Compression

1. Compression • The keys to understanding any deformation • are … (the cause) and … (the effect) • Rocks are squeezed or compressed by forces directed ... • Rocks are … by folding or faulting

2. Tension • Rocks are lengthened or pulled apart by forces … • Rocks are stretched and thinned

3. Shear • Forces act parallel to one another but … • Results in displacement of adjacent layers along closely spaced planes

4. Plate Boundary: Transform Faults

5. Rock Stress Rubber band Strain  Relationship between stress and strain Elastic behavior Fracture, breaks X Ductile behavior Permanent strain

7. What controls brittle vs. ductile? • Rate of … (fast = brittle) • Rock strength (strong = brittle) • … (… = brittle) • …. (… = brittle) • Just remember deeper = … • Near surface= rocks are …. • At depth= rocks are …

8. What controls brittle vs. ductile? Rate of … (strain rate) Low strain rates … (Mantle Convection) High strain rates  … (Earthquake waves)

9. Yield stress Elastic limit Effects of Temperature and Strain Rate

10. Brittle-DuctileTransition Limits the depths of … surface Brittle Low Temperature Low Pressure 15-20 km Higher Temperature Higher Pressure Ductile Crust Mantle

11. T=1300 C Yield strength=0 Stress Strain Lithosphere-Asthenosphere • Fig. 9.7 Schematic strength profile through continental lithosphere

12. Past Deformation: Folding Large scale and small scale folds

13. Folding: large and small scale

14. Past Deformation: Faulting Large scale and small scale

15. Measuring Deformation in the Rocks Strike & Dip

16. Faults • Fractures along which there is … motion parallel to the fracture • The fracture is called the fault plane • Vertical motion (dip-slip) • horizontal (strike-slip). • Most faults have a combination of both types of motion (oblique).

17. Types of Faults Classified according to: … … of relative movement

18. … Fault (dip-slip)

19. … Foot wall Hanging wall

20. Basin and Range Death Valley, CA Normal Faulting Horst-Graben Structures

22. Reverse Fault (dip slip) > 45° dip

23. Reverse Faults

24. Thrust Fault (dip-slip) < 45° dip

25. Thrust Fault Older rocks Younger rocks

26. Thrust Faults. Snake Range, Wy

27. Strike-Slip Fault (horizontal motion, no vertical motion)

28. Strike-Slip Fault

29. San Andreas Fault • Transform plate boundary (Pac / N.A.) • System of right lateral faults

30. Offset Streams (San Andreas Fault) A pair of streams that has been offset by right-lateral slip on the San Andreas fault (lineament extending from left to right edge of photograph). View northeastward across fault toward the Temblor Range. Photograph by Sandra Schultz Burford, U.S. Geological Survey.

31. Strike-slip fault Off-set stream Right-lateral Strike-slip Stress: shear

32. anticline syncline Typesof Folds During mountain building or compressional stress, rocks undergo ductile deformation to produce folds

33. Types of Folds

34. Anticline: Warped upwards. Limbs dip outward. When eroded, oldest rocks crop out in the center (assuming everything is right-side-up).

35. Syncline: Warped downwards. Limbs dip inward. When eroded, youngest rocks crop out in the center (assuming everything is right-side-up).

38. Basins and Domes resemble anticlines & synclines  vertical motions instead of lateral motions

40. Stress, Strain & Plate Tectonics • Plate collisions (convergent margins) • Compressive strsses • Folds & reverse faults

41. Stress, Strain & Plate Tectonics • Divergent plate boundaries • Tensional stresses • Normal faults

42. Stress, Strain & Plate Tectonics • Transform plate boundaries • Shear stress • Transform faults