✓✓✓✓~ Puts stationary objects in motion or changes the motions of moving
bodies
compressive strain
✓✓✓✓~ - negative
Continuous tectonic plate movement creates stresses and strains in the crust
Deformation
✓✓✓✓~ refers to all changes in the original form and/or size of a rock body
- Most crustal deformation occurs along or near plate margins
- Small amounts of strain over geological time cause large changes
elastic deformation
,✓✓✓✓~ region where the material will return to its original shape when the
stress is removed
brittle fracture
✓✓✓✓~ - Breaks into pieces
- Low temps and pressures near the surface
Ex. Faults, joints
ductile deformation
✓✓✓✓~ - Permanent deformation without breaking
- High temps and pressures deep: solid state flow
- Often with metamorphism
Ex. folds
differential stress
✓✓✓✓~ Applied unequally from different directions
,compressional stress
✓✓✓✓~ differential stress that shortens a rock body
tensional stress
✓✓✓✓~ elongates a rock body
shear stress
✓✓✓✓~ changes the shape of a rock body
crystal deformation
✓✓✓✓~ Under directed pressure (from tectonics), atoms can move (slowly)
within a solid to create shortening in one direction
faults
✓✓✓✓~ Faults are large scale shear ruptures and fractures in the crust both
locally and globally
, folds
✓✓✓✓~ ductile deformations outlined by folded strata or folded fabric that we
know used to be horizontal or vertical
- Most folds result from compressional stresses which shorten and thicken the
crust
PARTS:
*Limbs :*Two sides of a fold
*Axis:* Crest of the fold - Perpendicular to the shortening or the compression
*Plunge:* Incline axis
*Axial plane:* Divides a fold as symmetrically as possible
joints
✓✓✓✓~ smaller scale fractures that form an extension or shear, and *veins*
are those fractures that have been filled in with mineralization
- fractures that result from brittle deformation - typically no displacement
*SIGNIFICANCE OF JOINTS*:
- Chemical weathering concentrates around joints
- Many mineral deposits are emplaced along joint systems
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