crustal deformation. types of deformation folds faults & joints
TRANSCRIPT
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