1. Today’s list____________ Ch15: Rock Deformation
Mapping geologic structures
How rocks get deformed
3) Folds

2. Study questions____________ Ch15: Rock Deformation
·        
What type of tectonic forces makes a normal fault?
A reverse fault? A strike slip fault?
What is the difference between brittle and ductile deformation?
What are the strike and dip angle of a deformation?
What is the shape of an anticline, syncline, and what is the relative age of rocks exposed?
What type of deformation is the San Andreas Fault? The mid-ocean ridge?

3. 1) Mapping geologic structures
Deformational processes create faults, folds, joints
rock structures
Visible when rock beds are exposed at surface
out crops

4. 1) Mapping geologic structures Strike and dip
TSP 15.8

5. 1) Mapping geologic structures Strike and dip
Compass bearing of a rock layer relative to North
Angle of tilt of a bed from a horizontal plane
Strike
Dip
Fig.11.4

6. 1) Mapping geologic structures
N 75 E

7. 2) How rocks become deformed
Confining pressure: force equal in all directions
Differential stress: force not equal in all directions

8. 2) How rocks become deformed
Response to differential stress
1. Elastic deformation – the rock returns to nearly its original size and shape when the stress is removed
2. Brittle deformation
rocks crack/fracture
3. Ductile deformation
rocks flow
Shallow in crust
Deeper down

9. 2) How rocks become deformed
Fault definition: a fracture where displacement has occurred:
rocks on either side of fault have moved relative to each other.

10. 2) How rocks become deformed
Fault definition: a fracture where displacement has occurred:
rocks on either side of fault have moved relative to each other.

11. Joints Fractures where no slip has occurred Not same as a fault! Why?
Slip happens on faults!

12. 2) How rocks become deformed- brittle materials
Differential stress: force not equal in all directions
Compressive forces:
shortening

13. 2) How rocks become deformed- brittle materials
Differential stress: force not equal in all directions
Tensional forces:
stretching

14. 2) How rocks become deformed- brittle materials
Differential stress: force not equal in all directions
Shearing forces:
shearing

15. 2) How rocks become deformed - brittle materials

16. 2) How rocks become deformed - brittle materials
Fig
Rift valleys are the result of tensional forces in the crust, creating a series of normal faults.
The downfaulted blocks result in a Rift Valley.

17. 2) How rocks become deformed - brittle materials
St. Andreas fault is an example for a strike-slip fault
Because it is a plate boundary, it is also a transform fault
Fig

18. Fault System Example : San Andreas

19. shortening stretching Shearing/bending
2) How rocks become deformed- ductile materials
Differential stress: force not equal in all directions
Compressive forces:
shortening
Tensional forces:
stretching
Shearing forces:
Shearing/bending

20. 3) How rocks fold
series of wavelike undulations of once-flat rock layers
many sizes: microscopic to 100’s of meters
compressive stresses: shorten+thicken crust

21. 3) Folds Synclines fold downward… Anticlines fold upward…
Fig. Story 11.16

22. horizontal and plunging anticline
3) Folds
horizontal and plunging anticline
Plunging fold:
axis of fold
penetrates into
the ground
Fig

25. Plunging anticlines and synclines
See Fig

26. 3) Folds Types of folds Other deformations
Symmetrical, asymmetrical, overturning, plunging…..
dome - circular upwarping (anticlinal structure)
basin - circular downwarping (synclinal structure)
Fig 11.19