. Deformation and .
Mountain Building
A.
B.
C.
D.
E.
Plate Tectonics and Stress
Rock Deformation
Geologic Structures
Origin of Mountains
Continental Crust
Tectonic Stresses  Large Scale Strain
of the Crust i.e., Geologic Structures
Crust:
Rigid,
Thin

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Inner core: Solid iron
Outer core: Liquid iron,
convecting (magnetic field)
Mantle (Asthenosphere) :
Solid iron-magnesium
silicate, plastic, convecting
Crust (Lithosphere): Rigid, thin
5-30km
Mantle:
Plastic,
Convecting
Tectonics and
Structural Geology
Tectonic Stresses
resulting from
Internal Energy
(heat driving convection)
Strains (deforms) the Mantle
and Crust
Bends
Rocks, i.e.,
ductile strain (Folds)
Breaks Rock, i.e.,
brittle strain (Joints) and
Moves large blocks along
Faults and
Releases energy 
Earthquakes
Fig. 10-CO, p. 216
Folds and Faults (Palmdale, Ca)
See Fig. 10-2a, p. 219
Eastern Pennsylvania
Northwestern
Africa
Stresses
at Plate
Boundaries

Divergent
(Tensional)
|

Convergent
(Compressional)

|
Transform
(Shear)
e.g., Pacific NW
Geologic
Structures

Different stresses result in
various forms of strain
(geologic structures)

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Folds (compressive
stresses may cause ductile
strain)
Faults (Any type of stress
may cause brittle strain.
The type of fault depends
on the type of stress)
Stikes and Dips are used to
identify geologic structures
Strike and Dip

Define and map the orientation of
planar features

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Bedding planes (sedimentary rocks)
Foliation
Joints
Faults
Dikes
Sills
Ore Veins
Fig. 10-4, p. 221
Strike and Dip


Strike: The line of
intersection between the
plane and a horizontal
surface
Dip: Angle that the plane
makes with that horizontal
plane
Strike and Dip
Map Symbol
Fig. 10-4, p. 221
Sipping Bedding Planes
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Youngest (top)
P: Permian
P: Pennsylvanian
M: Mississippian
D: Devonian
S: Silurian
O: Ordovician
C: Cambrian

Oldest (bottom)
Sedimentary Rocks Dip in the
direction of younger rocks
D
S
O
Deciphering the Geology of Ohio
Using Dipping Bedding Planes

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Beds Dip 2o, West
Younger rocks, West
Mirror image east of
Sandusky?
Sandstone
M 2o
Shale
2o O
Limestone
2o
D
Anticline (fold)
Anticline (fold)
Syncline (fold)
Plunging
Anticline
Fold Terminology
Axis

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Axis
Axial Plane
Plunging
Age of rocks
and outcrops
Axis
Plunging Anticline, Colorado
Eastern Pennsylvania

Folds and faults resulting from
compressive stresses

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Anticlines (many plunging)
Synclines (many plunging)
Reverse faults
Thrust faults
Domes and Basins
Bedrock
Geology of the
Michigan Basin

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During and after
the deposition of
Michigan’s
sedimentary rocks
The crust warped
downward
Exposing younger
rocks in the center
and
Older rocks on the
rim (e.g. Toledo)
Brittle Strain  Joints

When shallow crust is strained
rocks tend to exhibit brittle strain
Sheet Joints
Defining Fault Orientation

Strike of fault plane
parallels the

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
fault trace and
fault scarp
Direction of Dip of
the fault plane
indicates the
Hanging wall block
Fig. 10-11a, p. 227
Fault:

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Movement occurring along a discontinuity
Brittle strain and subsequent movement as a
result of stress
Fault
terminology
Faults

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Fault: When
movement
occurs along
a discontinuity
Fault type
depends on
the type of
stress
Normal Faults
Normal Faults, Horsts and Grabens
Structures at Divergent Boundaries


Tensional Stresses cause brittle strain and
formation of sets of normal faults
i.e., Horsts and Grabens
Horsts and Grabens

Older Rocks are exposed along the ridges
formed by the horsts
Horst
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
Horst
Graben
Graben
Younger rocks lie beneath the grabens
Sediment fills in the linear valleys
Nevada
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“Washboard
topography” is the result
of Horsts and Grabens
A.k.a, Basin and Range
E.g., Humbolt Range
E.g., Death Valley
(Graben)
Horst and Graben, Nevada
Horst
Graben
Humboldt Range, Northern Nevada
Fig. 10-15b, p. 233
Horst and Graben, Nevada
Horst
Graben
Humboldt Range, Northern Nevada
Reverse and Thrust Faults


Compressive stress
causes the hanging
wall to move upward
relative to the foot wall
 Reverse Fault
At convergent plate
boundaries ancient
rocks can be thrust
over younger rocks
 Thrust Fault
Structures at a Passive
Continental Margin

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Resulting from continental breakup
E.g., The Americas and Africa
Salt Domes: e.g., Texas

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Rising of less
dense salt
Stretches overlying
crust
Forming normal
faults and
Oil traps
Structural Oil Traps
Thrust Fault:
Glacier NP, Montana
Old
Younger
Structures at a Convergent Boundary
Structures within Mountain Belts
Compressional and Tensional
Structures
E.g., The Apls

Intense folding and thrusting of
sedimentary rocks
Strike Slip Faults

Physiographic Features
San Andreas Fault
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What type of fault is this?
What other features are
associated with the fault?