Transcript Rock Deformation PowerPoint Presentation

Geological Structures
•
Joints
•
Faults
•
Shear Zones
•
Folds
•
Igneous Bodies
•
Unconformities
Geological Structures
Why do rocks deform?
STRESS (force per unit area)
• compressive stress
• tensional stress
• shear stress
Geological Structures
What is the result of stress?
STRAIN (deformation)
• brittle deformation
e.g. (faults/joints)
• plastic/ductile deformation
e.g. (folds/shear zones)
• elastic deformation
Geological Structures
What factors affect deformation?
Deforming everyday materials exercise!
Materials
Room temp
Chilled
Brittle
Ductile
Warmed
Elastic
Quick
Rubber
Band
Biscuit
Chocolate
Cling Film
Geological Structures
What factors affect deformation?
Deforming everyday materials exercise!
Materials
Rubber
Band
Room temp
elastic brittle brittle ductile
Chilled
elastic brittle brittle ductile
Ductile
Warmed
elastic brittle ductile ductile
Elastic
Quick
brittle brittle
Brittle
Biscuit
Chocolate
Cling Film
brittle brittle
Geological Structures
What factors affect deformation?
Deforming everyday materials exercise!
• temperature
• rate/speed of deformation (strain rate)
• properties of rock (competence)
Geological Structures
1. JOINTS
• Shrinkage joints
• Tectonic joints
• Pressure release joints
Geological Structures
2. FAULTS
• Normal fault
• Reverse fault
Vertical faults
• Thrust fault
• Tear fault
Horizontal faults
Normal Faults
NORMAL = lengthening of crust
due to tensional stress
ii
i
Upthrow side
iii
Dip of fault
Downthrow
side
i – throw
ii – net slip
iii – dip slip
Fault plane
Vertical Faults
NORMAL = lengthening of crust
due to tensional stress
Reverse Faults
REVERSE = shortening of crust due
to compressional stress
ii
i
i – throw
ii – net slip
iii – dip slip
iii
Dip of fault
Upthrow side
Downthrow
side
Fault plane
Thrust Faults
Dip of fault
Upthrow side
Downthrow
side
Fault plane
Tear Faults
Slickensides along Fault plane
Slickensides are
polished striated
rock surfaces
caused by one rock
mass moving
across another on
a fault.
Form minute steps
facing direction of
movement
Fault plane
Components of Principle Stress
Components of Principle Stress
Fault Structures
Thrust Fault Outcrop Pattern
Brampton BGS Map June 2000
Folds
Fold Geometry
Fold Geometry
Style of Folding
Fold Features
Interlimb Angles
Open ~ 120°
Close ~ 60°
Tight ~ 30°
Isoclinal ~ 0° (limbs parallel)
Fold Outcrop Patterns
Plunging Folds
Plunging Folds
Plunging Folds
Domes & Basins
Fold Mechanisms
Geological Structures
Flexural (parallel) Folds
•Thickness of individual layers are
constant, whether on crest or trough
•Impersistent – fold dies out as not
enough room to fit in
•Movement occurs along the boundaries
between layers by flexural movement
•Formed in strong/competent layers
•Thickness of the most competent
layer determines the fold wavelength
•Low temperature & pressure
•Outer zone of orogenic belt
•Slickenside lineations may occur
between layers
•Strain is low enough not to alter
thickness of the folded layer
•Helvetic Alps
Fold Mechanisms
Geological Structures
Flow (similar) Folds
•Maintains same curvature on the inner
and outer surfaces of the folded area
•Each layer is thinner on the flanks
and thicker on the axis of the fold
•Fold extends indefinitely – no space
problem
•Movement within layer occurs within
rock when it is ductile
•Develop in highly incompetent beds
which behave more as a viscous fluid
than a solid rock
•In slightly more competent rocks, shear folding occurs, this is
produced by differential movement along cleavage planes e.g.. slate
•Axial plane cleavage forms parallel to
fold axis
• High temperatures & pressure
•Inner zone of orogenic belt
•Pennine Alps
Unconformities
Unconformity
unconformity
Bedding
Folds
•
Bedding
•
Anticline/syncline
•
Joints
•
Upright/overturned/recumbent
•
Dip direction/angle
•
Symmetrical/asymmetrical
•
Strike
•
Axial plane
•
Trend
GEOLOGICAL
STRUCTURES
Faults
•
Normal
•
Reverse
• Lava flows
•
Thrust
• Dykes
•
Tear
Igneous Bodies
Unconformities
• Sills
• Batholiths
•
Formation
•
Recognition
Geological Structures
1. What sort of fault is this?
Geological Structures
2. What sort of fault is this?
Geological Structures
3. What sort of fault is this?
Geological Structures
4. What sort of structure is this?
Geological Structures
5. Describe this fold structure?
Geological Structures
6. What sort of fold is this?
Geological Structures
7. What structure is shown here?
Question 1
• Oldest beds are A & B
• Beds C to F dip NW
• The unconformity predates B
• The fault postdates A
Question 2
• The faults are reverse
• Unconformity predates the dyke
• Intrusions associated with the
faults
• Anticline postdates the dyke
Question 3
• Axial plane
• Fold axis
• Fold limb
• Fold dip
Question 4
• Fault below the outlier
downthrows West
• There are 2 dykes
• The intrusions are
associated with the faults
• The anticline postdates the
intrusions
Question 5
• Thrust faults
• Horst
• Strike-slip fault
• Rift valley
Question 6
• Gently dipping to the south
• Horizontal
• Gently dipping to the north
• Steeply dipping to the north
Question 7
A geologist measured the strike of
some strata as due East & their dip
as 10 degrees to the South. Which is
the correct notation?
• 180/10E
• 090/10S
• 010/090S
• 90/10S
Question 8
• Thrust fault
• Normal fault
• Strike-slip fault
• Reverse fault
Question 9
• Oldest rocks are A & B
• Beds C to F dip NW
• A & B are folded
• The fault is a strike-slip
fault
Question 10
• Fold limb
• Fold axis
• Fold nose
• Axial plane
Question 11
• Syncline plunging West
• Anticline plunging East
• Syncline plunging East
• Anticline plunging West
Question 12
• Reverse fault
• Normal fault
• Strike-slip fault
• Thrust fault
Question 13
• Steeply dipping to the South
• Steeply dipping to the North
• Vertical
• Gently dipping to the South
Question 14
• Sill is older than bed D
• Outlier was formed by erosion
• Unconformity postdates dyke
• Faults are reverse faults
Question 15
• Syncline plunging West
• Anticline plunging West
• Syncline plunging East
• Anticline plunging East
Question 16
• Syncline plunging East
• Anticline plunging West
• Anticline plunging East
• Syncline plunging West
Question 17
• Thrust fault
• Reverse fault
• Normal fault
• Strike-slip fault
Question 18
• Anticline
• Plunging anticline
• Plunging syncline
• Syncline
Question 19
• Thrust fault
• Rift valley
• Horst
• Strike-slip fault
Question 20
• Gently dipping to the North
• Beds are folded
• The fault is a reverse fault
• Green bed is the youngest