GY 111: Physical Geology - University of South Alabama · · 2015-11-13GY 111: Physical Geology ....
Transcript of GY 111: Physical Geology - University of South Alabama · · 2015-11-13GY 111: Physical Geology ....
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GY 111: Physical Geology
UNIVERSITY OF SOUTH ALABAMA
Lecture 22: Folds
Instructor: Dr. Douglas W. Haywick
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Last time (before the exam)
A) Confining pressure and rock deformation B) Elastic versus permanent deformation C) Types of deformation
Rock Deformation
Web notes 20 Lab Manual Chapter 5
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Rock Deformation
Rock deformation: any change in the volume, shape or orientation of a rock body.
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Rock Deformation
The strength of materials (including rocks) can be tested in labs using hydraulic presses. All materials behave elastically up to a point. Once past the elastic limit, deformation becomes permanent.
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Stress & Strain
Stress: a force applied to an area (Example: tire pressure in psi)
Strain: the amount of deformation produced by stress
Elastic strain: analogous to a steel spring or rubber band Plastic strain: analogous to deforming mud or putty
Brittle strain: analogous to breaking glass
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Stress vs. Strain Diagrams • Illustrate the mechanical behavior of rock materials • Ductile deformation requires a significant component of
plastic mechanical behavior
Strain %
Stress Elastic Limit
plastic Ductile Deformation
Distortion below the elastic limit is 100% recoverable
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Stress vs. Strain Diagrams • Illustrate the mechanical behavior of rock materials • Brittle: rocks near the surface of the Earth behave as brittle
materials
Strain %
Stress
Distortion below the elastic limit is 100% recoverable
Rupture
Brittle Deformation
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Mechanical Behavior of Rocks Near-surface rocks that are under low T-P conditions behave as brittle material:
– Fault fracture (slippage) – Joint fracture (no slippage)
Deep rocks under elevated T-P conditions behave as ductile material:
– Folding
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Today’s Agenda
Web notes 22 Lab Manual Chapter 6
A) Types of folds B) Anatomy of a fold (terminology) Last Call for Mac and Cheese Bonus
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Folds
http://www.geosci.unc.edu/faculty/glazner/Images/Structure/Folds.html
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Folds
http://www.parstimes.com/spaceimages/zagros_anticlines.jpg
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Folds
http://www.geology.wisc.edu/~maher/air/130-27v.jpg
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Folds
Anticlines: Open downwards Synclines: Open upwards
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Folds
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Folds
Please note: Folds are 3-dimensional structures
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Folds
Folds are simply bent planes and as such, can be described using strike and dip connotation
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Folds
Folds are simply bent planes and as such, can be described using strike and dip connotation
Fold axes on maps are indicated with the following symbols:
Anticline Syncline
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Folds
A simple geological map of an anticline
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Folds
At the point(s) of maximum curvature, the dip of the fold is 0º
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Folds
Folds can be horizontal or plunging
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Plunging Folds
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Asymmetrical Folds
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Folds on Maps Some of you will interpret these in an upcoming lab exercise
Oblique View Geological Map (no scale implied)
Anticline
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Folds on Maps
Oblique View Geological Map (no scale implied)
Syncline
Some of you will interpret these in an upcoming lab exercise
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Folds on Maps As well as more complex structures
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Today’s Homework 1. Study! Why wait for the day before the final?
2. Assignment 4 next Thursday 3. Thursday lab students: sed rock exam
4. Go up to a total stranger and give them a hug (then run away very fast)
Next Time Faults
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GY 111: Physical Geology
Lecture 22: Folds
Instructor: Dr. Doug Haywick
This is a free open access lecture, but not for commercial purposes. For personal use only.