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Stress: Force per unit areaStrain: Change in length/area/volume to original length/area/volumeRocks are subjected to great forces- particularly at plate margins
Compression- converging plate boundaryTension- diverging plate boundaryShearing- transform plate boundary
Strain- rocks response to stress
Chapter 9 Folds, Faults,and Chapter 9 Folds, Faults,and Mountains Mountains
Three types of stressesThree types of stresses
Types of DeformationTypes of DeformationELASTIC DEFORMATIONBRITTLE FAILUREPLASTIC DEFORMATIONElastic deformation
deformation not permanent (minor amount of stress)
Brittlestress amount exceeds the yield point or elastic limit
Plastic (Ductile) deformationstress applied gradually to deep warm rocks
Elastic DeformationElastic Deformation
Plastic DeformationPlastic Deformation
Brittle FailureBrittle Failure
Folding at Converging Plate BoundariesFolding at Converging Plate Boundaries
Factors affecting rock deformationFactors affecting rock deformation
Intensity of Applied StreeLithostatic PressureHeat
leads to stretching of rocks at near Earth’s surface without breaking
at depth- plastic deformation
TimeComposition
– different minerals have different strength
Deformed rocks in the fieldDeformed rocks in the field
Most apparent in Sedimentary RocksImportance of deformation
– Indicate Past Plate Motions– Indicates other Past Geological Events– Locates Specific Natural Resources
– Rock Orientation: Strike and Dip
Interpretation of Rock Deformation-Interpretation of Rock Deformation-FoldsFolds
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-likeAnticline- arch-likeTypes of folds- symmetrical, broad, open, overturn,
recumbent Basin
Rock deformation that is bowl shaped. Domes
Rock deformation that is ova-shaped bulges
Geometry of anticlines and synclinesGeometry of anticlines and synclines
Artificial valleys and synclinal ridgesArtificial valleys and synclinal ridges
Artificial valleys and synclinal ridges-Artificial valleys and synclinal ridges-contd.contd.
Various folds – Symmetrical (open)Various folds – Symmetrical (open)
Various Folds - AssymetricalVarious Folds - Assymetrical
Various Folds - OverturnedVarious Folds - Overturned
Various Folds - RecumbentVarious Folds - Recumbent
Various Folds - PlungingVarious Folds - Plunging
Structural Domes and BasinsStructural Domes and Basins
FaultsFaults 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 horizontal movement (transform plate boundary)
Dip-Slip fault Normal (tensional stress) Reserve (compressional stress) Thrust (low angle reserve fault) Oblique (combination of strike-slip & dip-slip)
Evidence of FaultsEvidence of FaultsVisible displacement of rocksPulverized rockSlickensidesDiscontinuity of Rock Sequences
Types of Faults:– Strike-Slip Fault– Dip-Slip Fault
Fault PlanesFault Planes
Fault DisruptionFault Disruption
Map of San Andreas FaultMap of San Andreas Fault
Horizontal movement along strike-slip faultHorizontal movement along strike-slip fault
Dip-slip FaultDip-slip Fault
Mid-Atlantic RidgeMid-Atlantic Ridge
Plate Tectonics and FaultingPlate 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 GlanceGeology at a Glance
Oblique SlipOblique Slip
Correlation of different fault typesCorrelation of different fault types
Accumulation of Oil & Natural GasAccumulation of Oil & Natural Gas
Accumulation of oil along fault planesAccumulation of oil along fault planes
A terrace-producing scenarioA terrace-producing scenario
The mountain ranges of North AmericaThe mountain ranges of North America
A terrace-producing scenarioA terrace-producing scenario
Provinces of the Applachian mountain systemProvinces of the Applachian mountain system
Mountainbelt collapsing Mountainbelt collapsing
Mountainbelt collapsing-contd.Mountainbelt collapsing-contd.