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DEFORMATION OF THE EARTHS CRUST
• Types of Deformation
1. folds
2. faults
Deformation
1. Elastic – nonpermanent, rock returns to original shape
2. Ductile – permanent, rock flows or bends
3. Brittle – permanent, rock breaks
Stress vs. Strain
Rheology
Deformation
For
ce
Ductile Brittle
How Rocks Become Deformed
1. compression forces
2. tensional forces
3. shearing forces
Stress vs. Strain
Rheology
Deformation
For
ce
Stress vs. Strain
Rheology
Deformation
For
ce
Folded Rocks
1. due to compressional forces
2. types of folds
i. monocline
ii. anticlines
iii. synclines
Monocline, WY
George Davis
Folded Rocks
3. anatomy of a fold
i. limbs
ii. axial plane
iii. plunge
Folded Rocks
2. types of folds
iv. overturned
v. asymmetrical
Bill Evarts
Axial plane
AnticlineAnticline
Fig. 10.11
Breck Kent
Asymmetric Folds
Phil Dombrowski Fig. 10.1
Overturned Folds
Folded Rocks
2. types of folds
vi. domes
vii. basins
Folded Rocks
2. effects of folds
i. mountain building (orogenies)
Fractured Rocks
1. How a rock breaks
i. joints
Fractured Rocks
1. How a rock breaks
i. joints
ii. faults
Anatomy of a fault
i. head wall (or hanging wall)
ii. foot wall
iii. fault plane
Anatomy of a fault
iv. strike & dip
Types of Faults• Strike-slip faults have movement that is predominantly
horizontal and parallel to the strike of the fault plane– A viewer looking across to the other side of a right-lateral
strike-slip fault would observe it to be offset to their right– A viewer looking across to the other side of a left-lateral
strike-slip fault would observe it to be offset to their left
• Oblique-slip faults have movement that with components parallel to both the strike and dip of the fault plane
Right-lateral San Andreas Fault
Effects of faulting
i. horsts and grabbens
Graben
Horst
Horst
Wildrose Graben, Southern California
NASA/TSADO/Tom Stack