structural geology

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structural geologymountain building
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key terms

• Deformation change in the original form, size
  or shape of a rock unit
• Stress amount of force applied to a given area
• Differential stress stress applied unequally in
  different directions
• Strain causes irreversible changes in the
  shape, size or orientation of a rock unit
• Elastic deformation recoverable stress, when
  stress is removed rock returns to its original
  shape size
• Ductile deformation elastic limit of rock is
  exceeded, the rock flows into a new shape, size
  or orientation
• Brittle deformation elastic limit and ductile
  limit of rock is surpassed, failure occurs, the
  rock breaks
• Joint a crack along which there is no motion

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Stress,strain deformation

• When does failure occur?
• How is deformation in a stick like deformation of
  a rock unit?

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effects of directional stress

• Compress ional stress causes rock units to
  shorten horizontally thicken vertically

• Tensional stress causes rock units to lengthen
  horizontally thin vertically

• Shear stress causes horizontal displacement
  along fault zones

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strike dip

• Strike compass direction of a line where a rock
  layer intersects the horizontal
• Dip angle of inclination or tilt of a rock
  layer from the horizontal

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Terminologyof folds

• Limb sides of a fold
• Axial plane imaginary plane that divides a fold
  as symmetrically as possible
• Axis intersection of axial plane with the
  surface
• Symmetrical limbs are mirror images of each
  other
• Asymmetrical limbs are not mirror images of
  each other
• Overturned a fold in which one limb is tilted
  beyond the vertical
• Recumbent a fold folded over on itself
• Plunge a fold in which the axis is tilted from
  the horizontal

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types of folds

• Syncline downwarping of strata, older strata
  are found on limbs, younger strata in the axial
  region

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types of folds

• Anticline upwarping of strata, older strata are
  found in axial region, younger strata on the limbs

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types of folds

• Asymmetrical either an anticline or syncline in
  which one limb is tilted at a different angle
  than the other

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types of folds

• Recumbent a fold which is folded over on itself

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fault terminology

• Fault fracture in rock along which there has
  been displacement
• Hanging wall rock surface above the fault
• Footwall rock surface below the fault
• Fault scarp exposed fault surface

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types of faults

• Normal fault a fault in which the hanging wall
  moves down relative to the footwall

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types of faults

• Reverse fault a fault in which the hanging wall
  moves up relative to the footwall

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types of faults

• Strike-slip fault a fault in which the motion
  is in the horizontal plane, also a transform fault

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types of faults

• Thrust fault hanging wall moves up and thrusts
  over the footwall, the dip is less than 45
  degrees, low angle fault

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domes basins

• Basin circular or elongated structure caused by
  downwarping of sedimentary rock
• Youngest rock found in the center of the basin,
  older on the flanks

• Dome circular or elongated structure caused by
  upwarping of sedimentary rock, usually overlying
  igneous or metamorphic rock
• Youngest rock found on the flanks of the dome,
  oldest in the center

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Hogbacks

• Ridges of steeply dipping strata
• Highly resistant sedimentary layers remain
  exposed along the edge of an uplifted block

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orogenesis

• Orogenesis processes by which mountain belts
  are created
• Oros mountain, genesis to come into being

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Types of mountains

• Fault block mountains mountain belts formed by
  extensional forces
• Mountains are associated with high angle normal
  faulting
• Examples include Sierra Nevada, Grand Tetons,
  Basin Range province

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Types of mountains

• Folded mountains result from large scale
  compressional forces
• Rock units are shortened and thickened as a
  series of synclines and anticlines forms a
  mountain belt
• Examples include the Appalachians Valley and
  Ridge Province

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Terrane accretion

• Small crustal fragments collide and merge with
  larger continental masses
• Accreted crustal blocks are called terranes
• Accretion of larger fragments may result in
  formation of a mountain range
• Examples include the western coast of North
  America

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