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

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

6. Duplex Duplex structures in quartzite

7. In-Sequence Thrusting

8. Out-of-Sequence Thrusting

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

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

11. Antiformal Duplex Displacement = length of horse Displacement = length of horse Rare Rare

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

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

14. Fenster (Window) and Klippe Fenster

15. Chief Mountain, Glacier National Park

16. Chief Mountain Compression Thrust initiation Thrust transport Erosion

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

18. Controlling Factors   If  i >  b, then  f(internal friction  i, basal friction  b, fluid pressure )  f(internal friction  i, basal friction  b, fluid pressure )  i,  i, bbbb  does not depend on length, width, or any size parameter

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

20. TaiwanWest East

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

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

23. 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