1 folds, faults and the deformation of earth’s crust cockscomb structure in utah
TRANSCRIPT
1
Folds, Faults and the Deformation of Earth’s Crust
Cockscomb structure in Utah
2
Pre-crash
Post-crash
What Happened to this car?
It was deformed (folded) because of the collision
1984
3
Coincidentally, note how this car is so much more safe
The car deformed like an accordionwhile the passenger compartment did not suffer.That is possible because the front part of thecar absorbs the stress by folding.
4
Stress vs. Strain
The force applied to some body is the stress.
The changes to that body are the strain that is recorded.
You work very hard lifting things.
Your back is strained.
5
Silly Putty
Silly Putty absorbs the Stress that is
applied to it when it hits the floor. However, the Strain is released when it bounces away from that Stress.
Silly Putty is elastic, it bounces if it were dropped on the floor.
6
The Slinky
The Slinky is Elastic i.e. it can be stretched and stretched but it snaps back to its original length.
7
The 1st Type of Stress: Compression: occurs when crustal rocks
are squeezed together
Can reduce the volume of rocks, can push the rocks higher up or deeper down into the crust
8
The 2nd Type of Stress Tension: the force that pulls rocks apart
Rocks that are pulled apart by tension tend to become thinner
9
The Final Type of Stress Shearing: pushes rocks in opposite
horizontal directions
These rocks bend, twist, or break apart as they slide past each other.
10
The Deformed Earth Plate tectonics and the movement of
lithospheric plates causes the Earth’s crust
to DEFORM….
“No, no, don’t look at me!!! I’m hideous!!”
11
Isostasy and the Mattress Test Have you ever seen the commercial for
foam mattresses where they place a glass of red wine on one side and a man jumps up and down on the other side?
Isostasy: the balancing of up-and-down movements of the earth’s crust.
12
What happened to these rocks?
What evidence do you see, which caused your interpretation?
13
A. compressive forcesB. shearing forcesC. tensional forcesD. all of the above
Which of the following types of tectonic forces tends to squeezeand shorten a rock body?
14
A. compressive forcesB. shearing forcesC. tensional forcesD. all of the above
Which of the following types of tectonic forces tends to squeeze and shorten a rock body?
This looks like the safe carbecause of how it folded
15
What type of forces dominate at convergent plate margins?
A. compressive forces
B. shearing forces
C. tensional forces
D. torsional forces
16
A. compressive forcesB. shearing forces
C. tensional forces
D. torsional forces
What type of forces dominate at convergent plate margins?
17
The San Andreas Fault is a result of what type of forces?
A. compressive forces
B. shearing forces
C. tensional forces
D. all of the above
18
The San Andreas Fault is a result of what type of forces?
A. compressive forces
B. shearing forcesC. tensional forces
D. all of the above
19
Which of the following statements best describes the behavior of rocks during deformation?
A. Brittle materials deform by faulting, whereas ductile materials deform by folding.
B. Brittle materials deform by folding, whereas ductile materials deform by faulting.
C. Both brittle and ductile materials deform by faulting.
D. Both brittle and ductile materials deform by folding.
20
Which of the following statements best describes the behavior of rocks during deformation?
Marble is specialbecause it can beBrittle or Ductile
depending onPressure and Temperature
Brittle materials deform by faulting
T- High or Low?P- High or Low?
T- High or Low?P- High or Low?
ductile materialsdeform by folding
21
The principles ofOriginal Horizontality and Superpositionapply-
These are Sedimentary Rocks
But these layers are not any longer Horizontal
folded
must
have beenThey
22
These Rocks were Brittle so they were fractured to form a Fault
The faults were not causedby Compression Forces
a
a
b
b
23
These Rocks were Brittle so they were fractured to form a Fault
The faults were not caused by Compression Forces
aa
b
b
The length of the rock formationis greater than the original lengthbecause of the type of fault
The faults were causedby Tension
24
More FOLDED Sedimentary Rocks
But HOW MUCH have they been folded?
or
How can one measure the angle that theyhave rotated from the original horizontal?
25
Measuring the orientationof a surface
26
Rocks also have a Strike and Dip
Strike- the direction to which the horizontal line points
27
Geological Map shows the rocks exposed on surface over which you are walking
28
3- D View of Geological Structures
Outcro
p the view w
here th
e rocks h
ave been verti
cally cut
thro
ugh for a
new h
ighway o
r natu
ral e
rosio
n
Plan view i.e. the surface that one looks down to see
The sameformation
29
Ductile Materials and Deformation
They undergo Plastic Deformation i.e.
they change shape and do not break but
do not return to their original form
30
Combinations of Stresses
31
A Rift Valley formed by Extension
32
Fresh Scarp Faceshowing surface exposed by a very recent earthquake
*
*
33
Symmetrical Folds
34