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Folds

Folds. Read Davis and Reynolds, Chapter 7. Why is it important? fundamental to deformation of the Earth’s crust; structural traps for oil ore deposits. Tectonic considerations. Folds, key to covergent margins, aid in resolving past stress regimes, crustal

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Folds

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  1. Folds Read Davis and Reynolds, Chapter 7

  2. Why is it important? • fundamental to deformation of the Earth’s crust; • structural traps for oil • ore deposits

  3. Tectonic considerations Folds, key to covergent margins, aid in resolving past stress regimes, crustal shortening, closure of sedimentary basins. Sensitive markers to tectonic forces.

  4. Relevance to oil and mining • Structural traps (anticlines are among the best traps • Folds control ore geometry especially in strata-bound deposits

  5. Descriptive analysis • Basic definitions (anticline, syncline,overturned, etc.) • Geometric analysis (hinge, limb, axial plane, etc) • Specific geometries

  6. Shapes of folds younger older • Anticlines, synclines • Antiform, synform • Anticlinorium, synclinorium younger old

  7. Antiforms, synforms, anticlinoria, synclinoria

  8. Do not forget axial surface Hinge line Hinge, hinge zone Limb Axial plane Inflection point

  9. Recumbent Fold lies on its side- typical for poly-deformed regions

  10. Chevron Ptygmatic Cuspate

  11. Geometry, size Heigth Median trace Width Amplitude Wavelength

  12. Hinge line and axial plane

  13. Topographic Surfaces and folds

  14. Layer thickness may change during folding Didn’t here- this is a “concentric” fold This one did- it is a “similar” fold

  15. Fold tightness Gentle Angle is >90 degrees

  16. tight (10ish degrees opening) to isoclinal (0 degrees)

  17. Symmetric, asymmetric

  18. Cylindrical (there is an axial surface) and non-cylindrical (too complex to have a defined axial surface) Poles to bedding Hinge line Hinge line readings

  19. Cylindrical or non-cylindrical

  20. More descriptive terms?

  21. Example: Analyze this alpine example: Eocene Paleocene

  22. A second example

  23. A final example

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