Term
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Definition
Refers to the force
Measured in force per unit area |
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Term
| Types of Stress and Strain |
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Definition
Compression, Tension, Shear (Stress)
Compresisonal, Tensional, Shear (Strain) |
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Term
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Definition
Refers to the deformation
The amount of deformation an object experienced compared to its original state |
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Term
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Definition
Brittle Deformation (Permanent)
Elastic Deformation (Non-permanent)
Plastic Deformation (Permanent) |
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Term
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Definition
(Permanent)
Breaks/fractures like a rigid body
Rocks are typically brittle at low pressures/temperatures |
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Term
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Definition
(Non-permanent)
Object deforms, but then returns to its original size and shape when the stress is released
Rubber band
Typically negligible in rocks |
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Term
| Plastic Deformation (Permanent) |
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Definition
(Permanent)
Object deforms, does not break, and undergoes non-reversible shape changes
Paper clip
Rocks deform plastically at high pressures/temperatures |
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Term
| Controlling Factors on Plastic versus Brittle Fracture Deformation |
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Definition
Temperature (High Temp = Plastic)
Confining Pressure
Strain Rate (High Strain Rate = Brittle)
Lithology (Rock types affect brittle/plastic)
Time |
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Term
| When will permanent deformation of rock occur? |
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Definition
| When the applied stress exceeds the strength of the rock. |
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Term
| When will nonpermanent (elastic) deformation occur? |
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Definition
| When weak stresses are applied. In such cases stress and strain are proportional. When the stress is reduced or removed the rock will return to its original form. |
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Term
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Definition
- The elastic response of the lithosphere following the removal of a large stress. (Continental glaciers, mountains, etc)
- Example of Elastic Deformation in geology
- Large mass deforms the crust elastically, when it is removed the crust bounces back to its original shape over thousands of years (about 1/10 of an inch/year) |
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Term
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Definition
| Isostatic rebound of the earth after glaciers receded. |
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Term
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Definition
The northern Great Lakes area is isostatically rebounding 5 mm per year. Eventually the Great Lakes will be drained via the Mississippi River system. |
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Term
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Definition
Anticlines and synclines are symmetric folds that form from bi-directional compressive stress. The anticline on the right is plunging into the slide. |
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Term
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Definition
As anticlines and synclines erode note the outcrop pattern in the center of the eroding fold. Which fold will expose the oldest rock in the center (near its axis) as it erodes. Note the difference in outcrop pattern of the plunging anticline versus the non-plunging folds on the left of the slide. |
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