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