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 km
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. These metamorphic rocks have been severely deformed and folded by the collision of tectonic plates in what is now Connecticut.

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
Figure 10.4: Strike and dip. The intersection of a horizontal plane (the water surface) and an inclined plane (the surface of any of the rock layers) forms a line known as strike. The dip of these layers is their maximum angular deviation from horizontal. Notice the strike and dip symbol with 50 adjacent to it, indicating the angle of dip.
Fig. 10-4, p. 221

14. Strike and Dip Map Symbol
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
Figure 10.4: Strike and dip. The intersection of a horizontal plane (the water surface) and an inclined plane (the surface of any of the rock layers) forms a line known as strike. The dip of these layers is their maximum angular deviation from horizontal. Notice the strike and dip symbol with 50 adjacent to it, indicating the angle of dip.
Fig. 10-4, p. 221

15. Anticline (fold)

16. Syncline (fold)

18. Plunging Anticline

19. Fold Terminology Hinge: the greatest curvature of a folded surface
Axial plane: a planar surface defined by the successive positions of fold hinges
Plunge
Axis Axis

20. Plunging Anticline, Colorado

21. Domes and Basins

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
Figure 10.11a: Fault terminology.

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
Younger rocks lie beneath the grabens
Sediment fills in the linear valleys
Horst
Horst
Graben
Graben

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
Figure 10.15b: View of the Humboldt Range in Nevada, which is a horst bounded by normal faults.
Graben
Humboldt Range, Northern Nevada

33. Horst and Graben, Nevada
Figure 10.15b: View of the Humboldt Range in Nevada, which is a horst bounded by normal faults.
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