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Shear Zone Structures (Mylonite Formation (Ductile deformation due to…
Shear Zone Structures
Mylonite Formation
- Ductile deformation due to intense shearing
during folding / faulting
- Original minerals almost completely broken down
- Recrystallise as smaller grains
--> tightly intergrown ∴ form hard, dense rock
- Preferential growth along foliation planes
--> parallel to direction of shear
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S-C
Fabric
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- Shear bands (slip surfaces) develop (C)
parallel to shear zone walls
- Foliation curves in & out of shear surfaces (C)
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S-C'
Fabric
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∴ New, oblique shear bands (C') form oblique to CS
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Shear Zone Nucleation
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i.e. micaceous layers, veins, fracture, dykes etc
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Example SZ Nucleation
- Fracture formed via brittle fracture
- Fracture allowed fluid ingress
- Facilitates retrogression in feldspar
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