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GLG310 Structural Geology
Announcements
• Reminder: Application exercise on Tuesday, Sept. 17 in class
• How do videos look and work?• Homework questions?
May 3, 2023 GLG310 Structural Geology
Strain and deformation
• Stretch (strain) ellipse• Rotation of lines in deformation• Pure and simple shear• Progressive deformation• Deformation by change of volume
May 3, 2023 GLG310 Structural Geology
May 3, 2023 GLG310 Structural Geology
Moving from 1 to 2 to 3 dimensional deformation
• E and s as we have defined them in the last two lectures are 1 dimensional (measured along lf).
• In a deformed material; however, we can define the minimum and maximum stretches and they will be perpendicular
Smin=lfmin/l0
Smax=lfmax/l0
l0
l0
lfmax
lfmin
May 3, 2023 GLG310 Structural Geology
Principal stretches
SphereEllipsoid
In 3D, S1 is max, S3 is min, and S2 is intermediate
Cube Prism
May 3, 2023 GLG310 Structural Geology
Deformed trilobites do exist!
Draw the stretch ellipse for each
May 3, 2023 GLG310 Structural Geology
GLG310 Structural Geology
Angular shear
May 3, 2023 GLG310 Structural Geology
May 3, 2023 GLG310 Structural Geology
“Coaxial deformation”: Lines parallel to principle axes do not rotate
“Pure Shear”
May 3, 2023
“Non-Coaxial deformation”: Principle axes are constant but lines rotate with progressive deformation
“Simple Shear”
Progressive deformation
Cloos’ strain study
GLG310 Structural Geology
Measured stretch ratios in rocks from around the world
“Flattening” More common
“Con
stri
ctio
n”
-Suppe, 1985
Deformation by loss of material-dissolution-”styolites”
http://www.earth.lsa.umich.edu/~vdpluijm/animations/stylolite.mov
http://www.geol.umd.edu/~jmerck/geol100/images/15/stylolite.jpg
May 3, 2023 GLG310 Structural Geology
Stylolite: Wave-like or tooth-like, serrated, interlocking surfaces most commonly seen in carbonate and quartz-rich rocks that contain concentrated insoluble residue such as clay minerals and iron oxides. Stylolites are thought to form by pressure solution, a dissolution process that reduces pore space under pressure during diagenesis.
Schlumberger Oilfield Glossary http://www.glossary.oilfield.slb.com/Display.cfm?Term=stylolite
http://www.asaa.com.au/publications/magazines/DS16_DrDripstoneStylolites.pdf
May 3, 2023 GLG310 Structural Geology
GLG310 Structural Geology
Pro
gres
sive
stra
in
His
tory
of r
egio
nal d
efor
mat
ion
in
sout
hern
Ari
zona
Stretching and Shortening working together in partnership
-Pollard and Fletcher, Fundamentals of Structural Geology, 2005