Lecture 5

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