Structural Geology
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 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
Folding
http://piru.alexandria.ucsb.edu/~geog3/concept_illus/1015_ex1.jpg
http://myweb.cwpost.liu.edu/vdivener/notes/faults_folds.gif
• Anticlines - where
layers are warped
upward
• Synclines - where
layers are warped
downward
• Compression of
ductile rocks
produces
alternating
anticlines and
synclines
Strongly Folded Rock
• Note quartzite
layer folded
back on itself Baraboo, WI
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
Devil’s Postpile Natl Mon, CA
Faults
Canyonlands Natl Park, UT
Merrimac Valley, NH
• Fractures in
rock along
which
movement has
occurred
• Different styles
reflect different
stresses
Dip-slip Faults
• Best seen in crosssection 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 Faults
• Result from
shear stresses best seen in
map view
(horizontal
offsets)
• Right-lateral vs.
left-lateral
http://epod.usra.edu/archive/images/carrizoplain.jpg
Bedrock Geology of Connecticut
http://soconnell.web.wesleyan.edu/courses/ees106/field_trips/ct_tectonics/images/CT_bedrockgeology_fault_enh.gif
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
http://z.about.com/d/geology/1/0/B/J/massgeomap.png