Rock Deformation

1
Rock Deformation
2

• rock deforms (changes shape) because of stress
  put on the rock
• stress is a force that acts on a body (rock in
  this case)
• differential stress is a force which is not equal
  in all directions
• when a rock is stressed differentially it can
  undergo 3 stages of deformation elastic,
  plastic, rupture
• elastic returns to original shape if the stress
  is removed
• plastic when stress is beyond the return point
  and the rocks does not return to original shape -
  folding
• rupture stress is so great that the rock breaks
  - faulting

3

• different rocks behave differently depending upon
  the chemistry of the rock - different minerals,
  and especially crystal structure
• rocks generally fit into 2 categories with
  respect to deformation brittle and ductile
• brittle rocks rupture before any plastic
  deformation occurs
• ductile rocks have a large range of plastic
  deformation between elastic deformation and the
  rupture point
• generally speaking, more crystalline rocks have a
  greater rupture strength, that is, they resist
  rupturing longer but have little plasticity

4
Brittle Rock
rupture point
elastic deformation
As stress increases so does deformation.
If the stress is removed, the rock will return to
its original shape unless it reaches the .
The rock is faulted.
5
Brittle Rock
Ductile Rock
rupture point
plastic deformation
elastic deformation
The rock is folded irreversibly during plastic
deformation.
Eventually,the stress leads to ...
faulting