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structural geology


structural geology & mountain building key terms Deformation change in the original form, size or shape of a rock unit Stress amount of force applied to a ... – PowerPoint PPT presentation

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Title: structural geology

structural geologymountain building
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

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

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

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

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
  • Symmetrical limbs are mirror images of each
  • 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

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

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

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

types of folds
  • Recumbent a fold which is folded over on itself

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

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

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

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

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

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

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

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

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

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

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

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