Transcript Dip-slip faults

Classroom presentations
to accompany
Understanding Earth, 3rd edition
prepared by
Peter Copeland and William Dupré
University of Houston
Chapter 10
Folds, Faults, and Other
Records of Rock Deformation
Deformation of Rocks
Deformation of rocks
• Folds and faults are geologic
structures.
• Structural geology is the
study of the deformation of
rocks and the effects of this
movement.
Small-scale Folds
Phil Dombrowski
Fig. 10.1
Small-scale Faults
Tom Bean
Fig. 10.2
Orientation of deformed rocks
We need some way to describe the
distribution of geologic structures.
Strike: bearing of a line defined by
the intersection of the plane in
question and the horizontal
Dip: acute angle between the plane
and the horizontal, measured
perpendicular to strike.
Fig. 10.4
Fig. 10.4
Dipping Sedimentary Beds
Chris Pellant
Fig. 10.3
Cockscomb Ridge, S. Utah
P.L.
Kresan
P.L.
Kresan
Cockscomb Ridge, S. Utah
Strike
Dip
P.L. Kresan
Geologic
Map and
Cross
Section
Fig. 10.5
Stress
(force per unit area)
Types of directed stresses include:
• Compression
• Extension
• Shear
Compression
Action of coincident oppositely directed forces
acting towards each other
Tension
Action of coincident oppositely directed
forces acting away from each other
Shear
Action of coincident oppositely directed
forces acting parallel to each other
across a surface in a couple
Strength
• Ability of an object to resist
deformation
• Compressive or tensile
Strain
Any change in original shape or size
of an object in response to stress
acting on the object
Types of deformation
• Elastic
• Ductile (plastic)
• Brittle (rupture)
Elastic deformation
Temporary change in shape or
size that is recovered when
the deforming force is
removed
Ductile (plastic) deformation
• Permanent change in
shape or size that is not
recovered when the stress
is removed
• Occurs by the slippage of
atoms or small groups of
atoms past each other in
the deforming material,
without loss of cohesion
Brittle deformation (rupture)
• Loss of cohesion of a
body under the
influence of deforming
stress
• Usually occurs along
sub-planar surfaces
that separate zones of
coherent material
Factors that affect deformation
• Temperature
• Pressure
• Strain rate
• Rock type
The variation of these factors
determines if a rock will fault or fold.
Effects of rock type on deformation
Some rocks are
stronger than
others.
competent: rocks that
deform only under
great stresses
incompetent: rocks
that deform under
moderate to low
stresses
Tectonic Forces and Resulting
Deformation
Fig. 10.6
Experimental Deformation of Marble
Brittle Deformation
Ductile Deformation
Fig. 10.7
M.S. Patterson
Types of folds
(bent planar structures)
anticline: older rocks on the inside
syncline: older rocks on the outside
(scale - from mm to tens of km)
Anticlines and Synclines
Fig. 10.9
Fold terms
• axial Plane: the plane of mirror
symmetry dividing the fold into two
limbs
• axis: line formed by the intersection of
the axial plane and a bedding plane
• horizontal fold: where the fold axis is
horizontal
• plunging fold: where the fold axis is
not horizontal
Fold Terminology
Fig. 10.10
Bill Evarts
Fig. 10.11
Symmetrical, Asymmetrical
and Overturned Folds
Fig. 10.12
Anticline
Axial plane
Bill Evarts
Fig. 10.11
Asymmetric Folds
Antiform
Breck Kent
Synform
Overturned Folds
Phil Dombrowski
Fig. 10.1
Overturned
Syncline,
Israel
Geological Survey of Israel
Fig. 10.13
Map View of
Plunging
Folds
Fig. 10.14
Oil Field at
crest of
Plunging
Anticline
Kurt N. Coonstenius
Axial Trace of
Plunging
Anticline*
* Note Landers Oil Field
on crest of anticline
Kurt N. Coonstenius
Valley and Ridge Province
P. L. Kresan
Plunging Folds in the
Valley and Ridge
J. Shelton, Geology illustrated
Fig. 10.15
Valley and
Ridge
Province of
the
Appalachian
Mountains
Fig. 10.19
Raplee Anticline, S.E. Utah
Raplee Anticline on the San Juan River, Utah
Domes and Basins
Fig. 10.16
Sinclair Dome, Wyoming
John S. Shelton
Fig. 10.17
Syncline
Fig. 10.18
Drape Fold over Reverse Fault, WY
George Davis
Columns
Formed by
Jointcontrolled
Weathering
Terry Englander
Fig. 10.20
Joint-controlled Landscape, S.E. Utah
Faults
Fractures in rocks created by
earthquakes
(hanging wall, footwall, displacement)
• Dip-slip faults
— normal
— reverse
• Strike-slip faults
• Oblique-slip faults
Faults may be "reactivated"
History of a fault may be very long.
Previously developed weakness is the
most likely place to break.
Reactivation may have opposite sense
as before.
Active = 10,000 to 100,000 years
Very important for dams and reactors
Dip-slip faults
Motion of the fault blocks,
parallel to the dip direction.
Classification of Faults
hanging wall
footwall
cross section
Classification of Faults
hanging wall
footwall
cross section
Normal Fault
hanging wall
footwall
cross section
Reverse Fault
hanging wall
footwall
cross section
Thrust Fault
Thrust faults are low-angle reverse faults.
hanging wall
footwall
cross section
Fig. 10.22
Fig. 10.22a
Normal Dip-slip Fault
Fig. 10.22b
Reverse Dip-slip Fault
Strike-slip faults
Motion of the fault blocks,
parallel to the strike direction.
Left-lateral Strike Slip Fault
map view
Right-lateral Strike Slip Fault
map view
Fig. 10.22c
Strikeslip
Fault
Gudmundar E. Sigvaldason
Fig. 10.21
Fig. 10.22d
Large-scale Overthrust Sheet
Fig. 10.23
Keystone Thrust Fault, S. Nevada
Cambrian Limestone
Jurassic
Sandstone
John S..Shelton
Fig. 10.24
Lewis
Thrust,
Sawtooth
Range,
Wyoming
Kurt N. Coonstenius
French Thrust, Wyoming
Mississippian
Limestone
Cretaceous Shale
Kurt N. Coonstenius
Rift Valley Formed by Extension
Fig. 10.25
Wildrose Graben, Southern California
NASA/TSADO/Tom Stack
Fig. 10.26
Stages in the Development of
the Basin and Range Province
in Nevada and Utah
Fig. 10.27
Stages in the Development of
the Basin and Range Province
in Nevada and Utah
Fig. 10.27
1872 Fault Scarp, Southern California
1988 Armenian Earthquake Fault Scarp
Armando Cisternas
Fig. 10.28
1992
Landers
Earthquake
Fault Scarp
Dating the order of deformation
Use geometry:
Inclusions
Cross-cutting relationships
Combine with fossils and radiometric
dating