Geology 3120 Introduction to Shear Zones

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Geology 3120 - Introduction to Shear Zones
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Outline

• Whats Going On With Shear Zones?
• Brittle Shear Zone
• Ductile Shear Zone
• Semi-Brittle Shear Zone
• Brittle-Ductile Shear Zone

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Formation of Shear Zones
All faults are shear zones but not all shear
zones are faults

• Brittle Deformation
• Ductile Deformation
• Zone of Deformation
• Discontinuous
• Continuous

• Brittle shear zones tend to form in the upper 5 -
  10 km
• Ductile shear zones are located in the mid-lower
  crust and aesthenosphere

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Controlling Factors

• Also mineralogy and grain size

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Brittle Shear Zones
P
A
E
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Brittle Shear Zones
A
E
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Brittle Shear Zones
E
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Brittle Shear Zones
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Example - Volcanic Tablelands
N
2 km
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Example - Volcanic Tablelands
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Volcanic Tablelands (horsetail splay)
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Ductile Shear Zones
Markers
Xenoliths/Plutons
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Ductile Shear Zones
Markers
Xenoliths/Plutons
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Ductile Shear Zones
Markers
Xenoliths/Plutons
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Example - Sheared Xenoliths
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Semibrittle Shear Zones
V
E
F
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Semibrittle Shear Zones
E
F
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Semibrittle Shear Zones
F
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Semibrittle Shear Zones
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En Echelon Vein Arrays

• Where is sigma 1?

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Brittle-Ductile Shear Zones
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Example - Brittle-Ductile Shear Zone

• Brittle deformation - feldspar crystals
• Ductile deformation - groundmass

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References
Slide 1 http//earth.leeds.ac.uk/shearzones/galler
y/kohi2.htm Slides 3, 5 - 8, 12 - 14, 16 - 19,
21 Davis. G. H. and S. J. Reynolds, Structural
Geology of Rocks and Regions, 2nd ed., John Wiley
Sons, New York, 776 p., 1996. Slide
9 http//terraserver.homeadvisor.msn.com/image.asp
x?t1s14x116y1296z11w2 Slide
15 http//earth.leeds.ac.uk/shearzones/gallery/lag
hetti.htm Slide 20 http//earth.leeds.ac.uk/minor
/tensiongash/index.htm Slide 22 www.brunel.ac.uk/
depts/geo/iainsub/ ShearKin/ShearKin.PPT