Geology 3120 Horses and Wedges 1 Outline Horses

  • Slides: 23
Download presentation
Geology 3120 Horses and Wedges 1

Geology 3120 Horses and Wedges 1

Outline • Horses and Wedges? • Duplexes • Fenster and Klippe • Critical Taper

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

Imbricate Fan Thrust sheets splay off a sole thrust 3

Imbricate Fan Thrust sheets splay off a sole thrust 3

4

4

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

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

Duplex structures in quartzite 6

Duplex structures in quartzite 6

In-Sequence Thrusting 7

In-Sequence Thrusting 7

Out-of-Sequence Thrusting 8

Out-of-Sequence Thrusting 8

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

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

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

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

Antiformal Duplex • Displacement = length of horse • Rare 11

Antiformal Duplex • Displacement = length of horse • Rare 11

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

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

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

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

Fenster (Window) and Klippe Fenster 14

Fenster (Window) and Klippe Fenster 14

Chief Mountain, Glacier National Park 15

Chief Mountain, Glacier National Park 15

Chief Mountain • Compression • Thrust initiation • Thrust transport • Erosion 16

Chief Mountain • Compression • Thrust initiation • Thrust transport • Erosion 16

Critical Tapered Wedge (Coulomb Wedge) • Shoveling snow • Bulldozing soil • Thrust systems

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

Controlling Factors a b m i, l mb If mi > mb, then (a

Controlling Factors a b m i, l mb If mi > mb, then (a + b) = f(internal friction mi, basal friction mb, fluid pressure l) 18 (a + b) does not depend on length, width, or any size parameter

Wedge States a b • Subcritical - no slip on the detachment; sedimentation and

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

Taiwan West East 20

Sean Willett’s movie of particle paths through a critical wedge Need url for his

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

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,

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, 2 nd 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 23