Structural Geology

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Structural Geology

• Deformation of rocks produces
• folds, joints, faults

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Monocline - southeastern Utah
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Northeastern California - note tilted layers
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http//faculty.uaeu.ac.ae/afarrag/physical20geol
ogy/GEODE1.jpg
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Wasatch Front NE of Salt Lake City, UT
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Types of Stresses

• Compressive ??? rocks are
  squeezed
• Tensile ??? rocks
  are pulled apart
• Shear ??? rocks
  are sheared

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Responses to Stress

• Folding - produced by compressive stress on
  ductile rocks
• Joints, Faults - produced by any type of stress
  on brittle rocks

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Folding

• Anticlines - where layers are warped upward
• Synclines - where layers are warped downward
• Compression of ductile rocks produces alternating
  anticlines and synclines

http//piru.alexandria.ucsb.edu/geog3/concept_ill
us/1015_ex1.jpg
http//myweb.cwpost.liu.edu/vdivener/notes/faults_
folds.gif
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Strongly Folded Rock

• Note quartzite layer folded back on itself -
  Baraboo, WI

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Joints

• Fractures in rock along which no movement has
  occurred - can form in response to any type of
  stress
• Often promote mechanical weathering since they
  provide access for water

Yellowstone Natl Park, WY
Devils Postpile Natl Mon, CA
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Faults

• Fractures in rock along which movement has
  occurred
• Different styles reflect different stresses

Canyonlands Natl Park, UT
Merrimac Valley, NH
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Dip-slip Faults

• Best seen in cross-section view (vertical
  offsets)
• Normal Faults - upper block slides down
  (tensional stress)
• Reverse Faults - upper block is pushed up
  (compressional stress)

http//northonline.northseattle.edu/gel101tb/image
s/fault2.jpg
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Faulting in Esker - near White River Jct., VT (??)
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Strike-slip Faults

• Result from shear stresses - best seen in map
  view (horizontal offsets)
• Right-lateral vs. left-lateral

http//epod.usra.edu/archive/images/carrizoplain.j
pg
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Bedrock Geology of Connecticut
http//soconnell.web.wesleyan.edu/courses/ees106/f
ield_trips/ct_tectonics/images/CT_bedrockgeology_f
ault_enh.gif
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Bedrock Geologic Map of Massachusetts

• Features to Note
• N-S striping compression from E-W
• NE-SW striping in E
• Cape consists of recent glacial sediment

http//z.about.com/d/geology/1/0/B/J/massgeomap.pn
g