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