Transcript Earth_Can01_ch09/15 Structures/Crustal

Chapter 9: Structures &
Mountain Building
 PowerPoint
Presentation
 Stan Hatfield . SW Illinois College
 Ken Pinzke . SW Illinois College
 Charles Henderson . University of
Calgary
 Tark Hamilton . Camosun College
Copyright (c) 2005 Pearson Education
Canada, Inc.
1
Chapter 9: Structural Deformation
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Forces
Origin
Nomenclature
Structural Geology: A Study of
Earth’s Architecture
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Earth is a dynamic planet. Some rock units in the
Canadian Rockies have been thrust for over 100
kilometres
Structural geologists study the architecture and
processes responsible for deformation of Earth’s
crust
A working knowledge of rock structures is
essential to our economic well-being for hazards
& resources
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15-5
Caledonides formed Late Paleozoic with the closing
of Iapetus Ocean, forming Pangea
Deformation
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Deformation involves
 Stress
- force applied to a given area
 Types of stress (differential stress that is applied
unequally in different directions)
Compressional stress – shortens a rock body
 Tensional stress – tends to elongate or pull apart a
rock unit
 Shear stress – produces a motion similar to the
slippage that occurs between individual playing
cards when the top of the stack is moved relative to
the bottom
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Compression
(convergence)
Tension
(uplift)
Shear
(lateral
rotation)
Deformation

How Rocks Deform
 Rocks
subjected to stresses greater than their own
strength begin to deform usually by folding,
flowing, or fracturing
Weaker rocks deform more easily (lithology, bedding)
 Fluids and Heat affect lower strength
 Pressure increases rock strength

 General
characteristics of rock deformation
Elastic deformation – the rock returns to nearly its
original size and shape when the stress is removed
 Once the elastic limit (strength) of a rock is surpassed, it
either flows slowly (ductile deformation) or fractures
quickly (brittle deformation)
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 This depends on Strain Rate and Time/Duration 15-10
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Deformed Lacustrine Strata,
{Normal Fault} Palmdale, CA
Increasing Confining Pressure/Depth
Brittle
S max
S int
S min
Ductile
Shear
reorients
Foliation
Strike: intersection of dipping
rock layer with horizontal surface
& contact direction on map
(azimuth relative to north)
Dip: Angle below horizontal
Folds
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During crustal deformation rocks are often bent
into a series of wave-like undulations called folds
Characteristics of folds
 Most
folds result from compressional stresses
which shorten & thicken the crust: mountain belts
 Parts of a fold
Limbs – refers to the two sides of a fold
 Axis – a line drawn down the points of maximum
curvature of each layer
 Axial plane – an imaginary surface that divides a fold
more or less symmetrically
 Asymmetry points in the direction of crustal transport,
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Education Canada
Inc. over, vergence
roll
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Strike & Dip Permits 3-D Visuals
Read the map symbols:
Visualize the Cross Sections
Folds
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Common types of folds
 Anticline
– upfolded or arched rock layers
Oldest in the middle
 Outwards directed, antithetic dips
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 Syncline
– downfolds or troughs of rock layers
Youngest in the middle
 Inwards directed, synthetic dips
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 Depending
on their orientation, anticlines and
synclines can be described as
Symmetrical, asymmetrical, recumbent (an overturned
fold), or plunging
 Antiform & Synform when age is unknown
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 Anticlinorium
or Synclinorium for continental size 15-17
Education Canada Inc.

