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Mountain Building

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Title: Mountain Building


1
Mountain Building
2
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

3
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

4
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)

5
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

6
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

7
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

8
Rock Deformation
  • Dome
  • When upwarping produces a circular or somewhat
    elongated structure
  • Basin
  • When downwarping produces a circular or somewhat
    elongated structure

9
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

10
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

11
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.

12
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.

13
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

14
Mountain Building
  • Convergent boundaries
  • Volcanic arcs are forming in most modern-day
    subduction zones
  • Aleutian-type subduction zones occur where two
    oceanic plates converge

15
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)

16
Mountain Building
  • Continents converge
  • Continental lithosphere is too buoyant to undergo
    subduction, a collision eventually results
  • Example India colliding with the Eurasian plate

17
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
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