Crustal Deformation

1. Crustal Deformation

2. Take-Away Points • Structures in the earth have practical implications • Basic terms for earth structures • Small structures provide clues to much larger structures • The earth’s crust is floating on the denser mantle beneath • Gentle uplifts and downwarps affect the interiors of continents

3. Economic Consequences of Geologic Structures • Tracing Coal Seams, Aquifers, etc. • Ore Deposits are often localized along faults and folds • Petroleum Traps 1. Structures in the earth have practical implications

4. The Big Picture 1. Structures in the earth have practical implications

5. Anticlines and Synclines 2. Basic terms for earth structures

6. Monoclines and Homoclines 2. Basic terms for earth structures

7. Axial Plane 2. Basic terms for earth structures

8. How Fast Can Folds Form?

9. Siesta Valley

10. Which Way was Up? Sedimentary Structures are governed by: • Gravity • Exposure to the Surface They all have a “right way up” 3. Small structures provide clues to much larger structures

11. Foliation Foliation is a sheetlike structure that forms when rocks are deformed. 3. Small structures provide clues to much larger structures

12. Foliation • Flattening • Grain Rotation • Solution • New Minerals • Partial Melting • Shearing 3. Small structures provide clues to much larger structures

13. Foliation In every case, the foliation is: • In the direction of least resistance • at right angles to the direction of greatest compression. 3. Small structures provide clues to much larger structures

14. Folds and Foliation • On a small scale (microscopic to centimeters), foliation forms by a variety of mechanisms, but always at right angles to the direction of greatest compression • On a large scale (centimeters to kilometers), rocks fold. The axial plane of the fold is also at right angles to the direction of greatest compression 3. Small structures provide clues to much larger structures

15. Folds and Foliation 3. Small structures provide clues to much larger structures

16. The Importance of Minor Folds 3. Small structures provide clues to much larger structures

17. How Geologists Use These Clues • Here's an outcrop that might be seen in the field. 3. Small structures provide clues to much larger structures

18. How Geologists Use These Clues • Picture the axial plane of the fold as parallel to the foliation. • The other side of the fold is roughly a mirror image of the side we can see. 3. Small structures provide clues to much larger structures

19. How Geologists Use These Clues • We can mentally fill out the sketch to get an idea of the shape of the fold. • Note that we still have no idea how big the fold is, only what kind it is. 3. Small structures provide clues to much larger structures

20. What if we did it the other way? 3. Small structures provide clues to much larger structures

21. Isostasy 4. The earth’s crust is floating on the denser mantle beneath

22. The Airy Model 4. The earth’s crust is floating on the denser mantle beneath

23. The Pratt Model 4. The earth’s crust is floating on the denser mantle beneath

24. Both Ideas are Correct at Times 4. The earth’s crust is floating on the denser mantle beneath

25. How Isostasy Works 4. The earth’s crust is floating on the denser mantle beneath

26. Isostatic Rebound in Canada 4. The earth’s crust is floating on the denser mantle beneath

27. Isostatic Rebound in Scandinavia 4. The earth’s crust is floating on the denser mantle beneath

28. Domes and Basins 5. Gentle uplifts and downwarps affect the interiors of continents

29. Domes and Basins 5. Gentle uplifts and downwarps affect the interiors of continents

30. Domes and Basins 5. Gentle uplifts and downwarps affect the interiors of continents

31. Take-Away Points • Structures in the earth have practical implications • Basic terms for earth structures • Small structures provide clues to much larger structures • The earth’s crust is floating on the denser mantle beneath • Gentle uplifts and downwarps affect the interiors of continents