Symmetric Anticline
Opposing outwards dips
Oldest beds in middle
Plunging Anticline
Strike wraps around
Nose points down plunge
East Verging Fold & Thrust Belt
 Vergence (transport) Direction 
Kink Folds, Sharp Axial Planes:
Syncline
Anticline
Plunging
Folds:
Tilted or
Refolded
Fold Belt
Doubly Plunging Anticline
or Asymmetric Dome
Chevrons on flank of Monocline
Compression
Drape Fold
Reverse Fault in Basement
Folds
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Common types of folds
 Monoclines
– large, step-like folds in otherwise
horizontal sedimentary strata
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Other types of folds
 Dome
Upwarped displacement of rocks
 Circular or slightly elongated structure
 Oldest rocks in centre, younger rocks on the flanks
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 Basin
Downwarped displacement of rocks
 Circular or slightly elongated structure
 Youngest rocks in centre, older rocks on the flanks
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15-25
Salt, Intrusion
Or Central Uplift
Subsidence
Black Hills, SD
Cretaceous
(Laramide
Orogeny)
Deforms Mesozoic
through
Precambrian
Rocks
Mz
Pz
Pc
Late Paleozoic
Michigan
Basin
Faults
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Faults are fractures in rocks along which appreciable
displacement has taken place
Brittle/Shallow in the upper crust
 Ductile/Deep in the lower crust
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Sudden movements along faults are the cause of most
earthquakes usually deeper than 5 km to about 660 km
Along faults, rock is often broken into breccia, pulverized
into gouge or polished as slickenslides
Faults are classified by their relative orientation &
movement which can be
Horizontal, vertical, or inclined
 Strike Slip, Dip Slip or Oblique Slip
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Normal Fault
(Tension)
Faults
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Types of Faults
 Dip-Slip
Faults: (Normal, Reverse & Thrust)
Movement is mainly parallel to the dip of the fault
surface
 May form in either compression or tension
 Normal faults thin the crust & miss out some strata
 Reverse & Thrust Faults thicken the crust & double
some strata
 May produce long, low cliffs called fault scarps
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Active if fault cuts to surface
Resequent if erosional & controlled by strata
Parts of a dip-slip fault include the hanging wall (rock
surface above the fault) and the footwall (rock surface
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below
the fault)
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
Normal Fault: (Extension)
Normal Fault: (Extension)
Hanging Wall Falls
Section Thins
Faults
Types of dip-slip faults
Normal Faults
 Hanging wall block moves down relative to the
footwall block
 Accommodate lengthening or extension of the crust
 Many are small like landslides with displacements of
a metre or so
 Larger scale normal faults are associated with Mid
Ocean Ridges, Rifts & Fault-block mountains,
Horsts & Grabens
Reverse & Thrust Faults
 Hanging wall block moves up relative to the footwall
block
 Accommodate shortening or compression of crust
 Larger scale thrust faults are associated with edges of
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Fold & Thrust Mountain Belts
Faults: Horst & Graben as in Rifts or
Basin & Range
Diagrammatic sketch of downfaulted (graben) and
upfaulted (horst) blocks.
Note that there are places where if you drilled there is
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missing
stratigraphy
due to extensional faulting.
Development of
a Normal Fault
Most
Normal
Faults
“sole-out”
and become
Listric with
depth.
Faults: Thrust & Reverse
 Types

of dip-slip faults
Reverse and Thrust Faults
 Hanging wall block moves up relative to the footwall
block
 Reverse faults have dips greater than 45o and thrust
faults have dips less than 45o
 Most thrust faults have flat soles and arise from a
common surface called a decollement
 Accommodate shortening of the crust
 Strong compressional forces
 Common in mountain belts like the Alps and Rockies
 An isolated outlying remnant of a thrust sheet is
called a klippe (old rocks surrounded by younger
rocks, Teeth point inwards)
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Reverse Fault: (Compression)
Hanging Wall Rises
Section Thickens
Angle > 15°
Thrust Fault: (Compression)
Laramide Orogeny Rockies
Section thickens
Older over younger
Thrust Vergence direction
Crowsnest
Mountain
Paleozoic Limestone
Klippe:
Thrust
Outlier
Cretaceous Shales
Right Lateral Strike Slip Fault:
Like Queen Charlotte & San Andreas
Columnar Joints: Thermal Cooling
Joints from from Decompression