Transcript map-view - Bakersfield College

Undisturbed Layers
How is rock deformation discussed?
(stress and strain relationships)
Stress
• force (pressure) acting on the rock surface
Strain
• a change in the shape (deformation) to the
response of stress
Compression
Tensional
undisturbed
cube
Shear
Types of stresses and strains
Confined Pressure
Differential Pressure
Stress is applied to the rock
“uniformially” in all directions
Stress is applied to the rock
in various directions
Uniformly “squeezed”
Strained in other directions
If you can see this cube “rotate”, then
you can picture diagrams in 3-D.
Structural Geology –
Structural geologists decipher earth history by
identifying and mapping deformational structures.
Why understand structural geology?
Decipher geologic history by looking at the subsurface
Look for oil resources
Look for mining resources
Monitoring groundwater flow
How does a geologist measure the orientation of
rock layers and use these measurements to predict the
geologic structure below the earth’s surface?
Strike and dip
Strike
The compass orientation of the line of intersection between
the a horizontal plane and a planer feature (a rock layer)
Dip
The angle between a tilted surface and a horizontal plane
Measuring the “strike” of strata
• represents the intersection of the tilted layer and
the imaginary horizontal plane
• A MAP symbol – showing the “directional trend”
of strata
Measuring the directional
trend
Map symbol
imaginary
plane
North
315
0
W 270
90 E
180
225
45
135
S
Strike is 45 degrees
How would you “plot” the strike of these rock layers
North
Geologic Maps
Strike represents the MAP orientation and
“general direction” of strata
Measuring the dip angle with respect to strike of
strata
• represents the ANGLE (tilt) of strata in
reference to the imaginary horizontal plane
• Dip is ALWAYS PERPENDICULAR to strike
Imaginary
plane
Strike and dip map symbols
12
20
Dip angle
0-90o
15
47
62
Let’s add some stresses and fold these rocks
Let’s add some stresses and bend the rock layers into
folds
Typical parts of a Fold
“leg” of the fold
The hinge line
apex of fold
Cuts the fold in
two equal parts
Interpreting folds
Young
Syncline fold
Youngest rocks
in the middle
Map Symbols
oldest
Anticline fold
Oldest rocks
in the middle
Map View
Map View
How can you tell the difference
between an anticline and syncline on the
MAP VIEW????
OLDEST found in middle
YOUNGEST found in middle
ANTICLINE
SYNCLINE
6
5 4
3
2
1
4
5
3 4
6
5
6
5
4
3
2
2
1
Folds are tilted or “plunged”
• How would the “map-view” of the plunging
fold appear from horizontal to steep tilt???
horizontal
Map Views
Slightly steep
Very Steep
Direction of plunge
• What happens to the map view of the anticline
as the plunge steepens?
Map view
Direction of plunge
Direction of plunge for anticlines
and synclines
Faults
Joint – fracture within a rock body
Fault – movement along a fracture or joint
B
A
fault
Joint
A
B
Determining the type of fault using the hanging-wall (HW)
and foot-wall (FW)
Normal Fault
• HW down relative to FW
• Tensional stress
HW
FW
FW
HW
HW
Reverse Fault
• HW up relative to FW
FW
• Compression stress
Vertical type faults
FW
HW
FW
HW
Normal faulting
FW
Reverse faulting
HW
HW
FW
Horizontal faulting – two blocks sliding past one another
Map View
Turned to Right
Turned to Left
What type of strike-slip fault?
Right-lateral – strike slip
Normal Fault
• hanging wall DOWN relative to footwall
• tensional forces (pulling apart)
• extension of crust (“crust grows”)
Reverse Fault
• hanging wall UP relative to footwall
• compressional forces (pushing together)
• shorting of crust (“crust shrinks”)
Strike-Slip fault
• horizontal movement (sliding past)
• moves rocks along a horizontal plane