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.