Deformation of rocks
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Deformation of Rocks. How Rocks Deform Brittle-Ductile Behavior Faulting and Folding. Stress and Strain. The keys to understanding any deformation are stress (the cause) and strain (the effect). Compression. Rocks are squeezed or compressed by forces directed toward one another.

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Deformation of Rocks

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Deformation of rocks

Deformation of Rocks

How Rocks Deform

Brittle-Ductile Behavior

Faulting and Folding


Stress and strain

Stress and Strain

  • The keys to understanding any deformation are stress (the cause) and strain (the effect)


Compression

Compression

  • Rocks are squeezed or compressed by forces directed toward one another.

  • Rocks are shortened by folding or faulting


Deformation of rocks

Plate Boundary: Convergence Zones


Tension

Tension

  • Rocks are lengthened or pulled apart by forces acting in opposite directions

  • Rocks are stretched and thinned


Deformation of rocks

Plate Boundary: Divergence Zones


Shear

Shear

  • Forces act parallel to one another but in opposite directions

  • Results in displacement of adjacent layers along closely spaced planes


Deformation of rocks

Plate Boundary: Transform Faults


Relationship between stress and strain

Rock

Stress

Rubber band

Strain 

Relationship between stress and strain

Elastic behavior

Fracture, breaks

X

Ductile behavior

Permanent strain


Relationship between stress and strain1

Stress

Strain 

Relationship between stress and strain

Brittle behavior:

Very little ductile deformation before fracturing

X

X

Fracture

Ductile behavior:

Extensive ductile deformation before fracturing


Deformation of rocks

Ductile

Brittle


Deformation of rocks

Ductile Behavior

Folding of Rocks

Brittle Behavior

Faulting of Rocks


What controls brittle vs ductile

What controls brittle vs. ductile?

  • Rate of deformation (fast = brittle)

  • Rock strength (strong = brittle)

  • Temperature (cold = brittle)

  • Confining pressure (shallow = brittle)

  • Just remember deeper = ductile

    • Near surface= rocks are brittle

    • At depth= rocks are ductile


  • What controls brittle vs ductile1

    What controls brittle vs. ductile?

    Rate of deformation (strain rate)

    Low strain rates Ductile (Mantle Convection)

    High strain rates  Brittle (Earthquake waves)


    Deformation of rocks

    Yield stress

    Elastic limit

    Effects of Temperature and Strain Rate


    Brittle ductile transition

    Brittle-DuctileTransition

    Limits the depths of

    earthquakes

    surface

    Brittle

    Low Temperature

    Low Pressure

    15-20 km

    Higher Temperature

    Higher Pressure

    Ductile

    Crust

    Mantle


    Deformation of rocks

    T=1300 C

    Yield

    strength=0

    Stress

    Strain

    Lithosphere-Asthenosphere

    schematic

    strength

    profile through

    continental

    lithosphere


    Deformation in progress

    Deformation in Progress


    Deformation of rocks

    Abrupt Movement along Faults


    Deformation of rocks

    Uplifted sea floor at Cape Cleare, Montague Island, Prince William Sound. Uplift about 33 ft


    Deformation of rocks

    LA

    SA

    uplift

    subsidence

    Gradual Movement: Perspective view of the Los Angeles region with superimposed InSAR( Interferometric Synthetic Aperture Radar) measurements of ground motions between May and September 1999. Large regions of metropolitan Los Angeles are rising and falling by up to 11 cm annually, and a large portion of the city of Santa Ana is sinking at a rate of 12 mm per year.


    Past deformation folding

    Past Deformation: Folding

    Large scale and small scale folds


    Folding large and small scale

    Folding: large and small scale


    Past deformation faulting

    Past Deformation: Faulting

    Large scale and small scale


    Deformation of rocks

    Strike and Dip


    Deformation of rocks

    Measuring Deformation in the Rocks Strike & Dip


    Faults

    Faults

    • Fractures along which there is relative motion parallel to the fracture

    • The fracture is called the fault plane

      • Vertical motion (dip-slip)

      • horizontal (strike-slip).

      • Most faults have a combination of both types of motion (oblique).


    Deformation of rocks

    Types of Faults

    Classified according to:

    Dip of fault

    Direction of relative movement


    Deformation of rocks

    Normal Fault (dip-slip)


    Normal faulting

    Normal Faulting

    Foot wall

    Hanging wall


    Deformation of rocks

    Tetons – fault range scale


    Basin and range

    Basin and Range

    Death Valley, CA

    Normal Faulting

    Horst-Graben Structures


    Deformation of rocks

    Reverse Fault (dip slip)

    > 45° dip


    Reverse faults

    Reverse Faults


    Deformation of rocks

    Thrust Fault (dip-slip)

    < 45° dip


    Deformation of rocks

    Thrust Fault

    Older rocks

    Younger rocks


    Deformation of rocks

    Thrust Faults. Snake Range, Wy


    Deformation of rocks

    Strike-Slip Fault (horizontal motion, no vertical motion)


    Strike slip fault

    Strike-Slip Fault


    San andreas fault

    San Andreas Fault

    • Transform plate boundary (Pac / N.A.)

    • System of right lateral faults


    Deformation of rocks

    Offset Streams (San Andreas Fault)

    A pair of streams that has been offset by right-lateral slip on the San Andreas fault (lineament extending from left to right edge of photograph). View northeastward across fault toward the Temblor Range. Photograph by Sandra Schultz Burford, U.S. Geological Survey.


    Strike slip fault1

    Strike-slip fault

    Off-set stream

    Right-lateral

    Strike-slip

    Stress: shear


    Types of folds

    anticline

    syncline

    Typesof Folds

    During mountain building or compressional stress, rocks undergo ductile deformation to produce folds


    Types of folds1

    Types of Folds


    Deformation of rocks

    Anticline: Warped upwards. Limbs dip outward. When eroded, oldest rocks crop out in the center (assuming everything is right-side-up).


    Deformation of rocks

    Syncline: Warped downwards. Limbs dip inward. When eroded, youngest rocks crop out in the center (assuming everything is right-side-up).


    Deformation of rocks

    Basins and Domes resemble anticlines & synclines

     vertical motions instead of lateral motions


    Stress strain plate tectonics

    Stress, Strain & Plate Tectonics

    • Plate collisions (convergent margins)

      • Compressive strsses

      • Folds & reverse faults


    Stress strain plate tectonics1

    Stress, Strain & Plate Tectonics

    • Divergent plate boundaries

      • Tensional stresses

      • Normal faults


    Stress strain plate tectonics2

    Stress, Strain & Plate Tectonics

    • Transform plate boundaries

      • Shear stress

      • Transform faults


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