deformation mechanisms: what strain occurred in this...
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Deformation Mechanisms: What strain Deformation Mechanisms: What strain occurred in this rock?occurred in this rock?
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OutlineOutline
Main Mechanisms and Factors:Main Mechanisms and Factors:
1.1. MicrofracturingMicrofracturing,, CataclasisCataclasis, and Frictional Sliding, and Frictional Sliding
2.2. Mechanical Twinning and KinkingMechanical Twinning and Kinking
3.3. Diffusion CreepDiffusion Creep
4.4. Dissolution CreepDissolution Creep
5.5. Dislocation CreepDislocation Creep
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Main Mechanisms and FactorsMain Mechanisms and Factors
Processes that permit Processes that permit
rocks to deform at rocks to deform at
microscopic and atomic microscopic and atomic
scales:scales:
•• Differential Stress and TemperatureDifferential Stress and Temperature
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Potential FactorsPotential Factors
•• MineralogyMineralogy
•• Grain sizeGrain size
•• TemperatureTemperature
•• Differential stressDifferential stress
•• Confining pressureConfining pressure
•• Strain rateStrain rate
•• Fluid (or lack of); fluid pressureFluid (or lack of); fluid pressure
•• Constructive and destructive effectsConstructive and destructive effects
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MicrofracturingMicrofracturing, , Cataclasis Cataclasis & Frictional Sliding& Frictional Sliding
•• Brittle deformation on the grain Brittle deformation on the grain toto subgrain subgrain scalescale
•• Development, propagation and Development, propagation and slip of slip of microcracksmicrocracks
•• Frictional sliding and flow of Frictional sliding and flow of crushed rock & crystal material crushed rock & crystal material ((Cataclastic Cataclastic FlowFlow) along grain ) along grain boundariesboundaries
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Mechanical Twinning & KinkingMechanical Twinning & Kinking
•• Bending of the crystalline Bending of the crystalline lattice without brittle failurelattice without brittle failure
•• Lattice is deformed along Lattice is deformed along discrete planesdiscrete planes
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CreepCreep
•• A slow, timeA slow, time--dependent straindependent strain
•• Differential stresses are not great enough to produce brittle Differential stresses are not great enough to produce brittle failurefailure
•• The The ThreeThree Creeps Creeps -- Diffusion, Dissolution, DislocationDiffusion, Dissolution, Dislocation
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Diffusion CreepDiffusion Creep
•• Influenced by average kinetic energy (temperature)Influenced by average kinetic energy (temperature)
•• A vacancy or defect needs to occur for atoms to move A vacancy or defect needs to occur for atoms to move through the crystal latticethrough the crystal lattice
•• Atoms can move through grains, along grain boundaries, Atoms can move through grains, along grain boundaries, and through pore space (with fluid present)and through pore space (with fluid present)
•• The presence of fluids speed up diffusion creep The presence of fluids speed up diffusion creep
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Three Types of Diffusion CreepThree Types of Diffusion Creep
••VolumeVolume--diffusion creepdiffusion creep -- diffusion occurring within a graindiffusion occurring within a grain
••GrainGrain--boundary diffusion creepboundary diffusion creep -- diffusion occurring along a diffusion occurring along a
grain boundarygrain boundary
••Superplastic Superplastic creepcreep -- graingrain--boundary sliding and grainboundary sliding and grain--
boundary diffusionboundary diffusion
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Dissolution CreepDissolution Creep
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Dissolution CreepDissolution Creep
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Dissolution CreepDissolution Creep
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Dislocation CreepDislocation Creep
•• Distortion of the crystal lattice on a slip planesDistortion of the crystal lattice on a slip planes
•• Bonds progressively break along the slip planeBonds progressively break along the slip plane
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Dislocation CreepDislocation Creep
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Dislocation CreepDislocation Creep
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Dislocation CreepDislocation Creep
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Dislocation CreepDislocation Creep
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Dislocation CreepDislocation Creep
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Dislocation CreepDislocation Creep
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Recovery andRecovery and RecrystallizationRecrystallization
•• To “repair” dislocations, the crystal structure must be returnedTo “repair” dislocations, the crystal structure must be returnedto the previous state ( i.e., no dislocations)to the previous state ( i.e., no dislocations)
•• RecoveryRecovery -- rearrangement and destruction of dislocationsrearrangement and destruction of dislocations
•• Recrystallization Recrystallization andand neomineralizationneomineralization -- transformation of transformation of old “defective” grains into brandold “defective” grains into brand--new grains or new new grains or new configurations of grains:configurations of grains:
•• Rotation of grain boundariesRotation of grain boundaries
•• Migration of grain boundariesMigration of grain boundaries
•• DynamicDynamic recrystallizationrecrystallization -- recovery andrecovery and recrystallization recrystallization during deformationduring deformation
•• AnnealingAnnealing -- recovery andrecovery and recrystallization recrystallization after deformation after deformation
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RecoveryRecovery
• Dislocation climb -
rearrangement of
dislocations
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RecrystallizationRecrystallization ExampleExample
100 100 µµmm
UndeformedUndeformed Black Hills Quartzite (average grain size 100 Black Hills Quartzite (average grain size 100 µµm)m)
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RecrystallizationRecrystallization
100 100 µµmm
50% shortening, 800°C, 120050% shortening, 800°C, 1200 MPaMPa, ~0.2% wt. H, ~0.2% wt. H22OO
Dislocation creep is occurringDislocation creep is occurring
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RecrystallizationRecrystallization
100 100 µµmm
57% shortening, 900°C, 120057% shortening, 900°C, 1200 MPaMPa, ~0.2% wt. H, ~0.2% wt. H22OO
RecrystallizationRecrystallization is occurringis occurring
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RecrystallizationRecrystallization
100 100 µµmm
60% shortening, 800°C, 120060% shortening, 800°C, 1200 MPaMPa, 120 hrs at 900°C, 120 hrs at 900°C
RecrystallizationRecrystallization and annealing completeand annealing complete
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ReferencesReferences
Slide 1Slide 1http://talc.geo.umn.edu/orgs/struct/microstructure/images/024.hthttp://talc.geo.umn.edu/orgs/struct/microstructure/images/024.htmlml
Slides 3, 5 Slides 3, 5 -- 19, 2119, 21Davis. G. H. and S. J. Reynolds, Structural Geology of Rocks andDavis. G. H. and S. J. Reynolds, Structural Geology of Rocks and Regions, 2nd ed., John Regions, 2nd ed., John Wiley & Sons, New York, 776 p., 1996.Wiley & Sons, New York, 776 p., 1996.
Slide 13Slide 13ScholzScholz, C. H., The Mechanics of Earthquakes and Faulting, 2nd. ed., Ca, C. H., The Mechanics of Earthquakes and Faulting, 2nd. ed., Cambridge mbridge University Press, 471 p., 2002.University Press, 471 p., 2002.
Slide 22Slide 22 http://talc.geo.umn.edu/orgs/struct/microstructure/images/005.html
Slide 23Slide 23 http://talc.geo.umn.edu/orgs/struct/microstructure/images/006.html
Slide 24Slide 24 http://talc.geo.umn.edu/orgs/struct/microstructure/images/010.html
Slide 25Slide 25 http://talc.geo.umn.edu/orgs/struct/microstructure/images/014.html