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Lecture Outlines Physical Geology, 10/e


Lecture Outlines Physical Geology, 10/e Plummer, McGeary & Carlson Lecture Outlines Physical Geology, 10/e Plummer, McGeary & Carlson Steve Kadel, Glendale Community ... – PowerPoint PPT presentation

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Title: Lecture Outlines Physical Geology, 10/e

Lecture OutlinesPhysical Geology, 10/e
  • Plummer, McGeary Carlson

Mountain Belts and the Continental
CrustPhysical Geology 10/e, Chapter 20
Steve Kadel, Glendale Community College
Mountain Belts and Earths Systems
  • Mountain belts are chains of mountain ranges that
    are 1000s of km long
  • Commonly located at or near the edges of
    continental landmasses
  • Composed of multiple mountain ranges
  • Mountain belts are part of the geosphere
  • Form and grow, by tectonic and volcanic
    processes, over tens of millions of years
  • As mountains grow higher, erosion by running
    water and ice (hydrosphere) occur at higher rates
  • Air (atmosphere) rising over mountain ranges
    directly results in precipitation and erosion

Characteristics of Mountain Belts
  • Mountain belts are very long compared to their
  • The North American Cordillera runs from
    southwestern Alaska down to Panama
  • Older mountain ranges (Appalachians) tend to be
    lower than younger ones (Himalayas) due to
    erosion over time
  • Young mountain belts are tens of millions of
    years old, whereas older ones may be hundreds of
    millions of years old
  • Even older mountain belts (billions of years)
    have eroded nearly flat and form the ancient
    stable cores (cratons) of the continents
  • Shields - areas of cratons laid bare by erosion

Rock Patterns in Mountain Belts
  • Mountain belts typically contain thick sequences
    of folded and faulted sedimentary rocks, often of
    marine origin
  • May also contain great thicknesses of volcanic
  • Fold and thrust belts (composed of many folds and
    reverse faults) are common, indicating large
    amounts of crustal shortening (and thickening)
    has taken place under compressional forces
  • Mountain belts are common at convergent
  • May contain large amounts of metamorphic rock
  • Erosion-resistant batholiths may be left behind
    as mountain ranges after long periods of erosion

Rock Patterns in Mountain Belts
  • Erosion-resistant batholiths may be left behind
    as mountain ranges after long periods of erosion
  • Localized tension in uplifting mountain belts can
    result in normal faulting
  • Horsts and grabens can produce mountains and
    valleys, respectively
  • Earthquakes common along faults in mountain

Evolution of Mountain Belts
  • Rocks (sedimentary and volcanic) that will later
    be uplifted into mountains are deposited during
    accumulation stage
  • Typically occurs in marine environment, such as
    an opening ocean basin or convergent plate
  • Mountains are uplifted at convergent boundaries
    during the orogenic stage
  • May be the result of ocean-continent,
    arc-continent, or continent-continent convergence
  • Subsequent gravitational collapse and spreading
    may allow deep-seated rocks to rise to the surface

Evolution of Mountain Belts
  • After convergence stops, a long period of
    erosion, uplift and block-faulting occurs
  • As erosion removes overlying rock, the crustal
    root of a mountain range rises by isostatic
  • Tension in uplifting and spreading crust results
    in normal faulting and production of fault-block
    mountain ranges

Evolution of Mountain Belts
  • Basin-and-Range province of western North America
    may be the result of delamination
  • Overthickened mantle lithosphere beneath old
    orogenic mountain belt may break off and sink
    (founder) into asthenosphere
  • Resulting inflow of hot asthenosphere can stretch
    and thin overlying crust, producing normal faults
    under tension

Growth of Continents
  • Continents grow larger as mountain belts evolve
    along their margins
  • Accumulation and igneous activity (e.g., when
    volcanic arcs plaster against continents during
    convergence) add new continental crust beyond old
  • New accreted terranes can be added with each
    episode of convergence
  • Western North America (especially Alaska)
    contains many such terranes
  • Numerous terranes, of gradually decreasing age,
    surround older cratons that form the cores of the

End of Chapter 20
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