Download - Structural Geology
Structural GeologyStructural Geology
Deformation of rocks produces:
folds, joints, faults
Deformation of rocks produces:
folds, joints, faults
Monocline - southeastern Utah
Northeastern California - note tilted layers
http://faculty.uaeu.ac.ae/~afarrag/physical%20geology/GEODE1.jpg
Wasatch Front NE of Salt Lake City, UT
Types of StressesTypes of Stresses
• Compressive →☐← rocks are squeezed
• Tensile ←☐→ rocks are pulled apart
• Shear ↑☐↓ rocks are sheared
• Compressive →☐← rocks are squeezed
• Tensile ←☐→ rocks are pulled apart
• Shear ↑☐↓ rocks are sheared
Responses to StressResponses to Stress
• Folding - produced by compressive stress on ductile rocks
• Joints, Faults - produced by any type of stress on brittle rocks
• Folding - produced by compressive stress on ductile rocks
• Joints, Faults - produced by any type of stress on brittle rocks
FoldingFolding
• Anticlines - where layers are warped upward
• Synclines - where layers are warped downward
• Compression of ductile rocks produces alternating anticlines and synclines
• 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_illus/1015_ex1.jpg
http://myweb.cwpost.liu.edu/vdivener/notes/faults_folds.gif
Strongly Folded RockStrongly Folded Rock
• Note quartzite layer folded back on itself - Baraboo, WI
• Note quartzite layer folded back on itself - Baraboo, WI
JointsJoints• 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
• 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
Devil’s Postpile Natl Mon, CA
FaultsFaults
• Fractures in rock along which movement has occurred
• Different styles reflect different stresses
• Fractures in rock along which movement has occurred
• Different styles reflect different stresses
Canyonlands Natl Park, UT
Merrimac Valley, NH
Dip-slip FaultsDip-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)
• 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/images/fault2.jpg
Faulting in Esker - near White River Jct., VT (??)
Strike-slip FaultsStrike-slip Faults
• Result from shear stresses - best seen in map view (horizontal offsets)
• Right-lateral vs. left-lateral
• Result from shear stresses - best seen in map view (horizontal offsets)
• Right-lateral vs. left-lateral
http://epod.usra.edu/archive/images/carrizoplain.jpg
http://soconnell.web.wesleyan.edu/courses/ees106/field_trips/ct_tectonics/images/CT_bedrockgeology_fault_enh.gif
Bedrock Geology of Connecticut
http://z.about.com/d/geology/1/0/B/J/massgeomap.png
Bedrock Geologic Map of Massachusetts
Features to Note:
1. N-S “striping”: compression from E-W
2. NE-SW “striping” in E
3. Cape consists of recent glacial sediment