Mountain Building

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Mountain Building
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Vocabulary

• Orogenesis
• Orosmountain
• Genesisto come into being
• Lithosphere
• The rigid outer layer of Earth, including the
  crust and upper mantle
• Accretion
• the increase in size of a tectonic plate by
  addition of material along a convergent boundary

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Crustal Uplift

• Evidence
• Marine fossils often found in high elevations in
  mountains
• Terraces hundreds of meters above sea level
• Isostasy
• A floating crust in gravitational balance
• Example blocks of wood floating in water
• Mountain belts stand higher above the surface of
  the Earth and have roots that extend deeper into
  the supporting material below.
• Crustal thicknesses for some mountain chains are
  twice as much as the average for the continental
  crust

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Crustal Uplift

• Crust beneath the oceans is thinner than that
  beneath the continents
• Oceanic rocks are denser than continental rocks
• adding weight to the crust makes it subside
• when weight is removed, crustal uplifting
  occurs (ex. cargo ship)

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Crustal Uplift

• Isostatic Adjustment
• Ice Age glaciers added weight to the continents,
  making them downwarp by hundreds of meters
• When glaciers melted, uplift occurred
• Erosion of mountains causes uplift, also

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Rock Deformation

• Elastic deformation
• When stress is applied, rocks bend, but will snap
  back if the stress is relieved
• Plastic deformation
• When the elastic limit is surpassed, rocks deform
  plastically or break (earthquakes)
• They are permanently altered through folding and
  flowing

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Rock Deformation

• Folds
• When flat-lying sedimentary and volcanic rocks
  are bent into a series of wavelike undulations
• Example pushing on one edge of a carpet until
  it folds
• Anticline
• Upfolding or arching of rock layers
• Syncline
• Downfolds, or troughs

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Rock Deformation

• Dome
• When upwarping produces a circular or somewhat
  elongated structure
• Basin
• When downwarping produces a circular or somewhat
  elongated structure

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Rock Deformation

• Faults and Joints
• Fractures in the Earths crust
• Dip-slip faults
• Vertical movement
• Hanging wallrock that is higher than the fault
  surface
• Footwallrock that is lower than the fault
  surface
• Normalhanging wall moves downward relative to
  the footwall
• Reversehanging wall moves upward relative to the
  footwall
• Thrust faultshave a very low angle

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Rock Deformation

• Strike-slip faults
• The dominant displacement is along the strike or
  trend, of the fault (horizontal)
• Transform faultsassociated with plate boundaries
• Oblique-slip faultsboth vertical and horizontal
  movement
• Tensional forcespull the crust apart
• Grabencentral block bounded by normal faults
  drop as the plates separate
• Horstsupfaulted structures that are adjacent to
  graben
• Compressional forcessections of crust are
  displaced toward one another

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Rock Deformation

• Joints
• Fractures along which no appreciable displacement
  has occurred
• Columnar joints form when igneous rocks cool and
  develop shrinkage fractures, producing elongated,
  pillarlike columns
• Sheeting produces a pattern of gently curved
  joints that develop more or less parallel to the
  surface of large exposed igneous bodies.

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Mountain Types

• Fault-block mountains
• Tensional stresses elongate and fracture the
  crust into numerous blocks. Movement along the
  fractures tilt the blocks producing parallel
  mountain ranges.

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Mountain Types

• Folded mountains (complex mountains)
• Upwarped mountains
• Caused by a broad arching of the crust or because
  of great vertical displacement along a high-angle
  fault
• Volcanic mountains

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Mountain Building

• Convergent boundaries
• Volcanic arcs are forming in most modern-day
  subduction zones
• Aleutian-type subduction zones occur where two
  oceanic plates converge

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Mountain Building

• Andean type subduction zones
• Passive continental marginpart of the same plate
  as the adjoining oceanic crust
• Becomes activesubduction zone forms and the
  deformation process begins
• The oceanic plate descends and becomes magma
  while there is an accumulation of sedimentary and
  metamorphic rocks along the subduction zone
  (accretionary wedge)

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Mountain Building

• Continents converge
• Continental lithosphere is too buoyant to undergo
  subduction, a collision eventually results
• Example India colliding with the Eurasian plate

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Mountain Building

• Mountain Building and Continental Accretion
• Smaller crustal fragments collide and accrete to
  continental margins
• Example mountainous regions rimming the Pacific
• As oceanic plates move, they carry with them
  embedded oceanic plateaus or microcontinents
• The upper portions of these thickened zones are
  peeled from the descending plate and thrust in
  relatively thin sheets onto the adjacent
  continental block.
• This increases the width of the continent
• Terraneaccreted crustal blocks