Geology 3120 Horses and Wedges

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Geology 3120 - Horses and Wedges
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Outline

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

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Imbricate Fan
Thrust sheets splay off a sole thrust
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(No Transcript)
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Duplex

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

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Duplex
Duplex structures in quartzite
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In-Sequence Thrusting
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Out-of-Sequence Thrusting
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Duplex Categories

• Dip of foreland and hinterland duplexes
• Displacement verses length of horses

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Hinterland-Dipping Duplex

• Displacement lt length of horse
• Most common

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Antiformal Duplex

• Displacement length of horse
• Rare

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Forward-Dipping Duplex

• Displacement gt length of horse
• Almost never

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Upheaval Dome Duplex

• Map the horses
• What kind of duplex is this?

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Fenster (Window) and Klippe
Fenster
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Chief Mountain, Glacier National Park
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Chief Mountain

• Compression
• Thrust initiation
• Thrust transport
• Erosion

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Critical Tapered Wedge (Coulomb Wedge)

• Shoveling snow
• Bulldozing soil
• Thrust systems in mountain belts

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Controlling Factors
a
mi, l
b
mb
If mi gt 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
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Wedge States

• 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

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Taiwan
West
East
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Sean Willetts movie of particle paths through a
critical wedge Need url for his website to run
movie
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Phaedra Uptons movies of critical wedge through
Puli, Taiwan
Vertical strain red erosion included
Vertical strain red erosion not included
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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/fa
ults/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