Folds and Faults

What allows a rock to deform?

What allows a rock to deform? Temperature Pressure ….?

Granite vs. gypsum?

Salt Dome

What allows a rock to deform? Temperature Pressure Rock type ….?

What allows a rock to deform? Temperature Pressure Rock type Time

Overturned fold Syncline Anticline Where are the oldest rocks?

Plunging folds

Plunging folds – need ages

Where’s the syncline? Where’s the anticline?

Domes and basins…what is their origin?

Domes and basins result from plate tectonic forces in continental interiors

Where’s the oldest material?

Domes and Basins

How do the ages vary? B

Brittle versus ductile deformation Strain – change in shape Stress - extension Stress - extension

Brittle versus ductile deformation Strain – change in shape Stress - extension Stress - extension Folding Faulting

What causes ductile deformation? Temperature Pressure Rock type Time

What causes ductile deformation? Temperature - high Pressure - high Rock type – low strength (i.e. gypsum) Time - long

What causes brittle deformation? Temperature Pressure Rock type Time

What causes brittle deformation? Temperature - low Pressure – high Rock type – high strength (i.e. granite) Time - short

Fold types: 2-dimensional 3-dimensional 1) ? ? 2) ? ? What kind of stress regime do these folds represent?

Fold types: 2-dimensional 3-dimensional 1) Anticlines Domes 2) Synclines Basins What kind of stress regime do these folds represent? - Compressional

Brittle versus ductile deformation Strain – change in shape Stress - extension Stress - extension Folding Faulting

Reverse Fault Thrust Fault

Compressional Setting Reverse Fault Thrust Fault

Extensional Setting

Compression or Extension?

What is the age progression? What kind of fault does this have to be? Extension or compression? ground surface Cap rock

Normal Fault Layers Repeat Extension 5 4 3 4 3 2 1 Cap rock

What is the age progression? What kind of fault does this have to be? Extension or compression? ground surface

Reverse Fault Layer Skipped Compression 6 5 4 2 1

Strike-slip fault – horizontal displacement only

What is the offset direction?

What is the offset direction? Left-lateral Right-lateral

San Andreas Fault

Loch Ness Is the Loch Ness Monster a Plesiosaur?

Loch Ness Great Glen Fault (strike-slip)

Three fault types: Fault Stress regime Motion (V/H)? 1) ? ? ? 2) ? ? ? 3) ? ? ?

Three fault types: Fault Stress regime Motion (V/H)? 1) Normal Extension Vertical 2) Reverse Compression Vertical (Thrust) 3) Strike-slip Bi-directional Horizontal

What causes this texture?

What causes this texture?

Expansion

What causes this texture?

Joints – 3 common formation mechanisms Joint type Cause 1) ? ? 2) ? ? 3) ? ?

Joints – 3 common formation mechanisms Joint type Cause 1) Columnar Contraction 2) Sheeting Expansion 3) Fault zone Prior faulting

Crustal Deformation – Folding Faulting Jointing Give information about stresses acting on the rock