3. About Deformation
• Deformation mainly occurs near plate
boundaries.
• Field observations of deformation show
us how to reconstruct geologic history.
• Deformation includes faulting of rigid
rocks and folding of rocks that can be
bent.
10. 2. Mapping Geologic Structure
● Measuring strike and dip
● strike is the compass
direction of a rock layer as it
intersects a horizontal surface
● dip is the amount of tilting of
the layer and is measured at
right angles to strike
11. 2. Mapping Geologic Structure
N
W
S
ion Strike d
ect
irecti
dir
on
Dip 45°
Dip
angle
E
N
W
S
45°
Dip angle
E
12. 2. Mapping Geologic Structure
N
W
S
ion Strike d
ect
irecti
dir
on
Dip 45°
Dip
angle
E
N
W
S
Water trickles down
slope parallel to dip.
45°
Dip angle
E
14. 2. Mapping Geologic Structure
● Geologic maps
● geologic maps represent
the rock formations
exposed at Earth’s surface
● a common scale for
geologic maps is 1:24,000
15. 2. Mapping Geologic Structure
● Geologic cross sections
● geologic cross sections –
diagrams showing the
features that would be
visible if vertical slices were
made through part of the
crust
16.
17. 3. How Rocks Deform
● Rock behavior in the laboratory
● brittle
● ductile
20. Under conditions
representative of the
shallow crust, the
marble is brittle.
Under conditions
representative of
the deeper crust,
marble is ductile.
An undeformed sample
21. 3. How Rocks Deform
● Rock behavior in the Earth’s crust
● depths affect brittle v. ductile
● rock type affects way rocks
deform
● rate of deformation is a factor
22. 4. Basic Deformation Structures
● Types of faults
● dip-slip – normal, reverse,
and thrust
● strike-slip – right- and leftlateral
● oblique-slip
49. Thought questions for this chapter
The submerged margin of a continent has a thick layer of
sediments overlying metamorphic basement rocks. That
continental margin collides with another continental
mass, and the compressive forces deform it into a fold
and thrust belt. During the deformation, which of the
following geologic formations would be likely to behave
as brittle materials and which as ductile materials?
(a) sedimentary formations in the upper few km
(b) metamorphic basement rocks at depths of 5-15
km
(c) lower crustal rocks below 20 km
In which of these layers would you expect earthquakes?
50. 6. Unraveling Geologic History
● Geologic history is a
succession of episodes
of deformation and other
geologic processes.
● Can be described in time
steps 1, 2, 3, …
