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Geology 3120 - Horses and Wedges

Geology 3120 - Horses and Wedges. Outline. Horses and Wedges? Duplexes Fenster and Klippe Critical Taper Wedges in Thrust Faulting. Imbricate Fan. Thrust sheets splay off a sole thrust. Duplex. Sole thrust and roof thrust Blocks are surrounded by faults - horses. Duplex.

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Geology 3120 - Horses and Wedges

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  1. Geology 3120 - Horses and Wedges

  2. Outline • Horses and Wedges? • Duplexes • Fenster and Klippe • Critical Taper Wedges in Thrust Faulting

  3. Imbricate Fan Thrust sheets splay off a sole thrust

  4. Duplex • Sole thrust and roof thrust • Blocks are surrounded by faults - horses

  5. Duplex Duplex structures in quartzite

  6. In-Sequence Thrusting

  7. Out-of-Sequence Thrusting

  8. Duplex Categories • Dip of foreland and hinterland duplexes • Displacement verses length of horses

  9. Hinterland-Dipping Duplex • Displacement < length of horse • Most common

  10. Antiformal Duplex • Displacement = length of horse • Rare

  11. Forward-Dipping Duplex • Displacement > length of horse • Almost never

  12. Upheaval Dome Duplex • Map the horses • What kind of duplex is this?

  13. Fenster (Window) and Klippe Fenster

  14. Chief Mountain, Glacier National Park

  15. Chief Mountain • Compression • Thrust initiation • Thrust transport • Erosion

  16. Critical Tapered Wedge (Coulomb Wedge) • Shoveling snow • Bulldozing soil • Thrust systems in mountain belts

  17. Controlling Factors a mi,l b mb If mi > mb, then (a + b) = f(internal friction mi, basal friction mb, fluid pressure l) (a + b) does not depend on length, width, or any size parameter

  18. Wedge States a b • Subcritical - no slip on the detachment; sedimentation and thrusting build the wedge, erosion degrades the wedge • Critical - metastable state of a and b ”Steady State” • Supercritical - slip on the detachment, no internal deformation of the wedge

  19. Taiwan West East

  20. Sean Willett’s movie of particle paths through a critical wedge Need url for his website to run movie…

  21. Phaedra Upton’s movies of critical wedge through Puli, Taiwan Vertical strain = red; erosion included Vertical strain = red; erosion not included

  22. References Slide 1 http://www.mitani.com.au/pws.htm Slides 3, 4, 6, 7, 15, 17, 18 Davis. G. H. and S. J. Reynolds, Structural Geology of Rocks and Regions, 2nd ed., John Wiley & Sons, New York, 776 p., 1996. Slide 5 http://earth.leeds.ac.uk/faults/thrust/belts/duplex.htm Slides 8, 9, 10, 11, 12 Twiss, R. J. and E. M. Moores, Structural Geology, W. H. Freeman & Co., New York, 532 p., 1992

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