1.  Stress: Force per unit area  Strain: Change in length/area/volume to original length/area/volume  Rocks are subjected to great forces- particularly at plate margins  Compression- converging plate boundary  Tension- diverging plate boundary  Shearing- transform plate boundary  Strain- rocks response to stress Chapter 9 Folds, Faults,and Mountains

2. Three types of stresses

3. Types of Deformation ELASTIC DEFORMATION BRITTLE FAILURE PLASTIC DEFORMATION Elastic deformation  deformation not permanent (minor amount of stress) Brittle  stress amount exceeds the yield point or elastic limit Plastic (Ductile) deformation  stress applied gradually to deep warm rocks

4. Elastic Deformation

5. Plastic Deformation

6. Brittle Failure

7. Folding at Converging Plate Boundaries

8. Factors affecting rock deformation Intensity of Applied Stree Lithostatic Pressure Heat  leads to stretching of rocks at near Earth’s surface without breaking  at depth- plastic deformation Time Composition – different minerals have different strength

9. Deformed rocks in the field Most apparent in Sedimentary Rocks Importance of deformation – Indicate Past Plate Motions – Indicates other Past Geological Events – Locates Specific Natural Resources – Rock Orientation: Strike and Dip

10. Interpretation of Rock Deformation- Folds In describing folds, need to know the orientation of the rock in space- STRIKE and the angle at which rock is inclined to the horizontal- DIP Folds- rocks deform plastically (most occur at convergent plates)  Syncline- trough-like  Anticline- arch-like  Types of folds- symmetrical, broad, open, overturn, recumbent Basin  Rock deformation that is bowl shaped. Domes  Rock deformation that is ova-shaped bulges

11. Geometry of anticlines and synclines

12. Artificial valleys and synclinal ridges

13. Artificial valleys and synclinal ridges- contd.

14. Various folds – Symmetrical (open)

15. Various Folds - Assymetrical

16. Various Folds - Overturned

17. Various Folds - Recumbent

18. Various Folds - Plunging

19. Structural Domes and Basins

20. Faults A fracture is a break in a rock (joint or a fault) Joints: Fractures with no relative movement Fault is when there is relative movement along the break Fault Types  Strike-Slip fault  horizontal movement (transform plate boundary)  Dip-Slip fault  Normal (tensional stress)  Reserve (compressional stress)  Thrust (low angle reserve fault)  Oblique (combination of strike-slip & dip-slip)

21. Evidence of Faults Visible displacement of rocks Pulverized rock Slickensides Discontinuity of Rock Sequences Types of Faults: – Strike-Slip Fault – Dip-Slip Fault

22. Fault Planes

23. Fault Disruption

24. Map of San Andreas Fault

25. Horizontal movement along strike-slip fault

26. Dip-slip Fault

27. Mid-Atlantic Ridge

28. Plate Tectonics and Faulting Normal Faults: Mid-Ocean Ridge & Continental Rifts Reverse and Thrust Faults: Convergent Plate Boundaries Strike-Slip Faults: Transform Boundaries

29. Geology at a Glance

30. Oblique Slip

31. Correlation of different fault types

32. Accumulation of Oil & Natural Gas

33. Accumulation of oil along fault planes

34. A terrace-producing scenario

35. The mountain ranges of North America

36. A terrace-producing scenario

37. Provinces of the Applachian mountain system

38. Mountainbelt collapsing

39. Mountainbelt collapsing-contd.