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II. Basic Techniques in Structural Geology

II. Basic Techniques in Structural Geology. Field measurements and mapping Terminology on faults and folds Stereographic projections From maps to cross-sections Growth Strata Fault-related folds Seismic Imaging. Growth and pre-growth strata.

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II. Basic Techniques in Structural Geology

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  1. II. Basic Techniques in Structural Geology • Field measurements and mapping • Terminology on faults and folds • Stereographic projections • From maps to cross-sections • Growth Strata • Fault-related folds • Seismic Imaging

  2. Growth and pre-growth strata • The assumption of beds with constant thickness holds generally for ‘pre-growth’ strata. Syntectonic deposition will induce lateral variations of bed thickness. Such strata are called ‘growth strata’.

  3. (Burbank and Verges, 1994)

  4. Fault-bend folding … The non planar fault has a flat-ramp-flat geometry. Translation of the thrust sheet along that fault requires axial surfaces. Note the difference between the active and passive axial surfaces Courtesy of Frederic Perrier

  5. Example: Structure of a Fault-bend fold with Growth strata Growth triangles (Suppe et al., 1997; Hubert-Ferrari et al, 2007)

  6. Pre-growth strata

  7. Growth strata

  8. (Suppe et al, Journal of Structural Geology, 1996)

  9. Growth triangle…

  10. foldscarp… buttress unconformity

  11. growth axial surface as disconformity…

  12. Buttress unconformity…

  13. angular unconformity…

  14. growth axial surface as unconformity…

  15. 2 growth unconformities…

  16. II. Basic Techniques in Structural Geology • Field measurements and mapping • Terminology on faults and folds • Stereographic projections • From maps to cross-sections • Growth Strata • Fault-related folds • Seismic Imaging

  17. Two types of fault-related fold(drawn here assuming flexural slip folding) Fault-bend fold Fault-propagation fold

  18. Fault-Bend Fold • Fault Bend Folds (FBF) =ramp anticlines • throughgoing faults - slip is conserved. • Fold amplitude is determined by the thickness above the lower hanging wall flat. • Once the fold has achieved maximum amplitude, it only grows in width.

  19. Duplex system

  20. Thrust fault hangingwall and footwall ramps and flats…

  21. Fault-Propagation Fold Fault Propagation Folds (FPF) • fault slip is not conserved. Fault displacement is taken up by folding • Fault tip is marked by a ductile ‘process zone’. • Ideally, FPF’s evolve into FBF’s

  22. Fault-tip Folds Detachment fold (folding is always non-parallel) Fault-propagation fold (non-parallel fold) Fault-propagation Fold (parallel fold)

  23. ‘Drag folds’ Footwall rocks are commonly deformed into synclines Could also relate to fault propagation

  24. Footwall syncline in the Canadian Cordillera

  25. Let’s practice…

  26. Primary strucure due to cross-bedding stratification. Not related to deformation

  27. Describe: from: http://earth.leeds.ac.uk/learnstructure/index.htm from: http://www.stmarys.ca/academic/science/geology/structural/

  28. similar fold parallel fold from: http://earth.leeds.ac.uk/learnstructure/index.htm from: http://www.stmarys.ca/academic/science/geology/structural/ Recumbent tight similar syncline and anticline Upright open parallel syncline

  29. try to sketch: shallowly plunging, upright, tight, similar syncline Assume fold axis plunges toward N45E

  30. Example from the Argentinian Cordillera

  31. What is it?

  32. Fault related Folds all from: http://earth.leeds.ac.uk/learnstructure/index.htm http://earth.leeds.ac.uk/learnstructure/index.htm

  33. Fault related Folds Fault-tip Fold Fault-bend Fold http://earth.leeds.ac.uk/learnstructure/index.htm

  34. Fault related Folds fault propagation fold fault-bend fold all from: http://earth.leeds.ac.uk/learnstructure/index.htm

  35. A case study of a fold and thrust belt: The North Tian Shan Piemont A B (Charreau et al, 2008)

  36. Growth strata record of Kink Band migration (Huerguosi Anticline) A B (Charreau et al, 2008) (Suppe et al., 1997; Hubert-Ferrari et al, 2007)

  37. Modeling 12 equations ex: Kinematic model (Charreau et al, 2008)

  38. (Charreau et al, 2008)

  39. Modeling dip angles Bedding expected from the pure Fault-bend fold model Bedding measured in surface Bedding expected from the fault-bend fold model with growth strata (Charreau et al, 2008)

  40. Long Term History of Shortening (Charreau et al, 2008)

  41. Sedimentation History Accumulation rates– Piggy back Accumulation rates- magnetostratigraphy (Charreau et al, 2008)

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