Chapter 9 Folds, Faults,and Mountains
Three types of stresses
Types of Deformation
 ELASTIC DEFORMATION
 BRITTLE FAILURE
 PLASTIC DEFORMATION
 Elastic deformation
deformation not permanent (minor amount of stress)
 Brittle
stress amount exceeds the yield point or elastic limit
 Plastic (Ductile) deformation
stress applied gradually to deep warm rocks
Elastic Deformation
Plastic Deformation
Brittle Failure
Folding at Converging Plate Boundaries
Factors affecting rock deformation
 Intensity of Applied Stree
 Lithostatic Pressure
 Heat
leads to stretching of rocks at near Earth’s surface without breaking
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at depth- plastic deformation
 Time
 Composition
– different minerals have different strength
Deformed rocks in the field
 Most apparent in Sedimentary Rocks
 Importance of deformation
– Indicate Past Plate Motions
– Indicates other Past Geological Events
– Locates Specific Natural Resources
– Rock Orientation: Strike and Dip
Interpretation of Rock Deformation-Folds
 In describing folds, need to know the orientation of the rock in space- STRIKE and the angle
at which rock is inclined to the horizontal- DIP
 Folds- rocks deform plastically (most occur at convergent plates)
 Syncline- trough-like
 Anticline- arch-like
 Types of folds- symmetrical, broad, open, overturn, recumbent
 Basin
 Rock deformation that is bowl shaped.
 Domes
 Rock deformation that is ova-shaped bulges
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Geometry of anticlines and synclines
Artificial valleys and synclinal ridges
Artificial valleys and synclinal ridges-contd.
Various folds – Symmetrical (open)
Various Folds - Assymetrical
Various Folds - Overturned
Various Folds - Recumbent
Various Folds - Plunging
Structural Domes and Basins
Faults
A fracture is a break in a rock (joint or a fault)
Joints: Fractures with no relative movement
Fault is when there is relative movement along the break
Fault Types
 Strike-Slip fault
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horizontal movement (transform plate boundary)
 Dip-Slip fault
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Normal (tensional stress)
Reserve (compressional stress)
Thrust (low angle reserve fault)
Oblique (combination of strike-slip & dip-slip)
Evidence of Faults
 Visible displacement of rocks
 Pulverized rock
 Slickensides
 Discontinuity of Rock Sequences
 Types of Faults:
– Strike-Slip Fault
– Dip-Slip Fault
Fault Planes
Fault Disruption
Map of San Andreas Fault
Horizontal movement along strike-slip fault
Dip-slip Fault
Mid-Atlantic Ridge
Plate Tectonics and Faulting
 Normal Faults: Mid-Ocean Ridge & Continental Rifts
 Reverse and Thrust Faults: Convergent Plate Boundaries
 Strike-Slip Faults: Transform Boundaries
Geology at a Glance
Oblique Slip
Correlation of different fault types
Accumulation of Oil & Natural Gas
Accumulation of oil along fault planes
A terrace-producing scenario
The mountain ranges of North America
A terrace-producing scenario
Provinces of the Applachian mountain system
Mountainbelt collapsing
Mountainbelt collapsing-contd.
CHAPTER SUMMARY
DEFINITIONS OF STRESS, STRAIN
TYPES OF STRESS AT CONVERGING PLATE BOUNDARY
DIVERGING PLATE BOUNDARY
TRANSFORM PLATE BOUNDARY
ELASTIC, PLASTIC DEFORMATION
ELASTIC LIMIT
BRITTLE FAILURE
ROCKS SUBJECT TO HIGH TEMPERATURE
STRIKE AND DIP
WHEN MOST EXTENSIVE TYPE OF FOLDING OCCURS
DOMES AND BASIN – COMMONLY FOUND WHERE
WHAT IS A MOUNTAIN, MOUNTAIN RANGE
OROGENESIS
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