Deformation is a general term that refers to all changes in the original form and/or size of a rock body.
Most crustal deformation occurs along plate margins.
Factors that influence the strength of a rock
Temperature
Confining Pressure
Rock Type
Time
Stress
Force per unit area or the force applied to rocks
Types of directed stresses
Compression
Tension
Shear
Compression
Action of oppositely directed forces acting towards each other at the same time
Tension
Action of coinciding and oppositely directed forces acting away from each other.
Shear
Action of coinciding and oppositely directed forces acting parallel to each other across a surface
Folds
Rocks bent into a series of waves
Most folds result from compressional forces that shorten and thicken the crust
Types of Folds
Anticline
Syncline
Can be symmetrical, asymmetrical, overturned, or plunging.
Anticline
Upfolded or arched rock layers; a sequence of folded rocks with the oldest rocks on the inside of the fold.
Syncline
Downfolded rock layers; a sequence of folded rocks with the youngest rocks on the inside of the fold
Symmetrical
Limbs are mirror images
Asymmetrical
Limbs are not mirror images
Overturned
One limb is tilted beyond the vertical
Plunging
Where folds die out or tilt
Types of Folds - cont'd
Dome
Circular
Oldest
Basin
Downwarped
Youngest
Dome
Circular or slightly elongated
Circular
circular displacement of rocks
Oldest
Oldest rocks in core
Basin
Circular or slightly elongated
Downwarped
downwarped displacement of rocks
Youngest
Youngest rocks in core
Orientation of Deformed Rocks
Strike
Dip
Strike
compass direction of an inclined rock layer as it intersects with a horizontal surface
Dip
Acute angle between the rock layer and the horizontal surface, measured perpendicular to the strike of the inclined rock layer (amount of tilting of the rock layer)