Crustal Deformation

Crustal Deformation

• Types of Deformation

• Folds

• Faults & Joints

Terms

• Dip angle– Angle of tilt away from horizontal

Types of Deformation

GEOL131: Crustal Deformation

Elastic• Rock bends but snaps back to original

shape– Earthquakes

• Elastic limit– Capacity of rock for elastic deformation

• If elastic limit exceeded, deformation is permanent

GEOL131: Crustal Deformation: Types of Deformation

Brittle• Rock breaks

• Colder, harder, and shallower rock tends to be brittle

GEOL131: Crustal Deformation: Types of Deformation

Ductile• Rock bends

permanently

• Deeper, hotter, weaker rock tends to be ductile

GEOL131: Crustal Deformation: Types of Deformation

Folds

GEOL131: Crustal Deformation

Folded Rocks• Product of ductile deformation

• Form at deep crustal levels– Rock is warmer

GEOL131: Crustal Deformation

Basic Fold AnatomyGEOL131: Crustal Deformation: Folds

Axis

Limb Lim

b

Anticlines & SynclinesGEOL131: Crustal Deformation: Folds

DomesGEOL131: Crustal Deformation: Folds

BasinsGEOL131: Crustal Deformation: Folds

MonoclinesGEOL131: Crustal Deformation: Folds

Fold OrientationsGEOL131: Crustal Deformation: Folds

• Symmetrical– Both limbs have same dip angle

• Asymmetrical– Limbs have different dip angles

Fold OrientationsGEOL131: Crustal Deformation: Folds

• Overturned– One limb tilted more than 90 degrees

• Recumbent– Both limbs horizontal

Fold OrientationsGEOL131: Crustal Deformation: Folds

•Upright– Fold axis

not tilted

•Plunging– Fold axis is

tilted

Recognizing folds in map view

GEOL131: Crustal Deformation: Folds

• What patterns do folds make on the Earth’s surface?

• There is usually no cross-section view available to geologists

Recognizing folds in map viewGEOL131: Crustal Deformation: Folds

• Upright anticline

• Upright syncline

Oldest layer

Youngest layer

Recognizing folds in map viewGEOL131: Crustal Deformation: Folds

• Upright anticline

• Upright syncline

Oldest layer at center

Youngest layer at center

Recognizing folds in map viewGEOL131: Crustal Deformation: Folds

Arrows show direction of fold axis tilt

Oldest layer at center

Youngest layer at center

Recognizing folds in map viewGEOL131: Crustal Deformation: Folds

Dome: oldest layer at center

Basin: youngest layer at center

Faults & Joints

GEOL131: Crustal Deformation

Basic Fault AnatomyGEOL131: Crustal Deformation: Faults & Joints

Hanging Wall

Footwall

• Normal faults

• Reverse faults

• Thrust faults

Dip-Slip FaultsGEOL131: Crustal Deformation: Faults & Joints

Dip-Slip Faults: NormalGEOL131: Crustal Deformation: Faults & Joints

Dip-Slip Faults: ReverseGEOL131: Crustal Deformation: Faults & Joints

Dip-Slip Faults: ThrustGEOL131: Crustal Deformation: Faults & Joints

• Normal faults– Tensional stress– Hanging wall moves down

• Reverse faults– Compressional stress– Hanging wall moves up

• Thrust faults– Compressional stress– Footwall moves up– Lower angle than reverse faults

Dip-Slip Faults: SummaryGEOL131: Crustal Deformation: Faults & Joints

• Left-lateral

• Right-lateral

• Caused by shear stress

Strike-Slip FaultsGEOL131: Crustal Deformation: Faults & Joints

Strike-Slip FaultsGEOL131: Crustal Deformation: Faults & Joints

(Right-lateral)

Joints• Fractures with no

movement

• Cause accelerated weathering

GEOL131: Crustal Deformation: Faults & Joints

Weathered joints in southern Utah

Mountain Building

GEOL131: Crustal Deformation

Types of Tectonic Mountain Building

•Subduction zone

•Continental collision

•Fault-block mountains

GEOL131: Crustal Deformation: Mountain Building

New Term

GEOL131: Crustal Deformation: Mountain Building

ACCRETIONARY WEDGE: Sediment & rock scraped off subducting plate onto overriding plate

Mountains Built at Subduction Zones

•Volcanic arc

•Uplifted accretionary wedge

•Uplifted igneous intrusions

•Accreted volcanic island arc

GEOL131: Crustal Deformation: Mountain Building

Mountains Built at Subduction Zones: Volcanic arc

GEOL131: Crustal Deformation: Mountain Building

Mountains Built at Subduction Zones: Uplifted accretionary wedge

GEOL131: Crustal Deformation: Mountain Building

Mountains Built at Subduction Zones: Uplifted accretionary wedge

GEOL131: Crustal Deformation: Mountain Building

Mountains Built at Subduction Zones: Uplifted igneous intrusions

GEOL131: Crustal Deformation: Mountain Building

Mountains Built at Subduction Zones: Accreted Volcanic Island Arc

GEOL131: Crustal Deformation: Mountain Building

Mountains Built by Continental Collisions

GEOL131: Crustal Deformation: Mountain Building

Mountains Built by Continental Collisions

GEOL131: Crustal Deformation: Mountain Building

Continental escape: blocks of continental crust are pushed away from a continental collision zone

Mountains Built by Continental Collisions

• Compressional stress

• Folding

• Reverse and thrust faulting

GEOL131: Crustal Deformation: Mountain Building

Fault Block Mountains

• Tensional stress

• Normal faulting

GEOL131: Crustal Deformation: Mountain Building

Fault Block Mountains

GEOL131: Crustal Deformation: Mountain Building

Grand Tetons

End of Chapter