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