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Structures & textures 1
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Today Updates: Evaluation today at end of class Lecture outline:
Deformation and textures Timing of crystal growth and deformation
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Metamorphic Textures Textures are small-scale penetrative features
Relict Textures Inherited from original rock Blastoporphyritic (<-> porphyroblastic) Any degree of preservation Pseudomorphs of minerals or pre-metamorphic textures/structures New Textures (following)
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New Textures
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Pressure solution
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Deformation within a crystal
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Point defect
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Line defect: edge dislocation
virtual2002.tau.ac.il/users/www/68379/PDF_Papers/2_Micro_Macro/Dislocations.pdf
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Slip virtual2002.tau.ac.il/users/www/68379/PDF_Papers/2_Micro_Macro/Dislocations.pdf
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Deformation twins
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Recovery Crystals recover from strain by: Migration of
Vacancies Dislocations Annihilation (opposite sense dislocations) Polygonization- general term for formation of low-strain subgrains: dislocations gather
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Defect migration
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Extinctions and subgrains
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Recrystallization Simple way to reduce lattice strain
Grain boundary migration Subgrain rotation Solid-state diffusion creep at higher T Grain boundary sliding and area reduction Coalescence- recovery and recrystallization by which large grains form by the addition of smaller strained grains by grain boundary migration
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Grain boundary migration and sub-grain rotation
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Coalescence in quartzite
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Examples of pre, syn, post-kinematic crystals
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Syn-kinematic crystals
Microboudinage: Growing zones try to keep up with stretching and breaking Spiral Porphyroblast: in shear zone shear results in crystal rotation: foliation captured, crystal rotates a bit, grows/captures
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Syn-kinematic garnet
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