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Compression

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

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Compression

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  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

  6. 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 …

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

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

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

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

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

  12. Folding: large and small scale

  13. Past Deformation: Faulting Large scale and small scale

  14. Measuring Deformation in the Rocks Strike & Dip

  15. 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).

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

  17. … Fault (dip-slip)

  18. … Foot wall Hanging wall

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

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

  21. Reverse Faults

  22. Thrust Fault (dip-slip) < 45° dip

  23. Thrust Fault Older rocks Younger rocks

  24. Thrust Faults. Snake Range, Wy

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

  26. Strike-Slip Fault

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

  28. 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.

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

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

  31. Types of Folds

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

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

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

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

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

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

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