Earth Sciences 1022A/B Lecture 9: Earth Science Lecture February 4 2016

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FEBRUARY 4 2016 LECTURE
CRUSTAL DEFORMATION
Rocks can be deformed to produce structures that can yield energy and ore reserves
Deformation
When rocks are stressed beyond their strength they change shape and size
Compressional Stress
oSqueezes rocks and shortens Earth’s crust
Tensional Stress
oStretches and lengths crust
Sheer Stress
oCauses sideways slip of crust
Strain
oWhat happens to rocks being stressed
Stress if force
Strain is results
Starts with elastic deformation where no permanent damage occurs but after stresses
pass the rock’s elastic limit (strength)
oPermanent damages occurs by brittle deformation that is common near the
surface under low pressure and temperature conditions or ductile deformation
that is common deep in the crust under high pressure and temperature
conditions
Mapping Geologic Structures
Geologists measure rock structures in outcrops using
oStrike
Compass direction of horizontal line on a planar surface of a bed or fault
oDip
Angle of inclination of the surface at a right angle to the strike
Folds
Due to compressional stress resulting in the shortening and thickening of the crust
Have limbs on either side of a fold axis and an axial plant that evenly divides the limbs
Anticline and syncline commonly occur together
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