Crustal Deformation Flashcards
Define Stress
The forces applied to objects, that cause rock deformation. Pushing or Pulling
Define Strain
Is the deformation resulting from applied stress
What are the 3 forces of stress
Compression: Convergent Zones
Tension: Divergent Zones
Sheer: Transform Zones
Styles of Deformation
Ductile: deformation is a solid that flows, stretches or bends with applied stress
Brittle: is where solid fractures, breaks or snaps with applied stress
Elastic: reverses when stress is removed
What do brittle responses to stress result in
Faults
Define Faults
a fracture in bedrock along which rock on one side has moved relative to the other side.
Define Strike and Dip *****possible test question
Geologists use a special symbol called strike and dip to represent inclined beds. Strike and dip map symbols look like the capital letter T, with a short trunk and extra-wide top line. The short trunk represents the dip and the top line represents the strike. Dip is the angle that a bed plunges into the Earth from the horizontal. A number next to the symbol represents dip angle.
What do ductile responses result in
Folds which are permanent wavelike deformations in layered rocks.
What do Compressive, tensional and shear forces result in
Compressive: reverse faulting
Tensional: Normal Faulting
Shear: Strike and Slip Faulting
What are strike and slip faults apart of
Transform boundaries, plates moving next to eachother.
What are the blocks on either side of a fault called*** possible question
Any rocks above the fault are called: Hanging wall
Any rocks below the fault are called: the Footwall
What occurs when something folds
A ductile deformation, this occurs at relatively high temperatures and pressures, however at some point the rock will break.
Define Anticline and Syncline
Anticline: is a fold with convex side upward (therefore oldest layers in the middle)
Syncline: is a fold with the concave side upward (therefore youngest layers in the middle)
Usually anticlines and synclines alternate in the field
Define Symmetrical folds
both limbs dip symmetrically away or towards axial planes
Anatomy of the fold
a fold is a stack of originally planar surfaces, such as sedimentary strata, that are bent or curved during permanent deformation.
Define Asymmetrical folds
A fold is pushed over, limbs dip in opposite directions but at different angles. The axial plane becomes tilted.
Defined overturned folds
a fold is pushed farther over. Limbs dip in same direction but at different angles.
The axial plane approaches horizontal
Define the two special folds, Structural Dome and Structural Basin
Structural Dome: anticlinal circular structure
Structural Basin: Synclinal circular structure
Define the Thrust Fault
It is a special case of reverse fault
Define Strike Slip Fault and the different laterals
motion is horizontal only. No vertical component
Rock units slide past each other.
Right lateral: opposite side moves to the right
Left lateral: opposite side moves to the left
What is the most famous strike slip or transform fault in North America
San Andreas
Define normal fault
Normal faults move by a vertical motion where the hanging-wall moves downward relative to the footwall along the dip of the fault. Normal faults are created by tensional forces in the crust. Normal faults and tensional forces commonly occur at divergent plate boundaries, where the crust is being stretched by tensional stresses
Define reverse fault
In reverse faults, compressional forces cause the hanging wall to move up relative to the footwall. A thrust fault is a reverse fault where the fault plane has a low dip angle of less than 45°. Thrust faults carry older rocks on top of younger rocks and can even cause repetition of rock units in the stratigraphic record.
