Transcript Structural Geology: Deformation and Mountain Building

1
Structural Geology:
Deformation and Mountain
Building
2
Tectonic Stresses  Large Scale Strain
of the Crust - Geologic Structures
Crust:
Rigid,
Thin
• Inner core: Solid iron
• Outer core: Liquid iron,
convecting (magnetic field)
• Mantle (Asthenosphere) : Solid
iron-magnesium silicate, plastic,
convecting
• Crust (Lithosphere): Rigid, thin
5-30km
Mantle:
Plastic,
Convecting
3
Tectonics and
Structural Geology
Tectonic Stresses resulting
from Internal Energy (heat
driving convection) Strains
(deforms) the Mantle and Crust
Bends Rocks
ductile strain (Folds)
•Breaks Rock
•brittle strain (Joints)
•Moves large blocks
•Faults
Releases energy Earthquakes
4
5
Folds and Faults (Palmdale, Ca)
6
Kaynasli, Turkey
7
Stresses at Plate
Boundaries
• Divergent
(Tensional)
|
• Convergent
(Compressional)
|
• Transform
(Shear)
e.g., Pacific NW
8
Geological
Structures
• Different stresses result in
various forms of strain
(geologic structures)
• Folds (compressive stresses
may cause ductile strain)
• Faults (Any type of stress
may cause brittle strain. The
type of fault depends on the
type of stress)
9
Geological Structures
• Fault: a discontinuity surface
across which there has been
shear displacement
• Hangingwall: the wall and body
of rock above an inclined fault
• Footwall: the wall and body of
rock beneath an inclined fault
10
Geological Structures
• Normal Fault: hanging wall
moved downwards compared
to the footwall
• Reverse Fault: hanging wall
moved upwards compared to
the footwall
• Thrust fault: low angle reverse
fault
11
Geological Structures
• Strike Slip Fault: displacement
parallel to the fault plane.
• Can be left or right handed!
12
Stikes and Dips are used to identify
geologic structures
13
Strike and Dip
• Define and map the orientation of planar
features
•
•
•
•
•
•
•
Bedding planes (sedimentary rocks)
Foliation
Joints
Faults
Dikes
Sills
Ore Veins
Fig. 10-4, p. 221
14
Strike and Dip
• Strike: The line of
intersection between the
plane and a horizontal
surface
• Dip: Angle that the plane
makes with that horizontal
plane
Strike and Dip Map
Symbol
Fig. 10-4, p. 221
15
Anticline (fold)
16
Syncline (fold)
17
18
Plunging
Anticline
19
Fold Terminology
• Hinge: the greatest
curvature of a folded
surface
Axis
• Axial plane: a planar
surface defined by the
successive positions of fold
hinges
• Plunge
Axis
20
Plunging Anticline, Colorado
21
Domes and Basins
22
23
Brittle Strain  Joints
• When shallow crust is strained
rocks tend to exhibit brittle strain
24
Sheet Joints
25
Defining Fault Orientation
• Strike of fault plane
parallels the
• fault trace
• fault scarp
• Direction of Dip of the
fault plane indicates the
Hanging wall block
26
Fault:
• Movement occurring along a discontinuity
• Brittle strain and subsequent movement as a result
of stress
• Fault terminology
27
Faults
• Fault: When
movement
occurs along a
discontinuity
• Fault type
depends on
the type of
stress
28
Normal Faults
29
Normal Faults, Horsts and Grabens
30
Horsts and Grabens
• Older Rocks are exposed along the ridges
formed by the horsts
Horst
Horst
Graben
Graben
• Younger rocks lie beneath the grabens
• Sediment fills in the linear valleys
31
Nevada
• “Washboard
topography” is the result
of Horsts and Grabens
• A.k.a, Basin and Range
• E.g., Humbolt Range
• E.g., Death Valley
(Graben)
32
Horst and Graben, Nevada
Horst
Graben
Humboldt Range, Northern Nevada
33
Horst and Graben, Nevada
Horst
Graben
Humboldt Range, Northern Nevada
34
Reverse and Thrust Faults
• Compressive stress
causes the hanging wall
to move upward
relative to the foot wall
 Reverse Fault
• At convergent plate
boundaries ancient
rocks can be thrust
over younger rocks 
Thrust Fault
35
Thrust Fault: Glacier NP, Montana
Old
Younger
36
Strike Slip Faults
• Physiographic Features